United StatesDepartmentof Agriculture
Forest Service
Rocky MountainResearch Station
ProceedingsRMRS-P-44
March 2007
Volcanic-Ash-Derived Forest Soils of the Inland Northwest: Properties and Implications for Management and Restoration
9-10 November 2005 Coeur d’Alene, ID
Page-Dumroese, Deborah; Miller, Richard; Mital, Jim; McDaniel, Paul; Miller, Dan, tech. eds. 2007. Volcanic-Ash-Derived Forest Soils of the Inland Northwest: Properties and Implications for Management and Restoration. 9-10 November 2005; Coeur d’Alene, ID. Proceedings RMRS-P-44; Fort Collins, CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station. 220 p.
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Abstract ________________________________________ Volcanic ash from the eruption of Mt. Mazama ~7,700 years ago has a strong influ-ence on many forested landscapes of the Pacific Northwest and Intermountain regions of the USA and Canada. Because of the unique biological, physical and chemical properties of the ash, it is closely tied to plant communities and forest productivity, and should therefore be considered as a resource to protect when harvesting, burning, or site preparation activities occur on it. How did this symposium get started? There has been a steady stream of questions, problems, and research on volcanic ash-cap soils for many decades. This symposium was designed to assemble experts to discuss our state-of-knowledge about volcanic ash-cap soil management and restoration. About 200 scientists and natural resource managers participated in this conference, which was held at the Coeur d’Alene Resort, Coeur d’Alene, ID in November 2005.
The Technical Committee __________________________Deborah S. Page-Dumroese is a Research Soil Scientist and Project Leader, Rocky Mountain Research Station. Debbie’s research has focused on long-term soil productivity after management activities, including belowground chemical, physical, and biological properties.
Richard E. Miller is a retired Research Soil Scientist from the Pacific Northwest Research Station. Dick is still actively involved in soil research and is currently working to address issues of soil quality and monitoring.
Jim Mital is the Forest Ecologist, Soil Scientist, and Weed Coordinator on the Clearwater National Forest. Jim has worked to help design “soil friendly” management options for resource managers.
Paul McDaniel is Professor of Soil Science in the College of Agricultural and Life Sci-ences at the University of Idaho. Paul’s research activities have included elucidating the unique chemical and physical properties of ash-cap soils.
Dan Miller is Silviculture Manager for Potlatch Forest Holdings, Inc., Lewiston, ID. Dan has been instrumental in working with logging contractors to reduce soil impacts during harvesting.
Contents______________________________________________________ Page
Properties, Characteristics, and Distribution of Ash-cap Soils .............................................. 1
Volcanic Ash-cap Forest Soils of the Inland Northwest Properties and Implications for Management and Restoration ............................................................................... 3 Steven B. Daley-Laursen
Ecological and Topographic Features of Volcanic Ash-Influenced Forest Soils ............................. 7 Mark Kimsey, Brian Gardner, and Alan Busacca
Field Identification of Andic Soil Properties for Soils of North-central Idaho ................................ 23 Brian Gardner
Physical and Chemical Characteristics of Ash-influenced Soils of Inland Northwest Forests ...... 31 P. A. McDaniel and M. A. Wilson
Assessing Quality in Volcanic Ash Soils ....................................................................................... 47 Terry L. Craigg and Steven W. Howes
Past Activities and Their Consequences on Ash-cap Soils .................................................. 67
Effects of Machine Traffic on the Physical Properties of Ash-Cap Soils ....................................... 69 Leonard R. Johnson, Debbie Page-Dumroese, and Han-Sup Han
Runoff and Erosion Effects after Prescribed Fire and Wildfire on Volcanic Ash-Cap Soils .......... 83 P. R. Robichaud, F. B. Pierson, and R. E. Brown
Management Alternatives for Ash-cap Soils ........................................................................... 95
Volcanic Ash Soils: Sustainable Soil Management Practices, With Examples of Harvest Effects and Root Disease Trends .................................................................................... 97 Mike Curran, Pat Green, and Doug Maynard
Restoring and Enhancing Productivity of Degraded Tephra-Derived Soils ................................ 121 Chuck Bulmer, Jim Archuleta, and Mike Curran
Ash Cap Influences on Site Productivity and Fertilizer Response in Forests of the Inland Northwest......................................................................................................................... 137 Mariann T. Garrison-Johnston, Peter G. Mika, Dan L. Miller, Phil Cannon, and Leonard R. Johnson
Economics of Soil Disturbance ................................................................................................... 165 Han-Sup Han
Special Topic—Grand Fir Mosaic ........................................................................................... 173
The Grand Fir Mosaic Ecosystem—History and Management Impacts ..................................... 175
D. E. Ferguson, J. L. Johnson-Maynard, and P. A. McDaniel
Chemical Changes Induced by pH Manipulations of Volcanic Ash-Influenced Soils .................. 185 Deborah Page-Dumroese, Dennis Ferguson, Paul McDaniel, and Jodi Johnson-Maynard
Summaries of Poster Papers .................................................................................................. 203
WEPP FuME Analysis for a North Idaho Site ............................................................................. 205 William Elliot, Ina Sue Miller, and David Hall
Erosion Risks in Selected Watersheds for the 2005 School Fire Located Near Pomeroy, Washington on Predominately Ash-Cap Soils .............................................................211 William Elliot, Ina Sue Miller, and Brandon Glaza
Conference Wrap-up .................................................................................................................. 215 Richard E. Miller
Properties, Characteristics, and Distribution of Ash-cap Soils
Past Activities and Their Consequences on Ash-cap Soils
Management Alternatives for Ash-cap Soils
Special Topic— Grand Fir Mosaic
Summaries of Poster Papers
�USDA Forest Service Proceedings RMRS-P-44. 2007
Volcanic Ash-cap Forest Soils of the Inland Northwest Properties and Implications for
Management and RestorationSteven B. Daley-Laursen
In: Page-Dumroese, Deborah; Miller, Richard; Mital, Jim; McDaniel, Paul; Miller, Dan, tech. eds. 2007. Volcanic-Ash-Derived Forest Soils of the Inland Northwest: Properties and Implications for Management and Restoration. 9-10 November 2005; Coeur d’Alene, ID. Proceedings RMRS-P-44; Fort Collins, CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station.
Steven B. Daley-Laursen, Dean and Professor, College of Natural Resources, University of Idaho.
GoodMorningandWelcome.Mytasktodayis toset thestageforaproductiveconferencebyprovidinganhistoricalcontext,anoverviewofthesubjectmattertobecovered,andachallengefornextstepsbyinterestedscientistsandpractitioners.
An Historical Perspective
VolcanoeshavebeenpartoftheEarth’shistoryeversinceithashadasolidsurface.And,volca-noeshavebeenapartofhumancultureforthousandsofyears.Insomeways,ourreactionstothemagnitudeofavolcanicexplosionhaven’tevolvedasmuchasonemightthink.Rangingfromancientcultureswhobelievedthatvictimsshouldbesacrificedinresponsetovolcaniceruption,toHarryTrumanwhostubbornlysacrificedhimselfduringthemostrecenteruptioninthecontinentalUnitedStates,volcanoeshaveimpactedourlivesinmanywaysandwillcontinuetodosointhefuture. Butdisastersometimesbringsfortune.HereontheWestCoastwheresomevolcanoeseruptvio-lentlyevery20-30yearsorso,weliveinoneofthegrandestash-caplocationsintheworld.SoilsthroughouttheInlandNorthwestregionoftheUnitedStatesextendingfromtheCascadeMountainsofOregonandWashington toNorthern IdahoandWesternMontanahavebeen influencedandoverlainbytephrafromcataclysmiceruptionsofMountMazama. About6,850yearsagoMountMazama,astrato-volcano,collapsedtoproduceCraterLake,oneoftheworld’sbestknowncalderas.Thecalderaisabout6miles(10km)wide.Thecatastrophicpyro-clasticeruptionreleasedabout12cubicmiles(50cubickm)ofmagmatothesurface.Itwasoneofthelargesteruptionsinthelast10,000years. TheMazamaeruptionwasfollowedbytheMay18,1980eruptionofMountSt.Helensinwest-centralWashington.Thiseruptionspreadlessthan1/100thoftheMazamaashvolumeoverareasofeasternWashingtonandNorthernIdaho.TheSt.Helensashplumecarriedbythejetstreamtook2weekstocircletheglobe!ThoughconsiderablysmallerinvolumeoutputthantheMazamaerup-tion,theMountSt.Helenseruptionanddepositionhadeffectsonsoilsandproductivityinourregionthatarestillvisibleandproudlymeasurable.
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Daley-Laursen Volcanic Ash-cap Forest Soils of the Inland Northwest Properties and Implications for Management and Restoration
Onapersonalnote,thesevolcanoesandtheconsequenceoftheireruptionshavehadadirectimpactonmylifeandcareerinthreeways.AsanOregonianbybirthIwasavisitortoCraterLakelearningaboutlocalgeologyandforests.AsaresidentofMoscow,IdahoduringtheMay1980eruptionofSt.Helens(andthenearly1-yearaftermath)Ihadtheexperienceofbeingblanketedwithashandhavinglife’spaceslowtoawalkwithamaskandgogglesinasnowywhitehaze.And,asastudentoftheHabitatTypeatUIandaresearcherdevelopingstandgrowthsimulationmodelsintheGrandfir,Douglas-firandcedarhemlocksystemsoftheInlandNorthwest,Ilearnedfirsthandabouttheimpactofashonsoilpropertiesandchemistryandsiteproductivityandpotentialvegetation.So,Ihaveforsometimebeenawedbythepoweroftheseprofoundphenomena—thevolcanoesthatproducetheash,andtheashcapsthataddvaluetotheregion’ssoils.
My experiencewith the aftermathof volcanic eruptionwas expanded anddeepenedthispastyear,whenIhadtheopportunitytotourLasVallesCalderainnorthernNewMexico.Thisisa50milewidecalderathatblewitstop1.2millionyearsago,leavingbehindaninspiringlandscapeofbiologicaldiversity.IwenttheretomeetupwithscientistsfromthreeNewMexicouniversitiesconductingresearchonwatersheddynamicsandcarbon-waterrelations.Thisisaremarkableplaceat10,000feetintheSouthernRockyMountains.Don’tmissyouropportunitytovisitandlearnaboutthepastandpresentconditionsofLasVallesCaldera.
Thesemajorvolcaniceruptionsanddepositionsallcreatedthesamewondrousoutcome;ash-capsoils.Asaresultoffrequentvolcanicactivity,thesoilsoftheNorthwestareuniqueandbehavedifferentlythananywhereelseintheUnitedStates.Asyou’llhearfromadozenresearchersandlandmanagersoverthenext2days,wenowknowmuchabout thepropertiesandcharacteristicsof thesedepositedsoilsandtheeffectsofouractivityonthem.
An Overview of Our State of Knowledge— Preview of the Conference _______________________________________
Weknow thedistributionofAndic soils, andMarkwill tell youmore.WeknowaboutthechemicalandphysicalpropertiesofAndisols.Theyarelightandfluffy,lowdensityandhaveremarkablewater-holdingcapacity.Paulwilltellusmoreaboutallof this,drawing fromhis2005 treatiseonAndisols.WeknowsomethingaboutAndic soilqualityandwillhearmoreabout that fromStevelaterthisafternoon.
Weknowthatthemostsignificantglassaccumulationsarefoundinforestedareas.IthasbeensuggestedthatoutsideaforeststructureliketheDouglas-fir,orthemoremesicGrandfirandcedarhemlockecosystems,volcanicashisnotretainedagainsterosion,certainlynotunderextremeconditionsofmanagementthatexacerbateerosion.
WealsoknowthereisastronglinkbetweenAndisoldistributionandforestproductivity;referencemyearliercommentsabouthabitat typeasapredictorvariableinstandgrowthsimulationmodels.Inthe1970s,HabitatTypewasex-plainingmuchvariationinourtreegrowthandforeststandsimulationmodels,actingasaneffectiveintegratorofslope,aspect,elevation,moistureandtem-peratureinthepredictionofspeciesoccurrenceandabundanceaswellastreeandshrubgrowthrate.Atthattime,manyscientistsandmanagerswerebeginning
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Volcanic Ash-cap Forest Soils of the Inland Northwest Properties and Implications for Management and Restoration Daley-Laursen
tobelievethattheonefactornotadequatelystratifiedinDaubenmire’sHabitatTypeschemewassoiltype.
Ash-capsoilsplayacriticalroleinwaterrelationsandnutritionalecology,andthus,plantdiversityinforestedecosystems.LaterattemptsathabitattypingintheUnitedStateshavetakensoiltypemuchmoreseriously.
Inmorerecentscienceonforestnutrition,soilparentmaterialhastakenoncelebritystatusasapredictorvariableinsiteproductivity.Researchersandlandmanagersnowspeakofgood and bad rocks(parentmaterial)andacknowledgethroughempiricalandlaboratorysciencethecharacteristicsofashsoilsandtheirdirectimpactonnutritionalecology.Throughcooperativeresearchandoutreach,thishashadadirectinfluenceonmanagementprescriptionsonbothpublicandprivateforestownerships.
From this body of research and practice, we know that properly managedAndicsoilscanbesomeofthemostproductiveonearth.DennisandLarrywillsharetheirknowledgeonmanagementregimesonforestedsystemswithash-capsoils.Mariannewillsharewaystoimprovetreeperformancethroughnutritionalaugmentationandsitedecisions.PetewilltellyouabouttheeffectsofdifferentfireregimesonAndicsoiltypes.
Weknowthesesoilsaresusceptibletocompaction,anddecreaseinvalueandvolumeunderintenseandfrequentfireanderosionfollowingirresponsibleforestman-agementpractices.HanandLeonardwillreviewtheeffectsofmachinetraffic,plansforalighterfootprintduringforestoperations,andtheoveralleconomicsoftimberoperationswithaneyetoecologicalandeconomicsustainability.Chuckwillintroduceustorestorationschemesfordegradedsoils.And,Mikewillsharebestmanagementpracticesrelatingtoinsectanddiseasepopulationsandharvestoperations.
The Challenge to Scientists and Practitioners— Where We Go From Here _________________________________________
Weknowmuch,andyou’vegatheredanimpressivecrewofscientistsandprac-titionerstosharethecurrentknowledgebase.But,theconferenceisaboutmorethanjustdumpingallthecurrentknowledgeonthetable.It’saboutsynthesizingcurrentknowledgeintoamorecoherentperspectiveonthesesoilsandtheman-agementtheycantolerate.And,justasimportant,it’saboutframingthenextsetofquestions…layingoutyourscienceroadmapforthefuture,anddoingittogether.
Ininterviewingsoilsfolksandmanagersinpreparationforthispresentation,IwastoldbymorethanonepersonthatmostofthestudiesonAndisolshaveoccurredintheMidwestandoverseas—inJapan,Iceland,andNewZealandforexample,andthatthebodyofinformationavailableintheU.S.isfleetingandincomplete.ItwouldbegoodtoorganizealistofhighestpriorityresearchtobeconductedonAndicsoilsinthisregion.
Mostalsoagreethataroundtheedgesofthisspottingsciencebase,therearementalvolumesofendemic,practitionerknowledgeaboutAndicsoilsstoredintheexpertsystemsthatareourexperiencedlocalforestmanagers.Itwouldbeusefultoallofyoutoorganizethisendemicknowledgeandsubjectittoscientificscrutiny,invalidationandconfirmation.That’swhyyou’rehere—tomatchtheinsightsandexperienceofforestmanagerswiththecuriosityofforestresearchers…todevelopa coherent research agenda that will lead to best practices for protection andsustainabilityofthisimportantAndicsoilresource.
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Daley-Laursen Volcanic Ash-cap Forest Soils of the Inland Northwest Properties and Implications for Management and Restoration
That’s therealreasonIacceptedtheinvitationtobewithyoutoday.Obvi-ously,Ican’tstandtoetotoewithyouonthescienceofsoilsortheintricaciesandart-formofmanagement.But,Ihavespentmycareerstraddlingtheresearchandoutreachworldsofacademia,strivingtobringtheresearcherandpractitionertogetheraroundacoherentandintegratedscienceandmanagementagenda.Thebestoutcomesofscienceareachievedwhenthescientistandpractitionercon-ceptualizeaproblemandresearchquestiontogetherandI’mpassionateaboutmakingthistypeofconnectionareality.Therewardsareprofoundforallwhosubscribe.
So,myclosingstatementisanadmonitioninthatspiritofcollaborationandcoordination.
Soilsare taken forgrantedandunderratedby theaverageperson. Justdirt,youknow—uncorruptableandforeverstaticintheaveragemind’seye.But,youandIknowthisisn’ttrue.Theyareinfactthesubstrateonwhichmostlifeandbiodiversityresides,theyarethephysicalbaseonwhichthewatersystemself-regulates,theyareoftenthedefiningfactorinwhatyoucanandcannotdowellonaparticularsite.Andtheyarefragile,corruptibleanddegradable. Inmanycases,ifyouscrewthemuponce,youdon’tgetasecondchance.Inextremecasesoferodibility,whenthey’regone,they’regone.
TheAndicsoilisparticularlyerodible.StudiesofAndicsoilscangivecluestootherhighlyerodiblesoilsinevenmorecriticalregionsofbiodiversity,likethetopics.
Aswecontinuetogrowourunderstandingoftheworkingprocessesandfunc-tionsofecosystems,andasasociety,werecognizeandattempttoquantify,andeventrade,thevaluesofnaturalcapital,soilandit’srelationshiptowaterandcarbonwillbekeyareasofinquiry,value,creditandtrade.
MostclimatemodelersandcarbonscientistsnowagreethattheInlandNorth-west,infacttheGrandfirandcedarhemlockecosystemswithmoist,relativelywarmtemperatureregimesandatlowtomidelevations,maybeoneofNorthAmerica’sbiggestcarbonsponges.Andicsoilsdefinitelyplayaroleinthisequa-tion.Inthemarketplacethatcharacterizesoureconomyandsociety,ourvaluingofthesesoilswillfollowonourunderstandingofthesesoils.
ScientistsandmanagersinwesternNorthAmericahaveintheirbackyardalivinglaboratoryinwhichtostudytheAndicsoil.You’reinthedriver’sseatforadvancingtheworld’sknowledgeonthesesoils,theirpropertiesandcharacter-istics,theiradditionstoecologicalpotentialandproduction,andtheirresponsestotheregimesofhumanactivity.And,you’regatheredheretoponderthis.
So, listen well to what you and your colleagues know and chart a coursetogetherthatwillfillintheblanks.Identifythekeymanagementquestionsandissuesrelatingtoashcapsoils.Identifythecategoriesofinquirythatareimportanttopursue.Identifyareaswhereyouneedtogobeyondanecdotetoscienceandmakesomeplanstotestandinvalidateyourmentalmodels.Letthepractitionersinfluencetheresearchagenda,andholdthescientistsaccountableforgettingthescienceoutinusableformtomanagersontheground.
TheUniversityofIdahoisalandgrantinstitutionwithamissiontoadvancebothscienceandpracticeinnaturalresourcemanagement.Wewillbelookingforwaystopartnerinyournoblepursuit.
Goodluckwithyourmeetingandthanksagainfortheinvitationtoparticipate.
7USDA Forest Service Proceedings RMRS-P-44. 2007
In: Page-Dumroese, Deborah; Miller, Richard; Mital, Jim; McDaniel, Paul; Miller, Dan, tech. eds. 2007. Volcanic-Ash-Derived Forest Soils of the Inland Northwest: Properties and Implications for Management and Restoration. 9-10 November 2005; Coeur d’Alene, ID. Proceedings RMRS-P-44; Fort Collins, CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station.
Mark Kimsey is a Research Assistant, Department of Forest Resources, University of Idaho, Moscow, ID. Brian Gardner is a Soil Scientist, U.S. Department of Agriculture, Natural Resources Conservation Service, Moscow, ID. Alan Busacca is a Crop and Soil Scientist, Department of Crops and Soil Science, Washington State University, Pullman, WA.
Abstract Volcanic ash distribution and thickness were determined for a forested region of north-centralIdaho.Meanashthicknessandmultiplelinearregressionanalyseswereusedtomodeltheeffectofenvironmentalvariablesonashthickness.Slopeandslopecurvaturerelationshipswithvolcanicashthicknessvariedonalocalspatialscaleacrossthestudyarea.Ashdistributionandaspectshowedweakcorrelation.Elevationandecologicallybasedplantassociationsaccountedforabout54percentoftheobservedvariationinvolcanicashthickness.Climaxplantassociationsmoisterthangrandfir/queencupbeadlily(Abies grandis/Clintonia uniflora)hadconsistentlythickashmantlesandsoilsthatwouldbeclassifiedaseitherAndisolsorandicsubgroupsusingSoilTaxonomy.Thestatisticalmodelerrorof10.7cmwassignificantlylowerthanthe>20cmvariationoftenfoundinlocalsoilseries.Thismodelquantitativelyassessesashdistributionandcanbeintegratedintootherlocalecologicalmodels.
Ecological and Topographic Features of Volcanic Ash-Influenced Forest Soils
Mark Kimsey, Brian Gardner, and Alan Busacca
Introduction
VolcanicashfromeruptionsalongthePacificNorthwestCascadeRangehassignificantlyinfluenced forest soils of the Inland Northwest, U.S.A. (Mullineaux 1986; Shipley andSarna-Wojcicki1983).TheHoloceneeraeruptionofMt.Mazama(nowCraterLake,OR)distributed>116km3ofvolcanictephraacrossthisregion(Bacon1983;Zdanowiczandothers1999).SoilsinfluencedbythedepositionofMt.MazamatephracanbefoundthroughoutthewesternUnitedStatesandintosouthwesternCanada(fig.1).Soilsformedin,orinflu-encedbyvolcanicashare important to forestmanagement.Volcanicash-influencedsoilshave lower bulk density, higher porosity, and higher water infiltration and retention thansoilslessinfluencedorunaffectedbyash(McDanielandothers2005;Nanzyoandothers1993;Nimlos1980;WarkentinandMaeda1980).Amongthebenefitsofthesepropertiesisthereductionindroughtstressonplantcommunitiesduringextendedsummerdryperiods.
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Kimsey, Gardner, and Busacca Ecological and Topographic Features of Volcanic Ash-Influenced Forest Soils
RegionaldepositionfollowingtheeruptionofMt.Mazamawasestimatedatapproximately15-20cmthickineasternWashington,withthinninginareasmoredistal to theeruption(Busaccaandothers2001).Thecurrentdistributionpat-ternofvolcanicglassderivedfromtheMazamaeventismuchdifferentthanthisoriginaldepositionpattern.AmapdepictingtheprevalenceofvolcanicglassinmodernsurfacesoilsofEasternWashingtonindicatesonlyweaktephrainfluenceinsoilsofthesouthwestColumbiaPlateaueventhoughtheseareasareclosesttothevolcanicsourceofthetephra(fig.2)(Busaccaandothers2001).Instead,glasscontentofthesurfacesoilsincreaseswithincreasingdownwinddistancefromthesourcevolcano.Also,noneof themodern tephra-influencedsurfacesoilsarecomposedofpurevolcanicejecta.SoilsoftheBlueMountains,OR,andClearwaterMountains,ID,havesomeofthebest-expressedandicsoilproperties
Figure 1—Estimated spatial distribution of Mt. Mazama volcanic ash across the western United States and southwestern Canada. The study area for this research project is located within the boxed area of north-central Idaho (Mt. Mazama ash distribution adapted from Williams and Goles 19��).
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Ecological and Topographic Features of Volcanic Ash-Influenced Forest Soils Kimsey, Gardner, and Busacca
intheregion,yetthesesoilsgenerallyhaveglasscontentsof20to50percentintheirsurfacelayers.
Severalmechanismshavebeenproposedasfactorsinthetransformationoftheoriginaltephrasheetintothemixeddistributionpatternsthatwesee.Theseinclude:1)apartialre-entrainmentofashbywindwithresultingredepositionfurtherdownwind(i.e.tothenortheast);2)burialofashmaterialbysubsequentepisodesofloessdeposition;3)bioturbationofthetephrabysoilfauna,whichservedtomixthevolcanicglassintothesurroundingsoilmass;and4)reducederosionlossandenhancedcaptureofremobilizedair-fallmaterialunderconiferousvegetationsuchasisfoundatthenorthernandeasternmarginsoftheColumbiaPlateau(Busaccaandothers2001;Hunter1988).
RecentNaturalResourceConservationService(NRCS)soilsurveyshaveex-tensivelymappedvolcanicash-influencedforestsoilsinportionsoftheInlandNorthwest. From these surveys, ash distribution and ecological/topographicrelationshipscanbeassessed.However,thesesoilsurveyrelationshipsareoftenpresented as a range in ash thickness. For example, volcanic ash thicknessesinHugusandBouldercreeksoilseriescommonlyfoundinourstudyareahavemappedvariations>20cm(SoilSurveyDivision2006).Asmoreinformationisgatheredontheroleofvolcanicashinforestproductivityandmanagement,for-estmanagersmayneedfinerresolutionofashdistributionthanarangeinashthickness.Theinherentvariationofsoilsurveysmaynotprovidethelevelofac-curacyneededfordecisionsupportsystems.Apotentiallyworkablealternativeisastatisticalre-analysisofindividualsoil-sitedescriptionscreatedduringlocalNRCSsoilsurveys.
Figure 2—Volcanic glass content of modern surface soils in eastern Washington (from Busacca and others 2001).
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Kimsey, Gardner, and Busacca Ecological and Topographic Features of Volcanic Ash-Influenced Forest Soils
Basedontheaboverationale,ourobjectivewas toselectarelativelysmallgeographicregionwithintheInlandNorthwestforwhichextensivesoilandenvi-ronmentaldatawasavailableto1)developadatasetofvolcanicashdepths,habitattypes,andterrainfeatures;2)conductstatisticalanalysestoassessrelationshipsbetweenashthicknessandselectedvegetativeandtopographicfeatures;and3)determinetheprecisionandfitofastatisticalmodeltoestimatethethicknessofvolcanicashacrossalandscape.
Materials and Methods __________________________________________
Study Area
TheareachosenforthisstudyistheNRCSID-612soilsurveyregionofnorth-centralIdaho(fig.1).Thissurveyareaencompassesabout336,250haofdiverseclimaticfactors,habitattypes,andcomplexterrainattributes.Landscapesofthisregionaregenerallycharacterizedasmountainousinthenorthandeast,whilethesouthandwestarecharacterizedasbasaltplateaus/benchlandincisedwithdeepcanyons.Elevationrangesfrom300minthesouthwestto>1700minthenorthandeast.Meanannualprecipitation(MAP)roughlyfollowstheelevationalgradient,with<300mmMAPinthesouthwestand>1500mminthenortheast.Ponderosapine(Pinus ponderosa)andDouglas-fir (Pseudotsuga menziesiivar.glauca)habitattypesdominatethesouthernregionsofthesoilsurvey.Westernredcedar(Thuja plicata)andwesternhemlock(Tsuga heterophylla)dominatethewarm,moistuplandregions;withSubalpinefir(Abies lasiocarpa)andmountainhemlock(Tsuga mertensiana)predominantinthecolder,higherelevations(Cooperandothers1991).
Data Analysis
Ninehundredandtwenty-onesoil-sitedescriptionsandtheirXYcoordinateswereobtainedfromtheOrofino,ID,NRCSfieldoffice.Fieldrecordscomposedofvolcanicashthickness,terrainattribute,andhabitattypeobservationswereenteredintoadatabase.Theeffectivenumberofobservationsavailableforanalysesvariedsinceitwasnotunusualforcertainfieldobservationstonotberecordedonthefieldform.Asummaryofthefielddescriptorsandtheirpotentialinfluenceonvolcanicashdistributionispresentedintable1.
Thecontinuousvariableselevation(ELE),slope(SLP),andaspect(ASP)weregroupedintodiscreteclassestofacilitatethecomparisonofincrementalchangesinashthicknesswithterrainattributes.ELEwasclassedinto200-mintervals,SLPat10percentbreaks,andASPin45-degreequadrants.CurvaturevalueswerederivedfromaUnitedStatesGeologicalSurvey(USGS)30-mdigitalelevationmodel(DEM)usinggridalgebrainageographicinformationsystem(GIS).Thenumericalcurvaturevalueswere thengrouped into their respective linear (L),concave(C),andconvex(C)classes.
Averageashthicknessbyclasswascomputedforeachofthevariablesdescribedabove.Standarderrorswerecomputedandt-testsperformedtotestforsignificantdifferencesinashthicknessusinganα-levelof0.1.Variablesthatshowedsignifi-cantclassdifferencesinvolcanicashthicknessweresubsequentlytestedforuseaspredictorvariablesinavolcanicashdistributionmodel.Astepwisevariable
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Ecological and Topographic Features of Volcanic Ash-Influenced Forest Soils Kimsey, Gardner, and Busacca
Table 1—Selected ecological and topographic features used in this study and their potential significance in determining volcanic ash distribution patterns (Cooper and others, 1991; Gallant, 2000).
Ecological/Topographic Features SignificanceElevation (meters): ELE Climate, vegetation type, potential energy 200-400 400-�00 �00-�00 �00-1000 1000-1200 1200-1400 1400+
Slope (%): SLP Overland and subsurface flow, velocity, and runoff 0-10 10-20 20-�0 �0-40 40-�0 �0-�0 �0+
Aspect (°): ASP Solar irradiation, wind erosion/deposition Flat N (�42.�-27.�) NE (27.�-72.�) E (72.�-117.�) SE (117.�-1�2.�) S (1�2.�-207.�) SW (207.�-2�2.�) W (272.�-297.�) NW (297.�-�42.�)
Up/Across Slope Curvature: PRCU/PLCU Flow acceleration, erosion/deposition rate, converging/diverging Linear flow, soil water content Concave Convex
Plant Associations: Climate, topography, site productivity, disturbance Vegetation Series: VS Pinus ponderosa (PIPO) Pseudotsuga menziesii (PSME) Abies grandis (ABGR) Thuja plicata (THPL) Tsuga heterophylla (TSHE) Tsuga mertensiana (TSME) Abies lasiocarpa (ABLA) Habitat Type: HT Festuca idahoensis (FEID) Physocarpus malvaceus (PHMA) Symphoricarpus albus (SYAL) Linnaea borealis (LIBO) Clintonia uniflora (CLUN) Asarum caudatum (ASCA) Adiantum pedatum (ADPE) Gymnocarpium dryopteris (GYDR)
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Kimsey, Gardner, and Busacca Ecological and Topographic Features of Volcanic Ash-Influenced Forest Soils
selectionprocedurewasusedwithintheframeworkofagenerallinearmodel(GLM)toassesswhichvariablesexplainedthegreatestvariationinvolcanicashthickness.Variablesthatwerewithintheupper0.1percentileofaTypeIIIsums-of-squaresF-distributionwereretainedwithinthemodel.Thepredictionequationwasdeemedreliableifitproducedahighcoefficientofdetermination(R2)andlowrootmeansquareerror(RMSE).
Results _________________________________________________________
Topographic and Vegetative Indicators
VolcanicashishighlycorrelatedwithELE(fig.2).Each200-mincrementissignificantlydifferentupto1200m(p<0.1).Above1200m,thereisnosignificantdifferenceinmeanashthickness.Forestsoilsbelow600minelevationhaveashthicknesses≤10cm.Manylowelevationsoilsexhibitsignificantmixingof theshallowashmantlewithunderlyingsoilmaterial.These lowerelevation forestsoilsareclassifiedasvitrandicsubgroupsofasoilorder(SoilSurveyStaff1999).Forestsoils locatedatelevationsbetween600mand1200mhavemeanashthicknesses24to35cm.Thesesoilsareclassifiedasandicsubgroups.Volcanicashmantleshaveameanthicknessofabout45cmabove1200melevation.Ashmantlesdeeperthan36cmthatmeetseveralotherNRCScriteriaareconsideredmembersoftheorderAndisols(SoilSurveyStaff1999)orAndosolsoftheWorldReferenceBase(FAO/ISRIC/ISSS1998).
Meanashthicknessshowednosignificantdecreasewithincreasingslopegradient(fig.3).Meanashthicknessshowedrelativelylittlevariationwithasmallrangeof25to34cmacrossallslopeclasses.Slopes<10percentshowedsignificantlylessvolcanicashthanallclassesexceptthe60percentclass.Ashdepthincreasesup
Figure 3—Mean volcanic ash thickness as a function of elevation (ELE) class. Y-axis bars represent standard errors, with letters indicating significant differences (p < 0.1).
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tothe20to30percentSLPclass;afterwhich,therearenosignificantdifferencesinashthicknessbySLPclass.The20to30percentclasshadsignificantlygreaterashdepthsthanallslopeclassesandwasmarginallygreaterthanthe40to50percentclass(p=0.12).
Northaspectsgenerallyexhibitthickerashmantlesthansouthfacingaspects(fig.4).N,NW,andSEaspectsshowmeanashdepths>32cm.NEandWfacingaspectshavethinnerashcaps(~30cm),butarenotsignificantlydifferentthanN,NW,orSEaspects.S,SW,andEaspectshavesignificantlythinnerashmantlesofabout27cm.
Figure 4—Mean volcanic ash thickness as a function of slope (SLP) class. Y-axis bars represent standard errors, with letters indicating significant differences (p < 0.1).
Slope curvature shows that nonlinear surfaces retain a greater thickness ofvolcanicashcomparedtolinearsurfaces(fig.5).Concaveandconvexsurfacesshowmeanashdepths>30cmforbothupslope(PRCU)andacrossslope(PLCU)surfacecurvature.LinearsurfacesinbothPRCUandPLCUaresignificantlylower(<25cm)thaneitherconvexorconcavesurfaces.Therewasnostatisticaldiffer-encebetweenconcaveandconvexineitherPRCUorPLCUslopecurvature.
Vegetationseriesandhabitattypeplantassociationsshowedthestrongestrela-tionshipwithvolcanicashthickness(fig.6).Overall,theponderosapine(PIPO)andDouglas-fir (PSME)vegetation serieshavevery thinvolcanicashmantles(<3cm)andshownosignificantchangebyhabitattypewithinseries.Grandfir(Abies grandis–ABGR)hasthewidestrangeinash-influenceofallvegetationseries.Meanashthicknessrangesfrom0to40cmdependingontheunderlyinghabitattypewithinseries.Themoisttwinflower(Linnaea borealis–LIBO)habitat
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Kimsey, Gardner, and Busacca Ecological and Topographic Features of Volcanic Ash-Influenced Forest Soils
Figure 5—Mean volcanic ash thickness as a function of aspect (ASP) class. Y-axis bars represent standard errors, with letters indicating significant differences (p < 0.1).
Figure 6—Mean volcanic ash thickness as a function of upslope curvature (PRCU) class. Y-axis bars represent standard errors, with letters indicating significant differences (p < 0.1).
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typeoftheABGRvegetationseriessurprisinglyshowsnosignificantashmantle(mean=0cm).AshthicknessinABGRhabitattypescanbedescribedasafunc-tionofincreasinglymoistunderstoryindicatorspecies,withtheexceptionofLIBO.HabitattyperankingsforvolcanicashthicknesswouldbeLIBO<PHMA/SYAL < CLUN < ASCA,wherePHMA,SYAL,CLUN,andASCA representninebark(Physocarpus malvaceus),snowberry(Symphoricarpus albus),queen-cupbeadlily(Clintonia uniflora),andwildginger(Asarum caudatum),respectively.Theserank-ingssuggestthatvitrandicintergradeswouldbemoreprevalentonPHMA/SYALandLIBOhabitattypes,andicintergradesonCLUN,andAndisolsonASCA.
Changing fromanABGR toawestern redcedar (THPL)vegetation series isaccompaniedbya5-cmincreaseinmeanashthicknesswhencomparingacrossCLUNhabitattypes.ThisshiftisnotevidentfortheASCAhabitattype,whichshows no significant differences between ABGR and THPL vegetation series.Maidenhair fern (Adiantum pedatum – ADPE) and oak-fern (Gymnocarpium dryopteris–GYDR)habitattypesshowareductionof>7cminmeanashthicknessoverABGR/THPL-ASCA.MeanashthicknessforCLUNandADPE/GYDRhabitattypessuggestthatandicintergradeswouldbemostcommon,withAndisols(inotherwords,ashmantle>36cm)occurringprimarilyunderanASCAhabitattype.Basedontheseobservations,understoryrankingsofhabitattypebyincreasingashthicknesswouldbeCLUN=ADPE/GYDR<ASCA.
Thewesternhemlock(TSHE)seriesdisplayedthelargestdifferenceinvolcanicash thickness between CLUN and ASCA habitat types (about 28 cm). TSHE-CLUNhabitattypesshowatleasta6-cmdecreaseinmeanashthicknesswhencomparedtoTHPL-CLUN;however,aTSHE-CLUNhabitattypewouldstillfallwithin the andic intergrade classification associated with other CLUN habitattypes.AshthicknessintheASCAhabitattypeissignificantlygreaterforTSHEvegetationseries than foranyother serieswithobservedASCAhabitat types.MeanashdepthsonTSHE-ASCAare54cm,whichwouldplacethemwellwithintheAndisolsoilorder.
Mountainhemlock(TSME)andsubalpinefir(ABLA)seriesaretypicallyfoundathigherelevationswhereairtemperaturesarerelativelylowandannualprecipitationhigh.Thewarmer,moisterASCAhabitatwasnotobserved.MeanashthicknessisgreateronTSME-CLUNthanABLA-CLUN,butthedifferenceisinsignificant.Volcanicash-thicknessonthesevegetationseriesis>36cm,thusplacingthemintotheAndisolorder.
Volcanic Ash Distribution Modeling
Theclassvariableslistedintable1wereaddedstepwiseintoamultiplelinearregressionequation.Variableswereassumedtobe independentandnormallydistributed.The finalmodel,withselectedvariablesactingas fixedeffectsonvolcanicashthickness,is:
ATjklmno=μ+PRCUj +ASPk+SLPl +ELEm+VS*HTn+εjklmno
where,
ATjklmnoisthepredictedvalueforobservationowithvegetationseries*habitat typeinteractionn atelevationmonslopelwithaspectkandupslope curvaturej,
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μisoverallvolcanicashthicknessmean,PRCUjisthefixedeffectofupslopecurvature(concave,convex,orlinear),ASPkisthefixedeffectofaspect(N,NE,E,SE,S,SW,W,NW,orFLAT),SLPlisthefixedeffectofpercentslope(0-10,10-20,20-30,30-40,40-50, 50-60,or60+),ELEmisthefixedeffectofelevationinmeters(200-400,400-600,600-800, 800-1000,1000-1200,1200-1400,1400+),VS*HTnisthefixedeffectofvegetationseries*habitatinteraction(where,VSare ponderosapine,Douglas-fir,grandfir,westernredcedar,westernhemlock, mountainhemlock,orsubalpinefir;andHTareIdahofescue,ninebark/ snowberry,twinflower,queen-cupbeadlily,wildginger,ormaidenhairfern/ oak-fern),εjklmnoistheerrorterm;
where,j=3forupslopecurvature,k=9foraspect,l=7forslope,m=7forelevation,n=13 for vegetation series*habitat type interaction, ando=1 fornumberofobservationsperlocation.
Allclassvariables,exceptPLCU,explainedasignificantportionofvariationinvolcanicashthickness(p<0.1)(table2).VariablesrankedfromleasttomostinvarianceexplainedarePRCU<ASP<SLP<ELE<VS*HT.Theinteractionterm,VS*HT,accountedforthelargestpercentageofexplainedvarianceat71.2percent.ELEwasthesecondlargestat18.2percent.SLPandASPaccountedfor8.9percentcombined,andPRCUexplainedtheleastat1.7percent.Theoverallmodelwassignificant(p <0.001)andaccountedfor60percentoftheobservedvariationinashthickness.AmodelRMSEof10.7cmandCVof36percentindicatethatthereisasignificantamountofvariationstillunaccountedfor;however,thepredictiveerrorissignificantlylowerthanthevariationfoundinlocalsoilseries.
Table 2—General linear model variables retained in an ash prediction analysis. Partial variance indicates the percent of the model R2 explained by each retained variable.
Upslope Vegetation Series* Elevation Slope Aspect Curvature Habitat Type
Partial Variance (%) 1�.2 4.7 4.2 1.7 71.2Significancea <0.0001 0.00� 0.04 0.0� <0.0001aSignificance level tested at α = 0.1.
Discussion ______________________________________________________
Ecological and Topographic Indicators
Itisevidentfromthebroadrelationshipspresentedthatvolcanicashdistribu-tionisstronglyassociatedwithvegetationpatternsandlessdependentonterrainattributes.Elevation,althougha topographic feature, shows strongcollinearitywith localprecipitationgradientsandvegetativecover (datanot shown).Thissituationsuggeststhatelevationserveslocallyasaproxyvariableforinteractionsbetweenprecipitationandvegetationpatternsandtheirsubsequenteffectonashdistribution.
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Slopeclassdidnothaveanegativeimpactonmeanashthicknesswithslopes>60percentshowingnosignificantdeclineinashdepths(fig.3).Thisresultsup-portsotherresearchonslopestabilityofvolcanicash.Inareviewofvolcanicashsoils,WarkentinandMaeda(1980)notethatvolcanicashonfree-standingslopesupto70degreesarecommoninregionsofhighrainfall.Theyattributethishighdegreeofstabilitytotheuniquepermeabilityofvolcanicash.
Thesignificantlylowermeanashthicknessinthe0-to-10percentslopeclassmaybeduetothegeographiclocationoftheseobservations.Amajorityoftheseobservations for nearly flat terrain were on the benchlands of the south andsouthwestportionofthestudyarea.ThisregionischaracterizedbylowelevationPSMEandABGRvegetationseries,whichoftenexhibitthinormixedvolcanicashmantles.
Theprevalenceofthickerashmantlesonnorthaspectsmaybeattributabletoseveralfactors(fig.4).Northaspectstypicallysupportmoisterplantcommunitiesinourstudyarea(Cooperandothers1991).Thesemoistplantcommunitiesmayprovidegreatersoilsurfacecover,whichwoulddecreasetheimpactofprecipitationandoverlandwaterflowonvolcanicashredistribution.Additionally,themoistureretainedwithinthesoilsafterprecipitationeventswouldbelesssusceptibletoevaporationfromsolarradiation.GiestandStrickler(1978)foundvolcanicashsoilsofOregontobesusceptibletowinderosiononceinadrystate.Assumingthatcurrentsouthwesterlyprevailingwindpatternsweresimilartohistoricpost-eruptionpatterns,dryvolcanicashonsouth-facingslopeswouldbeexpectedtobemoresusceptibletoredistributionbywindthannorthaspects.Thesignificantincrease inash thicknessonsoutheastslopes isanomalous to this theoryandsuggeststhattheoveralleffectofaspectonashdistributionislocalandintricatelytiedwithsurroundingtopographicandenvironmentalfactors.
Thesignificantdecreaseinashthicknessonlinearsurfacesshowninfigure5ispartiallycorrelatedwiththeslopeclasstheseobservationsshare.Areviewofthedatasetshowsthatabout67percentofthelinearsurfacesoccuronslopes<10percentwiththeremainderunevenlydividedamongseveralsteeperslopeclasses.Asdetailedinthepreviousdiscussionofslopeclasses,observationswithgradients<10percentarefoundprimarilyinthedrierbenchlandportionsofthestudyarea.Thecorrelationbetweenslopesteepnessandslopesurfacecurvaturewithinthedatasetmaymasklocaleffectsofslopecurvatureonashthickness.Surprisingly,convexsurfacesinbothupslopeandacrossslopepositionsdisplayednosignificantdecreaseinmeanashthicknessoverconcavesurfaces.Otherre-searchonvolcanicashdepositionaftertheeruptionofMt.St.Helenshasshownthatconcavesurfacessupportthickerashmantlesthanconvex(ZobelandAntos1991).Ourconflictingresultsmaybeduetothelevelofvariationfoundwithintheseclasses.Standarderrorsweresmallbecauseoflargesamplesizes,butthestandarddeviationswereoftenlargewithinthesurfaceclasses,reflectingsignifi-cantvariationwithinthedata.
Cooperandothers(1991)associateshiftsinclimaxplantassociationstodis-tinctive soil and/or topographicmicroclimate features.Habitat type shifts anddiffering soilashdepthareevidentacross thebroadhabitat typeassociationsobservedinourstudyarea(fig.7).Thesestrongrelationshipsmaybeattributedtomanycombinationsof topographic,climatic,oredaphic factors.Steeleandothers(1981)notedthattheinfluenceofvolcanicashcontributedtodistinctshiftsinIdahoplantcommunities.However,itisstillanopenquestionastowhether
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Kimsey, Gardner, and Busacca Ecological and Topographic Features of Volcanic Ash-Influenced Forest Soils
thepresenceofvolcanicashisresponsibleforshiftsinplantassociations,orthatvariations in plant community were responsible for differential ash retention.Despite thisuncertainty,volcanicash thickness ishighlycorrelatedwithplantassociationsandcanbeusedtoassessashdistributionpatterns.
PSMEandPIPOvegetationseriesshowtheleastashthicknesswithinourdata.Shiftstomoisterhabitattypeswithinthesevegetationseriesshownosignificantdependenceonvolcanicash.Ithasbeensuggestedthatthesevegetationseriesnowresideonlandscapesthat,post-Mazamaeruption,weredrieranddidnotsupportforestvegetationcover.Lackofoverstorycoveranddryclimaticcondi-tionspreventedtheselandscapesfromretainingvolcanicashmantlessubsequenttotheeruption.
VolcanicashthicknessinABGRcommunitiesishighlyvariable.Unlikesuc-cessivelymoisterplantassociations,anABGRvegetationseriesdoesnotalwaysindicate the presence of significant volcanic ash influence. This variability ispartlyattributabletothetransitionzonethatABGRinhabitsbetweenxericandudicsoilmoistureregimes.Nearthedryendofthespectrum,ABGRplantcom-munitieswouldbeassociatedwithminimal tonoashinfluence.Thissuggeststhatanincreaseinplantavailablesoilmoisturewouldshifttheunderstoryplantcommunitytowardsmoisterhabitattypes.Thus,drierhabitattypes(PHMA/SYAL)oftenexhibitlessashinfluenceinthesoilthantheCLUNandASCAtypes.
AnexceptiontothispatternistheABGR-LIBOassociation.LIBOisconsideredtoinhabitmoisterenvironmentsthanPHMA,suggestingthatvolcanicashmightbepresenton thishabitat type.TheabsenceofvolcanicashonLIBOhabitattypesmaybeattributabletothefactthatonlyfiveobservationswerecollected
Figure 7—Mean volcanic ash thickness as a function of overstory (VS) and understory (HT) indicator plant species. Y-axis bars represent standard errors, with letters indicating significant differences (p < 0.1) (Cooper and others 1991).
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withinthishabitattype,providingforapoorrepresentationoftherangeinashthickness.
All remaining plant associations moister than ABGR show significant ashinfluenceinthesoil.Thepresenceofathickashmantleisoftenidentifiedbythepresenceoftheseclimaxspecies.IncreasingashthicknessinthesoilisevidentinthehabitattypegradientswithintheTHPLseries;however,habitattypedif-ferencesareminimal.
TheTSHEvegetationseriesoccupiesanarrowecologicalrangeinnorthIdahoforestsandprimarilyinhabitsmoist,moderatetemperaturesitesandareintoler-anttodrought,excessmoisture,andfrost(Cooperandothers1991).Thenarrowecologicalrangesuggests thatotheredaphicandclimatic factorsmightplayalargerroleinTSHEdistributionthanvolcanicashinfluenceinthesoil.SuchfactorsmayalsoexplainwhyTSHE-CLUNplantassociationshavethinnerashmantlesthanTHPL-CLUN.TSHE-ASCAsitesdoshowsignificantincreasesinvolcanicashthickness.ThisresultsuggeststhatvolcanicashisassociatedwithashifttomoisterunderstoryplantcommunitieswithintheTSHEvegetationseries.
TSMEandABLAplantcommunitiesoccupyhighelevation siteswithup to1500mmofannualprecipitationwithinourstudyarea.Vegetationserieswithinthesezonesareprobablynotdependentonthepresenceofvolcanicashfortheirestablishment.Thehighprecipitationanddensevegetativecoveroftheseplantcommunitiesretainedvolcanicashsubsequenttooriginalashdeposition.
Volcanic Ash Distribution Modeling
Thestrengthoftherelationshipsbetweenelevation,plantcommunities,andvolcanicashproducesastrongpredictiveabilityforourashdistributionmodel.AnR2valueof0.6isconsideredanexcellentimprovementoverthelimitedre-gionalvolcanicashmodelingattempts(NimlosandZuuring1982).Predictionsfromthismodelallowquantitativeashassessmentswithaknownerrorwithinthestudyarea.Forestmanagerscanusethismodeltointegratethepredictionsintoageographicinformationsystem(GIS).Onemotivationbehinddevelopinga quantitative ash distribution model was to overcome the variation inherentwithinmappingunitsgeneratedthroughasoilsurvey.VolcanicashthicknessesinHugusandBouldercreeksoilseriescommonlyfoundinourstudyareahavemappedvariations>20cm(SoilSurveyDivision2006).Thepredictivemodel’sRMSEof10.7cmsignificantlyimprovesonthislevelofvariation,thusprovidingafinerresolutionsupporttoolforlocalforestsoilmanagement.
Furtherresearchshouldbeconductedtodeterminelocalaffectsoftopographicfeaturesonashdistributiondespitethesignificantimprovementthismodelpro-videsinpredictingashdepthanddistribution.Globalstatisticalproceduressuchasmultiplelinearregressionmaymasklocaltopographicinfluence.Adjustingastatisticalmodeltoperformamorelocalanalysismayyieldimprovedresults.Amorecostly,butperhapsinformativemethod,wouldbeadetailedsurveyofafinitelandscape.Researchatlocallevelsmayrevealtopographicandvolcanicashrelationshipsotherwisemaskedbylargeconventionalsoilsurveys.Regard-lessofwhichapproachisused,modelingashdistributionseemstobeinherentlyalocalexercise.Theextrapolationofmodelresultsoutsideastudyareaisnotrecommended.Theconceptsbehindthemodelpresentedinthispapermaybeapplicableelsewhere,buttherelationshipsasreflectedinthemodelparameterestimatesareunique.
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Kimsey, Gardner, and Busacca Ecological and Topographic Features of Volcanic Ash-Influenced Forest Soils
Summary ______________________________________________________Thisstudy’sfindingssuggestthatvolcanicashdistributionisintricatelylinked
withelevationandplantcommunityassociations.Elevationincreasesprecipita-tion,whichinturnsupportsdifferentclimaxplantcommunities.Increasingplantdensityateachsuccessiveclimaxcommunitymayservetoretainashdepositssubsequenttovolcaniceruptionsandentrapwind-transportedvolcanicashfromdrier, lowerelevationsites.Topographicvariables showrelatively little impactonashthicknesspatterns.Severaloftheterrainattributesshowedclusteringbygeographiclocationwithinourstudyarea.Gentlerslopes,whichwerepredomi-natelyfoundatdrier,lowerelevations,supportedthinnerashmantles.Theslopecurvaturevariablewasalsolinkedtogeographiclocation.Nonlinearslopesweremostoftenfoundinthemountainousregionofthestudyarea.Thestrongeffectofelevationandvegetationhabitattypeseriesreducedtheabilitytodistinguishmeanashthicknessdifferencesbetweenconvexandconcavesurfaces.
Statisticalmodelingaccountedfor60percentoftheobservedvariationinashthicknessandreturnedanRMSEof10.7cm.Thesemodelstatisticsindicateasignificantdevelopment in thepredictioncapabilityofvolcanicash thickness.Modelerrorissignificantlylowerthanthevariationof>20cmoftenobservedinlocalash-influencedsoilseries.However,itbecameevidentduringouranalysesthatashdistributionandthicknessisheavilyinfluencedbylocalecologicalandtopographic attributes that cannot be assumed to affect ash depth uniformlyacrossastudyarea.Futureashmodelingeffortsmustfocusonassessinglocalenvironmental influences and account for nonstationarity in the independentvariables.Suchananalysismayclarifytheecologicalandtopographiceffectsonashdistributionandthicknessthatareotherwisegeneralizedinaglobalregres-sionanalysis.
Literature Cited __________________________________________________Bacon,C.R.1983.EruptivehistoryofMountMazamaandCraterLakecaldera,CascadeRange,
U.S.A.J.Volcanol.Geotherm.Res.18:57-115.Busacca,A.J.;Marks,H.M.;Rossi,R.2001.VolcanicglassinsoilsoftheColumbiaPlateau,Pacific
Northwest,U.S.A.SoilSci.Soc.Am.J.65:161-168.Cooper,S.V.;Neiman,K.E.;Roberts,D.W.1991.ForesthabitattypesofnorthernIdaho:Asecond
approximation.Gen.Tech.Rep.INT-236.Ogden,UT:U.S.DepartmentofAgriculture,ForestService,IntermountainResearchStation.143p.
FAO/ISRIC/ISSS.1998.WorldReferenceBaseforSoilResources.Rome:FoodandAgriculturalOrganizationoftheUnitedNations,InternationalSoilReferenceandInformationCentre,andInternationalSocietyofSoilScience.WorldSoilResourcesReportNo.84.Available:http://www.fao.org/docrep/W8594E/W8594E00.htm.AccessedJuly7,2006.
Geist,J.M.;Strickler,G.S.1978.PhysicalandchemicalpropertiesofsomeBlueMountainsoilsinnortheastOregon.Res.Pap.PNW-236.Portland,OR:U.S.DepartmentofAgriculture,ForestService,PacificNorthwestForestandRangeExp.Station.19p.
Hunter, C. R. 1988. Pedogenesis in Mazama tephra along a bioclimatic gradient in the BlueMountains of southeastern Washington. Pullman, WA: Washington State University. 128 p.Ph.D.Dissertation.
McDaniel,P.A.;Wilson,M.A.;Burt,R.;Lammers,D.;Thorson,T.D.;McGrath,C.L.;Peterson,N.2005.AndicsoilsoftheInlandPacificNorthwest,U.S.A.:Propertiesandecologicalsignifi-cance.SoilScience.170:300-311.
Mullineaux,D.R.1986.Summaryofpre-1980tephra-falldepositseruptedfromMountSt.Helens,WashingtonState,U.S.A.Bull.Volcanol.48:16-26.
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Nanzyo,M.;Shoji,S.;Dahlgren,R.1993.Physicalcharacteristicsofvolcanicashsoils.In:Shoji,S.; Nanzyo, M.; Dahlgren, R., eds. Volcanic ash soils: Genesis, properties, and utilization.Amsterdam:Elsevier:189-207.
Nimlos,T.J.1980.Volcanicashsoils.WesternWildlands.6:22-24.Nimlos,T.J.;Zuuring,H.1982.ThedistributionandthicknessofvolcanicashinMontana.North-
westScience.56:190-197.Shipley, S.; Sarna-Wojcicki, A. M. 1983. Distribution, thickness, and mass of late Pleistocene
andHolocenetephrafrommajorvolcanoesinthenorthwesternUnitedStates:ApreliminaryassessmentofhazardsfromvolcanicejectatonuclearreactorsinthePacificNorthwest.U.S.Geol.Surv.Misc.FieldStudiesMap.MF-1435.Washington,DC.27p.
SoilSurveyDivision.2006.Officialsoilseriesdescriptions.NationalCooperativeSurvey.Available:http://ortho.ftw.nrcs.usda.gov/cgi-bin/osd/osdname.cgi?-P.AccessedMarch19,2006.
SoilSurveyStaff.1999.Soiltaxonomy.Abasicsystemofsoilclassificationformakingandinter-pretingsoilsurveys.2nded.U.S.DepartmentofAgriculture,NaturalResourcesConservationService.AgriculturalHandbookNo.436.Washington,DC:U.S.Govt.Print.Office.871p.
Steele,R.;Pfister,R.D.;Ryker,R.A.;Kittams,J.A.1981.ForesthabitattypesofcentralIdaho.Gen.Tech.Rep.INT-114.Ogden,UT:U.S.DepartmentofAgriculture,ForestService,IntermountainResearchStation.137p.
Warkentin,B.P.;Maeda,T.1980.PhysicalandmechanicalcharacteristicsofAndisols.In:Theng,B.K.G.,ed.Soilswithvariablecharge.PalmerstonNorth,NZ:OffsetPublications:281-301.
Williams,H.;Goles,G.1968.VolumeoftheMazamaash-fallandtheoriginofCraterLakecal-dera:AndesiteConferenceGuidebook.OregonDepartmentofGeologyandMineralIndustriesBulletin.62:37-41.
Zdanowicz,C.M.;Zielinksi,G.A.;Germani,M.S.1999.MountMazamaeruption:Calendircalageverifiedandatmosphericimpactassessed.Geology.27:621-624.
Zobel,D.B.;Antos,J.A.1991.1980tephrafromMt.St.Helens:Spatialandtemporalvariationbeneathforestcanopies.Biol.Fertil.Soils.12:60-66.
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In: Page-Dumroese, Deborah; Miller, Richard; Mital, Jim; McDaniel, Paul; Miller, Dan, tech. eds. 2007. Volcanic-Ash-Derived Forest Soils of the Inland Northwest: Properties and Implications for Management and Restoration. 9-10 November 2005; Coeur d’Alene, ID. Proceedings RMRS-P-44; Fort Collins, CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station.
Brian Gardner: U.S. Department of Agriculture, Moscow, Idaho.
Field Identification of Andic Soil Properties for Soils of North-central Idaho
Brian Gardner
Introduction
Currently,laboratorymeasurementsaredefinitiveforidentifyingandicsoilpropertiesinboththeUSDASoilTaxonomy(SoilSurveyStaff1999)andtheWorldReferenceBaseforSoilResources(FAO/ISRIC/ISSS1998).Andicsoilproperties,asdescribedinSoilTaxonomy,resultmainlyfromthepresenceofsignificantamountsofallophone,imogolite,ferrihydriteoralumi-num-humuscomplexesinsoils.Therequiredpropertiesarehighacid-oxalateextractablealumi-numandironpercentages,lowbulkdensity,andhighphosphateretention.Inaddition,glassisacommoncomponentofandicsoilsoftheInlandNorthwestregion(McDanielandothers2005). A large body of work has been devoted to characterizing ash soils for classificationandmanagementpurposes.SummariesofthisworkincludeShojiandothers(1993)andDahlgrenandothers(2004).Howevernoneoftheseeffortshaveaddressedtheproblemofidentifyingsoilswithandicsoilpropertiesdirectlyinthefield.Mostsoilmappingpro-fessionals working with ashy materials are able to identify andic properties under fieldconditions. However, there is currently no summary of the methods used by individu-als to accomplish this identification. A procedure for recognizing andic materials usingfieldcharacteristicswouldassistboth those lackingexperiencewith thesematerialsandthose assessing soils from written descriptions. Also, a logically derived set of selec-tion criteria for detecting andic properties could help even experienced professionalsinareaswherevolcanicash influencehasbeendilutedbymixingwithothermaterials.
24 USDA Forest Service Proceedings RMRS-P-44. 2007
Gardner Field Identification of Andic Soil Properties for Soils of North-central Idaho
Thispaperwillexaminetwoalternativesfordetectingandicsoilproperties.Thefirstisthedevelopmentofanempiricalmodelusingroutinelyobservedsoilfeaturesasrecordedinsoildescriptionsfromnorth-centralIdaho.Thesecondistheuseofsodium-fluoride(NaF)pHtodetectthepresenceofallophaneorsimilaramorphousmaterialsinsoils.Theobjectivesofthisprojectwereto:1)identifyasetoffield-observablecharacteristicsthatcanreliablyidentifysoilsderivedfromMountMazamatephra;2)developasimplemodelusingthesecharacteristicstoevaluatesamplesastowhethertheymeetandiccriteriaornot;and,3)evaluateuseofNaF-pHinthisregionasatestforrecognizingashinfluence.
Methods and Materials __________________________________________Asetof323NaturalResourcesConservationService(NRCS)pedondescriptions
(or945separatesoilhorizons)fromLatahCounty,Idahowasusedtoevaluatehowwellasetoffieldobservationsallowsanobservertodistinguishandicmaterialsfromothersoilmaterials.Onlyhorizonshavingacompletesetofobservationsforallpropertiesandoccurringwithin50cmofthesoilsurfacewereused.Eachhorizonhadbeendesignatedasashyornon-ashyaccordingtotheexpertopinionoftheNRCSsoilscientistrecordingthesoildescription.Thedatasetcontains468horizonsdesignatedasashyand477horizonsdesignatednon-ashy.
The set of field observable characteristics proposed for recognizing andicmaterialsaresoilcolor(dryandmoist),structure,consistence(consistenceisthesetofstickiness,plasticity,ruptureresistancedryandruptureresistancemoist),and root abundance. Soil color isdescribedusing standardMunsellnotation.Structure,consistenceandrootabundancearedescribedusingthemethodsandnomenclaturefoundinSchoenebergerandothers(2002).
Mostofthesoilpropertiesaredescribedusinganumberofcomponentele-ments.Forexample,soilcolorisdescribedbythesixcomponentsofdryhue,dryvalue,drychroma,moisthue,moistvalueandmoistchroma(seetable1).Thissubdivisionofpropertiesresultedinalistof17propertiesand/orcomponentsthatcouldbeusedtodistinguishbetweenashyandnon-ashysoilhorizons.Eachcomponentofapropertyhasbeenassignedoneofseveralpossibleclassesthatdescribethecomponentforagivensoil.Forexample,drysoilhuecouldbe5YR,7.5YRor10YR.Tables2through6showtherelativefrequencydistributionforeachclassusedtodescribethecomponentsofeachsoilpropertybytephraornon-tephraparentmaterials.
Therelativefrequenciesobservedfortheclassesdescribingthecomponentsofeachsoilpropertywereusedtoevaluatewhichcomponentswouldbeusefulindiscriminatingandicfromnonandic(or“other”)materials.Ausefuldiscriminatorwasdefinedasonethatshowed:1)aclusteringof60percentormoreofobserva-tionsforthetephramaterialononecomponentclass,and2)lessthan35percentofobservationsforthe‘other‘materialsoccurringinthatsameclass.
ThepHofasuspensioncontaining1gsoilin50mL1MNaFisusedasatestfor thepresenceof short-rangeorderminerals.Theseminerals are commonlyearlyproductsoftheweatheringofpyroclasticmaterials.Theactionof1MNaFonthesemineralsreleaseshydroxideions(OH–)tothesoilsolutionandincreasesthepH.A1MNaFpHofmorethan9.4at2minutesaftertheNaFsolutionisaddedisastrongindicator(innon-calcareoussoils)thatshort-rangeorderminer-alsdominatethesoilexchangecomplex(Burt2004).
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Field Identification of Andic Soil Properties for Soils of North-central Idaho Gardner
Table 1—Soil properties proposed as useful for field recognition of tephra derived soil materials with their component elements and descriptive classes.
Property Component elements Descriptive classesSoil color dry hue �YR, 7.�YR, 10YR dry value 2, 2.�, �, 4, �, �, 7 dry chroma 2, �, 4, � moist hue �YR, 7.�YR, 10YR moist value 2, 2.�, �, 4, �, �, 7 moist chroma 2, �, 4, �
Structure grade weak, moderate, strong sizea 1, 2, �, 4, � kindb abk, gr, pl, pr, sbk, massive
Consistence dry rupture resistance soft, slightly hard, moderately hard, hard, very hard moist rupture resistance very friable, friable, firm stickiness nonsticky, slightly sticky, moderately sticky, very sticky plasticity nonplastic, slightly plastic, moderately plastic, very plastic
Root abundancec very fine and fine roots few, common, many medium and coarse roots few, common, many
Textured none 1, 2, �, 4 ,� �, 7a Structure size classes are: 1 = very fine, very fine and fine or fine; 2 = very fine to medium or fine and medium; 3 = medium; 4 = fine to coarse or medium and coarse; 5 = coarse.b Structure kinds are: abk = angular blocky; gr = granular; pl = platy; pr = prismatic and sbk = subangular blocky.c Root abundance classes are: few = <2%, common = 2 to 20% and many = >20%.d Texture classes are: 1 = sil; 2 = l; 3 = fsl, vfsl; 4 = sicl; 5 = cl; 6 = sl; 7 = cosl, lcos for definitions of class terms see Schoenberger and others 2002.
Table 2—Observed frequencies for the components of soil color by moisture status and parent material.
Moist Dry Color tephra Other tephra Other component Classes count Freq count Freq count Freq count Freq
(no.) (no.) (no.) (no.) Hue 10yr 14� 0.�9 120 0.7� 240 0.74 1�� 0.90 7.�yr 229 0.�1 4� 0.2� �4 0.2� 14 0.09a
�yr 0 0 2 0.01 0 0 2 0.01
Value 2 0 0 � 0.02 0 0 0 0 2.� � 0.01 2 0.01 0 0 0 0 � 1�1 0.4� 4� 0.27 0 0 0 0 4 1�4 0.49 101 0.�0 2 0.01 11 0.07 � � 0.01 1� 0.10 127 0.�9 19 0.12 � 0 0 1 0.01 1�1 0.�� 104 0.�� 7 0 0 0 0 14 0.04 20 0.1�
Chroma 2 2 0.01 4 0.0� � 0.01 � 0.0� � �2 0.14 �� 0.41 21 0.07 �� 0.4� 4 2�� 0.�� �2 0.�� 2�1 0.�1 7� 0.�1 � �� 0.1� � 0.0� �� 0.12 � 0.0� a Component meets criteria for useful ashy soil identifier.
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Gardner Field Identification of Andic Soil Properties for Soils of North-central Idaho
Table 3—Observed frequencies for the components of soil structure by soil parent material.
Structure Tephra Other component Classes count Freq count Freq
(no.) (no.)Structure grade weak 419 0.�� 14� 0.29a
moderate �� 0.1� �49 0.�� strong � 0.01 20 0.04
Structure size 1 2�1 0.�2 12� 0.24 2 204 0.40 290 0.�� � 29 0.0� �0 0.12 4 1 0 29 0.0� � 9 0.02 11 0.02
Structure kind abk 0 0 2 0 gr 19� 0.�9 91 0.17 pl 0 0 11 0.02 pr 0 0 1� 0.0� sbk �11 0.�1 �9� 0.7� massive 1 0.00 1� 0.0�a Component meets criteria for useful ashy soil identifier.
Table 4—Observed frequencies for the components of soil consistence by soil parent material.
Consistence Tephra Other component Classes count Freq count Freq
(no.) (no.)Dry consistence soft(so) 474 0.9� 19 0.1�a
slightly hard (sh) 17 0.0� �2 0.24 moderately hard (mh) 1 0.00 �2 0.24 hard ( ha) 0 0.00 42 0.�2 very hard(vh) 1 0.00 � 0.0�
Moist consistence very friable(vfr ) �07 0.9� 2� 0.19a
friable(fr) 11 0.02 97 0.72 firm(fi) 0 0.00 12 0.09
Stickiness nonsticky(so ) 474 0.9� �4 0.2�a
slightly sticky(ss) �4 0.07 �� 0.�2 moderately sticky(ms) 0 0.00 1� 0.1� very sticky(vs) 0 0.00 1 0.01
Plasticity nonplastic(po) 4�� 0.91 1� 0.12a
slightly plastic(sp ) 4� 0.0� �1 0.�� moderately plastic(mp) 1 0.00 �4 0.40 very plastic(vp) 0 0.00 1� 0.11a Component meets criteria for useful ashy soil identifier.
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Field Identification of Andic Soil Properties for Soils of North-central Idaho Gardner
Table 5—Observed frequencies for root abundance by root size class and soil parent material.
Root Tephra Other abundance Classes count Freq count Freq
(no.) (no.)Very fine and fine roots none 2 0 4 0.01 few 12 0.0� �� 0.07 common 9� 0.20 22� 0.47 many ��� 0.77 21� 0.4�
Medium and coarse roots none 9� 0.20 171 0.�� few 1�� 0.�� 199 0.42 common 207 0.44 �� 0.1� many 1� 0.0� 1� 0.04
Table 6—Observed frequencies of soil textures (for the <2mm fraction) by parent material
Tephra OtherSoil texture name count Freq count Freq
(no.) (no.) sil (1) 4�� 0.99 �20 0.�7 l (2) � 0.01 112 0.2� fsl, vfsl (�) 0 0 10 0.02 sicl (4) 0 0 7 0.01 cl (�) 0 0 4 0.01 sl (�) 0 0 19 0.04 cosl, lcos (7) 0 0 � 0.01
Whileeachofthesevariablesisimportantinrecognizingashsoils,theclas-sificationcriteriaallowforinteractionbetweenthetwosothatnosinglevalueservestodiscriminateandicfromnonandichorizons.InanattempttodefinesuchathresholdvalueforNaF-pH,adatasetoflaboratorymeasurementsfromClearwa-terCounty,Idahowasobtainedforanalysis.Thedatasetcontained267horizonswithNaF-pHinformation.Thesewerethengroupedintoandic(73horizons)andnonandic(194horizons)soils.Table7reportsthemeanandstandarddeviationforthesetwosamplepopulations.Assuminganormaldistribution,itispossibletousethesemeansandstandarddeviationstocalculateaNaF-pHvaluethatcor-respondstothecriticalvaluefortheZstatisticatachosenlevelofprobability.Table7reportsthesecriticalvaluesasNaF-pHvaluesatP=.95andP=.99.
Table 7—Mean, standard deviation and NaF-pH values that are equivalent to the critical values of Z at two levels of probability.
Standard NaF-pH NaF-pH Mean deviation at P=.95 at P=.99
Nonandic �.�� 0.�0 9.�� 9.97
Andic 10.�� 0.�� 9.97 9.7�
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Gardner Field Identification of Andic Soil Properties for Soils of North-central Idaho
Results and Discussion ___________________________________________Soilcolorisstronglyinfluencedbyparentmaterial(RichardsonandDaniels
1993).Table2indicatesthattheonlycomponentofsoilcolorusefulforrecognizingashinfluencedsoilsinnorth-centralIdahoisthemoisthue.Theash-influencedmaterialsarenoticeablyredderinhue(7.5YRvs.10YR)thanothermaterialsformostsamples.Thisisassumedtobearesultoftheprevalenceofferrihydriteinashymaterials(Dahlgrenandothers2004;UgoliniandDahlgren2002).Ferrihy-drite-containingsoilshavehuesof5-7.5YRwhilesoilswithhuesbetween7.5YRand2.5Ytendtocontainsignificantamountsofgoethite(Schwertmann1993).
Soilstructureisacomplexphenomenonthatdependsinpartonfactorssuchasparentmaterial,climateandthephysicalandbiochemicalprocessesofsoilformation (Brady andWeil 2001).Andic soils have a tendency tohaveweakfinestructurethatisgranularinAhorizonsandsubangularblockyinBhorizons(table3).Soilsderivedfromothermaterialshavesimilarstructuresizeandkindbutexhibitstrongerdevelopmentwithagradeofmoderatebeingdominant.Therefore,structuregradeisrecognizedasasuitableidentifierforash-influencedsoils.
Consistenceisadescriptionofasoil’sphysicalconditionatvariousmoisturecontentsasevidencedbytheresponseofthesoiltomechanicalstressormanipula-tion.Theconsistenceofasoilisdeterminedtoalargeextentbytheparticle-sizedistributionofthesoil,butisalsorelatedtootherpropertiessuchasorganicmattercontentandmineralogy(http://organiclifestyles.tamu.edu/soilbasics/soilphysical.html).Andicsoilshaveuniqueconsistencepropertiesdisplayinglowrupturere-sistance(inbothdryandmoiststates),littlestickinessandlowplasticity(table4).Eachofthesecomponentsofconsistenceisusefultoseparateashinfluencedfromothermaterials.Theyareareflectionoftheverylowclaycontentsanduniquemineralogyoftheashymaterial.
Fieldobservationshavenotedahighdegreeofrootproliferationinashysurfacehorizonsinnorth-centralIdaho.Whilethedatashowaslighttrendtowardgreaterrootabundanceintheashymaterials,thedifferencecomparedtotheotherparentmaterialswasnotsufficienttoallowuseofthischaracteristicasadiscriminator(table5).Therecordingofrootabundanceasbroadclassesratherthanactualcountsperareamayhavereducedtheusefulnessofthiscomparison.
Aseriesofsimplemodelsforrecognizingash-influencedsoilmaterialswerecreatedusingthecomponentsidentifiedasusefuldiscriminatorsofashymaterial.Theyweretestedthroughaprocessoftrialanderror.Duringthistestingitwasdiscoveredthatsoiltexturecouldbeusedtohelpimprovemodelperformance.Thisistrueeventhoughthatpropertydidnotmeetthecriteriasetforrecogni-tionasausefuldiscriminator.Soiltextureprovedtobeaspecialcasewherethehighdegreeofclusteringon thesilt loamclass (99.6percentofobservations)fortheash-influencedmaterialhelpedthemodeltorecognizethesematerials.Thisimprovedperformanceresultsfrombetterseparationoftheash-influencedmaterialsfromlowplasticitymaterialsofotherorigins.Duringthisphase,itwasalso determined that moist rupture resistance would not be used in the finalmodel.Eventhoughthiscomponentmetthecriteriaforausefuldiscriminator,itisstronglyrelatedtodryruptureresistance.Theadditionofmoistruptureresis-tancedidnotimprovethemodel.Dryruptureresistancewaspreferredbecauseithadmore-easilyrecognizedclassesandgreaterconsistencyinapplicationbydifferentobservers.
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Field Identification of Andic Soil Properties for Soils of North-central Idaho Gardner
Afinalmodelwascreatedforevaluatingwhetherasoilsampleclassifiesasandicmaterial.Themodelscoresasoilbasedonthesixidentifiedpropertiesand/orcomponentsasfollows:
moisthue–7.5YR=1,other=0;structuregrade–weak=1,other=0;dryruptureresistance–soft=2,other=0;stickiness–nonsticky=2,other=0;plasticity–nonplastic=2,other=0;texture–siltloam=2,other=0.Ascore>=8isandicmaterialwhile<8isnonandic.
Thismodelwasusedtoevaluatetheoriginaldatasetandreturnedanerrorrateof7.6percent.Therewereapproximatelyequalpercentagesoffalsepositivesandfalsenegatives.Of the468horizonsdesignatedashyby theexpertobservers,themodel failed torecognize37.These37falsenegativesweredueprimarilytotheirlackoftheexpectedmoisthueandplasticitycharacteristics.Ofthe477horizonsdesignated-non-ashybyexpertobservers,35weremisidentifiedbythemodelasandicmaterials.These35horizonsaresiltloamsthatarelowinclayandthathaveruptureresistance,stickinessandplasticitycharacteristicssimilartoandicmaterials.Themodelcorrectlydiscriminatedbetweenandicandnonandicmaterialsin92.4percentofcases.
NaF-pHhasbeenidentifiedasasimpleandconvenientindexforthepresenceofandicmaterials(FieldesandPerrott1966).WorkbyKimseyandothers(2005)foundastrong(R2=.82)correlationbetweenNaF-pHandacidoxalateextractableAlandFe.AnotherstudybyBrownfieldandothers(2005)reportedagoodcor-relation(R2=.66)betweentephrapercent(basedongraincounts)andNaF-pH.AcriticalpHvalueof9.4hasbeensuggestedasthethresholdforrecognitionoftephradominatedmaterials(SoilSurveyStaff1995).Thecalculationsshownintable7indicatethat,fortheClearwaterCountydata,thisthresholdvalueistoolow.Thetableshowsthat95percentof thedistributionofNaF-pHvalues forandichorizonsisgreaterthanorequalto9.97.Interestingly,thesameNaF-pHvalueof9.97istheupperboundbelowwhich99percentofthedistributionofnonandicvaluesisfound.RoundingtoonedecimalplacegivesaNaF-pHof10.0asasuggestedthresholdforrecognizingandicmaterials.WhenappliedtotheClearwaterCountydata,thisthresholdcausesanerrorrateofabout10percent(7outof73horizonsmisidentified)forandichorizonsandabout3percent(6outof194horizonsmisidentified)fornonandichorizons.UsingathresholdpHvalueof10.0allowedforcorrectclassificationofhorizonsinabout95percentofcases.
Summary ______________________________________________________Twomethodsforfieldidentificationofvolcanicashinfluencedsoilhorizons
were explored. A simple empirical model was developed for ash recognitionusingtheeasilyobservablequalitativepropertiesofmoisthue,structuregrade,dryruptureresistance,stickiness,plasticityandtexture.Thismodelsuccessfullydiscriminatedbetweentephraandothermaterialsinabout92percentofcases.Amodellikethiscanbeusedtohelpthosenotexpertinsoilclassificationtorecognizeandicsoilmaterials,toevaluatewrittendescriptionswhensoilsamples
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Gardner Field Identification of Andic Soil Properties for Soils of North-central Idaho
arenotavailableandtohelpmoreexperiencedsoilclassifiersinconditionswherethetephraishighlymixedwithothermaterials.OneprincipalweaknessofthismodelisthatitisdevelopedforMountMazamaashinnorth-centralIdaho.Soilsformedinvolcanicejectainotherareasmayhaveadifferentsetofidentifyingcharacteristics.
ThesecondmethodforidentificationofandicmaterialswastheuseofNaF-pH.Whiletheanalysisusedheredependedonlaboratorymeasurements,theNaF-pHcanbereadilymeasuredinthefield.DatafromClearwaterCounty,Idahoshowedthatusingathresholdvalueof10.0pHunitscorrectlyclassifiedsoilhorizonsinabout95percentofcases.TheuseofNaF-pHtodetectallophanicmaterialhasbroadapplicationtomanydifferentvolcanicmaterials.However,identificationofthemostusefulthresholdvaluemaybesubjecttoregionalvariation.
Literature Cited __________________________________________________Brady,N.C.;Weil,R.R.2001.TheNatureandPropertiesofSoils.13thedition.Englewood,NJ:
PrenticeHall.960p.Brownfield,S.H.;Nettleton,W.D.;Weisel,C.J.;Peterson,N.;McGrath,C.2005.Tephrainfluence
onSpokane-floodterraces,BonnerCounty,Idaho.SoilSci.Am.J.69:1422-1431.Burt,R.,ed.2004.SoilSurveyLaboratoryMethodsManual.SoilSurvey InvestigationsReport
No. 42. Version 4.0. Natural Resources Conservation Service, National Soil Survey Center,Lincoln,NE.
Dahlgren,R.A.;Saigusa,M.;Ugolini,F.C.2004.Thenature,propertiesandmanagementofvolcanicsoils.In:Sparks,D.,ed.AdvancesinAgronomyVol.82.AcademicPress:113-182.
FAO/ISRIC/ISSS.1998.WorldReferenceBaseforSoilResources.Rome:FoodandAgriculturalOrganizationoftheUnitedNations,InternationalSoilReferenceandInformationCentre,andInternationalSocietyofSoilScience.WorldSoilResourcesReportNo.84.Available:http://www.fao.org/docrep/W8594E/W8594E00.htm.
Fieldes,M.;Perrott,K.W.1966.Thenatureofallophaneinsoils.III.Rapidfieldandlaboratorytestforallophane.NewZealandJ.Sci.9:623-629.
Kimsey,MarkJr.;McDaniel,Paul;Trawn,Dan;Moore,Jim.2005.Fateofappliedsulfateinvolcanicash-influencedforestsoils.SoilSci.Soc.Am.J.69:1507-1515.
McDaniel,P.A.;Wilson,M.A.;Burt,R.;Lammers,D.;Thorson,T.D.;McGrath,C.L.;Peterson,N.2005.AndicsoilsoftheInlandPacificNorthwest,USA:Propertiesandecological
significance.SoilScience.170:300-311.Richardson,J.L.;Daniels,R.B.1993.Stratigraphicandhydraulicinfluencesonsoilcolordevelop-
ment.In:Bigham,J.M.;Ciolkosz,E.J.,eds.SoilColor.SSASpecialPub.No.31:109-125.Schoenberger,P.J.;Wysocki,D.A.;Benham,E.C.;Broderson,W.D.,eds.2002.Fieldbookfor
samplinganddescribingsoils.Version2.0.NaturalResourcesConservationService,NationalSoilSurveyCenter,Lincoln,NE.
Schwertmann,U.1993.Relationsbetweenironoxides,soilcolor,andsoilformation.In:Bigham,J.M.;Ciolkosz,E.J.,eds.SoilColor.SSASpecialPub.No.31:51-69.
Shoji,S.;Nanzyo,M.;Dahlgren,R.A.1993.Volcanicashsoils:Genesis,properties,andutiliza-tion.In:Hartemink,A.E.;McBratney,A.,eds.Developmentsinsoilscience,21.Amsterdam,TheNetherlands:Elsevier.
SoilSurveyStaff.1995.SoilsurveyLaboratoryManual.WoilsurveyInvestigationsReportNo.45.NationalSoilSurveyCenter.SoilSurveyLaboratory,Lincoln,NE.81p.
SoilSurveyStaff.1999.Soiltaxonomy.Abasicsystemofsoilclassificationformakingandinter-pretingsoilsurveys.2nded.U.S.DepartmentofAgriculture,NaturalResourcesConservation.
Ugolini,F.C.;Dahlgren,R.A.2002.Soildevelopmentinvolcanicash.Available:http://www.airies.or.jp/publication/ger/pdf/06-2-09.pdf.
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In: Page-Dumroese, Deborah; Miller, Richard; Mital, Jim; McDaniel, Paul; Miller, Dan, tech. eds. 2007. Volcanic-Ash-Derived Forest Soils of the Inland Northwest: Properties and Implications for Management and Restoration. 9-10 November 2005; Coeur d’Alene, ID. Proceedings RMRS-P-44; Fort Collins, CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station.
P. A. McDaniel is a Professor of Soil Science, Soil & Land Resources Division, University of Idaho, Moscow, ID. M. A. Wilson is a Research Soil Scientist, U.S. Department of Agriculture, Natural Resources Conservation Service Soil Survey Center, Lincoln, NE.
Abstract HoloceneashfromthecataclysmiceruptionofMountMazama(nowCraterLake)insoutheasternOregonisamajorcomponentofmanyforestsoilsthatlietotheeastofCascadeMountainsinthePacificNorthwestregion.Therelativelyhighproductivityoftheregion’secosystemsiscloselylinkedtothisvolcanicashcomponent.Thispaperreportsontheecologicallyimportantpropertiesoftheseash-influencedsoilsbyexaminingsoilcharacterizationdatafromover500soilhorizonsoftheregioncontainedintheNationalSoilSurveydatabase.Volcanicash-captexturesaregenerallysiltyinareasdistaltotheeruption.Volumetricwater-holdingcapacityofash-caphorizonsisasmuchastwicethatofunderlyinghorizonsandunderscorestheimportanceofashcapsinseasonallydry,forestedecosystemsoftheInlandNorthwestregion.Cationexchangecapacity(CEC)determinedatfieldpH(ECEC)averages8.0cmolckg–1andislessthanone-thirdtheCECdeterminedatpH8.2,indicatingconsiderablevariablecharge.Thesedatasuggestthatash-influencedsoilshavelimitedabilitytostoreandexchangenutrientcationssuchasCa,Mg,andK.Inaddition,strongsorptionofSO4andPO4significantlylimitsthebioavailabilityofthesenutrients.Erosionandcompactionofashcapsaremajormanagementconcerns,butrelationshipsbetweentheseprocessesandash-capperformanceremainunclear.
Physical and Chemical Characteristics of Ash-influenced Soils of Inland Northwest Forests
P. A. McDaniel and M. A. Wilson
Introduction
Soilsformedentirelyorpartiallyinvolcanicejectasuchasash(glassyparticles<2mminsize),cinders (glassyparticles>2mminsize),andpumice (highlyvesicular fragments)arefundamentallydifferentfromothersoilsintermsoftheirphysical,chemical,andmineralogi-calproperties.Becauseofthis,Andisolswereestablishedasthe11thsoilorderinU.S.SoilTaxonomyin1989.TheWorldReferenceBaseofSoilResources(WRB)alsorecognizesthesesoilsasAndosols,oneofthe30soilreferencegroups(FAO/ISRIC/ISSS1998).Soilsformedinvolcanicash,suchastheash-capsoilsfoundinthePacificNorthwestregion,arecharacter-izedbywhatarereferredtoasandic propertiesinSoilTaxonomy(SoilSurveyStaff2003).Andicpropertiesrefertoacombinationofcharacteristics,includingthepresenceofglass,short-range-orderorpoorlycrystallineweatheringproductswithhighsurfacereactivity,andlowbulkdensity.
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McDaniel and Wilson Physical and Chemical Characteristics of Ash-influenced Soils of Inland Northwest Forests
VolcanicashfromtheeruptionofMt.Mazama(nowCraterLake,OR)~7,700yearsBP(Zdanowiczandothers1999)hasinfluencedmanymid-tohigh-elevationfor-estsoilsinthePacificNorthwestregion.Theuniquepropertiesoftheseash-capsareintricatelylinkedtoforestproductivityacrosstheregion(GeistandCochran1991;Meurisseandothers1991).Assuch,thesesoilsrepresentavaluableregionalresourcefrombothaneconomicandecologicperspective.Moreover,ash-capsoilsresponddifferentlytouseandmanagementthandosoilsformedinotherparentmaterials,anditisthereforeimportanttorecognizeandunderstandthebasicdifferencesinproperties.Inthispaper,wedescribesomeoftheimportantcharacteristicsofvolcanicash-influencedsoils.
WeusedtheNaturalResourcesConservationService(NRCS)—SoilSurveyLaboratorycharacterizationdatabaseforWashington,Oregon,Idaho,andMontanatoprovideanoverviewofphysicalandchemicalcharacteristicsofvolcanicash-capsoilsoftheregion.Thesoilsinthisdatabasearerepresentativeofthedomi-nantmappingunitcomponentsinsoilsurveyareas,andhavepropertiesthatareconsideredtypicalofsoilsacrosstheregion.Forinclusioninthedatabase,weidentifiedallhorizonsmeetingeitherthecriteriaforandicsoilpropertiesorandicsubgroupsinSoilTaxonomy(SoilSurveyStaff2003).Allcharacterizationdatawereobtainedusingstandardmethods(Burt2004)andhavebeensummarizedinMcDanielandothers(2005).
Soil Morphology ________________________________________________ThethicknessofashcapsacrosstheInlandNorthwestregionisvariable,but
followsageneraltrendofthinningwithincreasingdistancefromCraterLake(fig.1a).DatapresentedbyMcDanielandothers(2005)showedarangeinthicknessof2to152cmacrosstheregion,withanaveragethicknessof38cm.Itshouldbenotedthatthesereportedthicknessesincludeashcapsthinnedbyerosionaswellasthoseinwhichothersoilparentmaterialshavebeenmixedwiththevolcanicashafterinitialdeposition.Inthelattercase,thereportedthicknessesrepresentthoseofash-influencedmantlesratherthanpureashmantles.Itisimportanttorealizethattheashcapsfoundacrosstheregionhavebeenmixedtovaryingdegreesbypost-depositionalprocessesandrepresentarangeincomposition.Forpurposesofthispaperandotherscontainedintheseproceedings,thetermash capwillbeusedtoincludeallashmantles,regardlessofdegreeofmixing.
Mostoftheofficialsoilseriesdescriptions(SoilSurveyDivision2005)forash-capsoilsoftheregionincludeforestlitterlayersthatareunderlainbyAhorizonshavingthicknessestypicallyrangingfrom2.5-7.5cm(1-3inches).ThedevelopmentofAhorizonsformedinvolcanicashintheInlandNorthwest isusuallyweakdespitethefactthatash-capsoilsgenerallycontainrelativelylargeamountsoforganicmattercomparedtoothermineralsoils(Dahlgrenandothers2004).Thisweakdevelopmentisprobablyduetothefactthatmostash-influencedsoilsareforestsoils,wherethemajorityofcarboniscontainedinlitterlayersandrelativelysmallquantitiesareaddedtoAhorizonsintheformofroots.Thisfactorresultsinrelativelythin,light-coloredAhorizons.Verydark-coloredAhorizonscanforminvolcanic-influencedsoils thatsupportgrassesorunderstoryvegetationwithextensiverootsystems.Deep,darkAhorizonshavebeendescribedunderbrackenfern(Pteridium aquilinum)communitiesinnorthernIdaho(Johnson-Maynardandothers1997).Thesecommunitiesmayhaveasmuchas3,500g/m2ofbelowgroundbiomassintheformofrhizomesandfineroots(Jimenez2005).
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Physical and Chemical Characteristics of Ash-influenced Soils of Inland Northwest Forests McDaniel and Wilson
Figure 1—Change in (a) ash-cap thickness and (b) particle-size distribution of Mazama tephra as a function of distance from Crater Lake, OR. Particle-size data represent averages for the ash caps of Lapine, Angelpeak, Threebear, and Jimlake soils and are adapted from McDaniel and others (200�).
UnderlyingtheAhorizonsarereddish-toyellowish-brownBwhorizonsthatdonotexhibitsignificantincreasesinclaycontent.Huesofthesesubsoilhorizonsaretypically7.5YRto10YRwithchromasof4or6.ThesecharacteristiccolorsreflecttheweatheringofashtoformpoorlycrystallineFeoxidessuchasferrihy-drite(McDanielandothers2005).
Insomehigher-elevationareas,ash-capsoilsmayhaveundergonesufficientpodzolizationtodevelopE-Bh,Bhshorizonsequences.Thesesoilsaretypicallyinhigh-precipitationenvironmentsandhaveextremelyacidEhorizons.IntheSelkirkMountainsofnorthernIdaho,pHvaluesaslowas3.7havingbeenre-ported(McDanielandothers1997),thelowestpHvaluesfoundanywhereintheregionfornativesoils.
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McDaniel and Wilson Physical and Chemical Characteristics of Ash-influenced Soils of Inland Northwest Forests
Physical Properties ______________________________________________
Particle-Size Distribution
MuchofthetephradistributedthroughoutthePacificNorthwestwascarriedinsuspensionbyprevailingwesterlywinds,aprocessthathasresultedinfairlydistinctrangesofparticlesizesassociatedwithashcaps.Examinationofashcaptexturesacrosstheregionshowsadecreaseinoverallparticlesizewithincreas-ingdistancefromthesource(fig.1b).ThepumiceregionsofcentralOregonareincloserproximitytoCraterLake,andsand-sizedpumicedominatesinsoilslikeLapine.However,ashcapsfromtheBlueMountains(e.g.Angelpeaksoil),northernIdaho(Threebearsoil),andwesternMontana(Jimlakesoil)arepredominantlysilt-sized,reflectingthegreaterdistanceoftransport.Fine-earthfractionsoftheseashcapstypicallyhavesiltloamorloamtextures,whichcansubstantiallyenhancethewater-holdingcapacityofsoilprofiles.
Bulk Density
BulkdensityofAndisolstendstoberelativelylow,andthisisoneofthedefiningcharacteristicsofthesesoilsinSoilTaxonomyandtheWRB.Ofthe271horizonsexaminedacrosstheregion,theaveragebulkdensityis0.90gcm–3(fig.2).How-ever,only~60perecentofthehorizonshavebulkdensitiesof<0.90gcm–3,sug-gestingthatmixingand/orcompaction,bothofwhichwouldtendtoincreasebulkdensity,haveoccurredsincedeposition.Becausebulkdensityisinverselyrelatedtoporosity,anashcapwithabulkdensityof0.90gcm–3mayhave~40percentmoreporositythanatypicalmineralsoilwithabulkdensityof1.3gcm–3.
Figure 2—Bulk density data for andic soil horizons of the Pacific Northwest region. Taken from McDaniel and others (200�).
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Water-Holding Capacity
Andisols typically are able to retain large amounts ofwater (Dahlgren andothers2004).IntheInlandNorthwestregionwhereextendeddryperiodsoftenoccur during the growing season, this water-holding capacity is arguably themostimportantpropertyfromanecologicalstandpoint.Additionalwater-holdingcapacityassociatedwithash-capsoilsmaybecriticaltotheestablishmentandmaintenanceofsomeplantcommunities.Thebasisfortheadditionalwater-holdingcapacityimpartedtosoilsbyvolcanicashstemsfromthreefactors.First,asdis-cussedpreviously,ashcapshaverelativelyhighporosity.Secondly,muchofthedistalashissilt-sized,whichisdesirablefromthestandpointofwaterretentioncharacteristics.Thisisespeciallytrueinmanymountainousareaswherevolcanicashoverliescoarser-textured,oftenrockysoilswithrelativelylittleplant-available-water-holdingcapacity.Finally,weatheringofvolcanicashgivesrisetoacolloidalfractionthathashighsurfaceareaandisabletoretainconsiderablequantitiesofwater(Wada1989;Kimbleandothers2000;Dahlgrenandothers2004).
Theeffectofavolcanicashcaponthewater-holdingcapacityofanorthIdahosoilisillustratedinfigure3.Theashcapconsistsofthetoptwohorizons,whichhavemorethantwicethewater-holdingcapacity(onavolumebasis)oftheun-derlyingcoarser-texturedhorizonthathasformedinoutwash.Inthisexample,theashmantlecontributes8.6cm(~3.4inches)ofplant-availablewatertothesoilprofile.Ash-capsoftheregionhaveanaveragewaterretentionof~11percent(byweight)at1,500kPaofsoilmoisturetension(wiltingpoint)(McDanielandothers2005),orroughlytwicethatofsandysoils(BradyandWeil2004).
Figure 3—Water retention difference in the top �0 cm of the Bonner series (��ID017002) from north Idaho. Bars represent the difference in water content between –1,�00 and –�� kPa, expressed on a volume basis and corrected for rock fragment content. Shaded bars are for andic materials.
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Whencomparingorinterpretingwaterretentiondata,itisimportanttodistin-guishbetweendatareportedonagravimetric(weight)andthosereportedonavolumebasis.Becausesoilhorizonsformedinvolcanicashtypicallyhavebulkdensities<1.0g/cm3,watercontentswillbegreaterwhenexpressedonaweightbasisratherthanavolumebasis.Theoppositeistrueforothermineralsoilswithbulkdensities>1.0g/cm3.
A mantle or cap of volcanic ash also contributes to a more-favorable soilmoistureregimethroughamulchingeffect.Someoftheincreasesincropyieldsobservedafterthe1980MountSt.Helenseruptionwereattributedtothedeposi-tionoffreshashanditsroleinreducingevaporativewaterlosses(Dahlgrenandothers2004).
Other Physical Properties
SomeAndisolsexhibitthixotropy,whichisdescribedasareversiblegel-sol-geltransformation (Nanzyo and others 1993b). Upon application of pressure orvibration,awetsoilmasswillexperienceasuddenreversible lossofstrengthandbegintoflow.Itcaneasilybeobservedinawell-moistenedash-capsample.Byapplyingpressure to thematerialbetweenthethumbandforefinger,watercanbeforcedoutofthesoilmass;releaseofpressurewillcausethenwatertobere-absorbed.Onalargerscale,thixotropycanresult insoilcollapseunderroadwaysandbuildingfoundations(BradyandWeil2004).Thixotropyismostpronouncedinhighlyweatheredsoilsformedinvolcanicash(Buolandothers2003),andthereforeisnotoftenwellexpressedintherelativelyless-weatheredash-capsoilsoftheInlandNorthwestregion.Soilsformedinvolcanicashalsohavealowbearingcapacitybecauseoftheirlowbulkdensity(Kimbleandothers2000),andthismakesthemsusceptibletocompactionandcancreateproblemsfortraffickingandbuildingfoundations.
Mineralogical Properties _________________________________________
Volcanic Glass
TheprincipalcomponentofMazamavolcanicashisglass,whichwasformedbytheveryrapidcoolingofrhyodaciticmagmaasitwasejectedfromthevolcanoduringtheclimaticeruption(fig.4)(Bacon1983).Theamountofglassinvolcanicashmantlesacrosstheregionisvariable,andmostlikelyreflectspost-depositionalredistribution.IntheBlueMountainsofnortheasternOregonandsoutheasternWashington,relativelyundisturbedashmantlescontain60-90percentvolcanicglassandarefoundinmoisterlandscapepositionswithlowerfirefrequency(Wil-sonandothers2002).Inotherareaswithmoreactivesurficialprocessessuchaserosionafterfire,glasscontentsrangesfrom25-60percent,andthesearereferredtoasmixedmantles(Wilsonandothers2002).Theglasscontentof528ash-capsoilhorizonsoftheregionthatmeetandicsoilrequirementsinSoilTaxonomyaverages~42percentandexhibitsabimodaldistribution(McDanielandothers2005).Thissuggeststhatmixedmantlesarecommonacrosstheregion,andthatlocally,underlyingsoilshaveatleastsomeinfluenceonashcapproperties.
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Analysis of Mazama ash deposits shows an elemental composition of 70-72percentSiO2(Bacon1983).Inaddition,McDanielandothers(1997)reportedthatthecombinedAl2O3andSiO2contentofMazamaglasswas~87.5percent,withtheCaO,MgO,andK2Ocontentscomprisingonly4.9percentbyweight.Forcomparativepurposes,Bohnandothers(2001)reportanaverageCaO,MgO,andK2Ocontentforavarietyofigneousrocksof12percent.Itisclearfromthesedata thatvolcanicglass isnota rich sourceofplantnutrientsandshouldnotbethoughtofasahavingremarkablefertility.MinoramountsofplantnutrientssuchasSO4
2–,Ca2+,andPO42–presentintheoriginalMazamaashfallmayhave
providedshort-termfertilityinputs,aswasthecasewiththe1980eruptionofMountSt.Helens(Fosbergandothers1982;Mahlerandothers1984).However,long-termfertilityoftheglassisrelativelylow.
Clay Mineralogy
Becauseofthelackofacrystallinestructure,glassweathersrelativelyrapidlytoformpoorlycrystallineornon-crystallinemineralsintheclayfraction.InslightlytomoderatelyweatheredAndisolssuchasthosefoundinthePacificNorthwestregion,therearethreemineralassemblagesthattendtodominate:(1)Al-humuscomplexes,oftenwithAl-hydroxy-interlayered2:1minerals; (2)allophaneandimogolite,and;(3)poorlycrystallineFeoxides(ferrihydrite)(Dahlgrenandothers2004).Asashweathers,AlandFereleasedintosoilsolutioninsurfacehorizonscanformstableorganiccomplexes,especiallyatsoilpH<5(ParfittandKimble1989);thesepHvaluesarecommonunderconiferousforestvegetationathigherelevationintheInlandPacificNorthwest.Al-humuscomplexesrepresentactive
Figure 4—Volcanic glass shard from north Idaho soil. Glass is from the Mazama eruption and measures ~0.1 mm across. Photo from University of Idaho.
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formsofAlandmaycontributetoAltoxicity(Dahlgrenandothers2004).Intherelativeabsenceofhumusandlessacidconditions,suchasinBandChorizons,AlandSiprecipitatetoformallophaneandimogolite.Thesetwoaluminosilicatemineralsmayhavesimilarchemicalcomposition,butallophanetypicallyconsistsofsphericalunitswhileimogoliteappearsasthreadsortubes(Kimbleandothers2000).Allophaneand imogolitebothhave relativelyhigh surfacearea.UsingdatapresentedbyHarshandothers(2002),WhiteandDixon(2002),andMalla(2002),thesurfaceareaofimogoliteisasmuchas100timesgreaterthanthatofkaoliniteand40percentgreaterthanthatofvermiculite.Thisimportantpropertyisdirectlyrelatedtoboththehighwater-holdingcapacityandchemicalreactivityoftheseminerals.
Chemical Properties _____________________________________________
Soil Reaction
Themajorityofandicsoilhorizonsoftheregionaremoderatelytoslightlyacid.Approximately70percentof thehorizonsexaminedhavepHvaluesbetween5.6and6.5,withanaveragepHof6.02(fig.5).ThispHrangeisgenerallysuitableforplantgrowth,asmanynutrientsarepresentinplant-availableformswithinthisrangeandthepotentialforaluminumtoxicityislow(BradyandWeil2004).
Cation/Anion Exchange
Oneoftheimportantfeaturesofsoilsformedinvolcanicashisthevariablechargeassociatedwith thecolloidal fraction.Variablecharge,also sometimesreferredtoaspH-dependentcharge,meansthatthenetsurfacechargedepends
Figure 5—Soil pH data for ash-cap soil horizons from the Inland Pacific Northwest region.
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onthepHofthesoilsolution(SoilScienceSocietyofAmerica2001).Itisthisnetsurfacechargethatdeterminesthecationexchangecapacity(CEC)ofasoilanditsabilitytoretainandexchangenutrientcationssuchasCa2+,Mg2+,andK+.TheCECofandicsoilsdecreaseswithdecreasingpH,andmayinfact,bequitelowattheacidicpHvaluesthatcharacterizemanyforestsoils.Moreover,someandicsoilsmayhavesubstantialanionexchangecapacity(AEC)atacidicfieldpHvalues(Kimbleandothers2000),influencingtheretentionofionssuchaschlorideandnitrate.AlthoughPO4
2–andSO42–ionsaresorbedthroughanion
exchange, fixation of these ions (described below) is much greater than thisexchangereaction.
TheeffectofvariablesurfacechargeisillustratedbyCECandbasecationdatafromash-capsoilsacrosstheregion.Table1showsCECvaluesdeterminedfor515horizonsusingthreeprocedures.Thelowestvaluesareforeffectivecationexchangecapacity(ECEC),wheretheCECisdeterminedatthepHofthesoil.ThehighestvaluesareforCECdeterminedatpH8.2(CECpH8.2),whichisconsiderablyhigherthanthesoilpHoftheregion.AlthoughthislattermethodoverestimatestheCECthatexistsinthefield,thedifferenceinECECandCECpH8.2valuesillus-tratesthepotentialvariablechargethatexistsinthesesoils.Onaverage,CECpH8.2valuesareapproximatelyfourtimesgreaterthanECECvalues.
Table 1—Exchange properties of andic soil horizons of the Inland Northwest Region. Adapted from McDaniel and others (200�).
Ca2+ Mg2+ K+ Base saturation1 ECEC2 CEC pH 7 CEC pH 8.2
- - - - (cmolc /kg) - - - - (%) - - - - - - - - (cmolc /kg) - - - - - - - - Average 7.2 1.� 0.� 4�.0 �.� 19.1 2�.4 n �1� �1� �14 �14 11� �1� �1� Std. deviation �.7 2.0 0.7 2�.� �.4 11.� 1�.� Minimum 0 0 0 1 0.� �.4 7.0 Maximum ��.2 24.0 9.1 100 4�.7 101.0 12�.2
Anotherimportantcharacteristicofash-capsoilsistheirabilitytostronglyadsorbandimmobilizeplant-availableformsofPandS.Thisprocess,knownasfixation,resultsinlowconcentrationsofPO4
2–andSO42–insoilsolutionand
availableforplantuse(fig.6).TheabilitytofixPO42–resultsfromthestrongat-
tractionbetweenPO42–andtheedgesofallophane,imogolite,andferrihydrite,
andthereareprobablyseveralsorptionmechanismsinvolved(Wada1989).HighPO4
2–sorptionisoneofthecharacteristicsusedtodefineandicsoilpropertiesinSoilTaxonomyandandichorizonsinWRB.
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Figure 6—Sorption isotherms for (a) phosphorus additions (adapted from Jones and others 1979), and (b) sulfate additions (adapted from Kimsey and others 200�). Data points represent the proportions of sorbed (plant unavailable) and soluble (plant available) forms with additions of increasing quantities of phosphorus and sulfate.
Allophanic and Non-allophanic Andisols __________________________Becauseoftherangeincharacteristicsofvolcanicash-capsoils,arelatively
simpleclassificationschemehasbeendevisedthatrecognizesthesedifferencesfromamanagementperspective.Thissystemclassifiessoilsaseitherallophanicornon-allophanic(Nanzyoandothers1993a;Dahlgrenandothers2004).Allo-phanicAndisolsarethosethataredominatedbyinorganicweatheringproductssuchasallophaneandimogolite.Incontrast,organicallyboundcomplexesaremuchmoreimportantinnon-allophanicAndisols.Propertiesofthesetwoclassesofash-derivedsoilsaresummarizedintable2.Ingeneral,non-allophanicsoilspresentmoremanagementchallenges.Thesesoilshaveseveralpropertiesthatmayinhibitplantgrowth—greateracidityandgreaterpotentialforAl3+toxicity
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Physical and Chemical Characteristics of Ash-influenced Soils of Inland Northwest Forests McDaniel and Wilson
aretwoofthemostimportant.MostofthesoilsintheInlandNorthwestregionareclassifiedasallophanic(McDanielandothers2005).However,researchhasshown that shifts fromallophanic tonon-allophanicpropertiesandviceversacanoccurrelativelyquicklywithchangesinvegetation.AnexampleofthisfromnorthernIdahoisdescribedinthefollowingsection.
Response to Management _______________________________________
Erosion
Thescientific literaturecontainssometimes-contradictory informationaboutsusceptibilityofash-capsoilstoerosion.Soilsformedinvolcanicasharetypi-callydescribedashavingstrongresistance toerosion, largelyasa functionofstableaggregationandhighinfiltrationrates(Nanzyoandothers1993b;Dahlgrenandothers2004).However,becauseoftheirlowbulkdensitytheymaybeverysusceptibletowindandwatererosionwhenvegetativecoverisremoved(Kimbleand others 2000; Arnalds and others 2001). In the Inland Northwest region,maintenanceofforestcover,includingbothcanopyandlitterlayers,hasbeenanimportantfactorintheretentionofMazamaashcapsoverthemillenniasincedeposition(McDanielandothers2005).Thesefactorssuggestthaterodibilityofvolcanicashcapsisrelatedtodegreeofdisturbance;disturbancethatdestroysorremovescanopyandlitterlayerswilllikelyleadtosevereerosion.
Compaction
Perhapsoneof thebest-documentedresponsesofash-capsoils toland-useactivitiesiscompaction.Asdescribedearlier,andicsoilsaredefinedinpartbyabulkdensityof<0.90g/cm3.Numerousstudieshaveshownsignificantincreasesinash-capbulkdensityasaresultoftimberharvesttrafficking.IntheBlueMoun-tainsofeasternOregonandWashington,averagebulkdensity increasedfrom0.669gcm–3inunharvestedareasto0.725gcm–3inharvestedareas,represent-inganaverageincreaseof~9percent(Geistandothers1989).However,larger
Table 2—Comparison of properties of allophanic and non-allophanic Andisols (adapted from Dahlgren and others 2004; Nanzyo and others 199�a).
Property Allophanic Non-allophanicpH slightly to moderately acid strongly acid
Dominant mineralogy allophane/imogolite Al-interlayered 2:1 layer silicates and Al-organic complexes
Organic matter content moderate moderate to high
Al toxicity rare common
Compaction potential slight moderate
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bulkdensity increaseswereassociatedwithskid trailsand landings.Similarly,Cullenandothers(1991)reportedsignificantincreasesinash-capbulkdensityinmoderatelyandseverelytraffickedareasascomparedtonon-harvestedcontrols.In addition, they were able to quantify changes in soil hydrologic propertiesaccompanyingbulkdensityincreases.Watercontentatrelativelylowsoilmois-turetensionsdecreasedsignificantlyintraffickedareascomparedtothecontrols(Cullenandothers1991)(fig.7a).One-hourinfiltrationdecreasedaswell,withvaluesdecreasingfrom38.5cminthecontrolto7.3cmintheseverelytraffickedareas(Cullenandothers1991).
Figure 7—Changes in (a) water content of ash-cap soils due to timber harvest trafficking, and (b) 1-hour infiltration in ash-cap soils due to timber harvest traf-ficking. *, ** indicate values that differ from the untrafficked controls at the 0.01 and 0.0� significance levels, respectively. Data are adapted from Cullen and others (1991).
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Chemical/Mineralogical Changes
WorkbyJohnson-Maynardandothers(1997)innorthernIdahosuggeststhatdevelopmentofnon-allophanicpropertiesaccompaniesestablishmentofbrackenferncommunitiesafterclearcuttinginaslittleas30yearsandmaycontributetotheobservedlackoftimberregeneration.ThissubjectisdiscussedinmoredetailbyFergusonandothers (thisproceedings).Recent literature suggests that thismineralogicalconversionisnotirreversible.Takahashiandothers(2006)reportedthatadditionsoflimetonon-allophanicsoilswillraisepHandreducetheactiveformsofAl3+,therebyrepresentingapotentialreclamationstrategy.
Knowledge Gaps ________________________________________________Twomajorquestions related to thepropertiesandmanagementof ash-cap
soilsintheInlandPacificNorthwestregionremain.Thefirstquestionis:How much ash is there and where is it?Thisseemslikeabasicquestion,yetitisoneforwhichagoodanswerdoesnotcurrentlyexist.TheNationalCooperativeSoilSurveyprogramhasproduced in~1:24,000-scale soil surveys forpartsof theregion,andtheseprovidesufficientdetailtoassesstheextentandspatialdistri-butionofash-capsoils.However,muchoftheforestedlandareawhereash-capsoilsare foundhasnotbeensubject to this typeofsoilmapping.Asa result,detailedinformationabout thequantitiesandspatialdistributionofashacrosstheregionisoftenlacking,poorlydocumented,and/ornotreadilyaccessible.Developmentofmodelsthatpredictashcapdepthanddistributionwill likelybegreatlyenhancedbynewtechnologies in remotesensing.However, in theabsenceofmoredetailedmappingorpredictivemodels,atestsuchastheNaFpHmeasurementcanprovideaquickandeasy indicatorofash-capsoils.AnNaFpHvalue>9.4generallyindicatesthepresenceofweatheredvolcanicash(FieldesandPerrott1966;Wilsonandothers2002)andservesasaguidelineforidentifyingash-capsoils.
Asecondquestionis:What is the relationship between ash-cap soil properties and soil performance?Themajorityofresearchtodatehasfocusedonmeasure-mentofash-cappropertiesratherthanperformance.Forexample,compactionofash-capsoilshasbeenwelldocumented,butcompactedbulkdensitiesaretypicallywellwithintherangeconsideredtobeacceptableforothermineralsoils.Sowithregardtoperformance,doesanashcapwithbulkdensity1.1gcm3be-havedifferentlythanasoilwithoutanashcaphavingthesamebulkdensity?Ananswertothisquestionwillrequireabetterunderstandingofthechangesinporesizeandconnectivitythatoccurwithcompactioninash-capsoils.Effortsshouldbefocusedondeterminingcriticalthresholdsinandicsoilpropertiesatwhichtreegrowthandthehydrologicperformancewillbeadverselyaffected.Long-termstudieswillbeneededtoaddresstheseissues,andsuccessfulmanagementwillultimatelyrequireanunderstandingofthemechanismsinvolved.
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Wada,K.1989.Allophaneandimogolite.In:Dixon,J.B.;Weed,S.B.,eds.Mineralsinsoilenvi-ronments.2nded.Madison,WI:SoilScienceSocietyofAmerica:1051-1287.
White,G.N.;Dixon,J.B.2002.Kaolin-serpentineminerals.In:Dixon,J.B.;Schultze,D.G.,eds.Soilmineralogywithenvironmentalapplications.BookSeriesno.7.Madison,WI:SoilScienceSocietyofAmerica:389-414.
Wilson,M.A.;Burt,R.;Ottersburg,R.J.;Lammers,D.A.;Thorson,T.D.;Langridge,R.W.;Kreger,A.E.2002.Isoticmineralogy:CriteriareviewandapplicationinBlueMountains,Oregon.SoilSci.167:465-477.
Zdanowicz,C.M.;Zielinski,G.A.;Germani,M.S.1999.MountMazamaeruption:Calendricalageverifiedandatmosphericimpactassessed.Geology.27:621-624.
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In: Page-Dumroese, Deborah; Miller, Richard; Mital, Jim; McDaniel, Paul; Miller, Dan, tech. eds. 2007. Volcanic-Ash-Derived Forest Soils of the Inland Northwest: Properties and Implications for Management and Restoration. 9-10 November 2005; Coeur d’Alene, ID. Proceedings RMRS-P-44; Fort Collins, CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station.
Terry L. Craigg, Soil Scientist, Deschutes National Forest, Sisters OR. Steven W. Howes, Regional Soil Scientist, U.S. Department of Agriculture, Forest Service, Pacific Northwest Region, Portland, OR.
AbstractForestmanagersmustunderstandhowchangesinsoilqualityresultingfromprojectimplementationaffectlong-termproductivityandwatershedhealth.Volcanicashsoilshaveuniquepropertiesthataffecttheirqualityandfunction;andwhichmaywarrantsoilqualitystandardsandassessmenttech-niquesthataredifferentfromothersoils.Wediscusstheconceptofsoilqualityandhowitmaybealteredbyactivity-inducedsoildisturbances.Apracticalapplicationoftheuseofsoildisturbancecategoriesandphysicalsoilindicesusedtoperformoperationalsoilmonitoringonanashcapsoilisalsodiscussed.
Introduction
Soil disturbance resulting from forest management activities is of concern to both landmanagersandthepublic.OnNationalForestSystemlandsintheNorthwestmanycurrentprojectsarebeingadministrativelyappealedorlitigatedbasedontheassumptiontheywillresultinsoildegradation.Someclaimthatwhenimplementinggrounddisturbingactivities,theForestServicecommonlyexceedsitsownstandardsintendedtomaintainsoilquality.There is aneed forobjectiveandaccuratemeasuresof change in soilqualitycausedbymanagementactivities.Assessingchange in soilquality isdifficult andcanbe influencedby a number of complicating factors. Properties of volcanic ash soils may also requiredevelopment and application of unique soil quality standards and assessment protocols.
Properties of Volcanic Ash Soils that May Affect Quality and Function
Many soils in the Inland Northwest have been influenced by ashfall deposits from theeruptionofMt.Mazama(nowCraterLake)aswellasotherCascadevolcanoes(HarwardandYoungblood1969).ThesedepositsarefoundinmostsoilsoftheColumbiaPlateauofcentralandeasternOregonandWashington.Soilsrangeintexturefrom“popcornpumice”
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nearCraterLaketosandsandsiltsasdistancefromsourceincreases.Volcanicashsoilshavephysicalandchemicalpropertiesthataffecttheirqualityandfunction;andthatmakethemuniquewhencomparedtoothersoilparentmaterials.
AstudyconductedbyGeistandStrickler(1978)comparedsomephysicalandchemicalpropertiesofvolcanicashsoilstoresidualsoilsderivedfrombasaltintheBlueMountainsofnortheasternOregon.Insummary,volcanicashsoilshad:
• Lowerbulkdensity • Higherporosity • Weakerstructuraldevelopment • Lowercohesion • Lowercoarsefragment(>2mm)content
SuchpropertiesaredescribedindetailbyothersintheseProceedings.Thispaperfocusesonsoilswithadistinct“ashcap”orsurfacelayerofvolca-
nicashdeposits.Suchdepositsvaryfromafewcentimeterstooverameterindepthdependingondistance fromthesource, topography,windpatternsandsubsequenterosion.
Volcanicashsoilshavearelativelyuniformundisturbedsurfacesoilbulkden-sity(0.67)andadisproportionateconcentrationofnutrients(totalOM,N,K)intheupper30cmofthesoilprofile.Thesepropertiestendtomakevolcanicashsoilsmoresusceptibletosurface(sheet,rill,wind)erosionwhenexposed;andtodisplacementbyground-basedequipment.Theystoremorewaterbutyieldalargerproportionofitinthelowsuctionranges.Volcanicashsoilsalsoseemtocompacttothesamedegreeoverawide-rangeofmoisturecontents.
Pumicesoilshavemanyof thesamepropertiesasothervolcanicashsoils.Likeothervolcanicashsoilsthelowdensity,lackofcohesion,andconcentra-tionofsoilnutrientsintheuppersoilprofileofpumicesoils,makepumicesoilssusceptibletosoilcompactionandthelossofnutrientsthroughsoildisplacement.Becauseoftheirlowcohesionbetweenindividualpumiceparticles,compactioninpumicesoilscanresultfrombothcompressionandvibration.Pumicesoilsalsohavebeenfoundtobemostsusceptibletocompactionwhentheyareverydryoratornearsaturation.Soilmoisturecontentsbetweenthesetwoextremesap-peartoprovidesomecohesionbetweensoilparticlesreducingsusceptibilitytocompaction.Amountsofsoilorganicmatterisalsoimportantwhendeterminingtheirsusceptibilitytocompaction.
Whencompactiondoesoccur,soilstrength(asmeasuredbyresistancetopen-etration)hasbeenfoundtoincreaseexponentiallywithanincreaseinsoilbulkdensity(Chitwood1994).Incompactedsoilssoilstrengthhasalsobeenshowntoincreasequicklyasthesoildriesoutoverthegrowingseason(Craigg2006).Thusmeasurementsofsoilstrengthandsoilbulkdensityareprovidingdifferentinformationaboutchangesoccurringinthesoilwhencompactionoccurs.Sincethereisnotasimplelinearrelationshipbetweenmeasurementsofsoilstrengthandsoilbulkdensitywhensoilconditionschangeitwouldbedifficulttoreadilysubstituteonemeasurementfortheother.
Considerationoftheseproperties,alongwithash/pumicedepthandunderlyingsoilmaterial, is important indeveloping soilmanagementobjectives/prescrip-tions,inevaluatingpotentialimpactsofproposedactivities,andinestablishingmeaningfulsoilqualitystandards.
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Soil Disturbance and its Relationship to Soil Quality ________________Definitionsofsoilqualitydiffergreatlydependingonwhomoneasks.Most
wouldsaytheyrecognizeahighqualitysoil“when they see it”butwhenaskedtodefinesoilquality,eachwouldmostlikelyprovideadifferentanswerdependingontheirindividualobjectivesandpersonalbiases(Karlenandothers1997).Thequalityofanindividualsoilmayvaryfordifferingpurposes:ahighqualitysoilforproductionoftreesorforagemayhavelowqualityforproductionofcottonorwheat.Tosaythatonesoilisofhigherqualityor“better”thananotherisnotproperwithoutqualification.
Therearesomewhousetheterms“soilquality”and“soilhealth”interchange-ably(Warkentin1995).Eachsoilhasinherentphysical,chemical,andbiologicalpropertiesthataffectitsabilitytofunction asamediumforplantgrowth,toregulateandpartitionwaterflow,ortoserveasaneffectiveenvironmentalfilter.Whenanyoracombinationoftheseinherentfactorsisalteredtoapointwhereasoilcannolongerfunctionatitsmaximumpotentialforanyofthesepurposes,thenitsqualityorhealthissaidtobereducedorimpaired(LarsonandPierce1991).
Manyfactorsenterintomakingdeterminationsofsoilquality.Someofthesefactorscanbechangedbydisturbance (LarsonandPierce1991;Seyboldandothers1997;Grossmanandothers2001).Alterationofsoilproperties throughdisturbancemechanismsisnotnecessarilyharmful.Tillageisanextremeformofsoildisturbanceoftenusedtoimprovesoilqualityor“tilth”forproductionofagriculturalcrops.Inforestryapplications,sitepreparationtoimproveregenera-tionsuccessorsoilrestorationworkofteninvolvesoildisturbancetosomedegree(surface soilexposure, scalping, subsoiling).What sets theseapart fromotherformsofsoildisturbanceisthattheyareplannedandare,orshouldbe,carriedoutwithspecificobjectivesinmindunderprescribedconditions.
Managementactivitiesonforestandrangelandsoftenresultinvariousformsofdisturbancethatcanaltersoilfunction.Commonly,landmanagersareconcernedabouthowchangesinsoilqualityorfunctionresultingfromunplanned,activity-induceddisturbanceaffectthelong-termproductivityandhydrologicresponseofwatersheds.Inwildlandsituations,concernusuallyfocusesondisturbance-relateddeparturesfromnaturalsoilconditions(consideredtobemaximumpotentialorbestpossibleconditions),occurringaseitherlegacyimpactsorthosecausedbycurrentmanagementactivities.Understandably,therearedifferencesofopinionamong soil scientists and landmanagers aboutwhenandwhere “significant”thresholdsarereached.Thisiscomplicatedbythefactthatsoilsdifferintheirabilitytoresistandrecoverfromdisturbanceeffects(Seyboldandothers1999).
Disturbance may have negative, neutral, or even positive effects on a soildependingonitsinherentproperties.Meaningfulsoildisturbancestandardsorobjectivesmustbebasedonmeasuredanddocumentedrelationshipsbetweenthedegreeofsoildisturbanceandsubsequenttreegrowth,forageyield,orsedi-mentproduction.Studiesdesignedtodeterminetheserelationshipsarecommonlycarriedoutaspartofcontrolledandreplicatedresearchprojects.Thepaucityofsuchinformationhascausedproblemsindeterminingthresholdlevelsfor,ordefiningwhen,detrimentalsoildisturbanceexists;andindetermininghowmuchdisturbancecanbetoleratedonagivenareaoflandbeforeunacceptablechangesinsoilfunction(productivepotentialorhydrologicresponse)occur.Givennaturalvariabilityofsoilpropertiesacross the landscape,asinglesetofstandards forassessingdetrimentaldisturbanceseemsinappropriate.
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Defining Detrimental Soil Disturbance _____________________________Soildisturbanceexistsinanumberofforms.Inforest,range,andwatershed
managementapplications,itmostcommonlyoccursascompaction,displacement,andpuddlingresultingfromuseofground-basedharvestingandslashdisposalequipment.Theremovalofabovegroundorganicmatterisalsoaresultofthistypeofdisturbance.Soildisturbancecanalsooccurintheformofsheetandrillerosionorcharredsoilinintenselyburnedareas.
Effectsofsoildisturbanceonsiteproductivityorhydrologicfunctionofwa-tershedsisdependentonitsdegree,extent,distribution,andduration(Froehlich1976;SniderandMiller1985;Claytonandothers1987).Degree refers to theamountofchangeinaparticularsoilpropertysuchasporosity,bulkdensity,orstrengthandthedepthtowhichthatchangeoccurs.Extent referstotheamountoflandsurfaceoccupiedbythatchangeexpressedasapercentage of a specified area.Distributionofsoildisturbancewithinamanagementareamaylikelybemoreimportantthantheactualestimatedextent.Disturbancecanoccurassmallevenly-distributedpolygons,orinlargepolygonsinoneorafewlocations.Dura-tionisthelengthoftimedisturbanceeffectspersist.Forexample,compactioneffectshavebeenmeasuredover30yearsfollowingtimberharvestactivitiesonsomesoils(Froehlichandothers1985).
Degreeanddurationofeffectsarelargelydeterminedbyinherentsoilproper-tiesthatinfluenceresistanceto,andabilitytorecoverfrom,disturbance.Extent,distribution,and,insomeinstances,degreeofdisturbancecanbecontrolledbyimposingmanagementconstraintssuchaslimitingseasonofoperation,spacingofskidroadsandtrails,andnumberofequipmentpasses.
Achallengehasbeentoestablishmeaningfulsoilqualitystandardsgiventheinherentvariabilityofsoilsacrossthelandscape.Simplystatingasinglethresholdbeyondwhichdetrimentalsoilconditionsarethoughttoexistmaynotbeenough.Mostforestlandmanagersdonotwishtodamagetheirproductivebaseorcauseimpairedwatershedfunction.However,theyalsodonotwanttounnecessarilylimitmanagementopportunities.
Current Status and Needs ________________________________________Soilqualitycanbeimproved,maintained,ordegradedbyforestmanagement
activities.Inordertoidentifyandquantifysuchchanges,ascientificallyrigorousprotocolisrequired.Itmustquantifytypesandamountsofsoildisturbanceswithinaspecifiedarea;andidentifyareasofdisturbanceconsideredtobedetrimental.Protocolsmustbe:
• Statisticallyvalid • Relativelyeasytoimplement • Costeffective • Usableatdifferentscales • Abletodetermineifsoilqualityisbeingmaintained,improvedordegraded.
Numerousmethodsexistforsamplingsoildisturbanceinbothoperationalandresearchsettings.Methodsdifferwithrespecttosamplingobjectives,soilvariablesconsidered,andassessmentprotocols.Inconsistentapplicationofsoildisturbancemeasurementtechniquesacrossavarietyoflandownershipshasled,insomecases,tounreliableandincomparableresults.Moreeffectiveandefficient(cost,
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utilityofdata) soildisturbanceassessmentandmonitoringprogramscouldbeachievedthroughuseofcommonsoildisturbanceclassdefinitionsandconsistentuseofstatisticallyreliablesamplingprotocols(Curranandothers2005).
Definedsoildisturbancecategoriesmustberelatedtophysicalindicesofsoilqualityanddocumentedchangesinvegetationgrowthorhydrologicfunction.Adeterminationneedstobemadeif,infactoratwhatpoint,thesedisturbancecat-egoriesrepresent“detrimental”changesinsoilfunction.Inordertoevaluateimpactsofforestmanagementactivitiesonsoilquality,threedistinctlevelsofinformationareneeded.Thefirsttwoarecommonlygeneratedthroughagencyorcompanysoilmonitoringprograms.Thelastoneisprimarilyaresearchfunction.
Initialassessmentscanbeassimpleasdeterminingifspecifiedsoilconserva-tionorbestmanagementpractices(BMP)havebeenimplementedasplannedorifcontractual/legalrequirementsrelatingtosoildisturbancehavebeenmet.Thisisoftenreferredtoascomplianceorimplementationmonitoring.
After the initial compliance monitoring, soil disturbance assessment andmonitoringprojectsarecommonlydonetoevaluateeffectivenessofmanagementpractices.Theseassessmentsevaluatepre-determined,usuallyprovisional,soildisturbancestandardsorobjectivesbasedonbestavailableknowledge.Thisiscommonlyreferredtoasoperationaloreffectivenessmonitoring.
Soildisturbancestandardsorobjectivesmustalsobe testedorvalidated todetermineiftheyresultinunacceptablereductionsinproductivityorwatershedfunction,areappropriateforlocalsiteconditions,orifadjustmentsareneeded.Thisprocess isusually referred toasvalidationmonitoring.Validation isbestaccomplishedinaresearchenvironmentundercarefullycontrolledconditions.Ideally, research would be completed before standards were developed andimplemented.
Cost-effectiveapproachesareneededforoperationalsoildisturbanceassess-ments or monitoring that provides statistically valid and scientifically relevantdata.Monitoringmustmeetspecifiedquality-controlstandardsandcontributetoregionalstrategicdatabasesrelatingtreegrowthorhydrologicfunctiontodefinedclassesofdisturbance.Ourcurrentabilitytocompareresultsfromoperationaland research studies requiresmore commonor standardized soil disturbancedefinitionsandassessmentprotocols.
Tobecost-effective,operationalsoildisturbancemonitoringprotocolsmustmeet several criteria. Protocols (1) must provide scientifically and technicallysoundinformation,(2)mustbereliable,pertinent,andobtainedwithminimuminvestments,(3)mustbeclearlycommunicatedandunderstoodbyallaffectedparties,and (4)mustbeconsistentlyandefficiently implemented (Curranandothers2005).
USDA Forest Service Approach to Operational Soil Monitoring _______InForestServiceRegion6,initialassessmentsofactivity-inducedchangesin
soilqualityaretypicallymadethroughastratificationprocessinwhichvisuallyrecognizablesoildisturbancecategoriesanddisturbancesthatcanbeeasilyde-tectedbyprobingthesoilaredescribedandquantifiedwithinanactivityarea.Thisiscommonlyaccomplishedusingapointgridsystemincombinationwithpointobservationsalongaseriesofrandomlyorientedtransects.ThisprocessisdescribedindetailbyHowesandothers(1983).
Morerecently,pointobservationsarebeingreplacedbyvisualsoildisturbancecategories, developed and used to describe areas with a combination of soil
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disturbancesthatrepeatacrossanactivityareaandwhicharelikelylargeenoughinextentanddistributiontoaffectsoilfunction.Visualcategoriesalsoaccountforthefactthatvariousformsofdisturbancearenotmutuallyexclusive.Forex-ample,compactionanddisplacementoftenoccurtogether.AninterimprotocolofthisprocessthatisbasedonproceduresdescribedbyScottandothers(1979)iscurrentlybeingusedonnationalforestsintheBlueMountains.
Theprocessofquantifyingdifferentsoildisturbancecategoriesacrossaland-scapeprovidesarelativelyrapidandinexpensivemethodforquantifyingdiffer-enttypesofsoildisturbancesoverlargeacreagesandisrecognizedbytheFSasanessentialstepinthesoilassessmentprocess.This process, however, is often stopped at this point and the incorrect assumption made that any soil distur-bance is detrimental.
Toavoidthispotentialproblem,visualsoildisturbancecategoriesmustbefurtherevaluatedtodetermineiftheydo,infact,adequatelyrepresentdetrimentalsoilconditions.Thefirststepinevaluatingadisturbancecategoryistoidentifythesoilfunction(s)thatmaybenegativelyaffectedbyasoildisturbance.Forexample,ifsurfacesoilshavebeendisplaced,asoil’sabilitytosupplynutrientsmaybereduced.Incompactedskidroadsandlandings,changesinsoilresistancetorootpenetrationaswellasairandwatermovementinthesoilmaybethemostimpor-tantconsideration.Identificationofsoilfunction(s)affectedbydisturbanceallowsfortheselectionofthemostappropriatesoilindicatorswhichcanthenbeusedtoassessachangeintheabilityofthesoiltofunction.Caremustbetakenwhendevelopingandinterpretingsuchindices.Environmentalfactorssuchasmacro-andmicro-climatecanmaskchangesinsoilfunctionduetodisturbance.
Soilindicatorsorindicesaresoilparametersthatcanbequantitativelymea-suredusingstandardizedmethodsandcomparedbetweendisturbedandundis-turbedsites.OnNationalForestSystemlandsintheNorthwest,soildisturbanceisconsideredtobedetrimentalwhenasoilindexiseitherhigherorlowerthanadefinedthreshold.
Development and Application of Forest Service Soil Quality Standards ______________________________________________________
TheUSDAForestServiceisdirectedbylawtosustainproductivityatcurrentorenhancedlevelsandtoprotectandimprovethesoilsforwhichitisresponsible.Recognizingthisresponsibility,thePacificNorthwestRegion(R6)issuedaForestServiceManualSupplementdealingwithsoilproductivityprotection in1979.Ithasbeen revisedanumberof times since then (current versionFSM2520.R-6Supplement2500.98-1,EffectiveAugust24,1998).Thisdirectionspecifiesthresholdvalues(degree)forestimatingwhendetrimentalsoildisturbanceoccursandalsosetsarealimits(extent)fordetrimentalsoildisturbanceonanactivityareabasis.MostnationalforestswithinR6haveincorporatedthesevalues,withminormodifications,asstandardsintheirforestlandandresourcemanagementplans.OtherForestServiceRegionssubsequentlydevelopedsimilarpolicyanddirection (Powersandothers1998).Thresholds forestimatingdetrimentalsoilcompaction,displacement,puddling,andseverelyburnedsoilsweredevelopedbasedonapplicableresearchresultsavailableatthetime.
Standards emphasize both observable and measurable soil characteristicsthat field personnel can use to monitor effectiveness of activities in meeting
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soilmanagementobjectives.Allformsofdetrimentalsoildisturbance,includingpermanentfeaturesofthetransportationsystemsuchasroadsandlandings,arelimitedinextenttonomorethan20percentofanactivityarea.Inactivityareasthatexceed thisextent limiteitherasaresultofpreviousorcurrentactivities,restorationplansmustbeinplacebeforenewprojectsareimplemented.These standards are applied to all soils regardless of their inherent properties and ability to resist or recover from disturbance. Theonly special considerationgivenvolcanicashsoilsisanallowable20percentincreaseinsoilbulkdensitybeforetheyareconsidereddetrimentallycompacted.Thereasonforthisistheirrelativelylowundisturbedbulkdensitieswhencomparedtosoilsdevelopedinotherparentmaterials.
Application of Operational Soil Monitoring Techniques _____________Thefollowingisanexampleoftheuseofanoperationalsoilmonitoringproce-
durethatwasusedtoevaluatetheeffectsofaforestthinningoperationonthesoilresource.Theprocedureillustratestheapplicationofsoildisturbancecategoriesandphysicalsoilindices.
Overview
Duringthewinterof2005,theSistersRangerDistrictoftheDeschutesNationalForest in central Oregon implemented a thinning project designed to reducehazardousfuelsinpinestandswithinthewildlandurbaninterface.ATimberjackcut-to-lengthharvesterandaTimberjackforwarderwereusedtoremovetrees12inchesindiameterandsmaller,resultinginastandwithirregulartreespacingofabout20x20ft.
Projectobjectivesincluded:
• ReduceriskofwildfiretothenearbycommunityofBlackButteRanch. • Promoteresidualtreegrowthandmovestandtowardlargerdiametertrees. • Produceabiomassproductthatcouldbeusedtohelpoffsetthecostofthe
thinningoperation.
ThinningoperationsoccurredduringFebruaryandMarchof2005.Duringmuchofthistime,thesurface2to4inchesofsoilwasfrozen.Therewere,however,timeswhentemperaturesroseandsoilsweremoistbutnotfrozen.Severalsnowstormsalsooccurredduringthisperiod,depositingfromafewinchestooverafootofsnow.Soilconditionswerefavorableformostofthetwomonthperiodduringwhichoperationsoccurred.
Soilfunctionspotentiallyaffectedbytheprojectincluded:
• Abilityofthesoiltosupplywaterandnutrientstoresidualtrees. • Abilityofthesoiltoabsorbandtransmitwater. • Ability of the soil to resist other detrimental soil impacts including
displacement,puddling,severeburning,andsurfaceerosion.
Mitigationmeasuresused to reducepotentiallydetrimental soil impacts in-cludedoperatingoverfrozenground,snow,andslash;useofharvestequipmentdesignedtohavelowgroundpressure;designatingspacingofequipmenttrails;andhandpilingslash.
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Forestmanagerswishedtoknowifthesepracticeswereeffectiveinmeetingsoilqualityobjectivesonthisandothersimilarprojects.Inthiscase,managerswished toknow if soildisturbance resulting from theabovesuiteofpracticesexceeded20percentoftheactivityarea.Theyalsowishedtoknowifdifferentcategoriesofdisturbancecontaineddetrimentalsoilimpactsasdefinedin(FSM2520.R-6Supplement2500.98-1).
Project Area Soils
SoilsintheprojectareaweremappedaspartoftheSoilSurveyoftheUpperDeschutesRiverArea,Oregon(NRCS2002).TheyaredescribedastheSisters-Yapoahcomplex0-15percentslopes.Soilsareclassifiedas:
Sisterssoilseries–Ashyoverloamy,mixed,frigidHumicVitrixerandsYapoahsoilseries–Ashy-skeletal,frigidHumicVitrixerands
Harvester/Forwarder Transportation System
TheTimberjackcut-to-lengthharvesterusedinthisoperationwasequippedwithacuttingheadmountedona30footboom.Thisallowedtheharvestertocutandprocessmaterialswhilemakingparallelpassesacrosstheharvestunitataspacingofapproximately60feet.Harvestedmaterialsarepositionedsotheycanbereachedfromalternateharvestertrailsbytheforwardermachine.Thisresultsintwotypesoftrailswithintheharvestunit(1)thosethatbeendrivenacrossonlyonetimebytheharvester(ghosttrails)and(2)trailsthathavebeendrivenacrossbytheharvesterfollowedbytheforwarder(harvester-forwardertrails).Becausetreesarelimbedandtoppedatthetimeoffellingtherearenolandingswithintheharvestunit.Oncetheforwarderhascollectedharvestedmaterialstheyarepilednexttoahaulroadpriortoloadingonlogtrucks.
Description of Visual Soil Disturbance Categories
Acombinationofvisualobservationsandprobingofthesoilwithatilespadeormetalrodwasusedtoidentifyanddescribefourcategoriesofsoildisturbancewithinactivityareas.Thesecategoriesare:
Condition Class 1:Undisturbedstate,natural. • Noevidenceofpastequipmentoperation. • Nowheeltracksordepressionsevident. • Litteranddufflayersintact. • Nosoildisplacementevident.
Condition Class 2:Trailsusedbytheharvestermachineonly.Ghost trails. • TwotracktrailscreatedbyonepassofaTimberjack cut-to-lengthharvester. • Faintwheeltrackswithaslightdepressionevidentandare<4inchesdeep. • Litteranddufflayersintact. • Surface soil has not been displaced and shows minimal mixing with
subsoil.
Condition Class 3:Trailsusedbybothharvesterandforwarder. • TwotracktrailscreatedbyoneormorepassesofaTimberjackcut-to-length
harvesterandoneormorepassesofaTimberjackforwarder.
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• Wheel tracksevidentandare4 to6 inchesdeepwith theexceptionofareaswhereoperatorwasabletolaydownenoughslashtomitigatesoilimpacts.
• Litteranddufflayersarepartiallyintactormissing.
Condition Class 4:Skidtrailsfrompreviousentries.Allwerere-usedduringcurrententry. • Oldskidtrailscreatedintheearlypartof20thcenturywhenselectivehar-
vestoccurred. • Trailsappeartohavehighlevelsofsoilcompactionacrosstheentiretrail. • Evidenceoftopsoilremoval.
Soil Functions Affected by Soil Disturbances
Based on visual observations described above, it was determined that soilcompactionwasthemostprevalentformofsoildisturbancewithintheharvestedarea.Whencompactionoccurs,therearealterationsofbasicsoilpropertiessuchassoildensity,totalporevolume,poresizedistribution,macroporecontinuity,andsoilstrength(GreacenandSands1980).Soilsvaryintheirsusceptibilitytocompaction(Seyboldandothers1999).Onceasoilbecomescompacted,theconditioncanpersistfordecades(Froehlichandothers1985).This,inturn,af-fectssoilfunction.
Anumberofresearchershavemeasuredreductionsinsiteproductivityattributedtosoilcompaction(Froehlichandothers1986;CochranandBrock1985;HelmsandHipken1986).Effectsofsoilcompactiononsiteproductivity,however,arenotuniversallynegative.Gomezandothers(2002)lookedatarangeofforestsoiltypesinCaliforniaandfoundcompactiontobedetrimental,neutral,orbeneficialdependingonsoiltextureandwaterregime.
Quantifying Visual Soil Disturbance within an Activity Area
Toassistwithquantifying theamountof soilcompaction,a recordingpen-etrometerwasusedtodeterminetheaveragewidthofcompactedsoilsacrossboththeghosttrailsandtheharvester-forwardertrails(figs.1and2).Athresholdlevelfortheincreasedsoilstrengthof2.5MPawasusedtoidentifycompactedareas.Soilstrengthsbeyondthislevelwereconsideredtobehighenoughtobegintoinhibitplantrootgrowth.Basedonresultsharvesterghosttrailswereinitiallyconsideredtoconsistoftwodetrimentallycompactedtracks,eachapproximatelythreefeetinwidth.Harvesterforwardertrailswereconsideredtoconsistoftwodetrimentallycompactedtracks,eachapproximatelyfourfeetwide.
Arandomlyorientedsquaregridwithonegridintersectioneverytwoacreswasnextoverlainontheactivityareaandusedtolocatesamplepointsfordetermin-ingarealextentofsoildisturbancecategories(fig.3).Ateachofthegridinter-sections,arandomlyoriented,100-fttransectwasestablished.Thefourdefineddisturbancecategoriesweremeasuredalongeachtransectandlengthsoccupiedbyeachcategoryrecorded.Ameanforeachcategorywasthencomputedfortheentireactivityarea.Samplinginthismannerensuredanunbiased,representativesample.Itwasdeterminedthat17percentoftheactivityareawasoccupiedbysoildisturbance(totalofcategories2-4).A95percentconfidenceintervalaroundthisestimatewascalculatedtobeplusorminus2percent.
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Figure 1—Average soil resistance measured for the 10 to 2� cm soil depth. Measurements were made perpendicular to the harvester ghost trails.
Figure 2—Average soil resistance measured for the 10 to 2� cm soil depth. Measurements were made perpendicular to the harvester forwarder trails.
Use of Soil Indices to Interpret Visual Soil Disturbance Categories
ThreephysicalsoilindicesusedbytheForestServicetoassesschangesinsoilphysicalpropertiesattributedtocompactionareincreasesinsoilbulkdensity,increases in soil strength (resistance topenetration),andchanges in soilporesizedistribution.
Soil Bulk Density
Soilbulkdensityisdefinedasthemassperunitvolumeofsoilandrepresentstheratioofthemassofsolidstothetotalorbulkvolumeofthesoil(SoilSurveyStaff1996).ThedirectmeasurementofanincreaseinsoilbulkdensityfromsoilcompactionrequiresaminimumamountofsamplingequipmentandisthemostcommonlymademeasurementofsoilcompactionusedbytheForestService.Physical factors that affect soil bulk density and compactability include soil
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Figure 3—Example of a pre-established grid (randomly oriented) with transects oriented along random azimuths.
particlesizesanddensity,organicmattercontent,andmineralogy(Howardandothers1981).
Soilbulkdensitysampleswerecollectedinthespringoftheyearusingaham-mer-drivensoilcoresampler.Table1showssoilbulkdensitiesreportedforboththewholesoilandfor thefinefractionofsoil (soilparticles<2mmremoved).DeterminingsoilBDbasedonthefinefractionofsoilresultsinalowerBDvaluecomparedtothatdeterminedonawholesoilbasis.Thisisduetothehigherweighttovolumeratioofsoilcoarsefragmentsinthesoilcore,comparedtoanequalvolumeofsoilmaterial.Whendeterminedonawholesoilbasis,soilcompactionresultedinasignificantincreaseinsoilbulkdensityinboththeghosttrailsandtheforwardertrails.Soilbulkdensitiesdeterminedforthefinefractionsofsoilweresignificantlygreaterintheforwardertrailsbutnotintheghosttrails.
Table 1—Soil bulk density measurements determined based on the whole soil (including soil coarse fragments >2mm) and based on the fine fraction of soil.
% Volume Soil Soil Bulk Density Soil Bulk DensitySoil Condition Class Coarse Fragments Whole Soil (Mg/m3) Fine Fraction Soil (Mg/m3)
1 1 0.9�a 0.92a 2 2 1.02b 1.00ab � 2 1.0�b 1.0�b Columns within a soil bulk density analysis method are not significant at p = 0.05 if followed by the same letter. n = 3
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Inthiscase,fewcoarsefragmentswereencounteredandtherewaslittledif-ferenceinsoilBDbetweenresultsobtainedusingcoreswithandwithoutcoarsefragments.Iftherehadbeenmorecoarsefragmentsincoresoralargevariationincoarse fragmentsbetweencores, itwouldhavehadagreater influenceoncalculatedsoilbulkdensitiesandonthewayinwhichthesoilfunctions.Tocor-rectlyinterpretsoilbulkdensitymeasurements,itisnecessarytoreportsoilbulkdensitiesforwholesoilandthefinefractionofsoil.Itisalsonecessarytoknowtheamountsofcoarsefragmentsinthesoilcores.
ForestServicesoilqualitystandardsidentifyachangeinsoilbulkdensityof20percentormoreaboveundisturbedlevelsasathresholdfordeterminingdetrimentalcompactioninAndisols(soilsderivedfromvolcanicash).Whencalculatedonbothawholesoilandfinefractionofsoilbasis,nomeasuredincreasesinsoilbulkdensityexceededthe20percentrelativeincreasethreshold.Therefore,noneofthesoilbulkdensitychangesinanyofthevisualsoildisturbancecategoriesmettheForestServicedefinitionofadetrimentallycompactedsoiltable2.
Soil Strength
Soilstrengthdescribesthesoilhardnessorthesoilsresistancetopenetration.Soilprobesandspadescanbeusedtodetectchangesinsoilstrengthresultingfromsoilcompaction.Thistechniquecanbequantifiedbyusingarecordingsoilpenetrometer.Measuredsoilstrengthscanvarydependingonsoilparticlesizedistributionandshape,clayandorganicmattercontent(ByrdandCassel1980).Withinasoiltypechangesinsoilwatercontentandstructurecanalsoaffectsoilstrength(Gerard1965).
Changesinsoilstrengthresultingfromsoilcompactionweremeasuredwithindifferentdisturbancecategoriesusingarecordingsoilconepenetrometer,whichiscapableofrecording,atpredeterminedintervals, theforcerequiredtopushaconeintotheground(Millerandothers2001).Measurementsweremadeinearlyspring,shortlyafterharvestoperationswerecomplete.Fieldmeasurementsofgravimetricsoilmoisture,basedonthefinefractionofsoil,rangedfrom0.19to0.22g/gandwereslightlylessthanthe0.23g/gestimateofsoilfieldcapacitythatwasobtainedfromsoilcoresamplesusedtodeterminesoilporesizedistri-bution.Thepenetrometerwassettorecordsoilresistanceat1.5cmincrementsbetween0and60cmsoildepth.ReadingswerethendownloadedtoaMicrosoftExcelSpreadsheetforanalysis.
Table 2—Absolute and relative percentage increase in soil bulk density as a result of soil compaction.
Absolute Increase Relative % Soil Bulk Density Soil Bulk in Soil Bulk Increase in Soil Condition Class Determination Method Density (Mg/m3) Density (Mg/m3) Soil Bulk Density
1 Whole Soil 0.9� 2 Whole Soil 1.02 0.09 10 � Whole Soil 1.0� 0.1� 1�
1 Fine Fraction 0.92 2 Fine Fraction 1.00 0.0� 9 � Fine Fraction 1.0� 0.14 1�
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Soiltextureandseasonalchangesinsoilmoisturecangreatlyinfluencesoilstrengthmeasurements.Resistancetopenetrationhasbeenshowntoincreaseforbothuncompactedandcompactedsoilsas theydryoutover thegrowingseason.Theincreaseinresistancetopenetrationwithdecreasingsoilmoisture,however,tendstooccurmorerapidlyincompactedsoilsthaninuncompactedsoils(Craigg2006).Therefore,soilmoisturerelationshipsshouldbeconsideredwheninterpretingsoilresistancemeasurements.
Measurementsofsoilresistanceintheundisturbedareasgraduallyincreasedwithsoildepthreachingaresistanceof1MPainthefirst10cmandafinalsoilresistanceof2MPaatapproximately60cmsoildepth.Intheforwardertrailssoilresistanceincreasedmuchfaster,reachingaresistanceof3MPawithinthefirst10cmsoildepthandretainingthathighstrengththroughoutthe60cmdepth.Increasesinsoilresistanceintheghosttrailswerehigherthantheundisturbedbutlessthantheforwardertrails(fig.4).Duringthethinningoperationeffortsweremadetolimbharvestedtreesontheequipmenttrailsandthendriveontheslashmattomitigatesoilcompaction.Soilpenetrometermeasurementsindicatedthattheslashmatdidhaveatleastsomeaffectonmitigatingsoilcompaction(fig.5).
Currently,ForestServiceRegion6doesnothaveasoilqualityindexthresh-oldforincreasesinsoilresistanceresultingfromcompaction.Researchresultssuggestthatsoilresistancesof2MPaandgreatercanbegintoaffectplantrootgrowth(Siegel-Issemandothers2005).Thustheseresultssuggestdifferencesinsoilfunctionbetweenthedifferentsoilconditionclasses,inparticulartheabilityofrootstopenetratecompactedsoils.
Figure 4—Soil strength measured in the spring of 200� for different soil disturbance classes. Horizontal bars indicate one standard error. n = 30.
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Soil Pore Size Distribution
Soilporespaceaccountsforapproximatelyhalfofthetotalvolumeofmineralsoil.Changesintotalsoilporosityandporesizedistributionthatmayresultfromsoilcompactioncanaffectsoilfunctionsbyalteringairandwaterflowintoandthroughthesoil.Changesinsoilporositycanalsoaffecttheamountsofwaterstorageinthesoil(Scott2000).
Measuringafullrangeofsoilporesizesrequiresrelativelysophisticatedlabora-toryequipmentcomparedtothatneededformeasuringsoilbulkdensityorsoilstrength.Althoughtotalsoilporositycanbeestimatedfrombulkdensityandsoilparticledensity,thiscalculationprovidesnoinformationaboutporesizedistri-butionchangesoccurringinthesoil.Tobetterunderstandchangesinsoilporesizedistributionresultingfromsoilcompaction,arelativelysimplemethodwasusedwhichdoesnotrequiretheuseofsophisticatedlaboratoryequipment.Thistechniquemeasuresmainlytheporositychangesoccurringinthelargersoilporesizes(soilpores>30μm).
Intactsoilcoresformeasuringsoilporesizedistributionwerecollectedusingthesamehammer-drivencoresamplerusedtosamplesoilbulkdensity.Follow-ingcollectionofintactsoilcores,soilporesizedistributionwasdeterminedus-ingamodificationofthewaterdesorptionmethoddescribedin(DanielsonandSutherland1986).Briefly,ahangingwatercolumnwascreatedbyconnectingaBuchnerfunnelwithaporousceramicplateinthebottomtoapproximately3metersofplastictubingwithaburetteconnectedtotheotherend.Asoilcorewas thenplaced in the funnelandsaturatedwithwaterbyraising theburette
Figure 5—Soil strength measured in the spring of 200� for different soil dis-turbance classes with measurements on harvester forwarder trails separated depending upon whether or not slash was present. Horizontal bars indicate one standard error. n = 30 (undisturbed and ghost trails)n = 15 (forwarder trails)
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andcreatingaslightheadofwater.Aseriesofsuctionswerenextappliedtothesaturatedsoilcorebyraisingthefunnelaboveapredeterminedmarkonthebu-rette.Volumesofwaterremovedfromthesoilcoreswererecordedforaseriesofappliedsuctionsandtheequivalentradiusofthelargestsoilporesfilledwithwaterdeterminedbythecapillaryequation(Scott2000).
Resultsindicatedashiftinsoilporesizedistributionfromlargerporesizesormacropores(soilpores>30μm)tosmallerporesizes(soilpores<30μm)whensoilsbecamecompacted(fig.6).Whilesoilcompactiondidresultinasignificantdecreaseinmacroporesandasignificantincreaseinsmallersoilporesizes,therewasnotasignificantchangeintotalsoilporositybetweenthedifferentdisturbancecategories(table3).AlthoughstandardshavebeenestablishedinForestServiceRegion6formacroporespacereductionsinresidualsoils,nonehaveyetbeenestablishedforash-derivedsoils.
Figure 6—Shift in soil pore size distributions for different soil disturbance classes following soil compaction.
Table 3—Changes in soil pore size distribution and total soil porosity resulting from soil compaction.
Pore volume Pore volume Total pore volumeSoil condition Class >30µm (cm3/cm3) <30µm (cm3/cm3) (cm3/cm3)
1 0.��a 0.24a 0.�9a 2 0.29b 0.27b 0.��a � 0.2�b 0.�0c 0.��a n = 3 Columns within a pore size class are not significant at p = 0.05 if followed by the same letter.
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Interpretation of Results
Extentofsoildisturbancewithintheprojectareawasinitiallydeterminedbyfirstdescribingandquantifyingvisualsoildisturbancecategoriesandthenmea-suringasuiteofindiceswithineachcategory.Soilindexmeasurementsthatweremadewithindisturbedareaswerethencomparedtothosemeasurementsmadeinundisturbedareas.Degreeofchangeinspecifiedsoilindiceswasnextcomparedtodefinedthresholdsfordeterminingifthechangeisconsidered“detrimental”or“undesirable.”
AllmeasuredincreasesinsoilbulkdensitywerebelowthresholdvaluesdefinedbythePacificNorthwestRegionforsoilsderivedfromvolcanicash.Althoughin-creasesinsoilstrengthweremeasuredforghosttrailsandforharvester-forwardertrails,nothresholdvalueorsoilqualitystandardhasyetbeenestablishedinthePacificNorthwestRegionforsoilstrength.Reductionsinmacroporespacewerealsomeasured in ghost trails and forharvester-forwarder trails. Forest ServiceRegion6doesnotcurrentlyhaveasoilqualityindexthresholdestablishedformacroporespacereductionsinash-derivedsoils.Soilstrengthandreductionsinmacroporespaceappeartobereliableandeasilymeasurableindicesofsoilfunc-tion.Theyalsoprovideadditionalinformationaboutchangesoccurringinthesoilwhencompactionoccurs.Validationworkneedstobecompletedtodetermineappropriatethresholdsforeachoftheseindices.
Summary ______________________________________________________Soilqualitycanbedefined inanumberofwaysdependingonone’spoint
of view. For forest practitioners, management-induced changes in soil qualityareofconcernwhensiteproductivity ismeasurably reducedorwaterqualityisimpaired.Soildisturbancecanbeaccuratelydescribedandquantifiedusingconsistentvisualcategoriesandsound,cost-effectivesamplingprotocols.Assess-mentsofsoilqualitymustrelatevisualdisturbancecategoriestochangesintheabilityofthesoiltoprovidenutrientsortoabsorbandtransmitwater.Anumberofphysicalsoilindices(soilbulkdensity,soilstrength,soilporesizedistribution)areavailabletohelpdefinesuchrelationships.
Soilsvaryacrossthelandscapeandresponddifferentlytomanagementprac-tices.Caremustbetakenwhenmakingsoilqualityassessmentstoselectthemostappropriate soil indices, to followproper samplingprotocols, and to interpretresultscorrectly.Finally,withoutknowingeffectsofsoildisturbanceonsitepro-ductivityandsedimentyield,meaningfulassessmentsofsoilqualitycannotbemade.Validationofsuchcauseandeffectrelationshipsisastepintheprocessthatisoftennevercompleted.
References ______________________________________________________Byrd,C.W.;Cassel,D.K.1980.Theeffectofsandcontentuponconeindexandselectedphysical
properties.SoilScience.129:197-204.Chitwood,L.1994.SoilcompactionstudyphaseA,DeschutesNationalForest.DRAFTreport.Clayton, J.L.;Kellogg,G.;Forrester,N.1987.Soildisturbance-treegrowthrelations incentral
Idahoclearcuts.ResearchNoteINT-372.Ogden,UT:U.S.DepartmentofAgriculture,ForestService,IntermountainResearchStation.6p.
Cochran,P.H.;Brock,T.1985.Soilcompactionandinitialheightgrowthofplantedponderosapine.PacificNorthwestExtensionPublication-PNW434.3p.
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Craigg,T.L.2006.SoilSciences.Unpublished.Davis,CA:UniversityofCalifornia,Davis.MastersThesis.
Curran,M.P.;Miller,R.E.;Howes,S.W.;Maynard,D.G.;Terry,T.A.;Heninger,R.L.;Niemann,T.;vanRees,K.;Powers,R.F.;Schoenholtz,S.H.2005.Progresstowardmoreuniformassess-mentandreportingofsoildisturbanceforoperations,research,andsustainabilityprotocols.J.For.Ecol.Manage.220:7-30.
Danielson,R.E.;Sutherland,P.L.1986.Porosity.In:Klute,A.,ed.Methodsofsoilanalysis.SSSABookSeries:5Part1–Physicalandmineralogicalmethods.Madison,WI:SSSA.
Froehlich,H.A.1976.Theinfluenceofdifferentthinningsystemsondamagetosoilandtrees.Proceedings;XVIIUFORWorldCongressDivisionIV;Norway:UUFRO:333-334.
Froehlich,H.A.;Miles,D.W.R.;Robbins,R.W.1985.SoilbulkdensityrecoveryoncompactedskidtrailsincentralIdaho.SoilSci.Soc.Am.J.53:946-950.
Froehlich,H.A.;Miles,D.W.R.;Robbins,R.W.1986.GrowthofyoungPinus ponderosaandPinus contortaoncompactedsoilincentralWashington.ForestEcologyandManagement.15:285-294.
Geist,J.M.;Strickler,G.S.1978.PhysicalandchemicalpropertiesofsomeBlueMountainsoilsinnortheastOregon.Res.PapPNW-236.Portland,OR:U.S.DepartmentofAgriculture,ForestService,PacificNorthwestForestandRangeExperimentStation.19p.
Gerard,C.J.1965.Theinfluenceofsoilmoisture,soiltexture,dryingconditions,andexchange-ablecationsonsoilstrength.SoilSci.Soc.Amer.J.29:641-645.
Gomez,A.;Powers,R.F.;Singer,M.J.;Horwath,W.R.2002.Soilcompactioneffectsongrowthofyoungponderosapinefollowinglitterremoval inCalifornia’sSierraNevada.SoilScienceSoc.Amer.J.66:1334-1343.
Greacen,E.L.;Sands,R.1980.Compactionofforestsoils.Aust.J.Res.18:163-189.Grossman,R.B.;Harms,D.S.;Seybold,C.A.;Herrick,J.E.2001.Couplinguse-dependentanduse-
invariantdataforsoilqualityevaluationintheUnitedStates.J.SoilWaterConserv.56(1):63-68.Harward,M.E.;Youngberg,C.T.1969.SoilsfromMazamaashinOregon:identification,distri-
butionandproperties.Pedologyandquaternaryresearchsymposium:proceedings;1969May13-14,Edmonton,AB:UniversityofAlberta:163-178.
Helms,J.A.;Hipken,C.1986.EffectsofsoilcompactiononheightgrowthofaCaliforniapon-derosapineplantation.West.J.Appl.For1:121-124.
Howard,R. F.; Singer,M. J.; Franz,G.A.1981. Effectsof soil properties,water content, andcompactiveeffortoncompactionofselectedCaliforniaforestandrangesoils.SoilSci.Soc.Amer.J.45(2):231-237.
Howes,S.;Hazard, J.;Geist, J.M.1983.Guidelines forsamplingsomephysicalconditionsofsurfacesoils.R6-RWM-146-1983.Portland,OR:U.S.DepartmentofAgriculture,ForestService,PacificNorthwestRegion.
Karlen,D.L.;Mausbach,M.J.;Doran,J.W.;Cline,R.G.;Harris,R.F.;Schuman,G.E.1997.SoilSci.Soc.Am.J.61(1):139-49.
Larson,W.E.;Pierce,F.J.1991.Conservationandenhancementofsoilquality.In:EvaluationofSustainableLandManagementintheDevelopingWorld.Int.Bangkok,Thailand:BoardforSoilRes.andManagement:175-203.
Miller,R.E.;Hazard, J.;Howes,S.2001.Precision,accuracy,andefficiencyof four tools formeasuring soilbulkdensityor strength.Gen.Tech.Rep.PNW-RP-532.U.S.DepartmentofAgriculture,ForestService,PacificNorthwestResearchStation.16p.
NaturalResourcesConservationService(NRCS).2002.SoilSurveyofupperDeshutesriverarea,Oregon,includingpartsofDeschutes,Jefferson,andKlamathCounties.Report.U.S.Depart-mentofAgriculture,NaturalResourcesConservationService.515p.
Powers,R.F.;Tiarks,A.E.;Boyle,J.R.1998.Assessingsoilquality:practicalstandardsforsus-tainable forest productivity in theUnited States. In: The contributionof soil science to thedevelopmentandimplementationofcriteriaandindicatorsofsustainableforestmanagement.SSSASpec.Publ.53.Madison,WI:SSSA:53-80.
Scott,W.;Gillis,G.C.;Thronson,D.1979.Groundskiddingsoilmanagementguidelines.Wey-erhaeuserCompanyInternalReport.FederalWay,WA:WTC.34p.
Scott,D.H.2000.Soilphysicsagriculturalandenvironmentalapplications,IowaStateUniversityPress,FirstEdition.421p.
Seybold,C.A.;Mausbach,M.J.;Karlen,D.L.;Rogers,H.H.1997.QuantificationofSoilQual-ity.In:Stewart,B.A.;Lal,R.,eds.AdvancesinAgronomy.ProceedingsfromanInternationalSymposiumonCarbonSequestrationinSoil.LewisPubl.53-68.
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Seybold,C.A.;Herrick,J.E.;Bredja,J.J.1999.Soilresilience:afundamentalcomponentofsoilquality.SoilSci.164(4):224-234.
Siegel-Issem,C.M.;Burger,J.A.;Powers,R.F.;Ponder,F.;Patterson,S.C.2005.Seedlingrootgrowthasafunctionofsoildensityandwatercontent.SoilSci.Soc.Am.J.69:215-226
Snider,M.D.;Miller,R.F.1985.EffectsoftractorloggingonsoilsandvegetationineasternOr-egon.SoilScienceSocietyofAmericaJournal.49:1280-1282.
SoilSurveyStaff.1996.Soilsurveylaboratorymethodsmanual.SoilSurveyInvestigationsReportNo.42version3.0.
Warkentin,B.P.1995.Thechangingconceptofsoilquality.J.SoilWaterCons.50:226-228.
Timberjack cut-to-length harvester
Timberjack forwarder machine
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Harvester forwarder trail
Quantification of soil disturbance categories using randomly oriented 100 foot transects.
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Measuringsoilresistanceusingtherecordingsoilpenetrometer.
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In: Page-Dumroese, Deborah; Miller, Richard; Mital, Jim; McDaniel, Paul; Miller, Dan, tech. eds. 2007. Volcanic-Ash-Derived Forest Soils of the Inland Northwest: Properties and Implications for Management and Restoration. 9-10 November 2005; Coeur d’Alene, ID. Proceedings RMRS-P-44; Fort Collins, CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station.
Leonard R. Johnson and Han-Sup Han are faculty in the area of forest operations in the College of Natural Resources at the University of Idaho. Debbie Page-Dumroese is a Research Scientist with the Rocky Mountain Research Station, U.S. Department of Agriculture, Forest Service and is based in Moscow, Idaho.
Abstract Withpressureandvibrationonasoil,airspacesbetweensoilparticlescanbereducedbydisplacedsoilparticles.Activityassociatedwithheavymachinetrafficincreasesthedensityofthesoilandcanalsoincreasetheresistanceofthesoiltopenetration.Thispaperreviewsresearchrelatedtodisturbanceofforestsoilswithaprimaryfocusoncompactioninash-capsoils.Thegeneralprocessofcompac-tionisdescribedalongwithphysicalpropertiesofash-capsoilsthatrelatetocompaction.Ash-capsoilshavephysicalsoilpropertiesmostcloselyalignedtosilt-loamsoils.Undisturbedash-capsoilsoftenhavelowbulkdensitiestovariabledepths.Undermoistureconditionsnearfieldcapacity,thesesoilsaresusceptibletosignificantdisturbancefrommachinetraffic,andwhenthedisturbancecausesincreasesinbulkdensity,thesoilsarenotlikelytorecoverfromthisdisturbedconditionformanyyears.Machinetrafficonforestsoilsgenerallyoccursasaresultofsomeformofactivestandmanage-mentincludingprecommercialthinning,intermediateandfinaltimberharvest,andsitepreparationactivitiesinvolvingslashdisposalandtreatment.Thedirectcontactbetweenequipmentandtheforestsoilwillresultinsometypeofsoildisturbance.Thedegreeandextentofthesoildisturbanceismostoftencontrolledthroughguidelinesontheselectionandoperationofequipmentandbyrestrictingthelocationandoperatingseasonforequipment.
Effects of Machine Traffic on the Physical Properties of Ash-Cap Soils
Leonard R. Johnson, Debbie Page-Dumroese and Han-Sup Han
Introduction
General Process of Compaction
Compactionofsoilsiscreatedthroughtheenergyexertedonthesoil,usuallythroughvehiculartrafficinharvestingandsitepreparationoperations.Itresultsinthereductionofairspacesinthesoilwithacorrespondingincreaseinthebulkdensityofthesoil(weightperunitofvolume).Erosioncanalsoresultfromforestoperations.Erosiongenerallyoccursasaresultofsoildisplace-mentandismostoftenassociatedwithharvestandsitepreparationactivitiesonsteeperslopes. Althoughgenerallyviewedinanegativecontextwithrespecttoforestsoils,compactionisoftenadesirableprocessinconstructionactivities.Manyengineeringprojectsinvolvingearthworkinearthendams,structuralfoundations,androadsrequirepredictablestrengthinthesoilsthatareat
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thefoundationoftheconstructionprojects.Variouscompactionmethodshavebeendevelopedtoachieveadesiredlevelofsoilstrengthanddensity.Someoftheprinciplesderivedfromresearchincivilengineeringandsoilmechanicsonachievingdesiredlevelsofcompactioncanalsobeappliedtoforestsoilsinde-terminingconditionswherenaturalsoilsareatthegreatestriskofcompaction.CullenandMontagne(1981)conductedanextensivesummaryofliteratureonthegeneralrelationshipsbetweensoilpropertiesandcompaction.Theirreviewincludesthegeneralrelationshipbetweenthesoilpropertiesoftexture,fragmentcontent,structure,moisturecontentatthetimeofcompaction,andorganicmatterandthesusceptibilityofthesoiltocompaction.AmorerecentreviewbyMillerandothers(2004)summarizedcurrentliteratureontheeffectsofheavyequip-mentonsoilsandproductivity.Thediscussioninthissectiondrawsheavilyontheseliteraturereviews.
Engineering Compaction Methods
Compressionorkneadingcompactionisgenerallyachievedinthefieldwithequipmentthatexertsgraduallyincreasingpressureonthesoil.Pressureisgradu-allyincreasedtoamaximumandthenisgraduallydecreased.Adevicecommonlyusedtoaccomplishthistaskinconstructioniscalledasheepsfootroller.Rubbertiredrollersalsoexhibitthecharacteristicsofthiskneadingaction.Theinteractionofthetiresofrubber-tiredskiddersusedinforestoperationswiththesoilseemstoresemble thatofkneadingcompactionmachines,butwith far lesspressurethantheequipmentdesignedforthatpurpose.
Vibratory compactors usually combine pressure on the soil with vibration.Hand-heldmodelsutilizeavibratingplate.Largerversionscombinealargesteelrollerwithavibratoryimpulse.Thereissomeconjecturethattrackedequipmentusedinforestoperationscanduplicatethisaction,but,again,withfarlesscom-pactiveenergythanequipmentdesignedforthatpurpose.
Engineeringproperties of soils are important to compaction. In addition tomoisturecontent,importantfactorsincludeinitialsoilstrengthorbulkdensity,distributionofparticlesizes,percentorganicmatter,rock-fragmentcontent,andpercentsand,siltorclay(soiltexture).Thepresenceandinfluenceofclayinthesoilwillusuallydeterminewhetheritisclassifiedascohesiveornon-cohesive.Clayinfluencesthesusceptibilityofsoilstocompactionbecauseofthesmallparticlesizesofclay,claymineralogy,andthroughitseffectonshearstrength.Withsmallclayparticles,theshearstrengthonsoilscanbepartiallyattributedtothechemicalbondingandelectro-chemicalresistancebetweenparticles(Brown1977).
Soiltype,textureandstructurewillinfluencetheequipmentthatismostef-fectiveinachievingthehighestlevelofcompaction.MeansandParcher(1963)foundthat“maximumdensitiesforsoilswithcoarsetexturewereachievedwitha heavy smooth-wheeled rollerwith somevibratory effects.”Coarse texturedsoils,usuallythoseverylowinclaycontent,arenon-cohesiveandthesegenerallyrequirevibratorycompactors.Fine-texturedsoilsandsoilswithahighcontentofclayareusuallynotcompactedwellthroughvibratorycompactorsandrequirethekneadingactionofamechanismsimilartoasheepsfootroller(Ingersoll-Rand1975).Kryine(1951)notedthat,ingeneral,themaximumsoildensitiesachievedbyseveralmethodsoflaboratoryandfieldcompactiondecreasewithdecreasingsoilparticlesize.Thehighestdensitiesgenerallyoccurinsoilswithawiderangeinparticlesizeswhereparticlescanbereorientedinwaysthatallowthesmall
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particlestopackintothevoidsbetweenthelargerparticles(Li1956;CullenandMontagne1981;Millerandothers2004).
Ash-capsoilshaveuniquecharacteristicsthataffecttheirresponsetothevariouscompactionmethods.Whiletheparticlesizeisrelativelysmall,ash-capsoilsarealsoconsiderednon-cohesiveandnon-plastic(Cullenandothers1991).Becauseoftheirnon-cohesivenature,theyarelikelytobesusceptibletovibratorycom-paction(CullenandMontagne1981).Whilethekneadingactionofasheepsfootrollerwouldprobablyexceedtheshearstrengthofash-capsoilsandwouldnotbeeffectiveforcompaction,thepressureandmoresubtlekneadingactionproducedbyrubber-tiredandtrackedvehiclescouldincreasebulkdensities.
Froehlich and others (1980) completed a general report for the EquipmentDevelopmentCenteroftheU.S.ForestServicetoprovideabasisforpredictingsoilcompactiononforestedland.Observedsoiltypesincludedsandyloam,clayloamandloam.Thestudydevelopedequationstopredictabsoluteandpercentchangesinbulkdensitywithvehiculartraffic.Whilespecificvaluesassociatedwiththeequationsmaynotbeusefulinabroadsense,thestatisticallysignificantfactorsareofinterest.Theseincludethenumberoftripsbyequipment,initialsoilstrength(coneindex),initialsoildensity,machinederivedpressureofthevehicleinkilogramspersquarecentimeter,soilorganicmatterinpercent,soilmoisturecontentinpercent,andforestfloordepth.Themostsignificantofthesefactorswerenumberoftripsandtheinitialconeindexofthesoil,reflectingameasureofinitialsoilstrengthandthelevelofmachineactivityastwoprimaryfactorsindeterminingchangesinsoilcharacteristics.
Optimum Moisture Content
Theoptimummoisturecontentforcompactionisrelatedtotheenergygeneratedinthecompactioneffort.Ascompactioneffortincreases,soilswillbecompactedtohighersoilstrengthandbulkdensity.Themaximumbulkdensitywillalsooccuratloweroptimummoisturecontent.Soilsbelowtheoptimummoisturecontentwillnotbecompactedtoashighabulkdensityaswhentheyareattheoptimummoisturecontent(HåkanssonandLipiec2000).Uptoandincludingtheoptimummoisturecontent,watercanlubricateparticlesandallowtheirreorientationwithrespecttoeachother.Mostcompactionisseeninwetconditions,particularlynearsoilfieldmoisturecapacity(AlexanderandPoff1985).Whensoilmoistureexceedstheoptimummoisturecontentofthesoil,soilsbegintobecomeplasticortheincompressibilityofthewaterpreventsreorientationandpackingofthesoilparticles.AccordingtothereviewbyCullenandMontagne(1981),optimummoisturecontentforcompactiontendstoincreaseassoiltexturebecomesfiner(Felt1965).Thelessdensetheinitialsoilsample,thegreaterthemoisturecon-tentrequiredtoreachmaximumsoildensityforagivencompactiveeffort(Lull1959).
Optimum moisture content for compaction is determined for engineeringpurposesbyalaboratoryanalysiscalledtheProctortest.Thestandardproctortestinvolves25blowsofa2.5kghammerdroppedfromaheightof30.5cm.Becausethistestdidnotgeneratesufficientenergytopredictcompactioneffortsofmostmodernconstructionequipment,amodifiedproctortestwasdeveloped.Themodifiedtestincreasedthecompactionenergy,using25blowsofa4.5kghammerdroppedfromaheightof45.7cm.BoththestandardandmodifiedProc-tortestscreatedtoomuchcompactionenergytoeffectivelypredictcompaction
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fromequipmentusedinforestoperations(Froehlichandothers1980).Alightproctortestusing8%oftheenergyofthestandardProctortestappearedtobeeffectiveinpredictingthecompactioneffortofharvestingandsitepreparationequipment.Itinvolved10blowsofahammerweighing0.5kgdroppedfromaheightof30.5cm.Thegeneralrelationshipbetweenoptimummoisturecontent,maximumbulkdensityandlevelofcompactioneffortareillustratedinFigure1.Ascompactionenergyincreases,theoptimummoisturecontentforcompactiondecreases.
Soiltexturecanalsoaffecttheresponseofthesoiltocompactioneffortsanditssensitivity tomoisturecontent.Figure2 illustrates theoreticaldifferences inmaximumbulkdensityandsensitivitytomoistureforwellgradedanduniformsoilswhenotherfactorsofthesoilareheldconstant.AlthoughthelightProctortestcouldbeusedtopredictmaximumbulkdensitiesthatmightresultfromforestoperationsforsomesoiltypes,italsoshowedthatthesoilswerelesssensitivetomoisturecontentwhentherewaslesscompactionenergyapplied.Thecom-pactioncurvewasflatterand,insomecases,U-shapedasillustratedinFigure3(Froehlichandothers1980).
Davis(1992)usedthelightProctortestinhisstudiesofbulkdensitychangesintwocentralOregonsoils.Hefoundthelightproctortesttobeadequatefordescribingacobblyloamsoil,butfoundatestusingtheheavierhammerofthestandardproctortestwith5to10blowsofthehammer(ratherthan25)tobemoreaccurateinpredictingcompactionfortheash-capsoilwithsandyloamtexture.HisProctortestsshowedgraduallyincreasingbulkdensitiesascompactioneffortincreased,buttherewasnotahighsensitivitytosoilmoisturecontent.
Totalorganicmattercontentinthesoiliscloselyrelatedtoaggregatesizeandstability.Thusareductioninorganicmattercontentwillresultinalossofag-gregatestabilityandasubsequentincreaseinasoil’spotentialforcompaction(AlderferandMerkle1941).WorkingwithfoursoilsinNewYork,Freeandothers(1947)concludedthatsoilsamplescontainingthemostorganicmatterwouldbecompactedtheleastatgivenmoisturecontentsandcompactiveefforts.Thisre-lationshipbetweenorganicmatterandcompactibilityofsoilswasalsoconfirmedinthereviewconductedbyMillerandothers(2004).
Figure 1—General relationships between moisture content, compaction effort and maximum bulk density.
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Methods and Limitations of Measuring Compaction ________________Thereareseveralmethodsavailabletomeasurecompaction,butallhavelimita-
tionsinforestsoils.Twoofthemostcommoninclude:(1)thebulkdensityofthesoiland(2)soilstrengthasoftenmeasuredbytheresistanceofthesoiltopenetrationwithacalibratedpenetrometer.Whilemeasurementofbulkdensityorsoilstrengthbeforeandaftervehiculartrafficisidealbecauseitreducessamplingerror,itissel-domdone.Mostoftenthemeasurementsaretaken“onandoff”compactedareas.Ifthesoildisturbancehasalsodisplacedsoilsincompactedareas,thisleadstotheriskofcomparingsoilcharacteristicsinonesoilhorizonwiththoseinanother.
Figure 3—Proctor test results on light soil gravelly sandy loam soil with initial bulk density near 0.70 g/cm� (Mg/m� ) and 2% clay content adapted from Froehlich and others (19�0).
Figure 2—General relationships of optimum moisture content and maximum bulk density for well graded and uniform textured soils.
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Bulk Density
Bulkdensity,thedrymassofaunitvolumeofsoil(BlakeandHartge1986),iscommonlyusedtomeasuresoilcompaction.Bulkdensityandrockcontentmeasurementsarerequiredtoconvertsoilnutrient,water,andmicrobialmeasurestoamass-per-areabasistocomparebetweensiteswithdifferentbulkdensitiesandwithin-siteprocesses(McNabbandothers1986).Althoughrocksareoftennotalargecomponentofash-capsoils,rootsandsteepslopesmakeitextremelydifficulttoaccuratelydeterminesoilbulkdensity.Anumberofdifferentmeth-odshavebeenusedtodeterminebulkdensityinsoils.Thesecangenerallybecategorizedas(1)coresampling,(2)excavationandvolumedisplacementand(3)radiation.
Core samplingisasimple,straightforwardmethodformeasuringbulkdensity.Cylindersofaknownvolumearedrivenintothesoilandtheresultantsoilcoredriedandweighed.Insomecases,narrowandsmallcoresamplersmayover-estimatebulkdensitybycompactingsoilintothecylinderwhenitishammeredintothesoil.
Volume excavationisanappealingalternativetocoretechniquesbecauseitallowsforflexibilityinvolumeofsoilsampledbasedonthesizeofsoilcoarse-fragments,rootsorhardpans.Aholeisexcavatedtothedesireddepthandwidth,allsoilmaterialisremovedandcollectedforweightdeterminationandthevol-umeoftheholemeasured.Variousmethodshavebeenusedtomeasureholevolumeincludingknownquantitiesofsandorstyrofoamballs,waterasmeasuredinaplasticbagliningthehole(Kohl1988),andexpandingpolyurethanefoam(Page-Dumroeseandothers1999).
Radiation methodsareinstantaneous,produceminimalsoildisturbance,allowaccessibilitytosubsoilmeasurementswithoutexcavation,donothavetobeonalevelsite,andhavetheoptionofcontinuousorrepeatedmeasurementsofthesamepoint(BlakeandHartge1986).Withanuclearmoisture-densitygauge,thesourceprobe is lowered toselectedsoildepths throughaccess tubesand theaveragedensitybetween thesourceandsurface-locateddetector isobtained.However,usinganucleargaugeisnotcommononforestsitesfarfromaroadsinceitweighsabout18kg.Inaddition,theequipmentoperatormuchbecertifiedtohandleandtransportradioactivematerial(FlintandChilds1984).
Penetrometer
Soilpenetrabilityisameasureoftheeasewithwhichaprobecanbepushedordrivenintothesoil(Vazandothers2001).Theresistancetopenetrationisre-latedtothepressurerequiredtoformasphericalcavityinthesoil,largeenoughtoaccommodatetheconeof thepenetrometer,andallowingfor thefrictionalresistancebetweentheconeanditssurroundingsoil.Easeofpenetrationbytheprobeisinfluencedbybothsoilandprobecharacteristics.Soil-to-probefrictionisgovernedbyprobefactorssuchasconeangle,diameter,roughnessandrateofpenetration.Soilfactorsinfluencingpenetrationresistancearematricwaterpo-tential(watercontent),bulkdensity,soilcompressibility,soiltexture,andorganicmattercontent(Smithandothers1997;Vazandothers2001).
Majorfactorsthatlimittheuseandinterpretationofpenetrometersasfieldindi-catorsofexcessivecompactionaretheinfluencesofwatercontentandinitialbulkdensity,mostlybecausethereisaninsufficientdatabasetoallowadjustmentsfor
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thesefactors(GuptaandAllmara1987;BennieandBurger1988).Awidelyacceptedmethodistomeasurepenetrometerresistanceatornearfieldmoisturecapacity.
Penetrometer-measuredsoilstrengthhasbeenprincipallylinkedwithsoilbulkdensity,watercontent,claycontent,andorganiccarbon.Usuallysoilstrengthincreaseswithincreasingbulkdensityanddecreasingwatercontent,exceptatlowerlevelsofcompactionwhensoilstrengthdeclinesassoilsdryout(Smithandothers1997).Sincesoilstrengthisstronglyrelatedtowatercontent,itvariesconsiderablythroughouttheyearwitheachwettinganddryingcycle(Busscherandothers1997).Thisrelationshipisalsoinfluencedbythedegreeofcompac-tion(MirrehandKetcheson1972).Increasingclaycontentsappearstoreducetherateatwhichsoilstrengthincreasesassoilsdrytowiltingpoint.Withincreasingorganicmattercontent,soilstrengthvaluesarehighatfieldcapacity,especiallyathigherbulkdensities(Smithandothers1997).
Correlation between methods of measuring compaction
Increasesinbulkdensitygenerallyhaveapositivecorrelationtoincreasesintheresistancetopenetrationasmeasuredbyapenetrometer,butspecific,statisticalrelationshipsbetweenthesetwotypesofmeasurementhavebeenmuchmoredifficulttoestablish.Effortstocorrelatebulkdensitymeasurementstopenetrometerreadingsthroughregressionanalysishaveoftenfailedorresultedinanextremelylowcorrelationcoefficient(Landsbergandothers2003;Froese2004).Allbrook(1986)wasreasonablysuccessfulindevelopingastatisticalrelationshipbetweenbulkdensityandsoilstrength(R2=0.67)whenthesoilstrengthwasmeasuredatornearfieldcapacitymoisturecontent.ThestudywasconductedonvolcanicsoilsincentralOregonandcomparedbulkdensitiesandsoilstrengthinskidrutsandinadjacentundisturbedareas.Soilshadinitialsoilbulkdensitiesaveraging0.80Mg/m3.Atthe5cmdepthhefounda23.2%increaseinbulkdensitiesmea-suredwithanucleardensimeteranda143%increaseinsoilstrengthasmeasuredwithapenetrometer.Itappearsthatthesoilstrengthmeasurementsweremoresensitiveandresponsivetochangesinsoilconditions,butitisalsoclearthatastandardofdetrimentalsoildisturbancethatdictateslessthana15%changeinbulkdensitywillnotbetheappropriatepercentagestandardwhencomparingsoilstrength(penetrometer)readings.TheUSDAForestServiceusesathresholdvalueofa15%increaseinbulkdensityfordeterminingwhensoilcompactionhasreachedalevelthatisdetrimentaltobiomassproduction(Powersandothers1998).
Characterization of Ash-Cap Soils _________________________________Soilscharacterizedasash-capsoilsareoftenderivedfromavarietyofvolcanic
eruptions,themostcommonbeingtheeruptionofMountMazamaatCraterLake,Oregon.Thesesoilsareoftenconsideredsurficialdeposits,overlayingthesoilderivedfromthebaserockbydepthsthatvaryfrom15cmtoseveralmeters.Theyarefrequentlycharacterizedinthesiltloamorsandyloamtexturalcategoriesofsoils.Mostash-capsoilsarecharacterizedbylowbulkdensities,generallylessthan0.75g/cm3,andbyhighporosityandlowshearstrength(Page-Dumroese1993;CullenandMontagne1981;Davis1992).Thepredominanceofsilica(glassfragments)inthesoilcontributestothewaterholdingcapacityofthesoil.Thedistributionofmicro-andmacro-porespacesprovidesmanyareasforholding
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water,especiallyinthemicro-porespaces.Oneeffectofcompactionmaybetodecreasethemacro-porespacethatiseasilyassessabletoplants,butnotthemicro-porespace.Ash-capsoilscanalsobecharacterizedbyrelativelylowclaycontent.Thisgenerallymeansthattherewillbeverylittlecohesionandinternalbondinginthesoil.Withoutclay,therewillbeverylittleshrinkingandswellingandthismayaffecttherateofsoilrecoveryfromcompaction.
Althoughash-capinfluencedsoilsarenon-cohesive,theydonotseemtorecovereasilyfromcompaction.Froehlichandothers (1985)observedcompactiononandoffskidtrailsonseveralharvestedsitesincentralIdaho.Forsoilsofvolcanicorigin,therewasareductioninthepercentdifferenceindensityonandofftrailswithtime,buttheyalsofoundthatsoilbulkdensityonvolcanicsoilswerestill26%higherat15cmdepthinthetrailsthanofftrails20-25yearsafterharvest-ing.Oneriskwithsoilrecoverystudiesthatconsiderbulkdensitiesindisturbedandundisturbedareas is that theymaynotbecomparing thesamesoil typesandtexture.Forexample,ifthedisturbancealsodisplacedsoilonaskidtrail,thecomparisonmaybebetweenthesurfacehorizonoftheundisturbedsoilandasub-horizonofthesoilontheskidtrail.
Thereareseveralhypothesesonwhyash-capsoilsdonotrecovermorequickly.Oneisthatthecompactionactivitybreaksdownthesoilparticlesand/orrealignsthemintomoreofaplatystructurethatallowsthemtofitclosertogetheraftertraffic.Anotheristhatthejaggededgesofthesilicadominatedash-capsoilpar-ticlesarephysicallylockedduringcompaction.Sinceclaycontentislow,thereislittlenaturalshrinkageandswellinginthesoil.Otherfactorsmayberelatedtothehighinitialpercentchangeinbulkdensitythatgenerallyoccursandthelackofasignificantfreeze-thawcyclesinthedrierregionsoftheintermountainwesternUSA.
Cullen and others (1991) characterized two ash-cap soils in their work inwesternMontana.UsingastandardProctortesttheydeterminedtheoptimummoisturecontentforcompactionofashcapsoilstobeabout228g/kg(22.8%)and256g/kg(25.6%)inthesurfacelayerwithaprojectedmaximumbulkdensityatthismoisturecontentof1.50Mg/m3and1.36Mg/m3forashoverquartziteorlimestonetill,respectively.Thesebulkdensitiesaremuchhigherthanthoseen-counteredinevenheavilycompactedforestsoilsasaresultofforestoperations.GiventheresultsoftheworkofFroehlichandothers(1980),onewouldexpecttheoptimumwatercontentforcompactionfromforestoperationstobehigherthanthevalueobservedintheMontanatestsandtheresultingmaximumcompac-tiontobelower.FieldobservationsintheMontanasoilsshowedtheirseverelycompactedsitestohaveaveragebulkdensitiesatthe5cmdepthof1.01Mg/m3and0.97Mg/m3forashoverquartziteorlimestonetill,respectively.
Although the relatively lowbulkdensitiesofashcap soilsmake themverysusceptibletocompaction, theresultingbulkdensitiesofcompactedsoilssel-domexceed1.0Mg/m3.Theimpactofthisdegreeofchangeinbulkdensityonfutureforestproductivityisnotthesubjectofthispaperbutthegeneralimpactofcompactionontreegrowthhasbeenstudiedinanumberofdifferentsettingsovertheyears(Froehlich1979;Davis1992;Powersandothers2004).Whilein-creasedbulkdensityassociatedwithmachinetraffichasgenerallybeenshowntoreducetreegrowth,theextentofthegrowthreductioninash-capsoilsisnotwelldocumented.Growthreductioncanpossiblybeattributedtoareductioninthewaterholdingcapacityofthesoil,butthechangeinpore-sizedistribution
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withintheash-capsoilsaftercompactionmayalsoaffecttreegrowth(Powersandothers2004).Theuseof15%percentchange that isusedasa thresholdvaluefordeterminingdetrimentalsoilcompactionbytheUSDAForestServicemaybeineffectiveforallsoilssinceeachsoiltexturalclassvariesininitialbulkdensityvalueandbiologicalsignificanceofthatchange(WilliamsonandNeilsen2000).Blockandothers(2002)suggestthatcombiningsoilbulkdensityorsoilstrengthmeasurementswithasurfacedisturbanceregimecanbeausefulmethodformonitoringharvestingimpactsonsoil.
Case Studies of Operations on Ash-Cap Soils _______________________Compactiononsomeash-capsoilshasbeenfoundtopersistforlongperiods
oftime,particularlyatdepthsof15cmandgreater.Geistandothers(1989)foundsignificantcompactiononstudysitessampled14to23yearsafterharvestintheBlueMountainsofOregon.Althoughaveragebulkdensitiesdidnotvarygreatlybetweenharvestedandundisturbedareaformostsites,0.67Mg/m3onundisturbedversus0.71Mg/m3onharvested,therewasamuchwiderrangeofbulkdensitiesinthedisturbedareasindicatingareasofsignificantcompactionandareasoflikelydisplacement.Inthemostdisturbedunit,averagebulkdensitywas0.66Mg/m3ontheundisturbedareaand0.80Mg/m3ontheharvestedarea,buttherangeofobservedbulkdensitiesonthedisturbedsiteswasevenwider.
Davis(1992)observeddifferenceinbulkdensitiesondisturbedandundisturbedareas inanash-cap soilwith sandy loam texture.He found theaveragebulkdensityofdisturbedvolcanicashsoilstobe35%higherthantheundisturbed,0.73g/cm3versus0.98g/cm3.HeconductedstandardandlightProctortestsonthesoilanddeterminedamaximumbulkdensitywiththestandardProctortestof1.07g/cm3atamoisturecontentofabout35%.HealsofoundarelativelyflatcurveacrossarangeofmoisturecontentsforlighterProctortests.
AnotherstudyconductedintheBlueMountainsofOregon(SniderandMiller1985)illustratestheimpactofsoilmoisturecontentonoperationalresults.Theyestablishedastatisticalsplit-plotdesigntolookatsoilcharacteristicsonskidtrails,onbermsoftrails,inobviousfireringswhereslashhadbeenpiledandburned,inareaswithsomegeneraldisturbance,andinundisturbedareasfiveyearsafterthelastharvest/sitepreparationactivity.Bulkdensitiesinthecontrolareaaver-aged0.68Mg/m3atthe3.2cmdepth,0.89Mg/m3atthe10.8cmdepthand0.92Mg/m3atthe18.4cmdepth.Generallytherewerenosignificantdifferencesinbulkdensitiesatanydepthamong the fourvariationsand thecontrol.Theauthorssuggestthatthereducedlevelofcompactionmayhavebeenafunctionofdrysoilconditionsduringtheperiodofoperations.
AnexperimentontheColvilleNationalForestinnortheasternWashingtonin-volvedanalysisofharvestingeconomicsandsoilimpactsforanumbervariationsinharvestingsystemsandtrailspacingforharvestingequipmentonbothsteepandgentleslopes.Thesteepslopeunitsinvolveduseofacableyardingsystemcoupledwithmechanizedharvestingequipment.Oneunitalloweddownhillforwardingwithaground-basedcut-to-lengthforwarder.Gentleslopeunitsweredesignedwithvaria-tionsinthedesignatedtrailspacingwithsomeallowanceforthefellingmachinetotravelofftrailinsomeunits(Johnson1999;Keatley2000;Johnson2002).
Soilanalysisinvolvedbulkdensityandpenetrometermeasurementsbeforeandafterharvestoperations(Landsbergandothers2003).Studyconclusionssuggest
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thatcompactionresultingfromanearlier fire-salvageharvestingoperationhasremained for at least 70years.Conclusionsnote that compactionwasnot asgreatonsteepterrainwherethecablebasedsystemswereused,butalsonotethatthesoilsweresandierinthatareaandwerelikelytobemoreresistanttochangesinsoilstrength.Changesinsoilstrength,asmeasuredwitharecordingpenetrometer,showedanaverageof127%increaseinresistancetopenetrationinthesurfacelayer(0to10cm)andan89%increaseinresistancetopenetrationatdepthsof15to25cmonskidtrailsinthegroundbasedunits.Thiscontraststochangesof–3%forthesurfacelayerand43%atdepthsof15to25cminthesteeperunits.Differencesonandoffskidtrailsatthe0to10cmdepthaveraged63%inthegroundbasedunitsand10%inthesteepslopes.Differencesatthe15-25cmdepthaveraged26%forbothunits.Thereweresignificantdifferencesbetweenthetypesofharvestingsystem,however.Forexample,thedifferencesbetweenonandoff trail resistancetopenetrationfor thecut-to-lengthsystemwas15%atthe0-10cmdepthand3%atthe15-25cmdepth.Soilconditionsafterharvestingthatremainedwithinlimitsofthespecifiedguidelines,butresultsalsoreflecteddifficultiesassociatedwithinterpretationofpenetrometerresultswhenreadingsaretakenoverafullfieldseasonthatincludessignificantchangesinsoilmoisturecontent(Landsbergandothers2003).
Inonestudy,ash-capsoilsinnorthernIdahowereshowntoreachtheirmaxi-mumbulkdensityafter4tripswitharubber-tiredskidder.Subsequenttripsdidnot result in further increases inbulkdensity.However,pore-sizedistributioncontinuedtochangeafter4ormoretrips(Lenhard1986).Althoughbulkdensitydoesnotappear tochangeafterseveralpasses,otherphysicalpropertiesmaycontinuetochangetothedetrimentofsoilproductivity.Ifsoilpore-sizedistribu-tioncontinuestochange,thenplant-waterrelationshipsarelikelytobealteredorsoilpuddlingwilloccurforlongerperiodsoftime.
TheresultsreportedondrysoilsinnorthernIdahobyFroese(2004)weresimilartothosereportedinnortheasternOregon(SniderandMiller1985).Froese’thesisworkinvolvedstudyofacut-to-lengthsystemoperatingonashcapsoils.Bulkdensitiesinthecontrolaveraged0.95Mg/m3atthe10cmdepth,1.10Mg/m3atthe20cmdepthand1.21Mg/m3atthe30cmdepth.Thesevaluesarehigherthantypicalbulkdensitiesforash-capsoilswithminimaldisturbanceandmayhavecontributedtothelackofchangeafteroperations.TheyarealsotypicalofbulkdensitiesmeasuredonskidtrailsaftermachineoperationsasillustratedinthecasestudyforWesternMontana(Cullenandothers1991).Therewasvirtuallynochangeinbulkdensityafterthepassageoftheharvesterandonepassoftheforwarder.Someincreaseinbulkdensitywasdetectedatthesurfacelayerwithincreasednumbersofforwarderpasses.Operationswerealsoconductedinlatesummerwhensoilswerequitedry.
Cullenandothers(1991)reportedchangesinbulkdensityasaresultoftrafficat three soildepthson soils inWesternMontana.Bulkdensity in the surfacelayerofashoveralimestonetillat5cmchangedfrom0.61Mg/m3withnotraf-ficto0.84Mg/m3withmoderatetrafficandto0.97Mg/m3withseveretraffic.Thechangesat15cmwerealsosignificant,changingfrom0.53Mg/m3intheundisturbedcaseto0.97Mg/m3and0.93Mg/m3formoderateandseveretrafficrespectively. In their conclusions they note that the volcanic surface horizonoverlyingtheglacialtillsoilswaswell-graded,cohesionless,andwaspronetovibratorycompaction.
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Controlling Compaction __________________________________________Methodsoflimitingcompactionimpactsonsoilsgenerallyinvolvecontrolof
thetrafficpatternsofequipment,restrictionofvehiclestodesignatedtrailsandareas,andcontrolovertheseasonsofoperation.Sincetopographyplaysamajorroleintheredistributionofwateronasite,depressionsinthelandscapemayhavehighermoisturecontentandbemorepronetocompactiondamagethanareashigheronthelandscape.Designatedtrailscanavoidthesesiteswhenneeded.
Theuseoflowgroundpressuremachinesandcoveringoftrailswithslashmatssuchasthosegeneratedwithcut-to-lengthsystemscanlimittheconsequencesofoneortwopassesofequipment,butdonotappeartobeeffectiveinminimizingsoilcompactionwhenequipmentmustusetrailsmultipletimes(Froese2004;Han2005).Inseveralstudiesofmechanizedequipment,onepassoftheharvestingmachinedidnotappeartosignificantlychangebulkdensityinthesoils(Froese2004;Han2005).Subsequentpassesoftheskiddingorforwardingequipmentdidincreasesoilbulkdensities,butcompactionwaslimitedtothepercentoftheareainmajortrailsorjustintherutsofwelldefinedforwardertrails.
Increasingspacingbetweenoperationaltrailscandecreasetheoverallimpactonanarea,butcanalsohavenegativeeconomicconsequencesbecauseoftheincreasedcostofmovingcutlogsandtreesincreaseddistancestotheoperationaltrails(Johnson2002).Carefuloperationalplanningcanmitigatesomeofthehighercostsassociatedwithincreasedtrailspacing,however.Itmayalsobepossibletoallowthefellingequipmenttooperateinalimitedfashionoffestablishedtrailsandtobunchharvestedmaterialtothetrailforprocessingand/orforwarding.
Limitingoperationsduringperiodsofhighsoilmoisturecontentwillalsolimitsoilimpacts.Thisgenerallywilltranslateintoseasonalrestrictionsonequipment,withmostoperationstakingplaceinlatesummerandearlyfall.Drysoils(<15%soilmoisturecontent)caneffectivelysupporthighergroundpressuresandresultinmorelimitedsoilcompactiontothesurfacemineralsoil(>10cm)(Han2005).Winter operations may be possible with minimal soil impact if the ground isfrozentodepthsof10to15cm(Flatten2002)orhassufficientsnowcover(atleast15cm).
Another option for minimizing soil compaction, but which can also havesignificanteconomicconsequencesistoshiftfromground-basedharvestingtocableorhelicopterharvestingsystems.Bothoftheseoptionscanbestructuredtohaveminimalsoilimpacts,butwillgenerallyincurhighercoststhanground-basedsystems.
Summary and Suggested Areas of Future Research ________________Ash-capsoilsarederivedfromavarietyofvolcaniceruptionsandaremostoften
classifiedinthesiltorsandyloamcategories.Theyarealsocharacterizedwithlowbulkdensity,highporosity,andhighwaterholdingcapacity.Theytendtobenon-cohesiveandbecauseoftheirrelativelylowstrength,arehighlysusceptibletobothvibratoryandcompressivecompaction.Compactionisgenerallyviewedinanegativecontextwithrespecttolong-termsiteproductivityandsustainableforestmanagement.Theresultsofseveralstudiesintheintermountainwestillus-tratethatbothbulkdensityandsoilstrengthvaluesweresignificantlyincreasedduringground-basedharvestoperations,butthattheresultingbulkdensitiesofcompactedash-capsoilsareoftenbelowtheinitialbulkdensitiesofothersoil
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textures.Thelong-termeffectsofthechangesinfactorsonsiteproductivitystillneedtobestudiedthroughcontrolledexperiments.
Sinceash-capsoilshaverelativelylowbulkdensitiesbeforeoperations,theymayexperienceaveryhighpercentchangeinsoilstrengthandbulkdensity.Insettingstandards,it isnotclearwhetherthefocusshouldbeonthefinalbulkdensityorsoilstrengthreading,theabsoluteamountofchange,orthepercentchange.Ifsoilstrength,asmeasuredbythepenetrometer,isrecommendedasastandardmethodforsoilmeasurement,correspondingthresholdlevelsofpercentandabsolutechangewillneedtobeestablished.
Theprocessofsoilcompactioncanbeexplainedbyengineeringpropertiesofsoils,butthedegreeofsoilcompactioncreatedinfieldsettingsishighlyin-fluencedbyavarietyoffactorsincludingdistributionofparticlesizes,presenceoforganicmatter,soilmoisturecontent,andsoiltexture.Bulkdensityandsoilstrengtharecommonlyusedtomeasurethedegreeofsoilcompaction,butthestatisticalcorrelationsbetweentwovariablescanbeverylowwhensoilstrengthisnotmeasurednearfieldcapacityofthesoil.Therelationshipsbetweenbulkdensityandsoilstrengthandtheothercriticalsoilfactorssuchaswaterholdingcapacityislessclear,however.Additionalworkisalsoneededtodeterminetheeffectofthedepthoftheash-caponsoilresponsetomachinetraffic.
Although ash-cap soils are susceptible to both vibratory and compressionforces,thespecificvibratoryandcompressiveforcepotentialoftheequipmentoperatinginvariousharvestingandsitepreparationfunctions(cutting,transport-ing)isnotknown.Researchonthevibratoryeffectsofequipmentandwhetherchangesinmachinedesigncouldreducethiseffectwouldbeveryusefultoforestmanagementstrategies.
Several studiesalso found thatchanges inbulkdensityandsoil strength inash-caparelongterm(>70years)andthatrecoverytimeforash-capsoilsisex-pectedtobeslow.Thesestudiesnotedthatsoilcompactionwasgenerallylimitedtoskidtrailsandtopsoillayers(<30cm).Harvestingequipmentused,seasonofoperationandharvestplanningweremajorfactorsinaffectingsoilcompaction.Controllingcompactionofteninvolvesuseoflowimpactequipmentselection,useofdesignatedskidtrails,andlimitationofoperationstodryseasonsorwhenthegroundisfrozen.Theuseoflowgroundpressuremachinesandcoveringtrailswithslashinacut-to-lengthloggingmayhelpreduceimpactsonsoils,especiallysoildisplacement.
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In: Page-Dumroese, Deborah; Miller, Richard; Mital, Jim; McDaniel, Paul; Miller, Dan, tech. eds. 2007. Volcanic-Ash-Derived Forest Soils of the Inland Northwest: Properties and Implications for Management and Restoration. 9-10 November 2005; Coeur d’Alene, ID. Proceedings RMRS-P-44; Fort Collins, CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station.
P. R. Robichaud, U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Moscow, ID. F. B. Pierson, U.S. Department of Agriculture, Agricultural Research Service, Northwest Watershed Research Center, Boise, ID, . R. E. Brown, U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Moscow, ID.
Abstract Afterprescribedburnsatthreelocationsandonewildfire,rainfallsimulationsstudieswerecompletedtocomparepostfirerunoffratesandsedimentyieldsonash-capsoilinconiferforestregionsofnorthernIdahoandwesternMontana.Themeasuredfireeffectsweredifferentiatedbyburnseverity(unburned,low,moderate,andhigh). Resultsindicatethatthisdry,undisturbedash-capsoilexhibitshighrunoffratesandisnaturallywaterrepellentat thesurface.However, theunburned,undisturbedash-capsoil isnothighlyerodibleduetheprotectivedufflayeronthesurface.Whenash-capsoilwasexposedtoprolongedsoilheating(highseverityburn),surfacewaterrepellencywasdestroyedandastrongwaterrepellent layeroccurredafewcentimetersbeneaththesoilsurface.Withthesimulatedrainfall,thenon-waterrepellentsurfacelayerbecamesaturated;thusmakingthesoilabovethewaterrepellentlayerhighlyerodible—especiallyduringhighintensityrainfall.
Keywords: waterrepellentsoils,rainfallsimulation,burnseverity,runoff,erosion.
Runoff and Erosion Effects after Prescribed Fire and Wildfire on Volcanic Ash-Cap Soils
P. R. Robichaud, F. B. Pierson, and R. E. Brown
Introduction
Fireisanaturalandanimportantpartofdisturbanceregimeforforestecosystemsandmanylandscapesarewell-adaptedtothisnatural firecycle.Wildfiresuppressionhasdominatedforestmanagement for thepastcenturyandhas interferedwith thesenatural fire regimescausingunnaturalaccumulationsofforestfuels.Althoughmanagedforestsburnlessfrequentlythantheunmanagedforests,thewildfiresthatdooccurarelargerandmoreseverethaninthepast,causingmoresevereandlong-lastingeffects.Fireeffectsonforestsoilmayincludefire-inducedsoilwater repellency, reduced infiltration rates, increasedoverland flow,andincreasedpeakflow,whichoftenresultinincreasedwaterandsedimentyields.
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Burn Severity
Burnseverity,aqualitativemeasureoftheeffectsoffireonsiteresources,isausefulconceptforcomparingfires(HartfordandFrandsen1992;RyanandNoste1983).Arangeoffireandpostfireconditions,suchasfireintensity,fireduration,crownconsumption,soilcolor,andproportionoflitterremaining,aretypicallyusedtoclassifyburnedareasintodiscreteclassesofhigh,moderate,orlowburnseverity.Although someaspectsofburn severitycanbequantified,no singlenumbercanbedeterminedtomeasure‘resourceimpact’.
Thecomponentofburnseveritythatresultsinthemostdamagetosoilsisfireduration,becausedurationgenerallydeterminesthetemperatureanddepthofsoilheating.RyanandNoste(1983)createdaburnseverityclassificationsystem(expandedbyJain(2004))thatestimatestheamountofsoilheatingthatlikelyoc-curredduringthefirebasedonpostfirelitteramountsandmineralsoilcoloration.Becauseitisspecifictosoil,theRyanandNoste(1983)definitionofburnseveritywasusedtoevaluateburnseverityatresearchsitesdiscussedinthispaper.
Water Repellency
Naturallyoccurringwater repellent soilsoccur ineverycontinentandhavedifferentinfiltrationpropertiesthanwettablesoils(Letey2005).Firecreatesorenhanceswaterrepellencyinsoils(Doerrandothers2000).Assurfacevegetationisburnedandthesoilisheated,organicmatterinandonthesoilisvolatilized,andasignificantfractionofthesevaporizedorganiccompoundsmovefromthesurfaceintothesoilprofile(DeBanoandothers1976).Thesealiphatichydrocar-bonvaporscondenseonsoilparticlesinthecoolerlayersbeneaththesurfacetoformawaterrepellentlayer.Thiswaterrepellentlayerisgenerallywithinthetop5cmofthesoilprofile,non-continuous,androughlyparalleltothesurface(Clothierandothers2000;DeBano2000).Ingeneral,coarsesoils(lowclaycon-tent)aremoresusceptibletobecomingwaterrepellentthanfinersoils(highclaycontent)duetothelowerspecificsurfaceareaofcoarsesoilparticles.However,whenwaterrepellencyisestablishedinfine-grainedsoils,itcanbeequallyormoreseverethaninacoarse-texturedsoil(Doerrandothers2000;RobichaudandHungerford2000).
Fire-inducedsoilwaterrepellencyhashightemporalandspatialvariability(Letey2005).Thedegreeanddepthofpostfirewaterrepellencyisrelatedtosoilheatingduringthefire,which,becauseofitsdependenceonantecedentsoilmoisture,forestfloorthickness,burnduration,postfiresmoldering,etc.,ishighlyvariable.Fire-inducedsoilwaterrepellencyhasbeenfoundtovarybothinthehorizontalandtheverticaldirectionsatthe1cmscale(Hallettandothers2004;Gerkeandothers2001).Fire-inducedwaterrepellencyismostoftendetectedat1to3cmbelowthesurface(Huffmannandothers2001).Inaddition,soilwaterrepellencyistransientandisrelatedtosoilmoisture.Generally,bothnaturalandfire-inducedsoilwaterrepellencyislostduringlongwetperiodsandisre-establishedupondrying, causing short-term or seasonal variations (Robichaud and Hungerford2000).Fire-inducedsoilwaterrepellencyistemporarybecausethehydrophobicsubstancesresponsibleforwaterrepellencyareslightlywater-solubleandslowlydissolvesuchthatwaterrepellentsoilconditionsarebrokenuporwashedawaywithinseveralyearsafterthefire.
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Infiltration
Inwaterrepellentsoils,watermaymovethroughawettablesurfacelayer,anduponreachingawaterrepellentlayer,flowlaterallybelowthesurface(DeBano1981).Giventhespatialvariabilityofwaterrepellency,watermayflowprefer-entially,viacolumns,or‘fingers,’throughthelesswaterrepellentareasforminganunevenwettingfront(RitsemaandDekker1994,1995).Infiltrationonwaterrepellentsoilsisalsodependentonthetypeanddistributionofplantsoverthesurface(Shakesbyandothers2000).Someplants,suchaschaparral,decreaseinfiltrationbyaddinghydrophobiccompoundstothesoildirectlyunderthecanopy(DeBano1981).Conversely,infiltrationcanbeenhancedbyrootchannelsandmacropores(remainingafterrootsdecayorburn)thatcanactaspathwaysforinfiltratingwaterthroughwaterrepellentlayers(Meeuwig1971;Sevinkandothers1989;Burchandothers1989;Shakesbyandothers2000).
Overland Flow and Erosion
Overlandflowandsoilerosionratesaredependentonarangeofinter-relatedfactorsthatincluderainfall(e.g.,amount,intensity,duration),soil(e.g.,erodibility,particlesize,poresize,bulkdensity,waterrepellency),topography(e.g.,slope,aspect),andbiotic(e.g.,vegetation,groundcover,animaluse,naturalandhumandisturbances).Becauseof the reduction in infiltrationcapacity inwater repel-lentsoils,postfireincreasesinoverlandflowanderosionareoftenattributedtofire-inducedwaterrepellency(Doerrandothers2000).However,itisdifficulttodeterminetheproportionofpostfireincreasederosionthatcanbeattributedtosoilwaterrepellency.Firecanalsoincreasetheerodibilityofsoilthroughreduc-tionofprotectivegroundcoverandsoilorganicmatter,sealingofsoilpores,lossofwaterstoragecapacityinthelitterandduff,lossofsoilmoisture,breakdownsoilaggregates,andreductionof soilparticlesize (DeBanoandothers1998).Thus,thecontributionofsoilwaterrepellencyontotalpostfireerosionisoftendifficulttoseparatefromotherfireimpacts.
Cautionmustbeusedwhenextrapolatingmeasurementsofoverlandflowfromsmallplotstodeterminethepotentialrunoffonthehillslope-orcatchment-scalewheredifferentialflowpatternsmayhavesignificantlymoreeffect(Shakesbyandothers2000;Imesonandothers1992).AfteraEucalyptusforestfireinAustralia,ProsserandWilliams(1998)foundthatsmallplotsproducedgreaterrunoffandsedimenttransferthanwasobservedatthehillslopecatchmentoutlet.Thelackofspatialcontiguityinsoilwaterrepellencyandtheexistenceofdifferentialinfiltra-tionflowpatternsmaycreatescattered‘sink’areasacrossahillsidewherewaterinfiltratesand,asaresult,doesnotreachthebaseofacatchmentasoverlandflow(Imesonandothers1992;ProsserandWilliams1998).
Study Objectives
Smallplotrainsimulationdatafromthreeprescribedburns(northernIdaho)andonewildfire(westernMontana)areusedtocomparefireeffectsonrunoffanderosionofash-capsoils.Thetwostudies(prescribedfirestudyandthewild-firestudy)hadcommonsitecharacteristics(coniferforestedenvironmentsandash-cap soil types) and test procedures (rainfall simulation), which facilitated
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thecomparisonoffirstyearpostfiredatafromthefourfiresto:1)examinefire-inducedandnaturalash-capsoilwaterrepellency;2)comparerunoffrates;and3)comparesedimentconcentrationsandsedimentyields.
Methods _______________________________________________________
Prescribed Fire
Site Description—The prescribed fire study was conducted in the FernanRangerDistrict,IdahoPanhandleNationalForestintheCoeurd’AleneMountains(48°15’N,116°15’W).Studyplotswerelocatedbetween950to1500meleva-tionon14to46percentslopes.ThepredominantsoiltypeisTypicVitrandepts,asiltloamderivedfromvolcanicash-influencedloess28to45cmthick,overanEutircGlossoboralfs,amixedloamy-skeletalformedfromPrecambrianBeltrock.Averageannualprecipitationis34incheswithaboutonethirdofthatfallingassnowinthewintermonths(Abramovichandothers1998).Vegetationoftheareaistypicalofthewesternhemlock/queencupbeadlily(Tsuga heterophylla/Clintonia uniflora)habitattype(Cooperandothers1991).
IgnitionofthefirstharvestedunitwasinthespringonApril25(BumbleBee).IgnitionofthesecondburnoccurredinthefalltwoyearslateronSeptember30(Buckskin I). The third harvest unit was ignited in the summer on August 25(Buckskin II). For eachof the threeprescribedburns, ahelitorch-ignited stripheadfirewasstartedatthetopoftheslopewithfirestripsplacedaboutevery30-40mdowntheslope.Ignitionwasgenerallyveryrapid,andtheentireunitignitedwithin30min.
Plots—Beforeeachprescribedfire,sixpaired1-m2plotsweresystematicallyselectedinthestudyareastorepresenttheaveragefuelconditionandaverageslope,withoneplotdesignatedforrainfallsimulationandtheotherforsoiltemperaturemeasurements.Foursteelpinswereinstalledflushwiththeforestfloorsurfaceineachplottoestimateforestfloorconsumption.Inthetemperature-measurementplots, these forest floor pins were located near thermocouples. Temperaturesduringthefirewererecordedwitheightchromel-alumelthermocoupleslocatedatthelittersurface,inthehumus,atthehumus-mineralsoilinterface,andinthemineralsoilat1,2,4,8,and10cmbelowtheinterface.Temperaturesduringtheburnwerefirstrecordedwhenthesurfacetemperaturereached80°Candcontinuedeveryminutethereafterfor36h.Immediatelybeforeburning,samplesof thewoody fuels, forest floor,andmineral soilwerecollected todeterminemoisturecontent.
Oneachoftherainfallsimulationplots,afour-sidedsheetmetalframewasinstalled.Threeframesideswere15cmtallandinstalledwith5cminsertedintothemineralsoil,andthefourth,downslopesideoftheframewas5cmtallandinsertedfullyintothesoil(noextensionabovethesurfaceofthesoil)allowingrunoffandsedimenttoleavetheplot.
Rain Simulation—Withindaysof theprescribed fire,a30-min rainsimula-tionwasconductedattheexistingsoilmoistureconditionasdeterminedfromacompositesoilsamplewastakenneartheedgeoftheplotframe.ThesimulatedrainfallwasappliedtoeachplotusingaUSDA-ForestServicemodifiedPurdue-typeoscillatingnozzlerainfallsimulatorwithspecificationsasdescribedbyMeyer
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Runoff and Erosion Effects after Prescribed Fire and Wildfire on Volcanic Ash-Cap Soils Robichaud, Pierson, and Brown
andHarmon(1979).Therainfallsimulatorproducedanaveragerainfallintensityof38mmh–1fortheBumbleBee(spring92)burnsite.AftertheBumbleBeesimula-tions,thesimulatedrainfallintensitywasincreasedtoensurethattherainfallrateexceededtheinfiltrationcapacityofthesoil.Rainfallintensitywas100mmh–1fortheBuckskinI(autumn94)andBuckskinII(summer95)burnsites.Sevenraingaugeslocatedaroundthe1m2plotsverifiedtherainfallamount.
Acoveredtroughatthelowerendofeachplotconductedrunoff(waterandsediment)throughapipefittedwithavalvethatallowedfortimedvolumesampling.Thesamplesweremanuallycollectedin1000mlbottlesat1-minintervals.Attheendofthesimulationrun,anysedimentremaininginthetroughwaswashedintoasamplebottle.Allrunoffsampleswereweighedandoven-driedtodeterminerunoffratesandsedimentconcentrations.
Wildfire Study
Site Description—The wildfire study was conducted in the Bitterroot Na-tionalForest(46°4’N,114°0’W)ofwesternMontanawhere,inthesummerof2000,lightningstrikesignitedtheBitterrootComplexFires.Thesefiresburned101,000ha—40percentathighburnseverityasdeterminedbypostfireappear-ance(USDA2000).ThepredominantsoilisderivedfromvolcanicashoverhighlyweatheredgraniteandisclassifiedasasandyskeletalAndic-Dystrocryept.Themeanelevation isapproximately1,950meterswithslopes ranging from25 to55percentanddominantlywest-southwesternaspects.Vegetationoftheareaistypicalofthesubalpinefir/menziesii(Abies lasiocarpa/Menziesia ferrugineah.t.)foresthabitattype.
Plots—Withinanareaofhighburn severity, four study siteswere selectedbasedoncomparableslope,aspect,andgroundcovercharacteristics.Oneachofthefoursites,15plotsof0.5m2wererandomlylocatedanddelineatedbyafour-sidedsheetmetalframeaspreviouslydescribed.Approximately3kmnorthoftheburnedstudyarea,threeunburnedsiteswereselectedsuchthattheslope,aspect,andsoiltypewerecomparabletotheburnedareasitesand,inaddition,thevegetativecharacteristicswerecomparableamongtheunburnedstudysites.Ineachofthethreeunburnedsites,7plotsof0.5m2wererandomlylocatedanddefinedbytheinstallationofsheetmetalplotframesasdescribedabove.
Directlyadjacenttoeachplotframe,waterrepellencywasmeasuredusingthewaterdroppenetrationtime(WDPT)adaptedfromDeBano(1981).Eightwaterdropswereplacedonanexposedsurfaceof themineral soiland the time toinfiltrateintothesoilisobserved.Thedegreeofwaterrepellencyisdeterminedbythelengthoftimethewaterdropsitsonthesoilwithoutbeingabsorbed:0to5sec=none;6to60sec=slight;61to180sec=moderate;181to300ormore=severe.Themaximumobservationtimewaslimitedto5minutes.Ifthewaterdropsinfiltratedinlessthan5seconds,thetestwasrepeatedat1cmdepthbelowthesurface.Thisprocesswasrepeatedat1cmincrementstoamaximumdepthof5cm.
Neartheedgeoftheplotframe,acompositesoilsamplewastakentoassesssoilmoisture.Groundcoverwithineachplotwasdetermined.
Rainfall Simulation—Withindays after the firewas contained, a simulatedrainfalleventwithameanrainfallintensityof100mmh–1wasappliedtoeachofthe102plotsfor60minusingtheUSDA-ForestServiceandtheUSDA-Agricultural
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ResearchServiceoscillating-armrainfallsimulatorswithspecificationsasdescribedbyMeyerandHarmon(1979).Datafromthefirst30minutesofeachsimulationwereusedforcomparisonsandanalysis.Duringtherainfallsimulation,samplesofrunoffandsedimentwerecollectedthroughacoveredtroughatthedownslopeedgeofeachplotasdescribedfortheprescribedburnsabove.Thesamplesweremanuallycollectedat1-minintervalsforthefirst14min,thenat2-minintervalsfortheremainderofthe60-minrun.Allrunoffsampleswereweighedandoven-driedtodeterminerunoffvolumeforeachinterval,totalrunoffvolume,sedimentconcentrations.
Analytical Methods
ThedatafromtheBumbleBeeprescribedfiresitewerenotincludedinthestatisticalanalysisbecausetherainfallapplicationrateof38mmh–1wasmuchlessthan100mmh–1rainfallapplicationrateappliedatallothersites.Thetotalrunoffanddrysuspendedsedimentweightwerecalculatedforthefirst29to30minofthefirstsimulationfortheBuckskinIandIIsitesandforthefirst29to31minoftheyear2000simulationsattheBitterrootsites.Runoffandsuspendedsedimentwerenormalizedbyareatoaccountforthedifferentplotsizes.Runoffratiosaretotalrunoff(mm)dividedbytotalrainfallapplied(mm)foreachsimula-tion;therainfallisadjustedfortheplotsize.
Results and Discussion ___________________________________________
Burn Severity
Variedantecedentconditions for the threeprescribedburns resulted indif-ferentialsoilheatingandarangeoffireeffectsonthesoil.BumbleBee,aspringburn,hadthehighestpre-firesoilandduffmoisturecontents(61to69percentand125percent,respectively)andthelowestmineralsoiltemperatures(20to80°C)andproportionofduffconsumed(28percent)duringthefire(table1).BumbleBeewasalowburnseverityfire.BuckskinIwasburnedinthefallwiththedriestconditionsofthethreeprescribedburns(table1)andwasclassifiedmoderateburnseverity.BuckskinII,asummerburn,hadslightlyhigherpre-burnfuelandsoilmoistureconditionsthanBuckskinIandwasalsoclassifiedmoder-ateburnseverity (table1).ThestudyareaswithintheBitterrootComplexFireareawereinunburnedandhighburnseverityareas.Thesefourfiresonash-capsoils provided four burn severity conditions—unburned (Bitterroot), lowburnseverity(BumbleBee),moderateburnseverity(BuckskinIandII),andhighburnseverity(Bitterroot).
Moisture Content and Water Repellency
Soilmoisturesimmediatelypriortotherainfallsimulationswerehigherintheprescribedfiresitesthanthewildfiresites(table2),butprobablynothighenoughtochangethesoilwaterrepellencyresponse(RobichaudandHungerford2000).SoilwaterrepellencywasdirectlyassessedintheBitterrootstudy,wherebothburnedandunburnedsoilshadstrongwaterrepellentresponsesatdifferentdepths.Theunburnedsoilwasseverelywaterrepellentatthesurfacewhiletheburnedsoil
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Runoff and Erosion Effects after Prescribed Fire and Wildfire on Volcanic Ash-Cap Soils Robichaud, Pierson, and Brown
Table 1—Measured conditions before, during, and after three prescribed burns in northern Idaho.
Pre-prescribed BurnFuel and soil moisturecontents and weather conditions Bumble Bee Buckskin I Buckskin II
Fine fuels (0-7� mm) (%) 20 9 10Large fuels (77-�00 mm) (%) 41 11 2�Litter (%) �4 1� 11Humus (%) 12� 4� 4�Soil 0-2 cm (%) �9 40 49Soil 2-� cm (%) �1 29 40Ambient temperature (oC) 22 20 1�Wind speed (kph) �-1� 2-� 0-11Relative humidity (%) 1� �0 �7
Prescribed BurnMaximum soil temperatures (°C) Bumble Bee Buckskin I Buckskin II
Mineral soil surface 20-�0 40-�00 90-2�01 cm below min. soil surface 40-70 40-270 70-1202 cm below min. soil surface 20-�0 40-�0 �0-�0
Post-prescribed BurnOrganic material remaining (%) Bumble Bee Buckskin I Buckskin II
Fine fuels 12 � 0Duff 72 27 ��
Table 2—Pre-rainfall simulation mean ground cover and gravimetric soil moisture content by location.
Gravimetric soilLocations Ground cover water content
- - - - - - - - - - - - (%) - - - - - - - - - - -
Unburned Bitterroot 100 1� Bumble Bee 100 29Buckskin II 9� 2�Buckskin I 70 �0Burned Bitterroot 10 17
hadawaterrepellentlayerat1to2cmbelowthesurface(fig.1).Thecreationofafire-inducedwaterrepellentlayerhasbeenobservedbyotherresearchers(e.g.,McNabbandothers1989;BrockandDeBano1990;ScottandVanWyk1990;Doerrandothers2000).However,thehighburnseverityfireappearedtodestroythenaturalsurfacewaterrepellency,andcreateawaterrepellentlayeratdepth.Doerrandothers(inpress)observedthesameaffectafterwildfiresineucalyptusforestsinAustralia.
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Robichaud, Pierson, and Brown Runoff and Erosion Effects after Prescribed Fire and Wildfire on Volcanic Ash-Cap Soils
Runoff
Thehighest runoff ratio rates (fig.2)andmean runoff amounts (33and32mm)andrunoffratios(0.71and0.67)weremeasuredonthehighandmoderateseverityburnsites—Bitterroot-burnedandBuckskinI,respectively(table3).Theunburned-Bitterroot sites and themoderateburn severityBuckskin II sitehadsimilarrunoffratiorates(fig.2)andmeanrunoffamounts(26and24mm)andrunoffratios(0.54and0.53)(table3).Thisunexpectedlylargerunoffresponseintheunburned-Bitterrootsitesislikelyduetotheshorttimeframeofthesimula-tionandtheresistancetowettingofthedryorganicduffmaterialaswellasthenaturallywaterrepellentdrysurfacesoil.TheBumbleBeeprescribedburnsitehadlowrunoffratiorates(fig.2)andalowmeanrunoffamount(4.7mm)andrunoffratio(0.12)(table3).However,thesedataarenotdirectlycomparabletotheothersitesasthelowerrainfallapplicationratemaynothaveexceededtheinfiltrationcapacityofthesoil.
Sediment Concentrations and Yields
Sedimentconcentrationsandmeansedimentyieldsgenerallyincreasedwithincreasingburnseverity(fig.3andtable3).Sedimentconcentrationsintherainsimulationrunofftendedtopeakinthefirst5min,rapidlydecreaseduringthesecond5min,andslowlydecreaseduringtheremaining20minutesofthesimu-lation(fig.3).Theunburned-BitterrootsitesandtheBumbleBeesite(lowburnseverity)hadthelowestconcentrations,peakingat7and4gL–1,respectivelyanddecreasingtolessthan1gL–1at30min(fig.3).Theseconcentrationsresultedinmeansedimentyieldsof0.027and0.0091kgm–2,respectively(table3).ThelowerrainfallapplicationrateontheBumbleBeesiteprobablyhadlittleaffectonmeansedimentyield(table3)duetothehighgroundcoverremainingafter
Figure 1—OntheUnburned-andBurned-Bitterrootwildfiresites,theportionofwaterrepellentsoil,asmeasuredbytheWaterDropPenetrationTime(WDPT)tests,areindicatedforthesoilsurfaceand1,2,3,4,and5cmdepths.Theshading/hatchingwithineachbarindicatetheseverityofthemeasuredwaterrepellency.
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Table 3—Mean runoff, runoff ratio, and suspended sediment yield by location. Standard errors are in parentheses. Dif-ferent letters within a column indicate significant differences at α=0.05. Comparative statistics do not include the Bumble Bee data due to the lower applied rainfall at that site.
Location Disturbance type n Runoff Runoff ratio Sediment yield (mm) (kg m–2)
Unburned-Bitterroot Undisturbed 21 2� (1.�) a 0.�4 (0.0�2) a 0.027 (0.0�9) aBumble Bee Prescribed fire 4 4.7 (1.4) 0.2� (0.04�) 0.0091 (0.002�)Buckskin II Prescribed fire � 24 (2.�) a 0.�� (0.049) a 0.2� (0.90) abBuckskin I Prescribed fire � �2 (1.�) ab 0.�7 (0.19) ab 0.�0 (0.�0) abBurned-Bitterroot Wildfire �0 �� (0.�0) b 0.71 (0.12) b 0.�� (0.�1) b
Figure 2—Therunoffratio(runoff/rainfall)rateforallstudysitesareplotted.TheBumbleBeesitesreceivedaloweramountofrainfallascomparedtoothersites.
Figure 3—Thesedimentconcentrationrateforallstudysitesareplotted.TheBumbleBeesitesreceivedaloweramountofandlessintenserainfallascomparedtoothersites.
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thespringburn(table2).TheBuckskinIandII,bothmoderateburns,peakedat47and36gL–1,respectivelyanddecreasedtoabout1gL–1at30min.(fig.3),resultinginmeansedimentyieldsof0.50and0.26kgm–2,respectively(table3).Thehighseverityburned-Bitterrootsitespeakedat38gL–1,andremainedhigherthananyoftheothersitesthroughoutmostofthe30minsimulation,anddecreasedto20gL–1at30min.(fig.3),resultingina0.85kgm–2meansedimentyield,anorderofmagnitudegreaterthantheunburned-Bitterrootsites(table3).Thehighersedimentyieldsforthewildfiresitesreflectthehigherconsumptionoforganicmaterialduringawildfire (longer firedurationandhighersoil tem-peratures)ascomparedtoaprescribedfire.Thisdifferenceinfiresisreflectedinthepostfire,pre-rainfallmeangroundcovers,withtheBurned-Bitterrootsiteshaving10percentgroundcoverandtheBuckskinIandBuckskinIIsiteshaving70percentand98percent,respectively(table2).
Conclusions _____________________________________________________Astrongnaturalsoilwaterrepellencywasdetectedatthesurfaceofthemineral
soilintheunburned,undisturbedash-capsoilwithlowsoilmoisturecontent.The high burn severity wildfire appeared to destroy the surface water repel-lency,andcauseastrongwaterrepellentlayertodevelop1to2cmbelowthesurfaceofthemineralsoil.Soilwaterrepellency,atthesurfaceorslightlybelowthesurface, increasedrunoff;however,below-surfacewaterrepellencyresultsinamuchlargersedimentresponsethansurfacewaterrepellency.Whenthereisfire-induced,below-surfacesoilwaterrepellency,rainfallisreadilyabsorbedbythenon-repellentsurfacesoil(0to1-2cm)whichbecomessaturateddowntothemoreresistantwaterrepellentlayer.Thissaturatedsurfacelayeriseasilydetachedandentrainedwithinthesubsequentoverlandflow.Additionally,finerootsthatbindthesurfacesoiltogetherwerelikelypartiallyconsumedduringthefire,makingsoilparticlesvulnerabletodetachment.
Even in steep forest environments with dry conditions (i.e., severe surfacewaterrepellency),theundisturbed,unburnedsitewithitsintactdufflayerwasnothighlyerodible,despitehighrunoffrates.Duringthe30minofhighintensityrainfall,thedryduffdidnotabsorbmuchwaterandtherainfallflowedthroughthedufflayerandatopthewaterrepellentmineralsoiltotheoutletoftheplots.Consequently,therunoffratesfortheunburned-BitterrootsitesweresimilartothosefoundonthemoderateburnseverityBuckskinIIsite.However,thesedi-mentconcentrationsandsedimentyieldswerelessthantheBuckskinIIduetotheprotective layerofduffmaterial.TheBumbleBee lowseverityprescribedfirealsohadminimalsedimentresponsebecauseofthecharred,butintact,duffremainingafterthefire.Thefireeffectsonsedimentconcentrationsandsedimentyieldsincreasedwithincreasingburnseverity.
Management Implications
Ash-capsoilsareknownashighlyproductiveforestsoils,andprotectingthissoil resource isan important landmanagementconsideration.Prescribed firesshouldbeignitedwhenduffmoisturecontentwillpreventtotalconsumptionoftheprotectivedufflayer.Ash-capsoilsburnedathighseverityarehighlyerodibleandpostfirerehabilitationdecisionsshouldtakeintoaccountthepotentialpostfirehydrologicalandsedimentresponsefrompotentialrainevents.
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Robichaud,P.R.;Hungerford,R.D.2000.WaterrepellencybylaboratoryburningoffournorthernRockyMountainforestsoils.JournalofHydrology.231-232(1-4):207-219.
Ryan,K.C.;Noste,N.V.1983.Evaluatingprescribedfires.In:Lotan,J.E.;Kilgore,B.M.;Fischer,W.C.;Mutch,R.W.,tech.coords.Proceedingsofthesymposiumandworkshoponwilder-nessfire.Gen.Tech.Rep.INT-182.Ogden,UT:U.S.DepartmentofAgriculture,ForestService,IntermountainResearchStation:230-238.
Scott,D.F.;VanWyk,D.B.1990.Theeffectsofwildfireonsoilwettabilityandhydrologicalbehaviourofanafforestedcatchment.JournalofHydrology.121:239-256.
Sevik,J.;Imeson,A.D.;Verstratun,J.M.,1989.Humusformdevelopmentandhillsloperunoff,andtheeffectsoffireandmanagement,underMediterraneanforestinN.E.Spain.Catena.16:461-475.
Shakesby,R.A.;Doerr,S.H.;Walsh,R.P.D.2000.Theerosionalimpactofsoilhydrophobicity:currentproblemsandfutureresearchdirections.JournalofHydrology.231-232,178-191.
USDAForestService.2000.ValleyphaseI:burnedareaemergencyrehabilitation(BAER)reportFS-2500-8—funding request.Missoula,MT:U.S.DepartmentofAgriculture,ForestService,BitterrootNationalForest.253p.
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The Practice of Sustainable Soil Management
Sustainablesoilmanagementcanbedefinedasensuringthebiological,chemicalandphysi-cal integrityof the soil remains for futuregenerations. Sustainability shouldbeaddressedthroughoutallfacetsofforestmanagementincludingimplementationofindividualharvestorstand-tendingplans,developmentofagencyorcompanystandardsandbestmanagementpractices(BMPs),andthird-partycertification.Demonstrationofsustainablesoilmanagement
In: Page-Dumroese, Deborah; Miller, Richard; Mital, Jim; McDaniel, Paul; Miller, Dan, tech. eds. 2007. Volcanic-Ash-Derived Forest Soils of the Inland Northwest: Properties and Implications for Management and Restoration. 9-10 November 2005; Coeur d’Alene, ID. Proceedings RMRS-P-44; Fort Collins, CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station.
Mike Curran, Corresponding author, Research Soil Scientist, B.C. Ministry of Forests and Range, Forest Sciences Pro-gram, Kootenay Lake Forestry Centre, Nelson B.C., Canada. (also Adjunct Professor, Agroecology, University of B.C.). Pat Green, Forest Ecologist, Nez Perce National Forest, Grangeville, Idaho. Doug Maynard, Research Scientist, Natural Resources Canada, Canadian Forest Service, Victoria BC, Canada.
Abstract Sustainabilityprotocolsrecognizeforestsoildisturbanceasanimportantissueatnationalandinternationallevels.Atregional levelscontinualmonitoringandtestingofstandards,practices,andeffectsarenecessary forsuccessfulimplementationofsustainablesoilmanagement.Volcanicash-capsoilsareaffectedbysoildisturbanceandchangestosoilpropertiesinfluenceecosystemresponsessuchasproductivityandhydrologicfunction.Soildisturbancefromtimberharvesting,reforestation,orstandtendingismainlyaresultofmovingequipmentandtrees.Compactionandorganicmatterremovalareofprimaryconcern.Theseverityandextentofdisturbancedependontheharvestsystem,soil andclimaticconditions.Ash-cap soilscanbe susceptible todisturbanceand schemes topredictcompaction,displacementanderosionhazardsareusefulforplanningforestmanagementoperations.On-siteeffectsrangefrompermanentlossofgrowingsitesbecauseofroads,tomoresubtlechangesinsoilpropertiesthatultimatelyinfluencesiteproductivity.Off-siteeffectsmay includeerosionand landslides.Soildisturbanceduringoperationsshouldberegulatedandmonitoredtominimizebothon-andoff-siteeffects,whichcantakeyearsordecadestoappear.Foresthealthissuesvaryonvolcanicash-capsoils.AnanalysisofArmillariarootdiseaseincidenceacrosstheNationalFor-estsoftheInlandNorthwestindicatessomepotentialrelationshipsamongrootdisease,andsoilandsitefactors.Thestrongrelationsbetweenpresenceofsusceptiblehostanddevelopmentoffungalbiomassmaybethestrongestcausalagent,withthesoilandsitefactorssupportingthepresenceofthepathogenandsusceptiblehost.Thickerashsoilsofmorenortherlyareasarerelatedtohabitattypesthathistoricallysupportedwhitepineandahigherdiversityoflesssusceptiblespecies.Afterrootdiseasemortalityoccurs,thesemoremesicenvironmentsalsofillinwithotherspeciesrapidly,sohigherlevelsofrootdiseasearemoredifficulttodiscern.Recommendationsaremadeforsoilmanagementandaboutinformationneedsforsoildisturbanceandrootdiseaserelations.
Key words:volcanicash-capsoils,foresthealth,Armillaria,rootdisease,criteriaandindicators,organicmatterdeple-tion,soildisturbance,soilcompaction,sustainabilityprotocols
Volcanic Ash Soils: Sustainable Soil Management Practices, With Examples of Harvest Effects and Root Disease Trends
Mike Curran, Pat Green and Doug Maynard
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ispromoted through reportingprocedures requiredbyapplicable sustainabilityprotocols,andbyhavingthird-partycertificationofforestpracticesandproducts(Curranandothers2005a).
Sustainabilityprotocolsexistatinternationalandnationallevels.Attheinter-nationallevel,theMontrealProcess(MP)includesaWorkingGrouponCriteriaandIndicatorsfortheConservationandSustainableManagementofTemperateand Boreal Forests (Montreal Process Working Group 1997). Some countrieshavedevelopedtheirownprotocolsandproceduresdesignedtotrackandreportprogresstowardmeetingrequirementsofinternationalprotocolssuchastheMP.Forexample,theCanadianCouncilofForestMinistersrecentlydevelopedrevisedcriteriaandindicatorsforsustainableforestmanagement(CCFM2003).
Third-party(eco)certificationofforestpracticesandresultingwoodproductsaroseinresponsetosustainabilityprotocolsandthegreeningoftheglobalmarket-place.OrganizationssuchasSustainableForestryInitiative(AmericanForestandPaperAssociation),CanadianStandardsAssociation,ForestStewardshipCouncil(FSC),andISO1400.1allhavedocumentedreviewprocessesandproceduresforcertification.Protectingstreamsandnaturaldrainagepatterns,maintainingslopestability,and regulating soildisturbancearecommonelementsconsidered. Inaddition,mostrequiresomeadaptivemanagementprocesstoensurecontinuousimprovementofpracticesontheground.Compliancewithcurrentsoildisturbancestandardsisoftenusedasaproxyforensuringsustainability;however,acommonapproachtostandards,andvalidationofthestandardsthroughresearchareim-portantstepsthatmustnotbeoverlookedwhentheseareusedasproxies.Somecertificationschemesalsocallformorerestrictivestandards(e.g.,FSCinBritishColumbiacallsforlowerdisturbancelevelsthanProvincialregulations).
Atthelocallevel,whenmanagingharvest-effectsonsoils,treegrowthandlong-termproductivity,soildisturbancefrommechanicaloperationsisofmostconcern.Soildisturbanceoccurringattimeofoperationscanhavenegative,positive,ornodetectableeffectongrowthorhydrologicfunction.Soildisturbanceatthetimeofoperationsisoftenanindicatorusedinregulatinglong-termproductivityandhydrologiceffects.ThisisbecauseinmanyNAecosystems,weneedatleast10to20yearsdatatodrawconclusionsabouttheeffectsofvariouspracticesongrowthorhydrologicfunction.Indiscussingevidenceforlong-termproductivitychanges,MorrisandMiller(1994)indicatedslow-growingstandsrequire20ormoreyearsofgrowthbeforelong-termproductivityconsequencescanbeascer-tained.Soildisturbanceistheproxythatwecanobserveandregulateatthetimeofharvestingandsitepreparation.However,thisproxyalsoneedstobevalidatedandrevisedovertimeinanadaptivemanagementprocessthatincludesstandards,bestmanagementpractices,monitoring(compliance,effectivenessandvalidation),furtherresearchandstrategicdirectionandrevisionovertime(Curranandothers2005b).Acommonapproachisneededfordescribingsoildisturbancesothatresultsachievedindifferentareasarecomparable(Curranandothers2005c).
Management and Communication Frameworks for Sustainable Soil Management _______________________________________________
Justlikeecosystemclassificationschemes(e.g.,BraumandlandCurran1992)inneighboringBC,organizingsoilintomappableorotherwisedescribableunitsprovidesanimportantframeworkforcommunicatingmanagementexperience,
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researchresults,andconservationefforts.Detailedsoilor landtypemapsareavailableformuchoftheash-capsoilsintheUnitedStates,andreconnaissance-levelsoilmappingisavailableinsouthernBC.Mapsdesignatesoilunits(e.g.,soilseriesindetailedmappingandsoilorlandtypeassociationsinreconnaissancemapping)basedonsoil-formingfactorsofparentmaterial,topography,climateandvegetation,allactingovertime,whichvariesduetogeologiceventslikeglaciationandvolcaniceruptions.Asdiscussedabove,soildisturbancecanalsobeclassifiedandweareworkingtowardsacommonclassificationthereaswell.
Perhapsthemostusefulwayoforganizingsoilunitsforforestmanagementisaconsiderationoftheirriskofdamagefromsoildisturbance.Themostcommondisturbanceofconcerninforestmanagementisfrommachinetrafficduringhar-vesting,sitepreparation,orfuelmanagementtreatments.Thebiggestconcernsassociatedwithmachinetrafficaresoilcompaction,soildisplacement,andsoilerosion.Inaddition,slopestabilityisaconcernonsteeperandwettersites.Toidentifyandmitigatethepotentialforlandslides,terrainmappingand/orterrainstabilityfieldassessmentsareusedonsitesthatexceedcertainslopegradientsorhaveindicatorsofpotentialslopeinstability.
Determiningthesoildisturbancehazardsonagivensiteprovidesaframeworkfordevelopingharvestingstrategiesbyalertingtheprescriptiondevelopertothespecificsoildisturbanceconcernsonthatsite.Forexample,inBC,soildistur-bancedefaultstandardsundertheForestandRangePracticesAct(FRPA)permitup to5or10%netdisturbancewithinacutblockarea (excludingpermanentaccess).IntheInterior,thetriggerfor5%iswhenoneofthekeyhazardsisVeryHigh.AHighratingforanyhazardisprimarilyintendedtoalerttheprescriptiondeveloperandtheoperationalstaffofahazardthatmayrequirespecialtreatmenttopreventproblems(manageandmitigatethehazard).Highcompactionhazardalsoresultsinmoreequipmenttrafficdisturbancetypesbeing“counted”1underFRPAdisturbancecriteria. The soil disturbancehazards alsohelp identify siteconditionsthataresuitableforconstructionofexcavatedandbladedtrails(skidroadsorbackspartrails),and/ortemporarilyexceedingsoildisturbancelevelsandrehabilitatingslopehydrologyandforestsiteproductivity.Thehazardsaredefinedbelow,includingbriefdiscussionsofwhytheyareofconcern.2
Soil Compaction Hazard
Soilcompactionistheincreaseinsoilbulkdensitythatresultsfromtherear-rangementofsoilparticlesinresponsetoappliedexternalforces.Soilpuddlingisthedestructionofsoilstructureandtheassociatedlossofmacroporositythat
1InBC,theterm“counted”isusedinreferencetosoildisturbancetorecognizethefactthatsoildisturbancetypesortheirseverityvarywithsoilsensitivitytodisturbance.Moredisturbancetypesareofconcernonmoresensitivesoils,andlessareofconcernonmoreresilientsoils(e.g.,sandysoils).Thenetresultisthatmoredisturbancetypesare“counted”towardsthetotalcumula-tiveallowablelimitonmoresensitivesoils.
2Soildegradationhazardratingkeysforsoilcompaction,displacement,anderosionarefoundinLandManagementHandbook47(Curranetal.2000)andtheForest Practices Code of British Columbia, Hazard Assessment Keys for Evaluating Site Sensitivity to Soil Degrading Processes Guidebook.The general BCMOF Web site where these and other FPC information can be lo-cated is: http://www.for.gov.bc.ca/ (look under legislation).
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results fromworking the soilwhenwet.Organicmatter isoften incorporatedduringpuddlingandbecauseorganicmatterislighterthanmineralparticles,soilbulkdensitymaynotincrease;however,theotherpropertiesdescribedbelowarestillnegativelyaffected.ThescienceandrationalefortheBCcompactionhazardkeyarelaidoutinCarrandothers(1991).
Soilmoisturecontentisprobablythebestdeterminantofcompactionhazardatanygiventime.InBritishColumbia,thesoilcompactionhazardkeyranksthepotentialcompactionhazardbygroupingsoiltexturesthataremostsusceptibletostructuraldegradationfromcompactionandpuddling,andaremostlikelytoholdmoistureandremainwetforlongerperiods.Thesoilcompactionhazardkeyisatooltohelpwithplanningofanoperation,whilecarefulmonitoringofequipmenteffectsonthesoil,andhandtestsforsoilmoisturecontentarethetoolsthathelpguidetheoperation.
Soilcompactionandpuddlingareofconcernintimberharvestingoperationsbecauseofeffectsonrootsandsitewaterrelations.Compactedsoilshavehigherpenetration resistance thatcan impede rootgrowth.Compactedandpuddledsoils bothhave lower aerationporosity and lowerhydraulic conductivity andinfiltrationrates;however,insomecoarsertexturedsoils,compactionmayactu-allyincreasewaterholdingcapacity(thesesoilstypicallyhavelowercompactionhazardratings).
Loweraerationporosity results in reducedgasexchange thatcanadverselyaffectoxygen levels in the soil air; this reducesphysiologic functionof roots,whichinturncanleadtorootdieoffunderwetterconditions.Lowerhydraulicconductivityandinfiltrationratesofthecompactedorpuddledsoilcanresultinincreasedrunoffduringrainfallandsnowmeltevents.Thiscanleadtoincreasednetexportofwaterfromacutblock,whichcanaffectdownslopesites,naturaldrainagefeatures,andotherresourcevaluesduetoerosionandsedimentation.Increasedwaterexportalsomeanslesswatermaybestoredonsitetosupporttreegrowthduring summerdrought.Compacted soils canalso remainwetterlonger,therebyfurtheraffectingseedlingsbecausethesoilmaybecolderandhavepooraeration.
Monitoringoftraditionalspringharvestingonthreeash-capinfluencedsoilsinthesouthernRockyMountainTrenchnearCranbrookindicatedthatsignificantdeclinesinaerationporosityoccuredwhenevidenceofequipmenttrafficwasvisibleontheground(e.g.,wheellugmarksonthesoilorslightimpressionswithtrackgrousermarks) (Utzigandothers1992).Thesesiteswere typicalTrenchsoils:siltloamtosiltyclayloamtexturedsurfacesoilslowincoarsefragments,underlainbydensersubsoilswithmorecoarsefragments.
TheundisturbedsoilshadaerationporosityvaluesatorabovethethresholdrecommendedbytheUnitedStatesForestService(USFS)insomeofitspolicyforthePacificNorthwest(i.e.,15%at10J/kgwatertensionreferredtoinBoyer1979). Regardless of the severity of disturbance, aeration porosities were lessthan15% (fig.1). Effectson saturatedhydraulic conductivity (i.e.,water rela-tions)weresimilar(fig.2).Bulkdensityincreasedinasimilarbutoppositetrendtotheaerationporosityandsaturatedconductivity,aswouldbeexpected.Theconcernabouttheseeffectsishowextensivethemachinetrafficdisturbanceisonfullymechanizedharvesting.Onthethreesitesstudied,thecombinedtotalofthelightruts,5-cmruts,andmaintraildisturbancerangedfrom52to64%oftheentirecutblockarea,withlightermachinedisturbancecoveringfromabout30toover45%(fig.3).
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Figure 1—Aeration porosity at 10 J/kg tension for two sample depths at three sites in the southern Rocky Mountain Trench near Cranbrook, BC (Utzig and others 1992). U (undisturbed), VL (very light ruts, <� cm deep), 1 (ruts � cm or deeper), HT (heavy [main] trails).
Figure 2—Saturated hydraulic conductivity for two sample depths at three sites in the southern Rocky Mountain Trench near Cranbrook, BC (Utzig and others 1992). U (undisturbed), VL (very light ruts, <� cm deep), 1 (ruts � cm or deeper), HT (heavy [main] trails), from Curran (1999).
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TheseresultsareconsistentwithmonitoringstudiesofnearbysitesinnorthernWashington,Idaho,andMontana(Kuennenandothers1979;LaingandHowes1988,Svalberg1979). In theWashington study,basedon the literatureat thetime,LaingandHowes(1988)predicteda“conservativeestimateof35%volumereductionsoverthenextrotation”fordetrimentallycompactedareas(42%ofthecutblockareaintheirstudy).OnsimilarsitesinNorthernIdahoandMontana,Kuennenandothers (1979) suggested that changes in soil physicalpropertiesresultingfromcompactioncandecreasetheabilityoftreestocompetewithpinegrass.Itisnotclearwhetherthesetypeofeffectswouldberealizedonoursoils;however,intheabsenceoflong-termdatatothecontrary,weneedtocontinuetomonitortreegrowthonthesesites.LightcompactionisalsobeingstudiedaspartoftheNorthAmericanLong-termSoilProductivityStudy(LTSP).
Insummary, the implications forsitewaterstorage, runoff,and treegrowthareofconcernwhenrandomskiddingcausesthesetypesofdisturbances.Itisthereforeinferredthat,undercertainsoilconditions(e.g.,harvestingunderwetterthanoptimumsoilconditions),detrimentalcompactioncanoccurbeforesoildis-turbancecriteriaforrutsortrailsarereached.Harvestingstrategiesrecommendingdispersedskiddingtrafficneedtorecognizethisriskand“treadlightly.”Compac-tionisalong-livedphenomenon;naturalfreeze-thawandwet-drycycleshave
Figure 3—Aerial extent of soil disturbance at three sites in the southern Rocky Mountain Trench near Cranbrook, BC (Utzig and others 1992). LL (very light ruts, <� cm deep), HL (heavy [main] trails), 1&2 (ruts � cm or deeper), and L (very light and heavy, combined) from Curran (1999).
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notbeenobservedtoamelioratemachine-inducedcompactionatdepth.Intheash-capsoillocations,wheresummerdroughtisoneofthefactorsmostlimitingtotreegrowth,andintheabsenceoflong-termdatatothecontrary,preventionofwidespread“belowtheFRPAdepthlimit”compactionisprobablythebestbetandcanbeachievedeconomically.
Soil Displacement Hazard
Soildisplacementisthemechanicalmovementofsoilmaterialsbyequipmentandmovementoflogs.Itinvolvesexcavation,scalping,exposureofunderlyingmaterials,andburialoffertilesurfacesoils.Threeaspectsofdisplacementcanproducesoildegradation:
• Exposureofunfavourablesubsoils,suchasdenseparentmaterial,gravellysubsoil,andcalcareous(highpH)soils.
• Redistributionandlossofnutrients. • Alterationofslopehydrology,whichcanleadtohydrologiceffects(discussed
undercompaction,above).
SoildevelopmentisoftenshallowandmanyofthenutrientsthatarelimitingtotreegrowthareoftenbiocycledandconcentratedintheuppersoilhorizonsthroughouttheBritishColumbiaInterior.Asimilaraffectoccursonshallowash-cap soils that overlay less fertile subsoils.Most of the soil nutrients areoftenconcentratedintheforestfloorandtop20cmofmineralsoil(table1).Therefore,wedon’twanttodisplacethisfertiletopsoilawayfromseedlings,orreducetherootingvolumeofthesevitaltopsoillayers.
Table 1—Typical nutrient distribution in British Columbia Interior soils.
Nutrients in kg ha–1 (% of total)Soil layer Nitrogen Phosphorus Potassium
Forest floor 14�0 (44%) 112 (�2%) 224 (7�%)0-20 cm 10�0 1� ��20-40 cm �20 � 2�Total ��20 1�� �0�
Forest Floor Displacement Hazard
Forestfloordisplacementisthemechanicalmovementoftheupperorganicmaterialsbyequipmentandmovementoflogs.Itinvolvesexcavation,scalping,mineralsoilexposure,andburialof theforest floor.Theeffectsof forest floordisplacement range from beneficial to detrimental, depending on site factors(e.g.mineralsoilcharacteristics)andhowfartheforestfloorisdisplacedfromtheseedlings.
Forestfloorstypicallyrepresentamajorcomponentofthenutrientcapitalonaforestsite.IntheBritishColumbiaInterior,itisnotuncommonfortheforestfloortocontainover50%ofthesoilnitrogenand80%ofthephosphorus(table1).GiventhatmanyInteriorsitesareconsiderednitrogendeficient,conservationoftheforestfloorisimportant.Ondeeperash-caporolder,richersoils,muchofthenutrientcapitaloccursinthemineraltopsoilandforestfloordisplacementmaybeoflessconcern.
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Twoaspectsofforestfloordisplacementcanproducesoildegradation:
• Redistributionandlossofnutrients(e.g.chemicallyboundandunavailableinthemineralsoil,andaccelerateddecompositionoforganicmatter).
• Exposureofunfavourablerootingmedium.
AreviewofforestfloordisplacementandimplicationsfortreegrowthintheSouthernBritishColumbiaInteriorfoundthatwhiletherewereafewtrendsinsoilnutrientlevels,itwasdifficulttorelatedisplacementtoanynegativeeffectsontreegrowth(Hickling1997). IncooperationwithPopeandTalbotLtd.,weinstalledlong-termmonitoringplotsonvariousdisturbancetypesincludingsomeassociatedwithstumping(Hickling1998).
Most forestoperationswerewellbelow the forest floordisplacement limitsoriginallysetintheFPC,sodeterminingtheforestfloordisplacementhazardisnolongerofficiallyrequiredforharvestplanningandpermitting.However,useofthishazardinterpretationissupportedandrecommendedforplanningdispersedskiddingonsteeperslopes,rehabilitationofsoildisturbance,androotrottreat-ments.ForestfloordisplacementisalsomoreofaconcernoncalcareoussoilsduetothehigherpHofthemineralsoil
Surface Soil Erosion Hazard
Surfacesoilerosionisthewearingawayoftheearth’ssurfacebywaterandincludessplash,rill,andgullyerosion.Ithason-siteimpacts(soilloss,nutrientloss,lowerproductivity)andoff-siteimpacts(waterquality,sedimentation,habitatimpacts).Thesurfacesoilerosionhazardkeyfocusesonon-siteerosionandcon-servationofthefertiletopsoillayersneardevelopingseedlings.ThescienceandrationalefortheBritishColumbiakeywerelaidoutinCarrandothers(1991),andtheratingweightingstestedintheNelsonForestRegionbyCommandeur(1994),resulting inmodifications to the finalkeycurrently inuse.Otherassessmentsmaybeusedforhaulroaderosionandsedimentdeliverytostreams.Haulroadsandlandingsareofconcernbecauseerosionanddrainagediversionscanleadtosedimentationandstabilityproblems.Theyrequirecarefullayoutandattentiontoerosionhazardonhaulroadsandminimizingerosionandsedimentationduringconstructionandmaintenance.
Defining Soil Disturbance
Atechnicaldefinitionofsoildisturbanceisanydisturbancethatchangesthephysical,chemical,orbiologicalpropertiesofthesoil(Lewisandothers1991).Itisnotalwaysnegative.Foresterscommonlyprescribepurposefulsoildisturbanceas site preparation for seedling planting and establishment; these disturbancetypesareoftennotcountedinstandards(e.g.,underFRPAinBritishColumbia).Bycontrollinghowweharvestasite,wecancreatemore“sitepreparation”typedisturbanceandkeepmostofthepotentiallydetrimentaldisturbanceconfinedtotravelcorridors;thesemaintrailsmaythenberehabilitatedafterharvesting,asappropriate.Wheneverplanningsoildisturbance,thepreservationandrestorationofnaturaldrainagepatternsshouldbetheprimarygoal(necessaryrepetition).
Thestrategiesdescribedinthisdocumentstrikeabalancebetween“favourable”and“detrimental”disturbancebylimitingtheamountof“counted”soildisturbance.Regionally applicable soil disturbance standards recognize that some level ofdisturbanceisnecessarytopermitaccesstotimber.Counteddisturbanceusually
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includesmaintrailsandruts/impressionsofcertaindimensions,andundersomeschemes(e.g.,FRPAinBritishColumbia)alsoincludewideordeepgougesintothesoil.Thosedevelopingandimplementingaharvestingstrategyneedtorecognizethatonmoresensitivesites,disturbancetypesthat“count”maybecreatedmoreeasilyandmaybecountedsooner(e.g.,inInteriorBritishColumbia5-cmrutsandimpressionsonHighandVeryHighCompactionhazard,asopposedto15cmonothersoils;whenErosion,Displacement,orCompactionhazardsareVeryHigh).Onsiteswithlowerhazardratings,lessdisturbancecategoriesmaybecounted.
Theactualeffectofagivensoildisturbanceontreegrowthwilldependonthemostgrowth-limitingfactorsonagivensiteandhowthesefactorschangeoverthecourseofarotation.IntheBritishColumbiaInterior,commongrowth-limit-ingfactorsinclude:competingvegetation,soilmoisture(droughtorexcess),soiltemperature,summerfrost,rootingsubstrate(volume),soilnutritionalproblems(e.g.,calcareoussoils),androotrot.Theneteffectongrowthwillalsodependonwhethersoildisturbancehasintroducedanewlimitation,suchasreducedsoilaerationfromcompaction.Long-termeffectscouldincludeincreasedsusceptibilitytoblowdownbecauseofpoorrootingindetrimentallydisturbedsoil.
Regional ecology guides often summarize common growth-limiting factorsfor various ecosystems (Braumandl andCurran1992), andamodelhasbeendeveloped for comparingdisturbanceeffectsongrowth-limiting factorswhendecidingonsitepreparationprescriptions(CurranandJohnston1992;Sachsandothers2004).
Regardlessoftheactualtreegrowtheffects,anumberofsoildisturbancetypesarealsoofconcernbecauseofpotentialeffectsonsiteandslopehydrologyandthepotentialfordownslopeimpacts.On-sitehydrologychangesaredifficulttostudybutweneedtoerrontheconservativesideconsideringthatmuchofBritishColumbiaisnotflatandsummerdroughtisoftenoneofthemostgrowth-limit-ing factorsonmanysites (effectsonhydrologymayconfoundtreegrowthonapparently“undisturbed”micrositesintreegrowthstudies).Similarhydrologicconcernshavebeenvoicedbyotherresearchersinthelocalarea(Kuennenandothers1979).
Synthesis of Above Knowledge and Principles in Our Forest Practices _____________________________________________
Machine-Based Practices
Forestharvest,sitepreparation,andfuelmanagementtreatmentsaremostcom-monlyaccomplishedthroughtheuseofmachinery.Inthecaseoftimberharvestorfuels,thismayoccurthroughaerial,cable,orground-basedequipment.Becauseground-basedharvestingtypicallycreatesthemostdisturbance,it isdiscussedbelowbuttheprinciplesremainthesamefortheothermethods.
Basedontheenvironmentalframeworkdescribedintheprecedingsection,agivenharvestingstrategyshouldmeetthefollowingfourrequirements:
1. Besitespecificandresponsivetothesoilsensitivitiesonsiteanddownslope. 2. Offerareasonableamountofindependencefromclimaticinterruptions,. 3. Incorporaterehabilitation,ifnecessary,tolowerdisturbancebelowguidelines. 4. Itmustinstillenoughconfidenceatalllevelsofapprovalandoperations.
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Inthe1990sweworkedonanumberoftrialswithIndustryandDistrictstaff,toaddressconcernsaboutmanagingharvestingsoildisturbance.Trialshavead-dressedtreegrowthonrehabilitatedskidroads(DykstraandCurran1999),haulroads(Curran,unpublisheddata),andlandings(BulmerandCurran1999a).Memoswerecirculatedandaspecialpublication(Curran1999)summarizedsimplefieldtestsdevelopedduringoperationaltrialsofseasonalharvestingconstraints(i.e.,“howwetistoowet?”and“howmuchfrostisenoughfrost?”).Otherresearchtrialshavebeensuccessfulindemonstratingthefeasibilityofrehabilitatingsoildisturbance(BulmerandCurran1999b).Combined,thesetrialsweredesignedtotesttreegrowthonrehabilitateddisturbanceanddevelopstrategiestoreducethedependencyonweatherconditionsandreduceshutdownofoperationsduringwetterconditions.Researchandpracticalinnovationarestillongoing,andfurtherfieldguideswillbeproducedaswarranted(e.g.,wearedevelopingasimplersoiltexturekeyatthistime).
Basedonindustryinnovation,practicalexperience,andresearchtrials,wehaveidentifiedfourkeystrategiesthatwefeelmeettheabovecriteria:
a) closetrailspacingwithrehabilitation, b) closelyspacedtemporaryspur(haul)roadswithrehabilitation, c) combinationdesignatedanddispersed(random)skidding,and d) hoe-chucking,Interiorstyle(i.e.,forwardingtowiderspacedtrails).
Thesestrategiesmayormaynotincludefullymechanizedharvesting,eitherwithcut-to-lengthfeller-processorsandforwarders,orwithfeller-bunchersandgrappleskidders.Thestrategiesalsomayoffertheopportunitytoreducesitepreparationcostsbycreatingdisturbanceduringtheharvestingorrehabilitationphases.EachstrategyisdescribedinmoredetailinCurran(1999).OtherharvestingstrategieshavebeendescribedformeetingsoildisturbancestandardsundersiteconditionsinwesternWashingtonandOregonbyHeningerandothers(1997).Again,theobjective is tomatch equipment capabilities to site sensitivity to disturbance.Ground-basedequipmentmaybe restricted todesignated trailsorallowed totraveloverlanddependingonthesoilandclimaticconditions.
Studies on ash-cap influenced and similar soils in southern Interior BritishColumbiahaveshownthatlargeamountsofsoildisturbancecanoccurduringmechanicalrootremovalforrootdiseasemanagement(QuesnelandCurran2000;Curran, unpublished data). Tree growth responses to these disturbances varywithsitegrowthlimitingfactorsandovertime.OntwositesonsimilarclimateinsouthernBritishColumbia,stumpremovaltreatmentshaddifferingeffects(fig.4).Onanash-capinfluencedsoilatPhoenix,soildisturbanceeitherincreasedordidnotnegativelyaffecttreegrowth;whereasonasoilontheGatesCreeksitethathadmoreclay(12%versus4%),therewasaclearnegativetrendwithtreegrowthanddisturbanceseverity.Thelong-termgrowthtrendattheGatesCreeksiteisinterestingasitclearlydemonstratestheneedforlong-termtreegrowthresponsedata(fig.5).
Insect and DiseaseSome forest insects and pathogens are opportunistic organisms that cause
primarydamagetostressedhosttrees.Stressmayoccurduetosoildisturbanceeffectsontreegrowingenvironment,climatechangeresultingintemperatureormoisturestress,otherbioticorabioticenvironmentalfactors,ormultipleinteract-ingfactors.Interactingfactorsthatcontributetopestoutbreakarecomplex.For
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Figure 4—Fifteen-year volume of Douglas-fir seedlings growing in different disturbance types on the Canadian Forest Service Gates Creek and Phoenix stumping trial sites in southern British Columbia, which are gravelly sandy loam textured with 12% clay at Gates Creek and 4% clay at Phoenix (Curran and others 200�a adapted from Wass and Senyk 1999).
Figure 5—Comparison of relative growth of Douglas-fir on a stump removal trial in southern British Columbia at �, 10 and 1� years since treatment. All data is relative to the undisturbed condition (Curran and others 200�a adapted from Wass and Senyk 1999).
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example,largeareasofbarkbeetleinfestationsaresometimesattributedtoclimatechangeand/orrootdisease interactions (PartridgeandMiller1972).However,insectattackisalsodependentuponinherentdynamicsofinsectbehavior.ThefollowingtextfocusesonrootdiseaseorganismsinInlandNorthwest.
Environmental Factors Affecting the Distribution and Activity of Root Diseases
Biophysical Setting—Armillaria rootdisease (primarilycausedbyArmillaria ostoyae)andAnnosus rootdisease (causedbyHeterobasidion annonsum)arewidelydistributedinwesternconiferforests.Off-siteplantings,woundedtrees,andtreesgrowingoncompactedsoilsor inareaswithdrainageproblemsareparticularlylikelytobeaffectedbyArmillariarootdisease(GoheenandOtrosina1998;Wiensczykandothers1997).Douglas-firdominatedstands innorthernandcentralIdahoandnortheasternWashingtonexperiencesubstantialmortalityfromAnnosusrootdisease,especiallyondrysites (Schmittandothers2000).However,insoutherninteriorBC,Morrisonandothers(2000),foundsignificantlyhigherratesofArmillariasp.infectionondrysitesthanmoistorwetsites;andonceinfected,treesondriersiteswerelessabletoresistinfectionandweremorelikelytoshowabovegroundsymptoms.
Laminated root rot, (causedbyPhellinus weirii),occursmainly inhemlock,westernredcedarandgrandfirhabitattypesontheLoloNationalForest,butinfrequentlyinDouglas-firandsubalpinefirhabitattypes,whileArmillariaandAnnosumrootdiseasearedistributedmorewidely(Bylerandothers,1990).Hagleandothers(1994)similarlyfoundrootdiseasemostsevereingrandfirhabitattypes,andlowseveritydiseaseratingsoccurredmostoftenonDouglas-firhabitattypes.Declinesindiseaseseveritywerenotedafter160yearsasthemoresusceptiblespeciesdiedoutofthestand.TheysuggestthatgrandfirhabitattypesaremostlikelytosupportgrandfirandDouglas-firasseralandclimaxspecies,andthesearethemostsusceptiblespecies.
OntheLoloNationalForest,Bylerandothers(1990),foundhigherprobabili-tiesofArmillariarootdiseaseonDouglas-firhabitattypesonsoutherlyaspects.Moderateslopeshadahigherincidencethaneitherflatorverysteepslopes.
Soil Physical Properties—Inanotherstudy,Armillariaspp.infectionlevelsde-creasedwithincreasingclaycontent,whichiscorrelatedwithmoisture-holdingability (Wiensczykandothers,1997).This isconsistentwiththehazardratingsystemofFroelichandothers(1977).IntheWiensczykstudy,sandysoilsweremorehighlycorrelatedwithArmillaria spp.activity inblackspruce thanweresiltysoils,andasmoistureregimeincreased(basedonmottlesandgleying),Ar-millariaspp.frequencydecreased.ThismaybeduetoreducedgrowthofArmil-lariarhizomorphsinfinertexturedandmoistersoils,ortoimprovedtreevigor.Sand,largesoilpores,andhighbulkdensitywerealsopositivelycorrelatedwithAnnosumrootdiseaseinloblollypineplantations(Alexanderandothers,1975).It is thought that rapid infiltration in sandysoilsallowedeasy translocationofrootrotspores.Bakerandothers(1993)alsofoundthatlowsiltintheAhorizonwasanimportantpredictorofH. annosum infection.Blenisandothers(1989)alsofoundclayloamtobeleastfavorableforArmillariarootdiseaseandsandyloamthemostfavorable.Thepathogenisknowntobesensitivetolowlevelsofoxygenandhighlevelsofcarbondioxide.
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Soil Chemical Properties—Armillaria ostoyaeinfectionlevelswerefoundtoincreasewithincreasingphosphorousintheAhorizon(Wiensczykandothers1997).However,phosphorousinash-capsurfacesoilsisoftenheldinunavailableformandmaynotlocallycontributetoinfection.Reducedphosphorousmaylimittreerootelongation,whichcouldreducethelikelihoodofundergroundcontactwithA. ostoyae.
Rishbeth(1951)foundH. annosuminfectionratesfromstumpstobelowerinacidthanalkalinesoils.Heattributesthistocompetingfungiinmoreacidsoils.Bakerandothers(1993)foundH. annosum infectionincidencetobelowerinacidsoils,asdidBlenisandothers(1989).
Soil Microbiology—Rootmicroflora,suchasActinomycetesandfungi(e.g.,Trichodermaspp.,Phlebiopsisspp.,Bjerkanderaspp.,Hypholomasp.,etc.),canhavefungistaticeffectsonrootpathogens(HagleandShaw1991;HoldenreiderandGreig1998;Nelson1964,1973;NelsonandThies1985,1986;Raziq2000).Ithasbeensuggestedthatmixedstandswithfewerpotentialhostspecies,andinterruptionofsuccessionwithshrubandothernon-susceptiblespeciesreduceH. annosum inoculum(JohanssonandMarklund,1980)bysupportingenhancedpopulationsofActinomycetes.ChapmanandXiao(2000)confirmedtheabilityofasaprophyticfungus,Hypholoma fasciculare,toout-competeA. ostoyaeonavarietyofnonlivingsubstrates,suchasstumps.VeechandBoyce(1964)alsofoundhigher levelsofsoil fungi,Actinomycetes,andbacteria thaninareasofhigherH. annosuminfection.Greig(1962)alsofounddevelopmentofAnnosum rootdiseasetobelowerinplantationsestablishedonareasformerlyoccupiedbyhardwoodsthanonsecond-rotationconiferplantations.This“diversityofsoilmicroflora” ishypothesized tobemore typicalofnaturaldisturbance regimesthanstandsaffectedbyfiresuppressionandemphasisononeortwosusceptiblecropspecies,likegrandfirandDouglas-fir.
Ectomycorrhizalfungiassociatedwithtreerootsareknowntobeimportantformoistureandnutrientrelationshipsofthehosttree(Harveyandothers1986,1987).Decayedsoilwoodpromotesthisassociation.Rootpathogensmayinteractdirectlywithmycorrhizaesothatbiomassandenergyreservesofallpartiesarereduced(Graham2001;Sharmaandothers1992),butsometimespathogeneffectsonthehosttreearereduced(Morinandothers1999).Thiscomplexinteractionsuggestsweneed tosustainacontinuoussupplyof theorganicmaterials thatsupporthealthymycorrhizalpopulations.
Relation to Properties of Volcanic Ash—Surface soils formed in volcanicashtendtobesiltyintexture,havehighporosity,andlowbulkdensity,andlowinherentnutrientstatus,andlownutrient-holdingcapacity(McDanielandothers2005).Theymayadsorbphosphorusandholditinanunavailableform.Acid-ityistypicallyslightlyacidtoneutral.Treerootsareoftenconcentratedinthevolcanicashlayer,suggestingthatrootcontactcouldbecommonanddistancefromstumpinoculationpoint to live rootwouldbeshort.Thiswouldmake iteasier for infections to spread. High moisture-holding capacity suggests thatdrought-inducedstressduringsummerswouldbesomewhatmitigated,butthatthiscapacitywouldbereducedbycompactionordisplacement.Volcanicashishighlycorrelatedwithgrandfir,cedar,hemlock,andsubalpinefirhabitatseries,andtoalesserextentwithDouglas-fir.
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Management Effects—Fireexclusion,harvestoflesssusceptiblepineandlarch,anddeclinesinwhitepineduetoexoticblisterrust(Cronartium ribicola)haveallcontributedtotheincreaseinmoresusceptibleDouglas-firandgrandfir,andmoistureandnutrientstress,increasingtheprevalenceofrootdiseaseintherangeofvolcanicashsoils.Morestudesareneededtodeterminetheeffectsofpartialharvestandsoilcompaction/displacementonrootdiseaseinmanagedstands.
Climate Change, Root Disease, and Management on Volcanic Ash-cap Soils
Climatechangecanresultinmaturetreesthataremaladaptedtotheirenvi-ronment,whichcanincreasevulnerabilitytopathogens(AyresandLombardero,2000),aswellasotherdisturbanceslikefireorinsects.IntheInteriorNorthwest,increasing temperatures and reduced summer moisture (McKenzie and others2004;Moteandothers2003)increasestressontreesinmarginalsites(thinash-cap,compactedsoils),whichmaymakethemmoresusceptibletorootdiseases.Physiologicalmodelstopredicthowtreedefenseswouldalterwithclimatechangearelacking.Effectsofclimatechangeonrootdiseaseandcompetingorganismsarenotknown.
Firesuppressionandsubsequentlymoreseverefiresmayincreasetherateofrootdiseasebyprovidingmorefire-scarredtreewoundsasentrancepoints(OtrosinaandGarbelotto1997).Fireexclusionleadingtodominanceofsusceptibletruefirsandhighlevelsofrootdiseasewouldalsoleadtoincreasedsusceptibilitytofireandlargeinsectoutbreaks.Higherdensitystandsduetofireexclusioncouldincreasethelikelihoodofbelowgroundspreadofthepathogenfromtreetotree.Longerperiodsofhighheatanddroughtcouldsuppresssporegerminationandstumpcolonizationforlongerperiodsinthesummer,althoughBendz-HellgrenandStenlid(1998)foundnoeffectoftemperatureonstumpcolonizationbyH. annosum.
Management Opportunities:
• Limitmanagementinducedstressbyconfiningsoilcompactionanddisplace-menttolimitedareasandrehabilitatingthemafteruse.
• Provideconnectionsforspeciestomoveinresponsetochangedclimaticcontext(maintainingcontinuityofspeciesinspace,whileallowingformovement).
• Usespeciesanddensitymanagementtoallowforestspeciestousedistur-banceassteppingstonesformigration.
• Introduceandsustainspeciesresistanttorootdisease. • RootremovalhasbeenproposedtocontrolArmillariarootdisease(Roth
andothers2000),butsomestudieshaveconcludedthatinoculumremovalcannotbecompleteenoughtochangethedynamicsofrootdiseasedevelop-ment(Reavesandothers1993).Theassociatedsoildisturbance,particularlyinash-capsoils,islikelytohavedeleteriousphysicaleffects.
Theissueofsoilrestorationtorecoversuitablemoistureandairrelationshipsis complicated by other factors. Soil disturbance associated with roads, skidtrails,andprecommercial thinning (Hessburgandothers2001)wascorrelatedwithincidenceofblackstainrootdisease(causedbyLeptographium wageneri)insouthwestOregon.Alternatively,subsoilingtoalleviatesoilcompactionmayresultinrootdamageanddiebackofanyresidualtrees,attractingrootfeedingbeetles that carry black stain root disease. Kliejunas and Otrosina (1997) and
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Otrosinaandothers(1996)foundhigherlevelsofergosterolinsubsoiledareas,whichindicatedhigherlevelsoffungaldecomposeractivity.Thiswasattributedtosoildisplacementandrootsevering.Thissuggestsmanagersshouldlimittheextentofcompactedareasasmuchaspossibleandavoidsubsoilingneartreestoavoidbothaboveandbelowgrounddamage.Stumpremovalcouldhavesimilareffectsinadjacentlivetrees.
Analysis of North Idaho Root Disease Trends in Relation to Soil and Site Factors
SueHagle (Pathologist,USDAForestService,Region1) ratedstandswithinrandomlyselectedsubcompartmentsforrootdiseaseactivityusingphotointerpre-tationonascaleof0to9(Hagleandothers2000).OnthethreeIdahoNationalForests(IdahoPanhandle,Clearwater,andNezPerce)analyzedhere,1,204plotswereavailable,but11ofthesedidnothavegeologicinformationand29didnothavesoilsurveyinformation.Thestandpolygonswereinteractedwithgeospa-tiallayersincludingsoilsurveymapunits,lithology,meanannualprecipitation,elevation,aspect,latitude,longitude,andslope.
Soilsurveymapunitswereclassifiedintofourclassesbasedonvolcanicashdepth:
1:Nodescribedvolcanicashinfluence 2:Thinormixedash 3:Andicsubgroups 4:Thickash(Andosols)
Wheresoil typevariedbyaspect,aspectwasused to refine theashdepthfactor.
Geologicgroupsweredevelopedbasedonliteraturedescribingassociationsbetweenrootdiseaseandrocktype(GarrisonandMoore1998;Mooreandothers2004).Thisprocesswascomplicatedbydifferentscales,notation,anddepthofdescriptionofavailablegeologicmaps.Wetriedtoidentifypotentialstrongas-sociationsbyspatialexplorationofrootdiseaseactivityandgeologicformation.Patternsthatappearedstronginoneareawerenotconsistentinotherareas.Theresultinggroupsusedare:
2 =Granitics,predominantlyCretaceous,butalsoJurassic(292samples). 3 =Recentmetamorphics(youngerthanBeltAge)(21samples). 4 =Beltagemetamorphics,butnotincludingBeltquartzitesdescribedunder
11.(666samples).Thesewereexpectedtohavehigherinherentfertility. 5 =Tertiaryandmorerecentsediments(3samples). 6 =SevenDevilsvolcanicsofTriassicandPermianage(20samples).Thesesites
wereomittedfromthisanalysisbecausetheyarethoughttobeanomalous.Theyhadveryhighrootdiseaseactivityratings.Trendsandsignificanceweresimilarwithandwithoutthesesamples.
7 =Undifferentiated,suchasglacialdepositsoralluvium(65samples). 8 =Othervolcanics(2samples). 9 =Limestonenosamples. 10 =Beltagesedimentsnosamples. 11 =Beltquartzites(MiddleWallacequartzites,StripedPeakformation,Revett
quartzite,andPrichardquartzite(94samples).Thesewereexpectedtohavethelowestinherentfertility.
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EachstandwasadditionallyassignedtoamoistureandtemperaturegradientclassafterMcDonaldandothers(2000)usingthehabitattypeinformationas-sociatedwitheachstandpolygon:
Understory: Moisture RegimeNodata 0Drygrass 1Dryshrub 2Dryherb 3Moistherb 4Wetherb 5Wetfern 6Wetshrub 7
Overstory: Temperature RegimeNodata 0Coldfir 1Coolfir 2Cedarhemlock 3Douglas-fir 4Ponderosapine 5Pinyonjuniper 6
Thefollowingtablesandplotsdisplayexploratoryanalysisoftheassociationofrootdiseaseactivity(usingan8classrankingsystem)andcategoricalenvironmen-talvariables.Shownarethemedian,interquartilerange,extremes,andpossibleoutliers.Nopatternisapparentforaspectclassandrootdiseaseranking,
Root Disease and Ash Depth
Thinormixedashisassociatedwithhigherincidenceofrootdisease(table2).Lowrootdiseaseactivityassociatedwithareasofnovolcanicashareusuallyinverydrysteepslopesorpoorlydrainedareaswheresoilsareformedinmixedalluvium.
Soilswithnoashinfluencehavesignificantlylowerrootdiseaseactivity,butAndicsoilsandAndosolsdonotdiffersignificantly.
Table 2—Ash-cap depth as related to root disease ranking.
Ash Depth N
Mean RootDiseaseRanking* 95% C.I.
1 – None 25 2.2 1.5-2.9
2 – Thin or mixed 198 3.6 3.3-3.9
3 – Andic 247 3.2 2.9-3.4
4 – Andosol 638 3.0 2.9-3.2*See Hagle and others (2000) for detailed root disease activity scale.
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Geologic Group
No strong trends were noted, however there were some differences among lithologic groups.
Recentmetamorphicsshowedgreaterrootdiseaseactivitythaninundifferenti-ateddeposits(table3).Thegreatvariabilityinrecentsediments(group5)suggestsaneedforfurtherrefinementofthisclass.Beltagemetamorphics(group4)showedrelativelylowrootdiseaseactivity,withnumeroussamples,andweresignificantlyless thangranitics, recentmetamorphics,andBeltquartzites.Undifferentiatedrocktypes(recentdeposits)alsoshowedlowrootdiseaseactivity.TheBeltAgequartzites,anticipatedtobenaturallylowinpotassiumandwithhighlevelsofrootdiseaseactivity,weresignificantlyhigherthanotherBeltmetamorphicsandundifferentiatedrocktypes,butdidnotdifferfromgranitics,recentsediments,orrecentmetamorphics.
Table 3—Influence of geologic group on disease incidence.
Geologic Group N
Mean RootDiseaseRanking* 95% C.I.
2 – Granitics 292 3.5 3.3-3.7
3 – Metamorphics(not Belt Age)
21 3.9 2.8-4.9
4 – Belt AgeMetamorphics/notquartzites
666 2.9 2.8-3.0
5 – Tertiary andmore recentsediments
3 4.3 .5-8.1
7 – Undifferentiated(recent glacialdeposits or alluvium)
65 2.9 2.5-3.3
8 – Other volcanics 2 3.5 NA
11 – Belt quartzites 94 3.5 3.1-3.9
*See Hagle and others (2000) for detailed root disease activity scale.
Root Disease and Forest
TheIdahoPanhandleNationalForesthadthelowestdiseaseranking,followedbytheClearwaterNationalForest,andthenNezPerceNationalForest(table4).Thesedifferencescouldbecausedbydriersoils,changesingeology,soilnutri-tion,orotherinherentsitephysical,chemical,orbiologicalproperties.
Table 4—National Forest and incidence of disease.
National Forest N
Mean RootDiseaseRanking* 95% C.I.
4 – Idaho Panhandle 639 2.7 2.6-2.9
5 – Clearwater 331 3.4 3.2-3.6
17 – Nez Perce 173 4.0 3.7-4.3
*See Hagle and others (2000) for detailed root disease activity scale.
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Root Disease and Potential Vegetation (Habitat Type Group)
PotentialVegetationisanindicatorofsoilmoistureandtemperatureregimesandconstrainswhethersusceptiblespeciesarelikelytooccurasseralorclimaxonthesite.Whenhabitattypes(Cooperandothers1991)aregroupedaccord-ingtoJones(2004),itisevidentthatthosehabitattypesmostlikelytosupportsusceptiblegrandfirorDouglas-firandshowhigherlevelsofrootdiseaseactivity(datanotshown).Theoccurrenceandseverityofrootdiseasedependsstronglyontheabundanceofasusceptiblehost.Siteswithalongerhistoryofdominancebysuitablehostspecieswilllikelyhaveaccruedhigherlevelsoffungalbiomass.DriergrandfirandDouglas-firhabitattypes,whicharemorelikelytosupportmoreponderosapine,showlowerlevelsofrootdiseaseactivity.Itisinterestingtonotethatsomeextremelyhighvaluesofrootdiseaseactivityareassociatedwithmoremoistcedarorwesternhemlockhabitattypegroups.Itispossiblethatthesesitesarecapableofveryhighlevelsofinoculumwhereseralwhitepinehasbeeneliminatedforlongperiods.
Moisture and Temperature Regime
UsingthemoistureandtemperatureindicesdefinedbyMcDonaldandoth-ers(2000),wecompareddiseaserankingagainstmoistureindicator(understoryassociation)andtemperatureindicator(overstoryseries).
Siteswithmoderatelydrymoistureregimes(dryshrub)hadthehighestrootdiseaseactivity,anddifferedfromdrygrassanddryshrub,butnotmoistherb(table5).ThismaybeduetothehighincidenceofsusceptibleDouglas-fironthesemoisturesettings.
Siteswithmoderatelywarmtemperatureregimes(Douglas-fir)hadthehighestrootdiseaseactivity,anddifferedsignificantlyfromcoldfirandponderosapine.Coolfirtemperatureregimeshadhigherrootdiseasethancoldfir,cedarhemlock,andponderosapine(table6).Again,thepresenceofsusceptiblehostspeciesishighlycorrelatedwiththesetemperatureregimes.
Table 5—Root disease ranking as related to understory moisture indicator.
Moisture Regime N
Mean RootDiseaseRanking* 95% C.I.
1 – Dry grass 12 2.2 1.1-3.2
2 – Dry shrub 89 3.4 2.9-3.8
3 – Dry herb 303 2.9 2.7-3.1
4 – Moist herb 734 3.2 3.1-3.3
5 – Wet herb 1 3 NA
6 – Wet fern 1 0 NA
7 – Wet shrub 1 1 NA
*See Hagle and others (2000) for detailed root disease activity scale.
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Table 6—Root disease ranking as related to temperature regime.
Temperature Regime N
Mean RootDiseaseRanking* 95% C.I.
1 – Cold fir 366 3.0 2.8-3.2
2 – Cool fir 153 3.6 3.3-3.9
3 – Cedar hemlock 528 3.1 2.9-3.2
4 – Douglas-fir 90 3.5 3.0-3.9
5 – Ponderosa pine 3 1.3 0-4.2
*See Hagle and others (2000) for detailed root disease activity scale.
Association of Root Disease Ranking with Numeric Variables
Themostecologicallysignificantcorrelationsappeartobethatrootdiseaseactivity is positively associated with steep slopes, southerly latitude, westerlylongitude,potential forhost species (basedonhabitat typecover tables),anddecreasingannualprecipitation.
Conclusions _____________________________________________________Ash-capsoilsaresusceptibletodisturbance;schemestopredictcompaction,
displacement,anderosionhazardsareusefulinforestmanagementapplication.Whether more or less disturbance should be permitted on ash-cap soils is acontroversialtopicanditislikelymoreimportanttofocusontheindividualsitehazardsbecauseash-capsoilscanvaryconsiderablyintheirstateofweather-ing,texture,depthandinter-mixingwithothersoilmaterials.MachinetrafficcanbemanagedandasdemonstratedinBulmerandothers(thisproceedings),andmitigatedthroughrehabilitationinasetofharvest(machine-traffic)strategiesthatconsidersite.
Regardingrootdiseaseonash-capsoils,thispreliminarycoarse-scaleinves-tigation suggests some potential relationships among root disease (primarilyArmillaria in Idaho)and soil and site factors.The strong relationshipbetweenpresence of susceptible host and development of fungal biomass may be thestrongestcausalagent,andthesoilandsitefactorspromotethepresenceofthesusceptiblehost.
Thickerashsoilsofmorenortherlyareasarerelatedtohabitattypesthathis-toricallysupportedwhitepineandahigherdiversityoflesssusceptiblespecies.Thesemoremesicenvironmentsalsofillinwithotherspeciesrapidlyafterrootdiseasemortalityoccurs,sohigherlevelsofrootdiseaseactivityaremoredifficulttodiscern(Hagle,personalcommunication,2006).
Recommendations ______________________________________________Sustainablesoilmanagementonash-capsoilsneedstofollowprotocolsdeveloped
forallsiteswherebyanadaptivemanagement/continuousimprovementprocessneedstobesupportedbyresearch,bestmanagementpractices,andstrategiesthatincludealltypesofmonitoring(compliance,effectivenessandvalidation).
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Developmentofacommonapproachtodescribingsoildisturbanceandsoildisturbancehazardswillgoalongwaytowardmoreeffectivesharingofmanage-mentexperiencesonash-capsoils.
Moreworkisneededonthelong-termeffectsofcumulativeaerialextentofsoildisturbanceandonsoildisturbancecategories torefine theseandhazardratingsystems.
For the root disease work, more site-specific evaluation of soil properties,standhistory,andgeologicparentmaterials,bothmineralogicalcompositionandweatheringstate,wouldhelptosortouttheserelationships.
Acknowledgments ______________________________________________TheauthorsthankDr.R.E.Miller,emeritusresearchscientistatUSDAForest
Service,PacificNorthwestResearchStationforhisreviewofthemanuscript,andSueHagle,pathologistforUSDAForestServiceRegion1forherhelpfuladviceandreviewoftherootdiseasepartofthispaper.
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In: Page-Dumroese, Deborah; Miller, Richard; Mital, Jim; McDaniel, Paul; Miller, Dan, tech. eds. 2007. Volcanic-Ash-Derived Forest Soils of the Inland Northwest: Properties and Implications for Management and Restoration. 9-10 November 2005; Coeur d’Alene, ID. Proceedings RMRS-P-44; Fort Collins, CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station.
Chuck Bulmer is a Soil Scientist, BC Ministry of Forests and Range, Vernon B.C. Mike Curran is a Soil Scientist, BC Ministry of Forests and Range, Nelson, B.C. Jim Archuleta is a District Soil Scientist, Dia-mond Lake District, Umpqua National Forest, Idleyld Park, OR.
Abstract Soilrestoration(sometimestermedenhancement)isanimportantstrategyforsustainingtheproductivityofmanagedforestlandscapes.Tephra-derivedsoilshaveuniquephysicalandchemicalcharacteristicsthataffecttheirresponsetodisturbanceandrestoration.Avarietyoffactorsreduceforestproductivityondegradedsoils.Site-specific informationonsoilphysicalconditions,organicmatter,andnutrientstatus is requiredforefficientsoil restoration,butonly limitedresearchisavailable tohelp interpretsuchinformationandguideefforts torestore tephra-derivedsoils.Basedonsite-specificconditions,reclamationtreatmentscanbeidentifiedtocontrolwater,tillcompactedsoils,restoreorganicmatter,andrevegetatedisturbedareas.Successfulreclamationinvestmentswillofteninvolvesimpletreatmentsfocusingonlowcostoptionssuchasdecompaction,topsoilreplacement,fertilization,andtreeplant-ing.Avoidingdifficultsitessuchthoseinhighelevationenvironments,wetareasorfinetexturedsoilsisrecommendedwherepossible,astreatmentstoovercomesuchproblemsarelikelytobeexpensiveandhaveuncertainoutcomes.Restorationefforts involcanic terrain likelyneed tobeaccompaniedbyprogramstomonitorthebeneficialeffectsoftreatmentsonforestproductivity,inrelationtotheircosts.
Restoring and Enhancing Productivity of Degraded Tephra-Derived Soils
Chuck Bulmer, Jim Archuleta, Mike Curran
Introduction
Soilrestoration(sometimestermedenhancement)isanimportantstrategyforsustainingtheproductivityofmanagedforestedlandscapes(Richardsonandothers1999),andecosystems(Cairns1999).Restoration techniquesplayaroleas (a)plannedactivities for improving theefficiencyofaccessingandharvestingtimberwhilemeetingsoilconservationgoals,or(b)ameanstorepairunanticipateddamagetosoilscausedbyharvesting,orwherepreviousmanage-mentapproacheshavebeensupersededbystrategiesthatreducetheneedforsoildisturbance,andallowrestorationofpreviouslydisturbedareas. Tephra-derived soils have unique physical and chemical characteristics that affect theirresponse to disturbance and restoration. Volcanic materials have undeveloped crystallinestructureandweatherrapidlyinhumidenvironments,producingsoilsthatarecharacterizedbyhighwaterholdingcapacity (Moldrupandothers2003)andcationexchangecapacity,
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theabilitytostabilizesoilorganicmatter,andhighreactivitytowardsphosphate.InthePacificNorthwest,mountainoustopographyleadstostrongredistributionofashfallmaterialsthatwerelikelydepositedinfairlyuniformlayersthroughouttheselandscapes.StrongenvironmentalgradientsalsocreatediverseweatheringandpedogenicenvironmentsinPacificNorthwestforestsoils.Forthesereasons,theexpressionofandicsoilcharacteristicsshowsgreatvariationwithinlandscapes,creatingawiderangeofconditionsintephra-affectedsoils,andasimilarrangeof responses to soil disturbance and subsequent restoration or enhancementefforts.
In general, the goal of forest soil restoration is to recreate pre-disturbancegrowingconditions,sothattreegrowthratesonthereclaimedsoilwillapproxi-matethoseoftreesonundisturbedsoilsonsimilarsites.Effectivesoilrestorationemploystechniquesthatalleviategrowth-limitingconditionsonsitesthathavesuffereddegradingsoildisturbance.Degradedsoilsaredefinedhereassoilsthathaveexperienceddisturbanceleadingtoalossinproductivity.Forestproductiv-ityondegradedsoilscanbereducedbycompactionthatcausesplantrootstoexperiencelimitingconditionsofsoilmechanicalresistance,wateravailability,andaeration.Removalofsurfacesoillayersmaycausesimilareffectsbecauseorganicmattermaybedepletedfromthesite,orbecauseunproductivesubsoilmaterialsmaybeexposed.Degradedsoilsmayalsobemoresusceptibletoerosionwhichcancausefurtherlossofnutrientsandorganicmatterthatareessentialformaintainingsiteproductivity.Erosioncanalsocauseseriousoff-siteconsequencesforaquaticandterrestrialsystems.
Site-specificinformationonsoilphysicalconditions,organicmatter,andnu-trientstatusisrequiredforefficientsoilrestoration,butonlylimitedresearchisavailabletohelpinterpretsuchinformationandguideeffortstorestoredegradedsoilsderivedfromtephra.
Restorationtechniquesaimedatcontrollingerosioninclude(a)thoseaimedatstabilizingsoilssuchassloperecontouring,(b)thoseaimedatmanagingwatersuchasditchingoroutslopingand(c)thoseaimedatpreventingsoildetachmentsuch as revegetation. For compacted soils, tillage is often required to restoreconditionsconduciveforproductiverootgrowth.Restorationoforganicmatter,where appropriate, may be accomplished through replacing displaced topsoilmaterials,bymulchingwithorganicmaterialssuchasloggingdebris,orthroughthesoilbuildingactionofseededcovercrops.
Thismanuscriptoutlinestheroleofsoilrestorationinmaintainingtheproduc-tivityofmanagedforestlandscapes,reviewstheprinciplesthatgovernhowtheuniquecharacteristicsoftephra-derivedsoilsaffectrestorationplanninginvolcanicterrain,discusseshowinformationavailablefromelsewhereappliestoreclamationtechniquesinvolcanicterrainofthePacificNorthwest,andprovidesmanagementrecommendationstoguiderestorationandenhancementefforts.
Soil Restoration to Conserve and Enhance Productivity in Forested Landscapes _____________________________________________________
Minimizingdegradingsoildisturbance(Page-Dumroeseandothers2000)isanimportantfirststeptoensurethatsoilsaremaintainedinaproductivecondition,andthatforestmanagementissustainable.ThroughoutNorthAmerica,regula-torysystemsareinplaceforpreventingsoildegradationduringforestharvesting,
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accessdevelopment,andothermanagementactivities(Powersandothers1998;USDAForestServiceStandardsandGuidelines2521.1and2521.2;CCFM2002;BCMinistryofForests2001).Thesesystemsgenerallyspecifysitespecificlimitsfordefinedformsofdegradingsoildisturbance,andmayalsoprovideincentivesforrestoringsoilsthathavebeendegradedbyforestmanagementactivities.
InBritishColumbia,soilconservationpolicyallowsmoresoildisturbanceonsiteswithlowsensitivitytosoil-degradingprocesses(BCMinistryofForests2001).InthenorthwesternUnitedStates,higherintensityofsoilcompaction(i.e.20%increaseinbulkdensity)isconsideredacceptableonvolcanic-ashderivedsoils(Powersandothers1998),comparedtothosedevelopedonotherparentmaterials(maximum15%increase).Thesedifferencesrecognizethatmanyundisturbedtephra-derivedsoilshavelowbulkdensity,butmayalsoimplythattheyarelesssensitivethanothersoilstomodestchangesindensity.Tephra-derivedsoilsmayalsoresponddifferentlythanotherstoreclamationtreatments.
Restoringdegradedsoilsimprovesforestproductivity.Onaccessstructuresthatarenolongerneeded,restorationandreforestationincreasesthelandbaseavailableforgrowingtrees,andcantherebyincreasefuturetimbersupplies.Onareasthathavesuffereddegradingsoildisturbance,restorationcanimproveestablishmentsuccessandproductivityofplantedtreescomparedtoareaswheresoilsareleftinadegradedstate.Achievingfullbenefitfromsoilrestorationpracticesdependsonthedevelopmentofcost-effectivereclamationtechniques,andtheirapplica-tiontositeswherethecostofreclamationwillbeoffsetbyimprovedproductivityfromthereclaimedlands(Richardsonandothers1999).
Reclamationworkshouldbesubjected tocostbenefitanalysis thesameasanyothermanagementactivity.Suchanapproachavoidswrongly thinkingofrehabilitationasanintrinsicallygoodactivity,wherethetruecostsofreclamationworkcanbediscountedorignored.Costsofrestorationworkincludedollarcosts,diversionofscarceresourcesfromotheractivities,consumptionoffossilfuels,andrisktoworkersorproperty,alongwithpotentialnegativeconsequenceswhichmaynotbeanticipatedsuchaswaterdiversion,erosion,slopefailure,andweedinfestation.Atthesametime,thepotentialbenefitsofreclamationworkmayalsobeunderstatediftheanalysisisrestrictedtraditionaleconomicmeasures(dollarcostsonly),orifinappropriatediscountratesareappliedtotimberproduction.Thesocialandenvironmentalbenefitsofcarryingoutreclamationactivitiesmayhavebeenneglectedinthepast,butrecentevaluationshaveshowntheimportantrolethathealthyecosystemsplayinmaintainingeconomiesandsocieties(Hillel1991).Suchconsiderationsarelikelytobecomeevenmoreimportantasglobal-izationandpopulationgrowthexertincreasedpressureonnaturalenvironmentsallovertheworld.
Ingeneral,giventhealmostuniversalscarcityofresources,theuncertaintyofcostbenefitanalyses,andtherisksassociatedwithundertakinganyactivitythatimposessignificantdisturbancetoanaturalsystem,aprudentapproachwouldfocusreclamationeffortsonsiteswheresimpletechniqueshavebeenshowntohavesuccess.Treatmentofhighrisksitesanduseofexpensiveorexotictreatmentsare likelybest left to special situationswherepotentialvaluesarehigh, socialfactorswarrant,orwheresucheffortsaretreatedasanoperationaltrialorwheredetailedmonitoringwillimproveouroverallunderstandingofrehabilitationanditsroleinforestmanagement.
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Characteristics of Tephra-Derived Soils as They Affect Growth-Limiting Conditions and Restoration Efforts ________________________________
Variationinsoilpropertiesandgrowth-limitingfactorsintephra-derivedsoilsarisefrom(a)ecologicalcharacteristicsofthesiteassociatedwithclimate,topog-raphy,parentmaterials,andvegetation,(b)chemicalandphysicalcharacteristicsofthetephraasitwasdeposited,and(c)redistributionandalterationoftephrainthelandscapeinresponsetotopography,moistureetc.
StrategiesforreclaimingsoilswithouttephrainfluencehavebeendevelopedinthePacificNorthwestandelsewhere,andspecifydifferentapproachesforarangeofsoilsindiversegeographicsettings.Theapplicabilityofthesetotephra-derivedsoilsdependsonthedifferencesinsoilpropertiesbroughtaboutbythepresenceoftephra.Somequestionstoconsiderinclude:
• Havenaturaldepositionsoftephraledtoimprovedsoilfertilitybyprovidingasupplyofreadilyavailableinorganicnutrients?
• Whatistheweatheringstateofthetephra?Tephramaterialsweatherrapidlyinhumidsurfaceenvironments,butinthePacificNorthwesttherearemanyexamplesofrelativelyunweatheredmaterialseitherbecauseofdryclimatesorshortdurationofweatheringsincedeposition.
• Whatistheparticlesizeofthetephramaterials?InthePacificNorthwest,variationinphysicalandchemicalpropertiesastheyaffectplantgrowthprimarily results from particle size effects (including distance from thesource)andpostdepositionalalterationincludingorganicmatterretentionandweathering.
• Foragivenparticlesize,tephra-derivedsoilstendtohavephysicalcharac-teristics(i.e.waterholdingcapacity;specificsurface;organicmatterreten-tion)thatreflectthoseofothersoilmaterialswithfinertexture(i.e.sandytephramaterialsmaybehavemore like loamsderived fromotherparentmaterials).
Morphological Characteristics of Tephra-Derived Soils
Tephra-derivedsoilsincludethosewhereminoramountsoftephrawerede-positedtosoil,butarenolongerdiscernableasadistinctlayer.Inothersoils,adistinctlayeroftephraispresentasan“ash-cap’ofvaryingdepth(fig.1).Finally,somesoilsmaybeexclusivelyderivedfromvolcanicmaterialstothedepthofrooting,withlittleornoinfluencefromotherparentmaterialsonthevegetation.Manysoilswilldisplayintermediatecharacteristicstotheseidealizedcategories,especiallywheretephralayersbecomeintermixedwithsubsoilsduringconstruc-tionanduseofaccessstructures.Dependingontheproportionoftephra,andcharacteristicssuchasparticlesize,specialconsiderationsmayormaynotbeneededwhendevelopingreclamationstrategies.
Physical Characteristics of Tephra-Derived Soils
The presence of weathering products with highly reactive surfaces lead tothecommoncharacteristicsnoted forweatheredvolcanicmaterials, includinghighwaterretention,organicmatterstabilization,andwelldevelopedaggregatestructure.Thecharacteristicsareinter-relatedasorganicmatterispartlystabilizedbecauseofthesurfacereactivity,whilethepresenceoforganicmatterresultsin
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additionalreactivesurfaces.TheexpressionofAndiccharacteristicsdependsonthedegreeofweatheringofthematerial.
Akeycharacteristicaffectingreclamationisthelowbulkdensityobservedinmanytephra-derivedsoils,owinginparttotheirlowparticledensitybutalsotothetendencytodevelopwellaggregatedstructures.Millerandothers(1996)foundthatevenafterasubstantialincreaseinbulkdensityofashderivedsoilsincentralWashington, the bulk density was still less than 1000 kg m–3. For this reason,thresholdvaluesforgrowth-limitingconditionsneedtobedeterminedspecificallyforashderivedsoils,ratherthanusingvaluesderivedforothersoils.
Figure 1—Ash cap overlying ultramafic soil material in the Shulaps Range: interior British Columbia.
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Relationshipsbetweensoiltextureandmanagementimpactsreflectthevariableeffectsofashcharacteristicsandsoilenvironments.Forexample,poorlycrystallineweatheringproductsactasacementtocreateverystableaggregatesinAndisolsthatoccupywetsites.Also,theweatheringproductsofvolcanicparentmaterialshavehighsurfaceareacomparedtotheclaymineralsfoundinmostothersoils(Moldrupandothers2003).Inaddition,tephraparticlesoftenconsistofporousandfragilematerials,socoarse-grainedtephrasoilsareoftenlessresistanttofracturecomparedtonon-tephrasoils,andparticlesizedistributionmayshifttowardsfinersizefractionsfollowingmechanicaldisturbance(SahapholandMiura2005).
Tephra-derivedsoilsretainlargeamountsofwatercomparedtosoilsderivedfromotherparentmaterials.Conversely,theyarealsosubjecttochangesupondrying,whichcanincludethedevelopmentofwaterrepellency(Poulenardandothers 2004) and irreversible structural collapse (Poulenard and others 2003)whichismostlikelyforsoilsformedinwetenvironments(Shojiandothers1996).Inconsideringtheimpactofthischaracteristicondisturbanceandreclamation,thehighwaterretentionmayleadtoasoilwithlowbearingstrength,andhighsusceptibility toruttingwhenwet. Itmayalsomaketillageoperationsdifficultwhensoilsaremoist.Despitethis,thematerialsareexpectedtoprovideagoodgrowingmediumforplantroots,especiallyonmesicsites.
Unweatheredtephramaterialsareoftennon-cohesiveandpronetoerosionbywindandwater(BasherandPainter1997;ArnaldsandKimble2001),andthissusceptibilitymaylastforsometimeinunvegetatedareas.Forthisreason,plan-ningshouldconsidermeasuresforrapidrevegetationofexposedtephramaterialsresultingfromdisturbanceandreclamation.Tephra-derivedmaterialswithcoarseparticlesizeshavealsobeenusedasawaterconservingmulch(Tejedorandothers2002,2003).Thischaracteristicmayalsopresentchallengeswhenconsideringtheseedbedcharacteristicsofcoarse-texturedtephrasoils.
Theuniquephysical conditionsprovideboth challenges andopportunities,andbothneedtobeconsideredwhenplanningrestorationtreatmentsfortephra-derivedsoils.
Chemical Characteristics of Tephra-Derived Soils
Thechemicalcharacteristicsoftephravarydependingonthegeologicenviron-ment,andthesecharacteristicsareinheritedbythesoilsderivedfromvolcanicmaterials.Ingeneral,thecompositionoftephramaterialsinthePacificNorthwestaresimilartothoseofrhyolite,whichisexpectedtoprovideadequatesuppliesofmineral-boundplantavailablenutrientsinunweatheredormoderatelyweatheredsoils.Theweatheringproductsofvolcanicashhaveahighaffinityfororganicmatter,andthischaracteristicaccountsformanyoftheuniqueproperties,includ-ing high cation exchange capacity, and high availability of organically boundplant nutrients. Anion exchange capacity derives from the creation of poorlycrystallineoxidesofFeandAl,andalsofromshortrangeorderaluminosilicateslikeallophane.Theanionexchangecapacityaccountsforthehighreactivityoftephra-derivedsoilstophosphate.Despitethesefeatures,recenttephradepositswhichcharacterizemuchofthePacificNorthwestmayhavesimilarfertilitytootherparentmaterials(McDaniel,thisproceedings).
Thepresenceoflargeamountsoforganicmatterinweatheredashdepositsisexpectedtoleadtosoilmaterialsthatareresilienttodisturbance,butunweatheredmaterials incoldordryenvironments,mayhavelowlevelsoforganicmatter.
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Reclamationplanningshouldconsidertheneedfororganicmatterandnutrientadditionsinconsiderationofsoilconditionsandforestproductivityinundisturbedsoilsonsimilarsitetypesinthearea.
Planning Considerations for Restoring and Enhancing Productivity of Tephra-Derived Soils
Theuniquechemicalandphysicalcharacteristicsofsoilsderivedfromtephraplayanimportantroleindeterminingwhattreatmentsshouldbeconsideredforrehabilitating or enhancing a degraded soil. To develop the most appropriaterestorationapproach,thefollowinggeneralquestionsneedtobeansweredbycollectingfieldinformation:
1. Isthesoildegradedtothepointthatforestproductivityorothervaluesarelikelytobesignificantlyaffected?
2. Whatgrowth-limitingconditions(e.g.compaction,organicmatterloss)orotherissuessuchaserosion,sedimentdeliverytostreams,orvisualconcernsarepresentthatrequireamelioration?
3. Aretheresiteconditionsorotherfactors(e.g.culturalresources)thatprecludeorfavortheuseofonerehabilitationtechniqueorcombinationoftreatmentsoveranotherforaddressingthegrowthlimitingfactor(s)?
4. Areproventreatmentslikelytoincreasesiteproductivitytoanextentwheretheassociatedcostswillbereturned?
SeveralresearcheffortsinnorthwesternNorthAmericaandelsewherehaverecentlyfocusedonevaluatingtheeffectivenessofcommonlyusedsoilrehabilita-tiontechniques.Althoughresearchspecificallyaddressingdegradedtephra-derivedsoilsinthePacificNorthwestislimited,theprinciplesgoverningthesuccessorfailureofsuchworkareexpectedtobesimilartothosefromelsewhere,andondifferentsoiltypes.
Fortephra-influencedsoilsincoastalWashington,Millerandothers(1996)ob-servedthattreesoncompactedskidtrailsweregrowingatthesamerateastreesinundisturbedsoilsandtrailswheresoilsweredecompacted.Theyconcludedthatsitespecificfactorsdeterminedtheresponsetosoildisturbanceandrehabilitation.Whereclimatic factorswere favorable,andsoilpropertiesofcompactedsoilsremainedwithinthresholdsforgrowthlimitingfactors,productiveforestscoulddevelopondisturbedsoils.Forthetephra-influencedsoilsstudiedbyMillerandothers(1996),despitea50percentincreaseinbulkdensityafterharvestandvaluesofbulkdensitythatwere20percenthigherafter8years,thedisturbedsoilsstillhadbulkdensitybelow1000kgm–3.Partlybecauseoftheresults,theauthorsconcludedthat therelationshipbetweenpre-disturbanceandpost-disturbancebulkdensity,whichhasbeenusedasanindicatorofsoildegradationintheUnitedStates,wasnotagoodpredictorofproductivityeffects.
Thecomplexprocessesaffectingseedlingresponsetodisturbanceandrehabilita-tionwerefurtherillustratedbyresultsfromPriestRiver,Idaho,wheresoilcompactioneffectsontreerootgrowthwerestudiedonasoilderivedfromMazamatephra.Douglas-firandwesternwhitepineseedlingsgrowingincompactedsoilsforoneyearhadfewernonmycorrhizalroottipscomparedtosoilswithoutcompaction(Amaranthusandothers1996).EctomycorrhizalroottipabundanceanddiversitywasreducedbycompactionforDouglas-fir,butnotwesternwhitepine.Despitetheseresults,seedlinggrowthresponsewasnotsignificantlyaffected.Thusthe
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initial responsetocompaction,andtheneedforrehabilitationtreatments,notonlyvariesfordifferentsoilanddisturbancetypes,butalsomaydependonthetreespeciesundermanagement.
RecentresultsinBritishColumbiaonarangeofsoiltypesandclimaticcondi-tionshaveshownthatrelativelysimplerehabilitationtreatmentssuchassubsoil-ingfollowedbyplantingwithlodgepolepineoftenproducewell-stockednewforests (Plotnikoffandothers2002;BulmerandKrzic2003),butonwetsites,fine-texturedsoils,orwheretopsoilretrievalandreplacementwerenotcarriedout, growth ratesmay lag thoseof undisturbed areasof adjacent plantations.LodgepolepineisoftenplantedonrehabilitatedsitesinBritishColumbiaowingtohighsurvivalratesandrapidearlygrowth.Incontrasttothepreviousresults,soildecompactionwithout treeplanting led tounsatisfactorystockingon100sitesinBC’ssoutherninterior(BulmerandStaffeldt2004),indicatingthatnaturalregenerationshouldonlybereliedonasareforestationstrategyaftercarefullyevaluatingtheavailabilityofaseedsource.
Theseresearchstudiesshowthatitisdifficulttogeneralizewhenpredictingtheresponsetodisturbanceandrehabilitation.Site-specificinformationisessentialfordeterminingwhichresearcheffortsandconclusionsapplytoaparticularsite,andthereforewhichcourseofactionislikelytobemostsuccessfulandcost-effective.Thefollowingcriticalsitefactorscanaffecttheresponsetosoildisturbanceandrehabilitationonaparticularsite:
• Climatic conditions suchas temperatureandannualwaterdeficitaffecttherootingcharacteristicsoftrees,andtheextenttowhichtheyarelimitedbymoistureavailability,coldtemperatures,shortgrowingseason,orotherfactors.
• Slope characteristics and surface drainage patternsaffectthepotentialforerosionorslopefailurethatcouldaffectresourcesonandoffthesite.
• Soil texture and tephra influence affect the response of the soil to thedisturbance and subsequent rehabilitation treatments because fine tex-turedmaterialshavelowstrengthwhenwetandarehighlysusceptibletocompaction,whiletheporesystemincoarse-texturedmaterialsisgenerallyresistanttocompaction,andlesslikelytosuffersoildegradationassociatedwithmachinetraffic.
• Moisture regimestronglyaffectsthetreegrowthlimitingfactors,andthelikelihoodofrealizingsuitableconditionsfortillageequipment.Wetsitesinparticularoftensufferincreasedsoildisturbancebecauseoflowsoilstrength,andrestorationeffortsfacechallengesbecauseofpoorsoilstructureresult-ingfromtillageofwetsoils.
• Presence of unfavorable subsoilsandtheextenttowhichsurfacesoildis-placementhasexposedthemormayforceplantrootstogrowinthem.
• Rooting depthinundisturbedsoils,potentialrootingdepthonthedisturbedsite,andthedepthofsoildisturbanceaffecttheresponseoftrees.
Theexpectedlossofforestproductivityifthesitewasleftaloneneedstobebalancedagainstthebenefitsofinterventiontoimproveconditionsonthesite.Incaseswheretheexpectedbenefitsaresmall,notreatmentwouldbeindicated,andplantedtreescouldsimplybemonitoredtoevaluatetheneedforfertilizerinputsorotheractivitiestomaintaingrowthratesatdesirablelevels.Insuchcases,site
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productivitymaybeslightlylowerthanifsoildisturbancehadnotoccurred,butthelossinproductivitymaybesmallcomparedtocostofrestorationtreatments.
Insummary,reclamationtreatmentswilllikelydeliverthemostbenefitwhen:
• Climaticandothersiteconditionsfavourproductivetreegrowth • Severesoildisturbancewilllikelypreventseedlingestablishmentandsig-
nificantlyreducegrowthwithoutintervention • Provenandrelativelyinexpensivetreatmentssuchasdecompaction,topsoil
replacement,andrevegetationareappliedtomesicsiteswithmediumandcoarsetexturedsoils
• Difficultsites,wetareasandfine-texturedsoilsareavoided,astreatmentstoovercome these challenges are expensive and benefits unproven.
Restoration Treatments and Unique Aspects of Their Application to Tephra-Derived Soil ______________________________________________
Where soil disturbance is likely to reduce tree growth to an unsatisfactorydegree,andtreatmentsareindicated,abasicapproachtorehabilitationwouldinvolveattemptingtocreatesiteconditionsapproximatingthoseofundisturbedsoilsonsimilarsites inthearea,eventhoughthismaynotalwaysbepossible(e.g.wheresurfacesoilshavebeendisplacedandtheirretrievalisnotfeasible).Theconditionsonundisturbedsiteslikelyreflectwhatisconducivetoproduc-tiveforestgrowthinthearea.Todevelopacosteffectiveplanforimplementingreclamationtreatments,thereisaneedtoconsider:
• Theextenttowhichconditionsonthesiteareexpectedtoexceedthresh-oldsofgrowthlimitingfactorssuchasaerationporosity,soilmechanicalresistance,wateravailability,andnutrientcontent.
• Availabilityofdisplacedsurfacesoilthatcouldberetrievedandnatureofsurfacesoilsinnearbyundisturbedsoilsonsimilarsites
• Stones,stumpsorotherfactorsthatmayaffecttheoperationofequipment • Presenceofexistingvegetation,andlikelyseedsourcesforpreferredcrop
treesandotherspeciestobere-establishedonthesite • Expectedwildlifeorcattleusethatmayaffectthesuccessofreforestation
orrevegetationefforts
Basedonsite-specificconditions,reclamationtreatmentscanbeidentifiedtoaddresseachoffourobjectives.
Managing Water and Preventing Erosion
Watermanagementanderosioncontrolisthefirststepinreclamationplanning.Withoutastablesubstratethatisfreeoferosion,thebeneficialeffectsofrestorationtreatmentscouldbedestroyedbyremovaloforganicrichsurfacesoillayers,orbyexposureoflessfertilesubsoils.Inaddition,thehighcostsofpotentialoff-siteeffectsonwaterquality,fish,andpropertyrequirethatwateranderosioncontrolisgivenhighestpriority.Sitewatermanagementisalsoessentialforcorrectingdetrimentaleffectsofsoildisturbanceonthesoildrainageclassandmoistureregime.
Water management may be as simple as building a ditch to divert surfacewateraway froma roador landing,orcould involvemoreexpensiveoptionssuchassloperecontouringdesignedwithinternaldrainagetorestoretheflowofsubsurfacewater.
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Erodibilitymayberelatedtopoorcohesionofrecentlydepositedtephrama-terials,highwaterretention,andlowinternalstrengthofdeposits.Thesefactorsmaybeoffsetbyhighporosity.Thecharacteristicsofthesubsoilsandothersiteattributesneedtobeconsideredbeforeselectingtreatments.
LocalizederosionwasobservedinDiamondLakeDistrict,UmpquaNationalForest,whensurfacewaterflowpatternsweredisturbedbycompactionofdeeppumicesoils,routingwatertotheedgeoftheunit.Routedwateraffectedresidualtopsoilleftpost-harvest,and,wherecompactionenduresforlongperiods,waterroutinganderosionwouldcontinueintothefuturewithouttillage.
Treatmentstocontrolerosioninclude:
• outslopingdecompaction • sloperecontouring • diverting/managingsurfacewater • revegetation
Wherewatermanagement,erosion,slopestabilityissuesdonotposesevererestrictions,thenextstepistoproceedwitheffortstorestoresiteproductivity.
Tillage to Restore Soil Physical Conditions
Forcompactedsoilswithhighsoilstrengthorthosethathavesuffereddeterio-rationoftheporesystem,restoringsoilphysicalconditionsisanessentialpartofreclamation.Compactionaffectstheporesystemmostlybyreducingthenumberoflargepores.Thisleadstoincreasedwaterretentionandreducedinfiltration,andmayleadtosoilswithinsufficientairforplantroots.
Therearereasonstobelievethattreesgrowinginsomesoilsrichinvolcanicashmayresponddifferentlytocompactionthanforotherparentmaterials.Thehighlydevelopedaggregatestructureofweatheredanddevelopedsoilsderivedfromvolcanicmaterialsinotherareashasbeenwelldocumented,suggestingthatstableaggregatesinsuchsoilsmaysurvivethecompactionprocess,andprovidestabilityforlargepores.ForthePacificNorthwest,recenttephradepositslikelyhaverelativelystablemacrostructurewhereparticlestrengthishighenoughtoresistparticlebreakage.Onmesicanddrysites,thesecharacteristicsmayleadtoasoilthatisabletowithstandcompactionandstillprovideaproductiveenviron-mentforplantroots,and/oronethatisabletonaturallyregeneratesoilconditionssuitableforproductiveforestgrowthfollowingdisturbance.Despitethis,somespecificchallengescouldinclude:
• Water retention:Onwettersites,thehighwaterretentivityoftephrasoilsmayleadtosimilarproblemsasidentifiedforfine-texturedsoils,andcouldbe especially problematic in low-lying landscape positions. The majorproblemswouldincludeexcessivesoilwater,andlackofaeration.
• Particle breakage:Somevolcanicmaterialsaresusceptibletoparticlebreak-agewhendisturbed,whichincreasestheproportionoffinesintheparticlesizedistribution.ParticlebreakagemaybeafactorinpoorperformanceofregenerationonsomesitesinOregon.
• Irreversible drying:Cementationmayleadtomassivestructurewithhighsoilstrengthsthatplantrootsareincapableofpenetrating.AlthoughthisphenomenonisnotexpectedtobewidespreadinthePacificNorthwest,it
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couldaffectresultsinlowlyinglandscapepositionswithweatheredsoilsandwheresoilstructurehasbeendestroyed(puddling)byrepeatedmachinetraffic,andwheresitesaresubjecttooccasionaldryinginsummer.
Wheretillageisrequired,avarietyofimplementsareavailable,includingwingedsubsoilers,rockripper,excavatorswithbrushrakes,mulchingheads,orcustomattachmentssuchasthesubsoilinggrapplerakeandsubsoilingexcavatingbucket.Thebestimplementforthejoblikelydependsonfactorssuchasrequireddepth,soilstrength,waterstatus,andlogistics(e.g.availabilityofprimemovers).
Anexampleofanimplementthatwaspurpose-builtfordecompactingsoilsinvolcanicterrainisthesubsoilinggrapplerake,whichwasdevelopedandusedintheDiamondLakeRangerDistrict, UmpquaNationalForest(ArchuletaandKarr2004).Thisimplementisagrapplerakefittedwithsubsoilingshanksandwings. Itwasdesigned tomitigateeither legacycompactionornewlycreatedharvestimpacts,andisbestemployedwhenusedinconcertwithanongoingactivity,suchaspost-harvestslashreduction.AtDiamondLake,thecombinationof theseactivitiesreducedtheoverallcostof individualprojectswithaminorincreasetoeitherslashpilingorsubsoilingcosts.Thesubsoilingexcavatorbucketisanotherimplementthatisalsoequippedwithshanks,andallowscost-effec-tivedecommissioningofroads.Thisimplementalsoreducesthesubsoilingrateonsmalltillageprojectsandmakesadditionalequipment(i.e.dozerandtillageimplement)redundant.
Tillage is aimedat alleviating theeffectsofdetrimental compaction,whichincludeincreasesinsoilstrength,reducedaeration,andexcessivewaterreten-tion.Althoughtheeffectivenessoftillagehasbeenquestionedonfine-texturedsoilsincentralAlbertawheresubsoilsstayedwetandsoftforlongperiodsduringtheyear(McNabb1994),suchissuesmaybelessofaconcerninfine-texturedtephra-derivedsoilsinthePacificNorthwestbecauseof(a)thestrongaggrega-tionexpectedinfine-texturedsoilsderivedfromvolcanicmaterials,and(b)dryerclimates.Forrelativelyfreshvolcanicparentmaterials,particlesizesmaybecoarseandwaterinfiltrationandaerationmaynotbelimiting.
Insummary,forsuccessfultillage,consider:
• tillageisusedtoreducesoilstrengthandrestoretheporesystem, • avarietyofimplementsareavailable, • usetherootingdepthinnaturalforestsonsimilarsitesasaguidetotillage
depth • fordisperseddisturbance,andtoreducecosts,considerspottillage • theeffectsoftillingwetvolcanicsoils,whichmaybesubjecttoirreversible
dryingorconsolidation,needtobeevaluatedthroughmonitoring
Restoring Organic Matter and Nutrients
Ingeneral, themosteffectivemeansofrestoringsurfacesoilorganicmatteristoretrieveandreplacedisplacedtopsoil.Insituationswhererecoveryofdis-placedsurfacesoilisnotpractical,otherpotentialstrategiesincludedistributinggreenloggingslashfromharvestingoperationsoverthereclaimedarea.IncentralBC,chippedwastelogsenhancedsoilpropertiesandcontributedtosuccessfulestablishmentandearlygrowthofwhitespruceseedlings(Sanbornandothers2004).Despitetheirbenefits,organicamendmentsaregenerallyonlysuitableiftheyarelocallyavailable,astheyareexpensivetotransport.
1�2 USDA Forest Service Proceedings RMRS-P-44. 2007
Bulmer, Archuleta, and Curran Restoring and Enhancing Productivity of Degraded Tephra-derived Soils
Sincetephraderivedmaterialsareknowntohaveahighaffinityforsoilor-ganicmatter,acost-effectivealternativecouldinvolverevegetationwithgrassesandlegumesthatcanbuildsoilorganicmatterthroughdecompositionoftheirrootsystems.Inonestudy(notanashsoil),Bendfeldtandothers(2001)showedthatvegetationinputsofCwereanimportantsourceofsurfacesoilorganicmat-terlevelsaftersixteenyearsonreclaimedminesoilthatalsoreceivedaninitialamendmentwithwoodwaste.
Insummary,torestoreorganicmatterandnutrients,consider:
• Organic matter is an essential component of productive soil, but forestecosystemsvaryintheamountpresentinsurfacesoils.
• Retrievalofdisplacedtopsoilisacosteffectiveapproachforrestoringsuit-ablegrowingconditions.
• Usethecharacteristicsofsurfacesoilsonsimilarsitesasaguidetowhatsurfacesoilorganicmatterlevelsareappropriate,anditsdistributionasasurfacelayerorincorporatedintosurfacesoils.
• Revegetationwithagronomicgrassesandlegumescancontributesignificantquantitiesoforganicmatterovertime.
• Organicamendmentscaneffectivelyrestoresoilconditions,butareexpen-sivetotransport.
Revegetation
Successful revegetation and reforestation of disturbed areas is an importantfinalstepinreclamationefforts.Inmanycases,theobjectiveforthereclamationisdefinedbythetypeofvegetationcoverdesired.Forexample,grassandlegumecovermaybeprescribedtopreventerosion,forestrestorationprovidesfortimber,orothervaluesmayhaveprioritysuchaswildlife,watershedvalues,andaesthetics.Treeplantingisthemostcommonandeffectivemeanstoestablishanewforest,butnaturalregenerationcouldbeeffectiveifaseedsourceandsuitableseedbedconditionswerepresent.
Forsuccessfulandcost-effectiverevegetation,consider
• Revegetationisessentialforerosioncontrolinslopingterrain.
• Seeding agronomic grasses and legumes are proven means to preventerosion.
• Seedbed characteristicsareoftenbestimmediatelyaftertillageoperationsarecomplete.
• Droughtiness;mayhamperrevegetationeffortsincoarse-texturedtephraswherelowwaterretentionresultsinalackofseedbedmoisture.Seedingtreatmentsinsuchsoilswouldhavetobeconsideredcarefully,andconsiderthetiminginrelationtoexpectedprecipitation,alongwiththepossibleneedformulchestoconservemoisture.
• Ingress of native vegetation mayoccurwithoutinterventionwheredistur-bancesaresmall(e.g.roadsandtrails).
• Natural regeneration of tree seedlingsmaybea lowcostalternative toplantingwhereaseedsourceisavailableandslightlylongerregendelayisacceptable.
1��USDA Forest Service Proceedings RMRS-P-44. 2007
Restoring and Enhancing Productivity of Degraded Tephra-derived Soils Bulmer, Archuleta, and Curran
Information and Research Needs _________________________________Thepublishedinformationbaseislimitedandprovidesfewspecificexamples
oftheeffectsofsoildisturbance,enhancementandrestorationonforestsitepro-ductivityinvolcanicterraininwesternNorthAmerica.Thelackofinformationpartlyreflectsthedifficultyandexpenseindesigningandimplementingstudiesthatarerelevanttothewiderangeofsitetypes,soilconditions,andtreespeciesthatoccurintheregion.Despitethis,thereisconsiderableinformationonsoildisturbanceandrestorationeffectsforothersoiltypesinsimilarclimatesandmuchofthisinformationcanlikelybeextrapolatedtovolcanicsoilsintheNorthwest.Inaddition,soilscientistsandforestmanagersintheregionhaveconsiderableexperiencewithhowthesoilsrespondtomanagement.
Toaddressthelackofspecificpublishedinformation,ausefulapproachwouldbetocombineexistingresearchfromelsewherewithlocalknowledgeofthesoilsresponsetomanagementthroughretrospectivestudy,monitoring,andoperationaltrials.Althoughtheseapproacheshavetheirlimitationsforresolvingdetailedques-tions,theyareextremelyusefulforansweringthebroadquestionsthatariseduringtheinitialstagesofadetailedresearchprogram.Specificquestionstobeaddressed(andsuggestedapproachtostudy)include:
• Identifyingsitesmostsusceptibletodegradation,andthosewhererestorationorenhancementprovidethegreatestbenefit(monitoring and retrospective study)
• Evaluatingarangeoftreatmentoptionsforrestoringandenhancingproduc-tivity(monitoring results and operational trials)
• Characterizing theeffectof typicaloperationsonsoilpropertiessuchasbulkdensity,penetrationresistance,andorganicmatter(research)
• Determiningthresholdsforunacceptableproductivitydeclineonthemostcommonsitetypes(research)
Management Recommendations _________________________________1. Evaluate costs and benefits:Soilrestorationandenhancementshouldbe
consideredinvestmentswheretheexpectedbenefits,costsandrisksarecarefullyevaluated.Ingeneral,itisbesttofocuseffortsonsiteswiththebestexpectedreturnonrestorationdollars,anduselowcost,reliablemethodsforrestoration.Thebenefitsofrestorationandenhancementeffortstypicallyinclude:
• increasedtimbersupply, • reducedenvironmentalliabilityassociatedwithroads, • improvedwatershed,wildlife,andaestheticvalues.
2. Have a site-specific plan:Evaluatelimitationstoproductivity,riskofero-sion,andothersitespecificfactors,andthensetrealisticobjectivesforthework.Wherelegacyimpactsarepresent,combinationmachinessuchasthesubsoilinggrapplerakeandsubsoilingexcavatorbucketmayallowrestorationtobeblendedintootherworksuchasbrushpilingorroaddecommissioning.
3. Start simple (and cheap):Trythesimplesolutionfirst.Considertreatmentsinthefollowingorder:
• donothing(i.e.relyonnaturalregenerationtorecolonizelightlydisturbedareas)
1�4 USDA Forest Service Proceedings RMRS-P-44. 2007
Bulmer, Archuleta, and Curran Restoring and Enhancing Productivity of Degraded Tephra-derived Soils
• treeplanting • fertilization • decompaction/tillageplustopsoilrecovery • organicamendments • re-establishingnativespeciesbyplanting
4. Keep learning:Monitortheresultsofyoureffortsandthoseofothers.
Acknowledgments ______________________________________________ResearchdescribedherewassupportedbyBritishColumbia’sForestScience
Programandother fundingsources.UmpquaNationalForest supportedworkof J.Archuleta.MikeKarrprovidedworkon the subsoilingequipmenton theUmpquaNationalForest.
References ______________________________________________________Amaranthus,M.P.;Page-Dumroese,D.;Harvey,A.;Cazares,E.;Bednar,L.F.1996.Soilcompac-
tionandorganicmatteraffectconiferseedlingnonmycorrhizalandectomycorrhizalroottipabundanceanddiversity.PNW-RP-494.Portland,OR:U.S.DepartmentofAgriculture,ForestService,PacificNorthWestStation.12p.
Archuleta,J.G.;Karr,M.2004.Multipurposesubsoilingexcavatorattachments.Tech.Tip.SanDimastechnologydevelopmentCenter.U.S.DepartmentofAgriculture,Forestservice.
Arnalds,O.;Kimble,J.2001.AndisolsofdesertsinIceland.SoilSci.Soc.Am.J.65:1778-1786.Basher,L.R.;Painter,D.J.1997.WinderosioninNewZealand.In:ProceedingsoftheInterna-
tionalSymposiumonWindErosion;1997June3-5;Manhattan,Kansas:U.S.DepartmentofAgriculture,ARS:1-10.
Bendfeldt,E.A.;Burger,J.A.;Daniels,W.L.2001.Qualityofamendedminesoilaftersixteenyears.SoilSci.Soc.Am.J.65:1736-1744.
BritishColumbiaMinistryofForests.2001.Soilconservationguidebook.BCMin.For.Victoria.Available: http://www.for.gov.bc.ca/tasb/legsregs/fpc/fpcguide/soil/soil-toc.htm. AccessedOctober2005.
Bulmer,C.E.;Krzic,M.2003.SoilpropertiesandlodgepolepinegrowthonrehabilitatedlandingsinnortheasternBritishColumbia.Can.J.SoilSci.83:465-474.
Bulmer,C.E.;Staffeldt,P.2004.SalmonArmlandingrehabilitationmonitoringreport.Unpublishedtechnicalreportavailablefromtheauthor.
Cairns,J.Jr.1999.Ecologicalrestoration:Amajorcomponentofsustainableuseoftheplanet.RenewableResourcesJournal:7-11.
CanadianCouncil of ForestMinisters. 2002.Technicalworkinggroupdraft recommendationsforimprovedCCFMindicatorsforsustainableforestmanagementdraftcompiledbytheC&IsecretariatOctober2,2002.TWGChairsmeeting;2002October9–11;Edmonton,Alberta.CCCFMSecretariat8thFloor,580BoothStreetOttawa.
Hillel,D.1991.Outoftheearth.Berkeley,CA:UniversityofCaliforniaPress.322p.McNabb,D.H.1994.TillageofcompactedhaulroadsandlandingsintheborealforestsofAlberta,
Canada.For.Ecol.Mgmt.66:179-194.Miller,R.E.;Scott,W.;Hazard,J.W.1996.Soilcompactionandconifergrowthaftertractoryard-
ingatthreecoastalWashingtonlocations.Can.J.ForRes.26:225-236.Moldrup,P.;Yoshikawa,S.;Olesen,T.;Komatsu,T.;Rolston,D.E.2003.GasDiffusivityinUn-
disturbedVolcanicAshSoils:TestofSoil-Water-Characteristic-BasedPredictionModels.SoilSci.Soc.Am.J.67:41–51.
Page-Dumrose,D.;Jurgensen,M.;Elliot,W.;Rice,T.;Nesser,J.;Collins,T.;Meurisse,R.2000.SoilqualitystandardsandguidelinesforforestsustainabilityinnorthwesternNorthAmerica.For.Ecol.Manage.138:445-462.
Plotnikoff,M.R.;Bulmer,C.E.;Schmidt,M.G.2002.Soilpropertiesandtreegrowthonreha-bilitatedforestlandingsintheinteriorcedarhemlockbiogeoclimaticzone:BritishColumbia.For.Ecol.Mgmt.170:199-215.
1��USDA Forest Service Proceedings RMRS-P-44. 2007
Restoring and Enhancing Productivity of Degraded Tephra-derived Soils Bulmer, Archuleta, and Curran
Poulenard,J.;Podwojewski,P.;Herbillona,A.2003.Characteristicsofnon-allophanicAndisolswithhydricpropertiesfromtheEcuadorianparamos.Geoderma.117:267–281.
Poulenard,J.;Michel,J.C.;Bartoli,F.;Portal,J.M.2004.WaterrepellencyofvolcanicashsoilsfromEcuadorianparamos:effectofwatercontentandcharacteristicsofhydrophobicorganicmatter.EuropeanJournalofSoilScience.55:487–496.
Powers,R.F.;Tiarks,A.E.;Boyle, J.R.1998.Assessingsoilquality:Practicablestandards forsustainableforestproductivityintheUnitedStates.In:Thecontributionofsoilsciencetothedevelopmentofandimplementationofcriteriaandindicatorsofsustainableforestmanagement.Soil.Sci.Soc.Am.Spec.Pub.no.53.Madison,WI:SoilScienceSocietyofAmerica:53-79.
Richardson,B.;Skinner,M.F.;West,G.1999.Theroleofforestproductivityindefiningthesus-tainabilityofplantationforestsinnewZealand.For.Ecol.Manage.122:125-137.
Sahaphol,T.;Miura,S.2005.Shearmoduliofvolcanicsoils.SoilDyn.Earth.Eng.25:157-165.Sanborn,P.;Bulmer,C.;Coopersmith,D.2004.Useofwoodwasteinrehabilitationoflandings
constructedon fine-textured soils, central interiorBritishColumbia,Canada.West. J.Appl.For.19:175–183.
Shoji,S.;Nanzyo,M.;Dahlgren,R.A.;Quantin,P.1996.EvaluationandproposedrevisionsofcriteriaforAndosolsintheworldreferencebaseforsoilresources.SoilSci.161:604-615.
Tejedor,M.; Jimenez,C.C.;Dıaz,F.2002.SoilMoistureRegimeChangesinTephra-MulchedSoils:ImplicationsforSoilTaxonomy.SoilSci.Soc.Am.J.66:202–206.
Tejedor,M.;Jimenez,C.C.;Dıaz,F.2003.Volcanicmaterialsasmulchesforwaterconservation.Geoderma.117:283–295.
1�7USDA Forest Service Proceedings RMRS-P-44. 2007
In: Page-Dumroese, Deborah; Miller, Richard; Mital, Jim; McDaniel, Paul; Miller, Dan, tech. eds. 2007. Volcanic-Ash-Derived Forest Soils of the Inland Northwest: Properties and Implications for Management and Restoration. 9-10 November 2005; Coeur d’Alene, ID. Proceedings RMRS-P-44; Fort Collins, CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station.
Mariann T. Garrison-Johnston and Peter G. Mika are research scientists and Leonard R. Johnson is the director for the Intermountain Forest Tree Nutrition Cooperative, University of Idaho, Moscow, ID. Dan L. Miller is a silviculture manager for Potlatch Corporation, Lewiston, ID. Phil Cannon is the productivity manager for Forest Capital, North, Monmouth, OR.
Abstract Datafrom139researchsitesthroughouttheInlandNorthwestwereanalyzedforeffectsofashcaponsiteproductivity,nutrientavailabilityandfertilizationresponse.Standproductivityandnitrogen(N)fertilizerresponseweregreateronsiteswithashcapthanonsiteswithout.Whereashwaspresent,depthofashhadnoeffectonsiteproductivityorNfertilizerresponse.Siteproductivityincreasedwithincreasingpotentiallyavailablesoilwater.Potentiallyavailablesoilwater,inturn,increasedwithincreasingashdepth.Decreasingavailabilityofmagnesium(Mg)andcalcium(Ca)intheupper12inchesofsoilmayhaveconstrainedsiteproductivitywithincreasingashdepth.SoilmineralizableNandammoniumNwereunaffectedbyashpresenceordepthbutdidvarybyunderlyingparentmaterial.SiteproductivityandNfertilizerresponsevariedbyunderlyingparentmaterialevenafteraccountingforashpresence.Standvolumeresponsetosulfur(S)fertilizationdecreasedwithincreasingashdepth,suggestingpossibleSadsorptionbyashcap.NogrowthresponseorchangeinfoliarKstatuswasdiscernedfollowingKfertilization.Managementrecommendationsbyparentmaterialareprovided.
Ash Cap Influences on Site Productivity and Fertilizer Response in Forests of the Inland
NorthwestMariann T. Garrison-Johnston, Peter G. Mika, Dan L. Miller, Phil Cannon, and
Leonard R. Johnson
Background
Availabilitytoplantsofmostnutrientsbesidesnitrogen(N)isrelatedprimarilytomineralweatheringratesandsoilphysicalandchemicalproperties.CommonparentmaterialsofsoilsintheInlandNorthwestincludetheColumbiaRiverbasaltflows,BeltSeriesmetasedimentaryrocks,granites,andvariousglacialdeposits.Characteristicsthatthesematerialsimparttofor-estsoilssignificantlyaffectforestnutrition,productivityandresponsetofertilization(MooreandMika1997;Mooreandothers2004).However,surficiallydepositedparentmaterialsareoftenneglectedduringanalysesofparentrockeffectsonforestnutrition.ThisisparticularlytrueforwidespreadvolcanicashresultingfromtheeruptionofMountMazama(nowCraterLake)insouthwesternOregon.Theeffectsofsurficiallydepositedparentmaterialsonforestnutrition,productivityandresponsetofertilizationarepoorlyunderstood.
1�� USDA Forest Service Proceedings RMRS-P-44. 2007
Garrison-Johnston, Mika, Miller, Cannon, and Johnson Ash Cap Influences on Site Productivity and Fertilizer Response in Forests of the Inland Northwest
Ash-capsoilscommontotheInlandNorthwestareknownfortheircapabilitytoholdampleavailablemoisture,whichinturnisthoughttoenhancesitepro-ductivity (BrownandLowenstein1978;Mital1995).Becauseof theimprovedsoilmoisturestatus,foreststandsgrowingonash-capsoilsaregenerallyexpectedto show greater growth response to nitrogen (N) fertilization than stands onsoilswithoutashcap,atleastsolongassomeotherfactorisnotmorelimitingthan moisture and/or N. In a study of 90 Douglas-fir fertilization trial standsacrosstheInlandNorthwest,Mital(1995)foundapositivecorrelationbetweenDouglas-firgrowthresponsetoNfertilizationandashdepthatanapplicationrateof400lbac–1,whiletherelationshipwaslessstrongwhentheapplicationratewas200lbac–1.Inanotherstudy,Geist(1976)reportedthatforageproductiononvolcanicashsoilsshowedstrongfertilizationresponseonforestedrangesitesineasternOregonandWashington.
Withoutfertilizersorblendingwithorganicmatter,unweatheredash-capsoilsarenotparticularlyfertile,beingcomprisedlargelyofpoorlycrystallinealumi-nosilicatesandiron(Fe)andaluminum(Al)oxides.Theirnutrientcationstoragecapacity is low, suggesting that supply of the nutrient cations potassium (K),calcium(Ca)andmagnesium(Mg)maybepoor(McDanielandothers2005).Furthermore,stronganionadsorptioncapacitybyvolcanicashmayimpedetreefertilizationresponse.Inastudyofsulfur(S)adsorptionpropertiesofandicsoilsintheInlandNorthwest,Kimseyandothers(2005)suggestthatappliedSfertilizersmaybeineffectiveinincreasingS-availabilitytotreesunlessathresholdsorptioncapacityof theashcapisexceeded.Similar interactionsmaybeexpectedfortheanionicformsofotherelements,includingN,phosphorus(P)andboron(B).Suchaphenomenonmayexplain,inpart,thevariablerelationshipbetweenashcapdepthandN-fertilizationratesdescribedbyMital(1995),ifsomethresholdsorptioncapacityhadtobemet(suchasatthe400lbrate)beforetheappliedNbecameavailabletotheforestvegetation.Theashcapmaytakeonnutritionalcharacteristicsofunderlyingresidualsoils,thoughthisperceptionhasnotbeenscientificallytested.
AstatisticalanalysisofdatafromnutritionalresearchconductedbytheInter-mountainForestTreeNutritionCooperative(IFTNC)from1980tothepresentwasundertakentodeterminewhetherashdepositsaffectedtreeandsoilnutrition,for-estproductivityandfertilizationresponse.Wehypothesizedthatsiteproductivityandfertilizerresponsewouldbegreateronashsitesthannon-ashsitesandthatproductivityandresponsewouldincreasewithincreasingashdepth.
Methodology ___________________________________________________
Data Compilation
Data from139 IFTNC research siteswere compiled.Thedata set included94sitesfromthe1980-1982Douglas-firStudy,8siteseachfromthe1991and1993MixedConiferStudies,and29sitesfromthe1994-1996ForestHealthandNutritionStudy(table1).Soilprofiledescriptionswereusedtoestimateorganichorizondepth,surficialdepositdepthandresidualsoildepthto36inches.Sur-ficial deposits were categorized as ash, loess, glacial deposits, other modern(quarternaryera)deposits,andtertiarydeposits.Residualsoilswerethosederivedfromthebasegeology.Thedivisionbetweensurficialdepositsandbasegeology
1�9USDA Forest Service Proceedings RMRS-P-44. 2007
Ash Cap Influences on Site Productivity and Fertilizer Response in Forests of the Inland Northwest Garrison-Johnston, Mika, Miller, Cannon, and Johnson
Tabl
e 1—
List
of
sele
cted
fer
tiliz
atio
n st
udie
s es
tabl
ishe
d by
the
Int
erm
ount
ain
Fore
st T
ree
Nut
ritio
n C
oope
rativ
e be
twee
n 19
�0 a
nd 2
000.
R
egio
ns r
efer
to
nort
heas
tern
Ore
gon
(NE
OR
), ce
ntra
l Was
hing
ton
(C W
A), n
orth
east
ern
Was
hing
ton
(NE
WA)
, cen
tral I
daho
(C ID
), no
rthe
rn Id
aho
(N ID
) and
wes
tern
M
onta
na (W
MT)
.
No.
of
Year
(s)
Stan
d
Tria
l nam
e si
tes
esta
blis
hed
com
posi
tion
Reg
ion
Trea
tmen
ts a
nd r
ates
a
Dou
glas
-fir
trial
s 94
19
�0-1
9�2
Dou
glas
-fir
C ID
, C W
A,
cont
rol;
200
lb N
; 400
lb N
N
E W
A, N
E O
R,
N ID
, W M
T
Um
atill
a m
ixed
con
ifer
� 19
91
Mix
ed c
onife
r N
E O
R
cont
rol;
200
lb N
; 200
lb N
+ 1
00 lb
S
Oka
noga
n m
ixed
con
ifer
� 19
9�
Mix
ed c
onife
r C
WA
co
ntro
l; 20
0 lb
N; 2
00 lb
N +
170
lb K
Fore
st h
ealth
and
29
19
94-1
99�
Mix
ed c
onife
r C
ID, C
WA
, NE
19
94 (1
2 si
tes)
: c
ontro
l; �0
0 lb
N; 1
70 lb
K; �
00 lb
N +
170
lb K
nutri
tion
W
A, N
E O
R, N
ID
199�
(12
site
s):
con
trol;
�00
lb N
; 170
lb K
; �00
lb N
+ 1
70 lb
K;
�00
lb N
+ 1
70 lb
K +
100
lb S
19
9� (7
site
s):
con
trol;
�00
lb N
; 170
lb K
; �00
lb N
+ 1
70 lb
K;
�00
lb N
+ 1
70 lb
K +
100
lb S
+ �
lb B
+ 1
0 lb
Cu
+10
lb Z
n +
0.1
lb M
o
All
year
s: A
dditi
onal
N+K
com
bina
tions
rang
ing
from
0 lb
N a
nd
0 lb
K to
�00
lb N
and
�12
lb K
, per
exp
erim
enta
l des
ign
a R
ates
in lb
ac–
1 as
bro
adca
st a
pplic
atio
n
140 USDA Forest Service Proceedings RMRS-P-44. 2007
Garrison-Johnston, Mika, Miller, Cannon, and Johnson Ash Cap Influences on Site Productivity and Fertilizer Response in Forests of the Inland Northwest
wasnotalwaysclear.Becausethesoildepthparameterforthisstudywaslimitedto36inches,deepsurficialdepositswereoftentheonlyparentmaterialnoted.Therefore,thebasegeologicparentmaterialcategoriesforthispaperincludedbasalt,granite,sedimentaryrock,metasedimentaryrock,glacialdeposit,tertiarysedimentsandmodernsediments.Ashwasconsideredpresentifitwascontinu-ousandmeasurabletoadepthof1inchorgreater.Admixturesofashandothermaterialswerealsocountedasashcapiftheashwasapredominantandidentifi-ablecomponentofthemix.
Soilwater-holdingcapacitywasdetermined for theupper24 inchesof thesoil profile on 110 sites. Potential plant-available water was calculated as thedifferenceinmoisture-holdingcapacitybetween1/3and15barsforthosesites.Conventionallaboratorysoiltestswereperformedontheupper12inchesofsoilforall139sites,thoughsometestswereperformedononlyasubsetofthesites.AvailablePandKweretestedusingsodiumacetateextraction,whileNH4
+andNO3
–wereanalyzedusing2MKClextractionwithanalysisbycolorimetry(CaseandThyssen1996a;CaseandThyssen1996d).Sulfate-sulfurwasanalyzedbycalciumphosphateextractionandionchromatography,andBwasanalyzedbycalciumchlorideextractionandspectrophotometricdetermination(Case1996;CaseandThyssen1996c).ExtractableCa,Mg,KandNawereanalyzedby1NammoniumacetateextractionandICP,andmicronutrientsCu,Zn,MnandFebyDTPA(CaseandThyssen1996b;CaseandThyssen2000).
Twodifferentapproacheswereusedtoestimatesiteproductivity.Thefirstap-proachutilizedDouglas-firsiteindex(SI,Monserud1984),availablefor110ofthe139sites.Wealsoselectedcontrolplotgrowthrate(CGR)asaneasilycal-culatedproductivityestimateavailableforallsitesincludedinthestudy.Controlplotgrowthratewasestimatedastheaveragegrowthrateinft3ac–1yr–1overthefirst6yearsofeachstudy.Fertilizationresponsewasbasedon6-yearcubicfootvolumeresponse(ft3ac–1yr–1)toNfertilizersappliedat200to300lbNac–1.LimiteddatawereavailableforexaminationofvolumeresponsetoSfertilizersappliedat100lbSac–1andKfertilizersappliedat170lbKac–1.
Treenutritionwasassessedbychemicalanalysisoffoliagecollectedoneyearafterfertilizationfromtheupperthirdofthecrownondominantorco-dominanttrees.Becausefoliagechemistrydiffersfordifferenttreespecies,Douglas-firwasselectedforinclusioninthisanalysisasthespeciesmostcommonlyoccurringacrosstheselectedtestsites.Nutrientdeficiencieswereidentifiedbythecriticallevelsmethod,definedasthepointonayieldcurvewhereanincreaseinnutri-entconcentrationnolongerresultsinincreasedyield.Thus,the“criticallevel”istheoptimumnutrientconcentrationatwhichmaximumyieldisobtainedwithminimumnutrientinput.CurrentlyacceptedcriticallevelsforInlandNorthwestDouglas-firfoliageareshownintable2.
Data Analysis
Sites were arrayed in a matrix by geographic region, rock type, vegetationseriesandashcappresenceorabsencetoevaluatesamplesizesineachcategory.Analysisofvariancewasusedtodetecttheeffectsofregion,rocktype,vegetationseriesandashpresenceonsiteproductivity,soilandfoliagecharacteristicsandfertilizationresponse.Thebasicstatisticalmodelusedforthisanalysiswas:
Yijk=µ+αj+βk+(αβ)jk+εijk (1)
141USDA Forest Service Proceedings RMRS-P-44. 2007
Ash Cap Influences on Site Productivity and Fertilizer Response in Forests of the Inland Northwest Garrison-Johnston, Mika, Miller, Cannon, and Johnson
Table 2—Nutritional critical levels for Douglas-fir foliage. Adapted from Webster and Dobkowski (19��).
Nutrient Unit of concentration Critical levelNitrogen (N) % 1.40Phosphorus (P) % 0.12Potassium (K) % 0.�0Sulfur (S) % 0.11Calcium (Ca) % 0.1�Magnesium (Mg) % 0.0�Manganese (Mn) ppm 1�Iron (Fe) ppm 2�Zinc (Zn) ppm 10Copper (Cu) ppm 2Boron (B) ppm 10
Where:
Yijk=theproductivity,soilorfoliagecharacteristicmeasuredateachsiteµ=populationgrandmeanforproductivity,soilorfoliagecharacteristicαj=effectofregion,parentmaterialorvegetationseriesβk=effectofashpresenceorabsence(dummyvariable)(αβ)jk=effectofregion,parentmaterialorvegetationseriesbyashcapinteractionεijk=theerrorterm~NID(0, σ2)
BecauseCGRwasafunctionofinitialvolume,analysesofCGRincludedinitialvolumeasacovariateintheabovemodel.Similarly,becausefertilizationresponsedependedonstartingvolumeandstandgrowthrate,thosevariableswereusedascovariatesforthatanalysis.Ashdepthasacontinuousvariablewasalsoincor-poratedintotheabovemodeltoperformregressionanalysisoftheeffectsofashdepthonallvariablesexaminedinthisstudy.Resultswereconsideredsignificantatthe90%confidencelevel(p=0.10).
Results _________________________________________________________
Ash Distribution
SitesinnorthIdaho,northeastWashingtonandnortheastOregonweremorelikelytohaveashthansitesincentralWashington,MontanaandcentralIdaho(table3).Sitesontertiarydeposits,metasedimentaryrocksandglacialdepositsweremorelikelytohaveashthanthoseonbasalt,granite,modernsedimentarydepositsandsedimentaryrocks.Almostallwesternredcedarandwesternhemlockvegetationseriesoccurredonsiteswithash,whileonlyabouthalfthegrandfirseriesandaquarteroftheDouglas-firseriesoccurredonsiteswithashcap.Thestatisticaltermforthispatternwherebyashoccursinconjunctionwithcertaincharacteristicsandnotothersisknownas“confounding.”Confoundingbetweenashpresenceandothersitecharacteristicsmakestatisticalanalysisdifficultbecausewecannotdeter-minewhetherproductivityorresponsedifferencesbetweensitesareduetotheashpresence/absenceortheothersitecharacteristic(vegetationseries,parentrockorgeographicregion).Theoccurrenceofashinconjunctionwithcertainparentrocks
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orgeographicregionsislikelycoincidental,whiletheoccurrenceofashinconjunc-tionwithcertainvegetationseriesismoresuggestiveofacausalrelationship.
Site Productivity
Douglas-firSIwasanalyzedfor110sites(SIinformationwasnotavailablefortheForestHealthandNutritionStudysites).Overall,SIwas10.6%greateronsiteswithashcapthansiteswithout.BaseparentmaterialexplainedasignificantamountofSIvariation(R2=0.18),andtheadditionofashpresencetothismodelexplainedsomeadditionalvariationinSI(R2=0.28;fig.1a).Onallparentmaterialtypesexceptbasalt,thepresenceofashcapsomewhatincreasedsiteproductivitycomparedtothenon-ashsites.However,givenashpresence,asubsequentregres-sionanalysisrevealednosignificantinfluenceofashdepthonSI(fig.1b).AverageSIdidvarybygeographicregion(fig.1c);however,ashpresenceorabsencedidnotfurtherexplainvariationinSIoncethegeographicregionwasknown.Similarly,whileasignificantamountofvariationinSIwasexplainedbyvegetationseriesalone(fig.1d),ashpresencedidnotexplainanyfurthervariation.
Controlplotgrowthratewasavailableforall139sitesincludedintheanalysis,andwashighlycorrelatedwithSI(R2=0.59).Overall,CGRwas29.0%greateronashversusnon-ashsites.AshdepthdidnotaffectCGR(fig.2a).Controlplotgrowthratewassignificantlyaffectedbygeographicregion(R2=0.58;fig.2b),
Table 3—Number of research sites with and without ash cap by region, underlying geology and vegetation series.
Ash cap present? Percent sites Region no yes Total with ash cap
North Idaho � 2� �1 �4%Northeast Washington � 17 2� 74%Northeast Oregon 7 10 17 �9%Central Washington 2� 11 �4 �2%Montana 14 2 1� 1�%Central Idaho 17 1 1� �% Underlying geology
Tertiary deposits 1 � 7 ��%Metasedimentary rocks � 20 2� 71%Glacial deposits � 17 2� ��%Basalt 2� 1� �� �4%Granite 1� 9 27 ��%Modern deposits 7 2 9 22%Sedimentary rocks � 0 � 0%
Vegetation series
Western red cedar 1 22 2� 9�%Western hemlock 1 � � ��%Grand fir 29 24 �� 4�%Subalpine fir � 2 � 40%Douglas-fir �� 14 �2 27% Total sites with and without ash cap: 72 67 139 48%
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Figure 1a—Douglas-fir site index by base parent material and ash cap presence. Parent materials include basalt, glacial deposit (glacial), granite, metasedimentary (metased), sedimentary (sed), modern sedimentary deposits (mod sed) and tertiary sedimentary deposits (tert sed).
Figure 1b—Douglas-fir site index (ft at �0 years) by ash cap depth for sites with ash cap.
Figure 1d—Douglas-fir site index by vegetation series. Vegetation series include Douglas-fir (DF), grand fir (GF), subalpine fir (SAF), western hemlock (WH) and western red cedar (WRC).
Figure 1c—Douglas-fir site index by geographic region. Regions include central Idaho (C ID), central Washington (C WA), Montana (MT), north Idaho (N ID), northeast Oregon (NE OR) and northeast Washington (NE WA).
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vegetation series (R2=0.59; fig. 2c) and dominant parent material (R2=0.46;fig.2d).Ashpresencedidnotexplainanyadditionalvariationforthegeographicregionorthevegetationseriesmodels.However,ashpresencedidexplainsomeadditionalvariationinCGRintheparentmaterialmodel(R2=0.57;fig.2e).TheresultsweresimilartothoseforSI,withashpresencesomewhatincreasingCGRformostparentmaterials.AlsosimilartoSI,onceashwaspresentCGRdidnotchangewithashdepth.
Site Fertility
Soil moisture—Siteproductivityincreasedwithincreasingpotentiallyavailablewater(fig.3a).Potentiallyavailablewater,inturn,increasedwithincreasingashdepth.Whenarrayedbyvegetationseries,potentiallyavailablewaterwasgreater
Figure 2a—Control plot growth rate by ash cap depth for sites with ash cap.
Figure 2b—Control plot growth rate (ft�ac –1yr –1) by geographic region. Regions include central Idaho (C ID), central Washington (C WA),Montana (MT), north Idaho (N ID), northeast Oregon (NE OR) and northeast Washington (NE WA).
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Figure 2e—Control plot growth rate ft�ac –1yr –1) by base parent material and ash cap presence. Parent materials include basalt, glacial deposit (glacial), granite, metasedimentary (metased), sedimentary (sed), mod-ern sedimentary deposits (mod sed) and tertiary sedimentary deposits (tert sed).
Figure 2c—Control plot growth rate (ft�ac –1yr –1) by vegetation series. Vegetation series include Douglas-fir (DF), grand fir (GF), subalpine fir (SAF), western hemlock (WH) and western red cedar (WRC).
Figure 2d—Control plot growth rate ft�ac –1yr –1) by base parent material. Parent materials include basalt, glacial deposit (glacial), granite, metasedi-mentary (metased), sedimentary (sed), modern sedimentary deposits (mod sed) and tertiary sedimentary deposits (tert sed).
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onsitesonwesternredcedarseriescomparedtositesonDouglas-firandgrandfirseries(fig.3b).Whenarrayedbyparentmaterial(fig.3c),siteswithashcapsonbasaltandmetasedimentaryparentmaterialsaveragedhigherpotentialwateravailabilitythanthoseongraniteandglacialtillparentmaterials.However,whenashwasabsent,sitesonglacialtillparentmaterialshadhigherpotentiallyavail-ablewaterthansitesonmetasedimentaryorgraniticrocks.
Soil Acidity—SoilpHdatawereavailablefor135sites.Overall,pHincreasedwithincreasingashdepth.VegetationserieshadasignificanteffectonpH,withsitesonsubalpinefirserieslessacidthanthoseongrandfirorDouglas-firseries,whichinturnwerelessacidthansitesonwesternredcedarorwesternhemlockseries (fig. 4a). Parent material also affected soil pH, but interacted with ash
Figure 3a—Control plot growth rate ft�ac –1yr –1) and Douglas-fir site index (ft at �0 years) as a function of potential available water (inches) in the upper 24 inches of soil.
Figure 3c—Potentially available water (inches) in the upper 24 inches of soil as a function of ash depth (inches), by base parent material. Parent materials include basalt, glacial deposit (glacial), granite and metasedimentary (metased).
Figure 3b—Potential available water (inches) in the upper 24 inches of soil as a function of ash depth (inches), by vegetation series. Vegetation series include Douglas-fir (DF), grand fir (GF) and western red cedar (WRC).
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depth(fig.4b).Soilaciditydecreasedwithincreasingashdepthongraniteandperhapsbasaltparentmaterials,andincreasedwithincreasingashdepthonter-tiarysediments,butshowedlittlevariationwithashdepthonotherunderlyingparentmaterials.Intheabsenceofash,soilaciditywasaboutthesameforallunderlyingparentmaterials.
Nitrogen—Soil mineralizable N data were available for 119 sites, whileammonium-Ndatawereavailable for45sitesandnitrate-Ndata for44sites.Noneof these threemeasuresofsoil-availableNvariedwithashpresenceordepth.However,twoofthevariables,soilmineralizableNandammonium-N,variedbyparentmaterial(fig.5aand5b).Bothmeasuresshowedhighervaluesonmetasedimentaryandtertiarydepositparentmaterials,andlowervalueson
Figure 4a—Soil pH by vegetation series. Vegetation series include Douglas-fir (DF), grand fir (GF), subalpine fir (SAF), western hemlock (WH) and western red cedar (WRC).
Figure 4b—Soil pH as a function of ash depth (inches) and base parent material. Parent materials include basalt, glacial deposit (glacial), granite, metasedimentary (metased), sedimentary (sed), modern sedimentary deposits (mod sed) and tertiary sedimentary deposits (tert sed).
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graniticandbasalticmaterials.InanefforttodeterminewhyparentmaterialwouldaffectsoilmineralizableN,severaladditionalstatisticalanalyseswereperformedusingdataonpercentorganicmatter(29sites)andpercentcarbon(90sites).Min-eralizableNwasstronglyandpositivelycorrelatedwithbothsoilorganicmatter(R2=0.69)andsoilcarbon(R2=0.68),suggestingthatparentmaterialcouldaffectsoilmineralizableNbyaffectingsoilorganicmatterand/orcarboncontent.
FoliarNconcentrationsofunfertilizedDouglas-firtreeswerebelowthecriticallevelof1.4%formostsites,andweregenerallyunaffectedbyashpresenceordepth.However,foliarNwasaffectedbyunderlyingparentmaterial,withtreesonbasaltparentmaterialsshowinghigherfoliarNconcentrationsthantreesonotherparentmaterialtypes(fig.5c).ExaminationofSIasafunctionoffoliarNshowedapositiverelationship(R2=0.28;fig.5d).Theslopeoftherelationshipdidnotvarybyunderlyingparentmaterial,butSIwashigherontertiarysedimentsandmetasedimentaryrocks.FoliageNconcentrationswerealsoanalyzedasafunctionofsoil-available(mineralizable)N,withtheexpectationthatfoliageNlevelswouldincreasewithincreasingsoilmineralizableNlevels.However,thecorrelationwasveryweak(R2=0.05).Amodelcombiningtheeffectsofrocktype,mineralizableNandelevationbetterdescribedvariationinfoliageN(R2=0.27),withfoliageNpositivelyrelatedtomineralizableNandnegativelyrelatedtoel-evation.Interestingly,thismodelshowedthattreesonbasalt,sedimentaryrockormodernsedimentshadhigherfoliarNconcentrationsthanthoseonglacialtillsormetasedimentaryrocks.Othersitefactorsincludingsoilfertility,soilwaterpotential,aspectandslopewerenotrelatedtofoliageN,andfoliageNdidnotvarybyvegetationtypeorgeographicregion.ThissuggestedthatunderlyingrockdidsomehowinfluencefoliageNnutrition.
Cations—Extractablecationdatafromsoilsamplesfrom119sitesindicatedthatextractableKwasnotaffectedbyashcappresenceordepth,butwasaffectedbyunderlyingparentmaterial(fig.6a).ExtractableCaandMgbothdecreasedwithincreasingashdepth(Ca:R2=0.30,fig.6bandMg:R2=0.33,fig.6c).Giventhesamedepthofash,CaandMgwerelowestonsiteswithgraniticparentmateri-alsandhighestonbasaltandmetasedimentaryparentmaterials.Incontrastto
Figure 5a—Soil mineralizable nitrogen (N, ppm) by base parent material. Parent materials include basalt, glacial deposit (glacial), granite, metasedi-mentary (metased), sedimentary (sed), modern sedimentary deposits (mod sed) and tertiary sedimentary deposits (tert sed).
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Figure 5b—Soil ammonium-nitrogen (NH4-N, ppm) by base parent material. Parent materials include basalt, glacial deposit (glacial), granite, metasedimentary (metased), sedimentary (sed), modern sedimentary deposits (mod sed) and tertiary sedimentary deposits (tert sed).
Figure 5d—Site index (ft�ac –1yr –1) as a function of ash depth (inches), by base parent material. Parent materials include basalt, glacial deposit (glacial), granite, metasedimentary (metased), sedimentary (sed), modern sedimentary deposits (mod sed) and tertiary sedimentary deposits (tert sed).
Figure 5c—Douglas-fir foliar nitrogen (N) con-centration (percent) as a function of ash depth (inches), by base parent material. Parent materials include basalt, glacial deposit (glacial), granite, metasedimentary (metased), sedimentary (sed), modern sedimentary deposits (mod sed) and tertiary sedimentary deposits (tert sed).
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soilK,Douglas-fir foliarKwasunaffectedbyunderlyingparentrock,butwasconsistentlyhigherinthepresenceofash(fig.6d).Onceashwaspresent,ashdepthhadnoeffectonfoliarK.Douglas-firfoliarCa(fig.6d)andMg(fig.6e)concentrationsbehavedsimilarlytosoilavailabilityinthatbothdecreasedwithincreasingashdepth.UnderlyingparentmaterialdidnotaffectfoliarCaorMgvalues.FoliarK,CaandMgconcentrationsweregenerallyabovenutritionalcriti-callevels(table2).
Phosphorus—Soil-availablePdatawereavailableforonly45sites.Soil-availablePwasnotaffectedbyashpresenceordepth,butwasaffectedbyparentmaterial(fig.7a),withglacialdepositsshowingthehighestPavailabilityandmetasedi-mentaryrocksthelowest.Douglas-firfoliarPvaluesweregenerallyabovecriti-callevels(table2),andwerealsounaffectedbyashpresenceordepth.FoliarPconcentrationsdifferedbyparentmaterial,andwerehighestonglacialdeposits
Figure 6a—Extractable potassium (K, cmol kg–1) by base parent material. Parent materials include basalt, glacial deposit (glacial), granite, metasedimentary (metased), sedimentary (sed), modern sedimentary deposits (mod sed) and tertiary sedimentary deposits (tert sed).
Figure 6b—Extractable calcium (Ca, cmol kg–1) as a function of ash depth (inches), by base parent material. Parent materials include basalt, glacial deposit (glacial), granite, metasedimentary (metased), sedimentary (sed), modern sedimentary deposits (mod sed) and tertiary sedimentary deposits (tert sed).
Figure 6c—Extractable magnesium (Mg, cmol kg–1) as a function of ash depth (inches), by base parent material. Parent materials include basalt, glacial de-posit (glacial), granite, metasedimentary (metased), sedimentary (sed), modern sedimentary deposits (mod sed) and tertiary sedimentary deposits (tert sed).
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Figure 6f—Douglas-fir foliar magnesium (Mg) concentration (percent) as a function of ash depth (inches), by base parent material. Parent materials include basalt, glacial deposit (glacial), granite, metasedi-mentary (metased), sedimentary (sed), modern sedimentary deposits (mod sed) and tertiary sedimentary deposits (tert sed).
Figure 6d—Douglas-fir foliar potassium (K) concentration (percent) as a function of ash depth (inches), by base parent material. Parent materials include basalt, glacial deposit (glacial), granite, metasedi-mentary (metased), sedimentary (sed), modern sedimentary deposits (mod sed) and tertiary sedimentary deposits (tert sed).
Figure 6e—Douglas-fir foliar calcium (Ca) concentration (percent) as a function of ash depth (inches), by base parent material. Parent materi-als include basalt, glacial deposit (glacial), granite, metasedimentary (metased), sedimentary (sed), modern sedimentary deposits (mod sed) and tertiary sedimentary deposits (tert sed).
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andlowestonmetasedimentaryrocks(fig.7b).NeitherfoliarPconcentrationsnorsoilPtestssuggestedanyeffectofashonPavailabilityduringthisstudy.
Sulfur, B and Cu—SufficientdatawereavailabletoperformstatisticalanalysesforavailableBandS(45sites)andCu(29sites).Givenashpresence,availableBincreasedwithincreasingashdepth(fig.8a).Therewasnoevidencethatpar-entmaterialorvegetationseriesaffectedsoilBavailability.Incontrast,availableCuwasnotaffectedbyashpresenceordepth,butdidvarybyparentmaterial,ranging from0.46ppmongranitic sites to1.03ppmonmodernsedimentary
Figure 7a—Available phosphorus (P, ppm) by base parent material. Parent materials include basalt, glacial deposit (glacial), granite, metasedimentary (metased), sedimentary (sed), modern sedimentary deposits (mod sed) and tertiary sedimentary deposits (tert sed).
Figure 7b—Douglas-fir foliar phosphorus (P) concentration (percent) as a function of ash depth (inches), by base parent material. Parent materials include basalt, glacial deposit (glacial), granite, metasedi-mentary (metased), sedimentary (sed), modern sedimentary deposits (mod sed) and tertiary sedimentary deposits (tert sed).
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deposits(fig.8b).Sulfate-Savailabilitywasnotaffectedbyash,parentmaterialorvegetationseries.
Douglas-firfoliarBvaluesincreasedwithincreasingashdepth,showinggoodagreementwithsoil-availableBtests(fig.8c).FoliarBwasalsoaffectedbypar-entmaterial,rangingfromabout23ppmongraniticrockstoabout29ppmontertiarysedimentsintheabsenceofash.FoliarCuvalues,incontrast,werenotaffectedbyparentmaterialorashpresenceordepth.FoliarBandCuvaluesweregenerallyabovenutritionalcriticallevels(table2).WhilefoliarSconcentrationswereatorabovecriticallevelmostofthetime,Swasthenextmostlikelyele-ment,afterN,toshowdeficiencylevels.
Figure 8a—Soil available boron (B, ppm) as a function of ash depth (inches).
Figure 8b—Available copper (Cu, ppm) by base parent mate-rial. Parent materials include basalt, glacial deposit (glacial), granite, metasedimentary (metased), sedimentary (sed), mod-ern sedimentary deposits (mod sed) and tertiary sedimentary deposits (tert sed).
Figure 8c—Douglas-fir foliar boron (B) concentration (ppm) as a function of ash depth (inches), by base parent material. Parent materials include basalt, glacial deposit (glacial), gran-ite, metasedimentary (metased), sedimentary (sed), modern sedimentary deposits (mod sed) and tertiary sedimentary deposits (tert sed).
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Fertilization Response
Nitrogen Fertilizer Response—Acrossallgeographicregions,baseparentma-terialsandvegetationseries,6-yeargrossvolumeresponsetoNfertilizerofstandsonash-capsiteswas49.6%greateronaveragethanfertilizerresponseofstandsonnon-ashsites.However,onceashwaspresent,ashdepthhadnoeffect.Thecombinedeffectofparentmaterialandashpresencemoreeffectivelydescribedvariationinresponsethanashcapalone.Ashpresenceincreasedvolumeresponseby87%onglacialdeposits,76%ontertiarysediments,48%onmodernsedimentsand34%onbasalts(fig.9a).Ashpresencedidnotaffectvolumeresponseonmetasedimentaryorgraniticparentmaterials.Vegetationseriesdidnotdescribeanyadditionalfertilizationresponseonceashpresencewasaccountedfor.Amodelcombiningparentmaterialandvegetationserieswasmoreeffectiveatexplain-ingvariationinresponse(fig.9b)thantheparentmaterialandashmodel.SitesonwesternredcedarvegetationseriesandbasaltorglacialtillparentmaterialsshowedthehighestNfertilizerresponse,whilesitesonDouglas-firvegetationseriesandmetasedimentaryparentmaterialsshowedthelowestresponse,withothersitesfallinginbetween.Eventhoughthisrelationshipbetweenresponseandvegetationseriessuggestedthatsoilmoisturemayaffectresponse,therelationshipbetweenvolumeresponsetoNfertilizationandpotentiallyavailablewaterintheupper24inchesofsoilwasstatisticallynonsignificant.
VolumeresponsetoNfertilizerdecreasedwithincreasingsoilmineralizableN(R2=0.34;fig.9c)andammonium-N.However,volumeresponsetoNfertilizershowednorelationshiptounfertilizedfoliarNlevels.ChangesinfoliarNcon-centrationcausedbyNfertilizationwereinverselyrelatedtounfertilizedfoliarNconcentrations(fig.9d).Inotherwords,thelowertheuntreatedfoliarNlevels,thegreaterthechangeinfoliarNresultingfromNfertilization.Neitherashpresencenordepthinfluencedthischange,thusthepresenceofashdidnotappeartoaffecttheavailabilityofappliedNtotrees.Furthermore,neithervegetationseriesnorrocktypeaffectedthefertilization-inducedchangeinfoliarNconcentration.
Figure 9a—Six-year nitrogen (N) fertilization response (ft�ac –1yr –1) by base parent material and ash cap presence. Parent materials include basalt, glacial deposit (glacial), granite, metasedimentary (metased), sedimentary (sed), modern sedimentary deposits (mod sed) and tertiary sedimentary deposits (tert sed).
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Figure 9d—Change in Douglas-fir foliar nitrogen (N) concentration (percent) following N fertilization as a function of control plot (unfertil-ized) foliar N concentration (percent).
Figure 9b—Six-year nitrogen (N) fertilization response (ft�ac –1yr –1) by base parent material and vegetation series. Parent materials include basalt, glacial deposit (glacial), granite and metasedimentary (metased). Vegetation series include Douglas-fir (DF), grand fir (GF) and western red cedar (WRC).
Figure 9c—Six-year nitrogen (N) fertilization response (ft�ac –1yr –1) as a function of soil mineralizable nitrogen (N, ppm).
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Discussion ______________________________________________________
Ash distribution
Ashpresencegenerallyexplainedthesamevariationasgeographicregion,par-entmaterialandvegetationseries.Theconfoundingwithvegetationserieswasnotunexpected.Ithaslongbeenknown,forexample,thatwesternredcedarhabitattypesarehighlylikelytohaveashcap.ItisalsoknownthatashcapismorewidelydistributedinnorthIdaho,northeastWashingtonandnortheastOregonandlesscommonlyfoundincentralWashingtonandcentralIdaho.Theconfoundingofashpresencewithunderlyingparentmaterialtypeisperhapslessintuitive,butislikelyrelatedtothegeographicdistributionofthoseparentmaterials.Siteslocatedontertiarysedimentarydeposits,metasedimentaryrocksandglacialdepositsaremorelikelytooccurinnorthIdahoandnortheastWashington,whilesiteslocatedonbasalts,granites,moderndepositsandsedimentaryrocksaremorelikelytooccurincentralWashingtonandcentralIdaho.
Site Productivity
WhileSIwasavailableforonly110sitesandCGRforall139sites, thetwovariableswerehighlycorrelated(R2=0.59),suggestingthatbothvariablesbehavedsimilarlyasdescriptorsofsiteproductivity.Forbothvariables,ashpresenceatadepthof1inchorgreatersignificantlyincreasedsiteproductivityrelativetonon-ash sites. The increasewasgreater forCGR, suggesting that this variablewasamoresensitiveindicatoroftheeffectofashpresenceonsiteproductivity.However,additionalashdepthhadnoeffectoneitherofthesiteproductivityvariables.Thus,onceashwaspresent,itdidnotappeartomatterhowdeeptheashwasintermsofpredictingsiteproductivity.
Even though potentially available water was positively correlated with ashdepthandsiteproductivity,siteproductivitywasunaffectedbyincreasingashdepth.Thismeantthatsomethingabouttheashbesidespotentiallyavailablewaterwasaffectingsiteproductivity.Decreasednutrientavailabilitywasonepossiblefactorlimitingsiteproductivity.Foliageandsoil-availableMgandCagenerallydecreasedwithincreasingashdepth.Decreasedavailabilityoftheseelementsonsiteswithdeeperashcapscouldhelpexplainthelackofacorrespondingincreaseinsiteproductivityeventhoughpotentiallyavailablewaterwashigheronsuchsites.PositiverelationshipsbetweenashandnutrientavailabilityofB,PandKsuggestedthat theseelementswerenotlikelygrowth-limitinginthepresenceofash.
Site Fertility
Soil Moisture—Potentialavailablewaterisadescriptorofthecapabilityofasitetoretainandsupplymoisturetotheplantsgrowingonthatsite.Potentiallyavailablewaterincreasedwithincreasingashdepth,asseemedreasonablebasedonourexperiencewithash-capsoils.ThefindingthatpotentiallyavailablewaterwasgreateronwesternredcedarseriesthanongrandfirorDouglas-firseriesalso seemed reasonable, given that most western red cedar sites occurred inconjunctionwithash-capsoils.However,variationinpotentiallyavailablewaterbyvegetationseriesandashdepth(fig.3b)suggestedthatsitesonwesternred
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cedarvegetationseriesstillhadhigheravailablewaterthansitesongrandfirorDouglas-fir series evenafter accounting for ash.Thus, somethingbesides ashpresenceanddepthaffectedpotentiallyavailablewaterandtheresultingvegeta-tionseries.Factorsbesidesashlikelytoaffectsoilmoistureandvegetationseriesareclimate,soiltemperatureregime,soildepth,soiltexture,parentmaterialandtopographicposition(slope,aspect,andelevation).
Someofthevariationinpotentiallyavailablewateramongparentmaterialsinthepresenceofashlikelyreflecteddifferencesinunderlyingsoiltextureaswellasashdepth.Basaltandmetasedimentaryrocksweathertofinersize-classsoilswithinherentlyhigherpotentialmoistureavailabilitycomparedtothecoarser-grainedandmorepermeable soilsderived fromgranitic rocksandglacialde-posits.However,theinteractionbetweenashpresenceandparentmaterialwaslesseasilyexplained.Sitesongraniticrocksandglacialdepositsshowedhighermoistureavailabilityintheabsenceofashthaninthepresenceofashallowashlayer(fig.3c).Sitesongraniticrocksneededabout7inchesofashandglacialsitesabout16inchesofashtoachievethesamepotentiallyavailablemoistureasthenon-ashsitesonthesesamerocktypes.Aftermeetingthesethresholdlevels,potentiallyavailablemoisturecontinuedtoincreasewithincreasingashdepthonbothrocktypes.Perhapssomedegreeofsoilmixingoccurredbetweenashandtheunderlyingresidualsoilsthatnegativelyimpactedmoisture-holdingcapacityattheshallowerashdepths.
Soil Acidity—SoilpHtendedtoincreasewithincreasingashdepth.However,acomplexrelationshipbetweenparentmaterialandashdepthsuggeststhatthisincreasewasdrivenprimarilybydatafromsitesongraniticandbasalticsubstrates,whereincreasingashdepthledtoincreasedpH.Onallotherparentmaterials,whichweresedimentaryinorigin,ashdepthhadnoeffectonsoilpH.Therea-sonsforthisbehaviorarenotentirelyclear.SoilpHlevelsoftheresearchsitesincludedinthisstudywerewithinarangewherenutrientavailabilityanduptakeofappliedfertilizerelementsshouldnotbeadverselyaffected.
Nitrogen—FoliarandsoilmeasuresofNavailabilitysuggestedthatNwasaffectedbyparentmaterial,butunaffectedbyashpresenceordepth.Soilmineraliz-ableNandavailableammonium-Nwereconsistentlyhigheronmetasedimentaryandtertiarydepositsitesandlowerongraniticandbasalticsites.Incontrast,foliaranalysessuggestedthatNuptakewasgreatestonsiteswithbasaltparentmaterials.Thissuggeststhattreesgrowingonbasaltparentmaterialswerebet-terabletotakeadvantageofsoil-availableNthantreesonotherrocktypes,orconverselythattreesonmetasedimentaryandtertiarysedimentarydepositswerelessabletoutilizesoil-availableN.
Reasonsforthecontrastingeffectsofparentmaterialonsoil-availableNpoolswerenotclearfromthisanalysis.ParentmaterialcouldpositivelyaffectNsupplybyimpartingsoiltexturalorchemicalconditionsthatareconducivetoincreasedN-mineralizationrates.Conversely,parentmaterialmaynegativelyaffectplantuptakeofNthroughintroductionofamoresignificantgrowth-limitingfactor,suchaslowmoistureavailability(affectedbysoiltexture)orlownutrientavailability(affectedbyparentmaterialmineralogy).EitherscenariocouldcontributetoanincreaseinthesoilmineralizableNpool.MineralizableNwasstronglycorrelatedwithsoilorganicmatterandsoilcarbon,suggestingthatN-mineralizationrateswerealsogovernedbyorganicmatteravailability.Climaticconditionsmayaffectorganicmatterproductionbyaffectingproductivityand/orbyaffectingconditions
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conducivetoNmineralization.WhilefoliarNwasonlyweaklycorrelatedwithmineralizableN,itwasnegativelycorrelatedwithelevation,suggestinggreaterNavailabilityonwarmer,lowerelevationsites.Othersitefactorsincludingsitefertility,soilwaterpotentialandtopographicfactorshadnoeffectonfoliageNconcentrations.
Cations—LikeN,cationswerealsoaffectedbybaseparentmaterials,thoughinamorepredictablefashion.Intheabsenceofash,soil-extractableCaandMgconcentrationsintheupper12inchesofsoilwerehigheronbasaltparentmaterialsandlowerongranites.BecausebasaltsarehigherinCa-andMg-bearingmineralsthangranites,thisfindingisplausible.However,onceashwaspresent,availableCaandMgdecreasedwithincreasingashdepthonbothbasaltsandgranites.ThissuggeststhatCaandMgstorageinashispooreveninthepresenceofCa-andMg-richunderlyingparentmaterials,andthatsoilCaandMgavailabilitymaybeloweronsiteswithdeeperashcaps.Thismayreflectthedilutionofresidualsoilswithincreasingashpresence,andaresultingdilutionofCaandMgpoolsintheupper12inchesofsoil.Foliarchemistryalsosuggestedthatplantuptakeofbothelementsdecreasedatincreasingashdepths.
IncontrasttoCaandMg,soil-extractableKwasunaffectedbyashpresenceordepth,andwasonlyaffectedbyparentmaterial.Theparentmaterialeffectwasdrivenbybasalt,whichshowedhigherextractableKthanotherrocktypes.However,foliarKwasunrelatedtoparentmaterial,andwaspositivelyaffectedbyashpresence(butnotaffectedbydepth).Thelackofarelationshipbetweensoil-extractableKandfoliarKcouldindicatethateitherthesoilorfoliartestforKwasinadequate.TheseresultscouldalsosuggestthatashpresencesomehowfacilitatedtreeuptakeofK,eventhoughsoil-extractableKappearedunaffectedbyashpresence.ThismayalsobeanindicatoroflowcationretentionbyashsoilsandthehighmobilityoftheK+ion.
Phosphorus—DespiteconcernsofpossiblePadsorptionbyashsoils,soilandfoliartestssuggestedthatPavailabilityanduptakewereunaffectedbyashpresenceordepth.Onallsites,foliarPconcentrationswereatorabovenutritionalcriticallevels,suggestingthatsufficientPwasavailablefortreegrowthandfunction.
Boron, Cu and S—Boronshowedincreasingsoilavailabilityandfoliarconcen-trationwithincreasingashdepth.ThispositiverelationshipsuggeststhatashmayprovideefficientstorageforB,andalsothatashdoesnotadsorbBtoanextentthatmakestheBunavailableforplantuptake.AshdidnotaffectsoilorfoliarCuvalues.Soil-availableCushowedsomevariationbyparentmaterialthatwaslikelyrelatedtotracemineralsinthevariousparentmaterials.However,therewaspooragreementbetweensoil-availableandfoliarCuconcentrationsinthatfoliarCushowednocorrespondingparentmaterialeffect.Soil-availableSwasunaffectedbyashpresenceordepth,orbyparentmaterial.
Fertilization Response
Nitrogen—Overall,volumegrowthresponsetoNfertilizationwasmuchbetteronsiteswithashthanonsiteswithout.IncludingbaseparentmaterialinthemodelwithashcontributedanadditionaldegreeofpredictabilityofvolumeresponsetoNfertilization.Ashwasparticularlyvaluableinincreasingfertilizationresponseonthesedimentarydeposits(includingglacialdeposits)andsomewhatlesssoonthebasalt,graniteandmetasedimentaryrocks.
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TherelationshipoffertilizationresponsetosoilmineralizableNsuggestedthatthelowerthemineralizableN,thehigherthefertilizationresponse.Thissupportsthe idea thatN-deficient sites should showahigherdegreeof response toNfertilization.Similarly,thechangeinfoliarNconcentrationfollowingfertilizationshould indicate theeffectivenessof the fertilization treatment inchanging theamountofNavailabletothetreesforgrowth.However,unfertilizedfoliarNcon-centrations,whileinverselyproportionaltothechangeinfoliarNconcentrationfollowingNapplication,didnotshowanyrelationshiptofertilizationresponse.Thus,whilelowerfoliarNlevelswerepredictiveofagreaterincreaseinfoliarNafterfertilization,theywerenotnecessarilypredictiveofagreaterNfertilizationresponse.IncreasesinfoliarbiomassfollowingNfertilizationhavebeenshowntobemorepredictiveoffuturevolumeresponsethanchangesinNconcentrationalone(WeetmanandFournier1986;HasseandRose1995;Brockley2000).
Sulfur and K—SiteswithashgenerallyrespondedbettertoSfertilizationthanthosewithout.However,onceashwaspresent,thetrendwasdecreasingresponsewithincreasingashdepth,suggestingpossibleSadsorptionbyash-capsoils.Noevidencewas foundtosuggest thatashpresenceaffectedgrowthresponseorfoliarKstatusfollowingKfertilization.
Nutritional Characteristics of Ash
Anionadsorptionmaybeanissueofconcerninashsoilsduetothecharacter-isticvariablechargeofash(McDanielandothers2005;Kimseyandothers2005).ThedecreaseintreegrowthresponsetoSfertilizationwithincreasingashdepthsuggestspossiblesulfateretentionbyashsoils.HowevernoevidenceofnitrateretentionappearedfollowingNapplicationasureaorammonium.Foliar testssuggestedthatappliedNwastakenupbythetrees,and6-yeargrowthresponsesuggeststhatN-fertilizationdidincreasebiomassandvolumeproduction.Phos-phorusandBwerenotappliedduring these fertilization trialsbecause foliagetestsindicatedthattheseelementswerenotdeficient.Ourresultsalsosuggestedthatashdidnothaveanyeffectonsoil-availableorfoliarP,implyingthatPisnotlikelyagrowth-limitingelementonash-capsoils.Boronavailabilityappearedtoincreasewithincreasingashdepthaccordingtobothsoil-availableandfoliagetests.WhileinsufficientdatawereavailabletotestforthefateofBfollowingap-plication,Badsorptiondidnotseemtobeagrowth-limitingcharacteristicofashsoilsduringthisanalysis.
Theinabilityofpure,unweatheredashtostoreandsupplycationsmayalsobeanissueofconcerninandicsoils(McDanielandothers2005).Despitethedegreeofmixingandweatheringexhibitedbytheash-capsoilsinourstudy,storageandsupplymaystillhavebeenanissueforMg2+andCa2+.Bothelementsshoweddecreasedsoilavailabilityandfoliarconcentrationwithincreasingashdepth.ThisoccurredevenwhentheunderlyingparentmaterialswerehighinCaandMg,suggestingpossibledilutionofresidualsoilnutrientpoolsbyash.Incontrast,soil-extractableKwasunaffectedbyashpresenceordepth,andwasonlyaffectedbyparentmate-rial.Thus,ashsoilsappearedcapableoftakingontheKcharacteristicofunderlyingparentmaterial,butnottheCaorMgcharacteristic.ThiscouldoccurbecauseK+isamoremobileionandislikelytobetakenupbyplantsanddepositedonthesoilsurface.Also,foliarKwaspositivelyaffectedbyashpresence,suggestingthatashsoilswerebetterabletosupplyK,thoughnotnecessarilystoreit,comparedtonon-ashsoils.Thus,cationstorageandsupplyornutrientpooldilutionofthe
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divalentcationsappearedpotentiallyproblematicinashsoils,whilethemonovalentKionwaslessaffectedbyashretentionanddilutionissues.
Management Recommendations _________________________________Site Nutrition and Nutrient Management
“Nutrient management” refers to silvicultural activities as they affect thenutrientcapitalofaforeststand.Itcanincludefertilizationtreatmentsandac-tivitiesthatretainnutrientsonsiteduringsilviculturalactivities.Becausemostnutrientsareheldinlimbsandfoliage(Coleandothers1967;Pangandothers1987;Millerandothers1993;Moller2000),aconservativenutrientmanage-mentstrategywouldbetoleavethetopsandlimbsofharvestedtreeson-sitethroughavarietyofbole-onlyharvestingtechniques.Whole-treeoperationsinlatefallandwinter,whenbreakageismorelikely,shouldalsobeeffectiveatretainingsomenutrientsonthesite.Speciesdifferinnutrientdemand(Gordon1983;Gowerandothers1993;Millerandothers1993;Mooreandothers2004).Therefore,plantingnutritionallychallengedsiteswithless-demandingspeciesand favoring less-demanding species during silvicultural operations are alsoconservativenutrientmanagementstrategies.
Testsoffoliageandsoilchemistrymaybeperformedassitespecificindicatorsofproductivityandpotentialfertilizationresponse.FoliarNwasabetterpredictorofsiteproductivity,whilesoilmineralizableNwasabetterpredictoroffertilizerresponse.Ifsatisfactoryinformationonsiteproductivityisavailableandtheparentmaterial/ashcombinationsuggeststhatthesitemayberesponsivetofertilization,managersshouldconsiderfocusingontestsofsoilmineralizableN.Ifmineraliz-ableNisbelow70ppm,thesiteshouldshowa6-yearvolumeresponseof10%ormore,withthepotentialresponseincreasingasmineralizableNdecreases.FoliarNmaybetestedasanindicatorofoverallsiteproductivity;however,theeffortandexpenseofthistestmakeitlessdesirablethanperformingsimplesiteheight/agemeasurements.
Nutrient Management Recommendations by Parent Material and Ash Presence
Basalts, Glacial and Modern Deposits—Sitesonbasalts,glacialdepositsandmodern sedimentarydeposits showednochange in siteproductivity in termsofCGRinthepresenceofash.Howeverthesesitesdidshowmoderate(basaltandmodernsedimentary)tohigh(glacialdeposit)increasesinvolumegrowthresponsestoNfertilizationwhenashwaspresent.ThissuggeststhatsitesontheseparentmaterialsshouldrespondreasonablywelltoNfertilizationwithoutash,andrespondevenbetterwhenashispresent.Therewasweakevidencethatonbasaltparentmaterials,thepresenceofashinhibitedvolumeresponsetoSfertiliza-tion.However,otherIFTNCstudieshaveshownthatSissometimesnecessarytostimulateagrowthresponsetoNfertilizationonbasaltparentmaterials(Garrisonandothers2000).WhileallparentmaterialsinthiscategoryshouldrespondwelltofertilizationwithNonly,strongergrowthresponsesmightbeinducedbymulti-nutrientfertilizationthatincludesS.Conservativenutrientmanagementstrategiesshouldbeevaluated,butmaybelesscrucialontheseparentmaterialscomparedtootherparentmaterials.
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Ash Cap Influences on Site Productivity and Fertilizer Response in Forests of the Inland Northwest Garrison-Johnston, Mika, Miller, Cannon, and Johnson
Metasedimentary and Granite—Metasedimentaryparentmaterials showedrelatively lower site productivity and granites showed moderate productivitycomparedtootherparentmaterials.Siteproductivityincreasedinthepresenceofashonbothparentmaterialtypes,withmetasedimentaryproductivitydoublingintermsofCGR.However,N-fertilizerresponsewasunaffectedbyashpresenceforeitherparentmaterial.Thissuggeststhat(1)treesgrowbetteronmetasedimentaryandgraniticrockswhenashispresent,and(2)fertilizationwithNalonewillnotincreaseproductivityonashsitesoverthatofnon-ashsitesonmetasedimentaryorgraniticrocks.TherewasweakevidencethatmetasedimentaryandgraniticsiteswithashmayrespondpositivelytoSfertilization.Preliminaryresultsofre-centfertilizationscreeningtrialsonbothparentmaterialtypesshowedgenerallypoorgrowthresponsetofertilizationwithNalone,andstrongerresponsetoacombinedtreatmentofN,K,S,andBwhenashwaspresent(Garrison-Johnstonandothers2005,unpublisheddata).Thus,multinutrientfertilizationismorelikelytostimulategrowthresponseonashsoilsonmetasedimentaryandgraniticparentmaterials.Generalnutritionalchallengesofthesesitessuggestuseofconservativenutrientmanagementstrategies.
Tertiary Sedimentary Deposits—Tertiarysedimentaryparentmaterialsbehavedsomewhatdifferentlythantheotherparentmaterialsinthatbothsiteproductiv-ityandNfertilizationresponsewereenhancedinthepresenceofash.Becausetheavailabledatafortertiarysedimentarysiteswassparse,theseresultsforthisdeposittypeshouldbeviewedcautiously.However,thissuggeststhatifstandsontertiarysedimentsaregrowingwell,theyshouldrespondwelltoNfertilizationintheabsenceofash,andevenbetterwhenashispresent.Somecautionshouldbeexercisedinapplyingfertilizer,however,asfieldexperiencehasalsoshownthattertiarysedimentarydepositscaninherentlybequitevariableincomposition.Pendingfurtherinvestigation,useofconservativenutrientmanagementstrategiesisalsorecommended.
Conclusions _____________________________________________________Standproductivitywasgreateronsiteswithashcapthanonsiteswithout;how-
everonceashwaspresent,changesinashdepthdidnotaffectsiteproductivity.Becauseashpresenceorabsencetendedtocoincidewithparticularvegetationseriesandgeographicregions,ashpresencedidnotfurtherexplainvariationinsiteproductivitybeyondthatdescribedbythosevariables.Whileashpresencealsotendedtocoincidewithparticularparentmaterialtypes,ashpresencestillexplainedsomevariation insiteproductivitybeyond thatexplainedbyparentmaterial.Ashpresencewasmostlikelytoincreasesiteproductivityonmetasedi-mentaryrocks,granitesandperhapstertiarysediments.
Althoughsiteproductivitywaspositivelycorrelatedwithpotentiallyavailablewaterandpotentiallyavailablewaterwaspositivelycorrelatedwithashdepth,therewasnocorrelationbetweensiteproductivityandashdepth.Thissuggeststhatsomethingelseabouttheash,suchaspoornutrition,affectedproductivity.Soil-availableandfoliarMgandCadecreasedwithincreasingashdepth.Thus,whileincreasingashdepthmayhaveapositiveeffectonsoilmoisturepotential,itmayhaveanegativeeffectonnutrientavailability,particularlyforMgandCa,andthereforeonsiteproductivity.
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SoilNavailability (mineralizableandammonium)and foliageNconcentra-tionswerenotaffectedbyashpresenceordepth,butwereaffectedbyparentmaterial.Reasonsfortheparentmaterialeffectwerenotentirelyclear,howeverthesiteproductivityandsoil texturalandchemicalconditionsassociatedwithparticularunderlyingparentmaterialslikelyaffectedorganicmatterproductionandcycling.SoilorganicmatterandcarboncontentwerehighlycorrelatedwithsoilNavailability.ClimateandelevationlikelyinteractedwithparentmaterialstohaveaneffectonNavailability,aswell.
Possiblenutrientadsorptionandsupplybyashwerealsoconsidered.AdsorptionofappliedNdidnotappeartooccurinash-capsoilsinthisstudy.Incontrast,decreasing growth response to S-fertilization at greater ash depths suggestedthatadsorptionofappliedSmayhaveoccurred.Foliageandsoil-availabilityofPandBeithershowednochange(P)orincreasedavailability(B)withincreasingashdepth,suggestingthatavailabilityoftheseelementsmaynotbeanissueofconcerninash-capsoils.LackofsoilMgandCastorageandsupplyatgreaterashdepths,orperhapsdilutionofMgandCasupplybyincreasingquantitiesofash,didappeartooccur.SoilKwasunaffectedbyashpresenceordepth,whilefoliarKconcentrationsincreasedwhenashwaspresent,suggestingthatKsupplywasperhapsenhancedbyashpresence.
Averagevolumeresponse toN fertilizationwasalmost50%greateronashcomparedtonon-ashsites.Howeverchangesinashdepthdidnotfurtheraffectvolumeresponse.AshpresenceincreasedvolumeresponsetoNfertilizationonglacialdeposits, tertiarysediments,modernsedimentsandbasalts,butnotongraniteormetasedimentaryparentmaterials.Volumeresponsewasgreatestonwesternredcedarvegetationseries,followedbygrandfirandthenDouglas-firvegetationseries.Howeverashpresenceordepthdidnotfurtheraffectvolumeresponseoncevegetationserieswasknown.Parentmaterialcombinedwithveg-etationseriesbestdescribedvolumeresponsetoN-fertilization.
References ______________________________________________________Brockley,R.P.2000.Usingfoliarvariablestopredicttheresponseoflodgepolepinetonitrogen
andsulphurfertilization.CanadianJournalofForestResearch.30:1389-1399.Brown,H.G.;Lowenstein,H.1978.Predictingsiteproductivityofmixedconiferstandsinnorth-
ern Idahofromsoilandtopographicvariables.SoilScienceSocietyofAmerica Journal.48:910-913.
Case, T. E. 1996. Sulfate-sulfur in soils. Analytical Sciences Laboratory Standard MethodsSMM.85.090.03.Moscow,ID:UniversityofIdaho.4p.
Case,T.E.;Thyssen,B.C.1996a.Availablephosphorusandpotassiuminsoilssodiumacetatemethod. Analytical Sciences Laboratory Standard Methods SMM.85.050.04. Moscow, ID:UniversityofIdaho.6p.
Case, T. E.; Thyssen,B.C. 1996b. Extractable andexchangeable cations.Analytical SciencesLaboratoryStandardMethodsSMM.85.100.03.Moscow,ID:UniversityofIdaho.4p.
Case,T.E.;Thyssen,B.C.1996c.Soilboron,pouchmethod.AnalyticalSciencesLaboratoryStandardMethodsSMM.85.060.02.Moscow,ID:UniversityofIdaho.5p.
Case,T.E.;Thyssen,B.C.1996d.Soilnitrateandammoniumnitrogenextractionmethod.Analyti-calSciencesLaboratoryStandardMethodsSMM.85.080.03.Moscow,ID:UniversityofIdaho.6p.
Case,T.E.;Thyssen,B.C.2000.Zn,Mn,Cu,Fe,Pb,Cd,NiandAsinsoils—DTPAMethod.AnalyticalSciencesLaboratoryStandardMethodsSMM.85.110.04.Moscow,ID:UniversityofIdaho.4p.
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Cole,D.W.;Gessel,S.P.;Dice,S.F.1967.Distributionandcyclingofnitrogen,phosphorus,po-tassiumandcalciuminasecond-growthDouglas-firecosystem.In:Symposiumontheprimaryproductivityandmineralcyclinginnaturalecosystems:proceedings:1967;EcologicalSocietyofAmerica,AmericanAssociationfortheAdvancementofScienceAnnualMeeting:197-232.
Garrison,M.T.;Moore,J.A.;Shaw,T.M.;Mika,P.G.2000.Foliarnutrientandtreegrowthre-sponseofmixed-coniferstandstothreefertilizationtreatmentsinnortheastOregonandnorthcentralWashington.ForestEcologyandManagement.132:183-198.
Geist, J.M.1976.ForestedrangefertilizationineasternOregonandWashington.Rangeman’sJournal.3:116-118.
Gordon,A.G.1983.NutrientcyclingdynamicsindifferingspruceandmixedwoodecosystemsinOntarioand theeffectsofnutrient removals throughharvesting. In:Wein,R.W.;Riewe,R.R.;Methven,I.R.ResourcesandDynamicsoftheBorealZone:proceedings;1982August;Thunder Bay, Ontario. Ottawa, Canada: Association of Canadian Universities for NorthernStudies:97-118.
Gower,S.T.;Reich,P.B.;Son,Y.1993.Canopydynamicsandabovegroundproductionoffivetreespecieswithdifferentleaflongevities.TreePhysiology.12:327-345.
Hasse,D.L.;Rose,R.1995.Vectoranalysisanditsusefor interpretingplantnutrientshifts inresponsetosilviculturaltreatments.ForestScience.41:54-66.
Kimsey,M.;McDaniel,P.;Strawn,D.;Moore, J.2005.Fateofappliedsulfateinvolcanicash-influencedforestsoils.SoilScienceSocietyofAmericaJournal.69:1507-1515.
McDaniel,P.A.;Wilson,M.A.;Burt,R.;Lammers,D.;Thorson,T.D.;McGrath,C.L.;Peterson,N.2005.AndicsoilsoftheInlandPacificNorthwest,USA:propertiesandecologicalsignifi-cance.SoilScience.170(4):300-311.
Miller, J.D.;Cooper, J.M.;Miller,H.G. 1993.A comparisonof above-ground componentweightsandelementamountsinfourforestspeciesatKirktonGlen.JournalofHydrology.145:419-438.
Mital,J.M.1995.Relatingsoil,vegetation,andsitecharacteristicstoDouglas-firresponsetonitrogenfertilizationintheInlandNorthwest.Moscow,ID:UniversityofIdaho.PhDDissertation.
Moller,I.S.2000.Calculationofbiomassandnutrientremovalfordifferentharvestingintensities.NewZealandJournalofForestScience.30(1/2):29-45.
Monserud,R.A.1984.HeightgrowthandsiteindexcurvesforinlandDouglas-firbasedonstemanalysisdataandhabitattype.ForestScience.30:943-965.
Moore,J.A.;Mika,P.G.1997.InfluenceofsoilparentmaterialonthenutritionandhealthofestablishedconiferstandsintheInlandNorthwest.In:Haase,D.L.;Rose,R.ForestSeedlingNutritionFromtheNurserytotheField:proceedings;Corvallis,Oregon:NurseryTechnologyCooperative,OregonStateUniversity:144-153.
Moore,J.A.;Mika,P.G.;Shaw,T.M.;Garrison-Johnston,M.T.2004.Foliarnutrientcharacter-isticsoffourconiferspeciesintheInteriorNorthwestUnitedStates.WesternJournalofAppliedForestry.19(1):13-24.
Pang,P.C.;Barclay,H.J.;McCullough,K.1987.AbovegroundnutrientdistributionwithintreesandstandsinthinnedandfertilizedDouglas-fir.CanadianJournalofForestResearch.17:1379-1384.
Webster,S.R.;Dobkowski,A.1983.Concentrationsoffoliarnutrientsfortreesandthedosagefrequencyoffertilizertrials.WeyerhaeuserResearchReportNo.1;Project050-3920/3.25p.
Weetman,G.F.;Fournier,R.M.1986.Constructionandinterpretationoffoliargraphicaldiagnostictechnique.In:Interiorforestfertilizationworkshop:proceedings;Kamloops,BritishColumbia:55-76.
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In: Page-Dumroese, Deborah; Miller, Richard; Mital, Jim; McDaniel, Paul; Miller, Dan, tech. eds. 2007. Volcanic-Ash-Derived Forest Soils of the Inland Northwest: Properties and Implications for Management and Restoration. 9-10 November 2005; Coeur d’Alene, ID. Proceedings RMRS-P-44; Fort Collins, CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station.
Han-Sup Han is an academic faculty, Forest Products Department, College of Natural Resources, University of Idaho, Moscow.
Abstract Economic implicationsof soildisturbancearediscussed in fourcategories:planningand layout,selection of harvesting systems and equipment, long-term site productivity loss, and rehabilitationtreatments.Preventivemeasuresaremoreeffectiveinminimizingimpactsonsoilsthanrehabilitationtreatments becauseof the remedial expenses, loss of productivity untilmitigationoccurs, and thepossibilitythatoriginalsoilconditionsmaynotberestored.Alternativeharvestingpracticesthataredesignedtominimizeimpactsonsoils,suchasuseofdesignatedskidtrailsandwidetrail-spacing,increaseoverallharvestingcosts.Siteswithhighriskforsoildisturbancemayrequireuseofexpensivewoodextractionmethods(e.g.,skylineyarding),asopposedtolowercostoptions(e.g.groundskidding).Tillagetreatmentsinseverelycompactedareasappeartobecosteffectiveifproperlyimplemented.Anaccurateestimationofeconomicconsequencesfromlong-termsiteproductivitylossesisdifficult,althoughthereisageneralconsensusthatsoildisturbanceatsomelocationscanreducetreegrowth.
Economics of Soil Disturbance
Han-Sup Han
Introduction
Questionsontheeconomicsofsoildisturbanceareoftenraisedregardinglong-termpro-ductivitylosses,effortstominimizesoilimpacts,andrehabilitationofdamagedsoils.Whatarepotentialfinancialimpactsfromsiteproductivitylosses?Shouldwerequireeveryground-skiddingmachineonhigh-risksitestousedesignatedskidtrailsandhowdoesthisaffectloggingcosts?Woulditbecost-effectivetoamelioratecompactedsoils?Arewefinanciallygettingasignificantbenefitfromsoilrehabilitationtreatments?Thesequestionshavenotbeenextensivelyansweredbecauseofthedifficultyinobtainingappropriatedataabouttreeresponsestositedisturbanceacrossanentirerotation,thevalueofoffsiteimpacts,andotherpertinentinfor-mationsuchaspreventiveandremediationmeasures(Lousier1990;Millerandothers2004).
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Han Economics of Soil Disturbance
Lackofinformationontheeconomicsofsoildisturbancelimitsforestpraction-ersfromattemptingtodevelopharvestingplansandtimbersales.Aharvestingplanneedstoaccountforsoildisturbancerisks,previousimpactsonsoils,andpreventivemeasuresthatminimizefurtherdamagetosoils.Preventivemeasuresmayrequirecableloggingsystemsongentleslopes(<30percent)orwiderspacingofdesignatedskidtrails,buttheseoftenresultinhigherloggingcosts.Lackofcompellingevidencetojustifythesehighloggingoptionsoftencausesdisagree-mentsamong forestmanagers,although there isageneralconsensus that soildisturbancemayreducetreegrowthatsomelocations(Millerandothers2004).Onewouldalsowonderifthesepreventivemeasureswouldfinanciallybenefitlandownersinthelongrun.
Thispapersummarizeseconomicinformationrelatedtosoilimpactsinfourcategories:planningandlayout,selectionofharvestingsystemsandequipment,long-termsiteproductivityloss,andrehabilitationtreatments.Inthispaper,soildis-turbancesincludesoilcompaction,scalping,puddling,andsoildisplacement.
Planning and Layout: Measures to Prevent Soil Disturbance _________Soildisturbancefromtimberharvestingmaynotbeavoidable,butcanbemini-
mizedthroughcarefulplanningandoperations.Preventivemeasuresaremoreeffectiveinminimizingimpactsonsoilsthanremedialmitigationbecauseoftheremedialexpenses,lossofproductivityuntilmitigationoccurs,andthepossibilitythatoriginalsoilconditionsmaynotberestored(Millerandothers2004).Exist-ingguidelinesandrequirementsforsoilprotectionshouldalwaysbeobservedwhentheharvestingplanisdeveloped.Agoodharvestplancanminimizesoildisturbance by recognizing and identifying the risk of soil disturbance. Someimportantfactorsdetermining“riskrating”includesoiltexture,moisturecontent,slope,andorganicmaterialsatthetopsoil.
Planningandlayoutcomponents for timberharvestingincludelocations forroadsandlandings,markingtreestocutorleave,andflaggingskidtrailsorsky-linecorridors.Thesevarywithdifferentharvestingsystems.Forexample,skylineyardingrequireslocatinganchorsforriggingandground-profileanalysisforavail-abledeflection,causinghigherplanningandlayoutcostsforcableloggingthanground-basedharvestingsystem.Kelloggandothers(1998)comparedplanningandlayoutcostforloggingcontractorsinvarioussilviculturaltreatments.TheyfoundthataCTLsystemusingamixofrandomanddesignatedskidtrails(60-ftspacing)hadthelowestcost,followedbythetractor-basedwinchingsystemforhand-felledtreesthatused130-ftspacingdesignatedskidtrails.Theskylinesys-temshadthehighestcost.
Useofdesignatedskidtrailshasbeenrecommendedinpastsoilcompactionstudiesbecauseiteffectivelyreducestheskidtrailareasinaharvestingunitandfacilitatesrehabilitationefforts(AndrusandFroehlich1983).Designatedskidtrailsatawidespacingincreaseloggingcosts.Inanearlierstudy(Bradshaw1979),theharvestunitwithpre-plannedskidtrailsandwinchinghada29percenthigherskidcostthantheconventionallyharvestedunit.However,only4percentofitsareawasinskidtrails,comparedto22percentfortheconventionallyharvestedunit.
Thereareotherplanningandlayoutcomponentsthatincreasecosts,butaredifficult to estimate. These include expenses related to evaluating soil distur-bancerisks, identifyingareasinthefieldthatposeahighriskforsoildamage
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anderosion,anddevelopmentstrategiesandguidelinestominimizesoilimpact.Delayingloggingoperationstodryseasonsorwinterseasonloggingandstrictrequirementsforbestmanagementpractices(BMP)areexamplesforpreventiveeffortsataplanningstage.Theseexpensesusuallyoccurintheformofoverheadoradministrativecostandcanbeestimatedbasedoncompaniesoragencies’indirectcostrates.
Selection of Harvesting Systems and Equipment ___________________Because harvest equipment creates ground pressures and soil disturbance
types(e.g.,compactionandscalping),choiceofharvestingsystemsandequip-menttypecangreatlyaffectthedegreeandextentofsoilimpacts.Cablesystemsareoftenpreferredoverground-basedsystemsbecausecableloggingdoesnotrequireheavymachinesmovingonharvestingareas.Logsarefullyorpartiallysuspendedtotheskylineandpulledtothelandings.Allen(1997)reportedthataskylinethinningoperationinwesternOregonleftonly2percentofsoildistur-bancewhileasingleentryofcut-to-length(CTL)systemcaused25percentoftheharvestareacompacted.
However,cableloggingistypicallymoreexpensivethanaground-basedsystem:cableyardingcostsare65to160percenthigherthanconventionalground-basedlogging(Lousier1990).Forexample,Keeganandothers(1995)surveyedstump-to-truckharvestcostsintheMontanaandnorthernIdahoregionandfoundthatthecostforground-basedsystemswaslowest($87to$124/thousandboardfeet(MBF)), followedbycablesystemsranging from$13 to$164/MBF.Helicoptersystemsweremostexpensiveat$233/MBF.Comparedtomechanizedground-basedsystems,cable loggingrequiresmore labor tomanuallyhandle treesorlogsonsteepgrounds(typically>30percentslope)aswellastoset-upandteardownanentireyardingsystem,whichresultsinlowdailyproductionoftimber.Timespentchangingskylineroadsandriggingalsocontributestohighcostsincable logging. High logging costs in cable logging becomes more noticeablewhenhandlingsmall-diametertrees.Ataverage10-inchdiameteratbreastheight(DBH),skylineandhelicopterstump-to-truckloggingandchippingcostswereabout3and6timesmoreexpensive,respectively,comparedwithamechanizedwhole-treeharvestingsystemthatshowedthelowestcostat$34.23/100cubicfeet(Hanandothers2004).
Cableyarding,combinedwithmechanizedfellingandprocessing,hasbeenconsideredasawayof reducing soil compactionandother typesof soildis-turbance from the ground skidding or forwarding phase of timber harvesting.Althoughmechanizedfellingandin-woodsprocessingusingafeller-buncheroraharvesterhaveinsignificantimpactsonsoils,subsequentgroundskiddingandforwardingcausesignificantincreaseinsoilbulkdensity(Allen1997).Theques-tionishowmuchmoreexpensiveitistouseskylineyardingthanground-basedskidding.Johnson(1999)reportedthatcableyarding($0.51/ft3)resultedin113percentcost increaseover forwarding ($0.24/ft3)of logs felledandprocessedbyaCTLharvester.However,theaverageforwardingdistance(212ft)forcableyardingwasmuchlongerthattheone(129ft)withforwarding.Thismaylowerthe roaddensity required for timberharvestingactivitiesand reduce theareaofsoilsdisturbed.IneasternOregon,askylineyarderwasusedtoextractlogsprocessedbyaCTLharvesterinanefforttoavoidfurtherdamagetosoilfrom
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fuelreductionthinningonslopesthataveraged12percentorlessonallunits,withmaximumsof25percent(Drewsandothers2000).Theyreportedthattheharvester-yardersystemaveragedmuchhigher($80/greenton)stump-to-millcoststhantheharvester-forwardersystem($46/greenton).
Lowground-pressuremachines,suchaslogloadersandwide-tiredskidders,forwoodextractionfromstumptolandingarealsooftenconsideredtominimizesoilcompaction.Shovelloggingusesahydrauliclogloadertorepeatedlyswingthelogstoreachtheroadorlandingarea,andhasbeenusedasanalternativetoacablesystemonmoderategrounds(20to40percentslope)oraground-basedsystemongentleslopes(<20percent).TheaverageunitproductioncostforshovellogginginwesternWashingtonwas40percentlessthantheonewithcableloggingatanaverageexternalyardingdistanceof600feet(Fisher1999).Useofaskidderequippedwithwidetirestoreducegroundpressurehasbeenusedbymachinerymanufacturersasmachineshaveincreasedinsizeandweight(Brinkerandothers1996).Paststudiesindicatedthatwidertiresresultedin13to23percentincrease(Meek1994)ornosignificantdifference(Klepacandothers2001)inskiddingcost.Klepacandothers(2001)alsonotedthatloggersarere-luctanttousewidetiresbecauseofadditionaloverhangduringmachinetransportfromonesitetoanother,andrequirementforahighertorque,heavy-dutyrearaxleintheskidder.
Whenselectingamechanized,ground-basedsystemfortimberharvesting,aCTLsystemisoftencomparedwithawholetreesystemconsistingofafeller-buncher,skidder,aprocessor,andaloaderforitsharvestingproductivityandcost.Whileproductionratesandcostsforthesetwosystemsarecomparable(Hartsoughandothers1997;LanfordandStokes1996;Gingras1994),impactsonsitescandif-fersignificantly(LanfordandStokes1995;Gingras1994).ACTLsystemisoftenfavoredoverawhole-treeharvestingsystembecauseaharvesterprocessestreestologlengthatthestump,leavingallbranchesandtreetopsonsite.Aforwarderdrivesovertheslashmat,andthishelpstominimizeimpactsonsoils.
Long-term Site Productivity Losses _______________________________Aconcernforsiteproductivitylossesaftersoildisturbancefromtimberharvesting
activitiesisaprimaryreasonforimposingstrictrequirementsforsoilprotectioninthecontextofsustainableforestry.Somestudieshaveshownthatsoilcompactionadverselyimpacttreegrowth.However,estimationofactualorpossibleproductivitylossesresultingfromsoildisturbanceisacomplicatedissuebecauseofdifficultiesofaccurateestimationofsoildisturbancesconsequencesontreegrowth(Millerandothers2004;Heningerandothers2002;Lousier1990;Helmsandothers1986).Millerandothers(2004)suggestedthatforecastsofreducedtimberyieldfromdegradedsoilsareuncertainbecausetreeresponsetosoildisturbanceisgreatlyaffectedbyothersite-specific,growth-determiningfactors.
In addition to tree’s biological and physical responses to soil disturbances,discountratesalsohavesignificantimpactontheoveralleconomicanalysisofsoildisturbances;theanalysisperformsovertheentiretreerotationperiodanddiscountratesaregreatlysensitivetotime.Stewartandothers(1988)developedaneconomicmodel thataddressed financial impactsofsoilcompactiononalong-termbasis.Themodeluseda stand-growth simulatorand includedvari-ousscenariosofmanagementoptions.Ata4percentdiscountrate,net-presentvalueanalysisshowedpositivevalues,thusencouragingpreventiveefforts(wide
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trailspacing)andindicatinghigheraffordabilityforcarefullogging.Underanas-sumptionthattreeyieldwasreducedon100percentofskidtrailareas,thenetpresentvalue(NPV)with4percentwas$504/acwhileitwas$144/acwith8percentdiscountrate.Onecouldaffordtospendanextra$144/actoavoidtheseyieldreductions.
Rehabilitation ___________________________________________________Soilrehabilitationinvolvesmechanicalmeasures(e.g.tillage)tobreakupse-
verelycompactedsoils.Ithelpspromotewaterandairmovement(AndrusandFroehlich1983)andincreasenutrientavailability(Millerandothers2004)inacompactedsoil.Theefficacyoftillageinlooseningcompactedsoilsdependsonequipmenttypesusedandsoilproperties(UngerandCassel1991;AndrusandFroehlich1983),numberofmachinepasses(AndrusandFroehlich1983),andtillagedepth (McNabbandHobbs1989).Theoverallcostof tilling isdirectlyinfluencedbythesefactors.
AndrusandFroehlich(1983)studiedproductionratesandcostsforskid-trailtillageatselectedsitesinOregonandWashington.Fourtypesoftillageequipmentwereevaluatedinthestudy:diskharrow,rockripper,brushblade,andwingedsubsoiler.Productionrateswerehighestwhentillingwithonepassofthemachine.Uphilltillingonsteepgroundsrequiredalargecrawlertractoratahighermachinecost.Thewinged subsoiler lossenedmore than80percentof thecompactedsoilinasinglepassandwasthemostcost-effectivetillagemethod(fig.1).Theauthorsindicatedthattillageresultsforthesesiteswouldhaveimprovedifthetill-ageimprovementhadmadeadditionalpassesalongtheskidtrails,butadditionalpasseswouldincreasethecostoftilling.
Figure 1—Tillage costs and rates for various type of tillage equipment (Andrus and Froehlich 19��)
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Ifproperlyimplemented,tillagemaybecost-effectiveunderthemostextremecompaction situations, such as landing areas and heavily traveled skid trails.Stewartandothers(1988)estimatedthejustifiableincreasedcostforhigh-costloggingorrehabilitationperharvestentrywith125-ftskidtrailspacing.Thenetfinancialbenefitfromtillagewasnotablyaffectedbydiscountratesandsiteindexandrangedfrom$86/acto$284/ac.Thisrangeofjustifiablecostsis farmorethanacostestimate($20/acor$176/mile)forskidtrailrestorationwithawingedsubsoilermountedbehindCatD6Ccrawlertractor(FroehlichandMiles1984).
Conclusion ______________________________________________________Economicsofsoildisturbanceiscomplicatedandrequiresmeasuringeconomic
consequencesfromlong-termsiteproductivitylossesandexpensesforpreventiveandrehabilitationmeasures.Anaccurateestimationofsoildisturbancesconse-quencesontreegrowthisdifficultbecausethetree’sresponsetosoildisturbanceisaffectedbyothersite-specific,growth-determiningfactors.Manyassumptionsareneededtoestimatefuturegrowthandyieldandthesegreatlyaffectoverallfinancialanalyses.Althoughdirectcostsforpreventionandrehabilitationcanbeestimated,directandindirectfinancialbenefitsfromthesepracticesarenotwelldocumented.Majoruncertaintiesoriginatefromtherequirementforlong-termeconomicanalysisofunknownbiologicalimpactsfromsoildisturbanceandin-consistentdiscountratesusedintheanalysis.
Preventivemeasuresaremoreeffectiveinminimizingimpactsonsoilsthanrehabilitationtreatmentsbecauseofremedialexpenses,lossofproductivityuntilmitigationoccurs, and thepossibility that original soil conditionsmaynot berestored.Carefulplanningand layoutandselectionofharvestingsystemsandequipmentoftenincreaseoverallharvestingcosts.Alternativeharvestingprac-ticesthataredesignedtominimizeimpactsonsoils,suchasuseofdesignatedskidtrailsandwidetrailspacing,increaseoverallharvestingcosts.Rehabilitationexpensesareadditionaltotheseincreasedcosts.However,theseinitialexpensescanbejustifiedwhenpreventiveandrehabilitationmeasuresarefocusedonhighrisksitesandseverelydisturbedareas.Expensesforcarefulplanningandlayout,alternativeloggingpracticesandrehabilitationmeasuresshouldberecognizedaspartofoverallloggingcostestimationtosupporttheideaofminimizingimpactsonsoils.
Literature Cited __________________________________________________Allen, M. M. 1997. Soil compaction and disturbance following a thinning of second-growth
Douglas-firwithacut-to-lengthandaskylinesysteminOregoncascade.Corvallis,OR:OregonStateUniversity.105p.MSthesis.
Andrus,W.C.;Froehlich,H.A.1983.AnevaluationoffourimplementsusedtotillcompactedforestsoilsinthePacificNorthwest.Res.Bulletin45.Corvallis,OR:OregonStateUniversity.12p.
Bradshaw,G.1979.Preplannedskidtrailsandwinchingversusconventionalharvestingonapartialcut.Res.Note62.Corvallis,OR:OregonStateUniversity.4p.
Brinker,R.W.;Klepac,J.F.;Stokes,B.J.;Roberson,J.D.1996.Effectoftiresizeonskidderproduc-tivity.In:ProceedingsofaJointConferenceoftheCanadianWoodlandsForum,theCanadianPulpandPaperAssociation, and the InternationalUnionof ForestResearchOrganizations;1996September9-11;QuebecCity,Quebec.Montreal,Quebec:CanadianPulpandPaperAssociation:85-89.
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Drews, E. S.; Doyal, J. A.; Hartsough, B. R.; Kellogg, L. D. 2000. Harvester-forwarder andharvester-yardersystemsforfuelreductiontreatments.Int.J.ofFor.Eng.12(1):81-91.
Fisher,J.1999.Shovellogging:costeffectivesystemsgainsground.ProceedingsofInternationalMountain Logging and10th PacificNorthwest Skyline Symposium;1999March28-April 1;Corvallis,Oregon:61-67.
Froehlich,H.A.;Miles,D.W.R.1984.Wingedsubsoiler tillscompacted forestsoil.For. Ind.111(2):42-43.
Gingras,J.-F.1994.Acomparisonoffull-treeversuscut-to-lengthsystemsintheManitobaModelForest.ForestEngineeringInstituteofCanada.SpecialReport,SR-92.16p.
Han,H.-S.;Lee,H.W.;Johnson,L.R.2004.Economicfeasibilityofanintegratedharvestingsystemforsmall-diametertreesinsouthwestIdaho.For.Prod.J.54(2):21-27.
Hartsough,B.R.;Drews, E. S.;McNeel, J. F.;Durston, T.A.; Stokes,B. J. 1997.Comparisonof mechinized systems for thinning ponderosa pine and mixed conifer stands. For. Prod. J.47(11/12):59-68.
Helms,J.A.;Hipkin,C.;Alexander,E.B.1986.EffectsofsoilcompactiononheightgrowthofaCaliforniaponderosapineplantation.West.J.Appl.For.1(4):104-108.
Heninger,R.;Scott,W.;Dobkowski,A.;Miller,R.;Anderson,H.;Duke,S.2002.Soildisturbanceand10-yeargrowthresponseofcoastDouglas-fironnontilledandtilledskidtrailsintheOregonCascades.Can.J.For.Res.32:233-246.
Johnson,L.R.1999.Combiningcut-to-lengthandcableyardingoperation.ProceedingsofInter-nationalMountainLoggingand10thPacificNorthwestSkylineSymposium;1999March28-April1;Corvallis,Oregon:42-52.
Keegan,C.E.;Fiedler,C.E.;Wichman,D.P.1995.CostsassociatedwithharvestactivitiesformajorharvestsystemsinMontana.For.Prod.J.45(7/8):78-82.
Kellogg,L.D.;Milota,G.V.;Stringham,B.1998.Loggingplanningandlayoutcostsforthinning:experiencefromtheWillametteYoungStandProject.Res.Contribution20.OregonStateUni-versity,CollegeofForestry.12p.
Klepac, J.; Stokes,B.;Roberson, J.2001.Effectof tire sizeon skidderproductivityunderwetconditions.Int.J.ofFor.Eng.12(1):61-69.
Lanford,B.L.;Stokes,B. J.1995.Comparisonof two thinning systems.Part1.Standand siteimpacts.For.Prod.J.45(5):74-79.
Lanford,B.L.;Stokes,B.J.1996.Comparisonoftwothinningsystems.Part2.Productivityandcost.For.Prod.J.46(11/12):47-53.
Lousier, J.D.,comp.1990. Impactsof forestharvestingandregenerationon forestsites.LandManagementReport67.Victoria:BritishColumbiaMinistryofForests.90p.
McNabb,D.H.;Hobbs,S.D.1989.Shallowtillagefailstoincrease5-yeargrowthofponderosapineseedlings.NorthwestScience.63:241-245.
Meek,P.1994.Acomparisonoftwoskiddersequippedwithwideandextra-widetires.FieldNoteNo.:Skidding/Forwarding-28.ForestEngineeringInstituteofCanada.48p.
Miller,R.E.;Colbert,S.R.;Morris,L.A.2004.Effectofheavyequipmentonphysicalpropertiesofsoilsandonlong-termproductivity:Areviewofliteratureandcurrentresearch.TechnicalBulletinNo.887.ResearchTrianglePark,NC:NationalCouncilforAirandStreamImprove-ment(NCASI),Inc.76p.
Stewart,R.;Froehlich,H.;Olsen,E.1988.Soilcompaction:aneconomicmodel.West.J.Appl.For.3(1):20-22.
Unger,P.W.;Cassel,D.K.1991.Tillageimplementdisturbanceeffectsonsoilpropertiesrelatedtosoilandwaterconservation:Aliteraturereview.SoilandTillageResearch.19:363-382.
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In: Page-Dumroese, Deborah; Miller, Richard; Mital, Jim; McDaniel, Paul; Miller, Dan, tech. eds. 2007. Volcanic-Ash-Derived Forest Soils of the Inland Northwest: Properties and Implications for Management and Restoration. 9-10 November 2005; Coeur d’Alene, ID. Proceedings RMRS-P-44; Fort Collins, CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station.
D. E. Ferguson is a research forester, Rocky Mountain Research Station, Moscow, ID. J. L. Johnson-Maynard and P. A. McDaniel are soil scientists, Soil & Land Resources Division, University of Idaho, Moscow, ID.
Abstract TheGrandFirMosaic(GFM)ecosystemisfoundonash-capsoilsinsomemid-elevationforestsofnorthernIdahoandnortheasternOregon.HarvestingonGFMsitesresults insuccessionalplantcommunities that are dominated by bracken fern (Pteridium aquilinum) and western coneflower(Rudbeckia occidentalis),andhavelargepopulationsofpocketgophers(Thomomys talpoides).SuccessiontotreesandshrubsisveryslowondisturbedGFMsites.Fourfactorscontributetotheprotractedstagesofbrackenfernplantcommunitiesandtheslowrateofsuccessiontowoodyplants:(1)competitionamongplantsforsiteresources,(2)allelopathyfrombrackenfernandwesternconeflower,(3)pocketgopheractivity,and(4)anonallophanicsoilformingprocess.Nonallophanicsoilsoccurunderthebrackenfernsuccessionalplantcommunities—theyaredominatedbyAl-humuscomplexes,havestronglyacidpH,havehighKCl-extractableAl,andmaycauseAltoxicitytoplants.Allophanicsoilsoccurunderforestedconditions—theyaredominatedbyallophaneandimogolite,haveweaklytomoderatelyacidpH,andhavelowAlavailability.Allophanicandnonallophanicsoilsexistside-by-sideintheGFM,withmineralogybeingdependentuponthedominantvegetation.Brackenfernandwesternconeflower,withbelow-groundcarboninputsfromtheirwell-developedrootsystems,provideamechanismthatpromotestheshiftfromallophanictononallophanicsoils.RecommendationsforreforestingGFMsitesareprovided.
The Grand Fir Mosaic Ecosystem—History and Management Impacts
D. E. Ferguson, J. L. Johnson-Maynard, P. A. McDaniel
Introduction
ImagineamoistforestenvironmentinthenorthernRockyMountainswheresupposedlyseralplantcommunitiesdominatedbybrackenfern(Pteridium aquilinum)andwesternconeflower(Rudbeckia occidentalis)arereallyclimaxplantcommunitiesthatpersistwithinamatrixofovermaturegrandfir(Abies grandis)andwesternredcedar(Thuja plicata)forests.Therearefewwildfireshere,sonaturalsuccessionhasreducedtheoccurrenceofseralconiferssuchaslodgepolepine(Pinus contorta),Douglas-fir(Pseudotsuga menziesii),westernwhitepine(Pinus monticola),andwesternlarch(Larix occidentalis).Latesuccessional,shade-tolerantspe-cieslikegrandfir,westernredcedar,Pacificyew(Taxus brevifolia),andsometimesmountain
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hemlock(Tsuga mertensiana)andsubalpinefir(Abies lasiocarpa),arecommonalongwithmid-successionalEngelmannspruce(Picea engelmannii).RegenerationofconifersinforestcanopyopeningsisaslowandunreliableprocessintheselowpHvolcanicash-capsoilsthathaveabundantpopulationsofpocketgophers(Thomomys talpoides).Disjunctandrareplantspeciesoccurinandneartheseforests, including evergreen synthyris (Synthyris platycarpa), Oregon bluebell(Mertensia bella),Dasynotus(Dasynotus daubenmirei),andCase’scorydalis(Co-rydalis caseana).ThesemoistforestsarecollectivelycalledtheGrandFirMosaic(GFM)ecosystem.
GrandFirMosaicforestsoccuronproductivevolcanicash-capsoilsinandneartheClearwater,NezPerce,andsouthernSt.JoeNationalForestsinnorthernIdaho,andtheUmatillaNationalForestinnortheasternOregon.ThenamefortheGFMcomesfromthedominantconifer(grandfir)andthevarietyofsizesandshapesofnaturalopeningsintheforestcanopy.TheGFMencompassesapproximately500,000acresatelevationsprimarilybetween4,500and5,500ft,butisfoundaslowas4,200ftandashighas6,000ft(FergusonandJohnson1996).ThemostcommonhabitattypeisAbies grandis/Asarum caudatum(grandfir/wildginger),acool,moisthabitatdefinedbyCooperandothers(1991).
SuccessionalplantcommunitiesintheGFMaredominatedbybrackenfernandwesternconeflower.Brackenfernisusuallypresentinlowdensitiesunderforestcanopies,butrapidlyexpandsfollowingdisturbance,andcanreachheightsof6ftanddensitiesof116,000frondsperacre(Znerold1979).Below-groundbrackenbiomass,primarilyrhizomesandfineroots,maybeasmuchas27,280lbsperacre(Jimenez2005).
Bracken ferngladesareplant communitiesdominatedbybracken fernandwesternconeflowerthatappeartopersistformillennia.CharcoalsamplesfoundatornearthelowerboundaryofGFMash-capswerefoundtobe1,335±75and7,755±75cal.yrsBPusingradiocarbondating(Jimenez2005).Thesecharcoalsamplessuggestthatwoodyvegetationhasbeenabsentforthousandsofyears,perhapsdatingback to the timeof ashdepositionduring theeruptionofMt.Mazama(CraterLake,OR)~7,600yrsBP(Zdanowiczandothers1999).
Pocket gophers also alter the course of secondary succession in the GFM,particularlyforplantedconifers.Entireplantationsofseedlingscanbekilledbypocketgophers.Smallseedlingsareusuallypulledfrombelowgroundintotunnelswherethewholetreeiseaten.Gophersmayeatallormostoftherootsystemoflargerseedlingsandsaplings.
OurinvestigationsontheGFMwereinitiatedbecauseofdifficultyinregen-eratingharvestedareasintheGFM.Thefirsttaskwastodefinekeyecologicalprocessesthatmightaccountforthelackofregenerationandtheabsenceofotherwoodyspecies.Researchwasplannedandimplementedtostudycompetitionand allelopathy from bracken fern and western coneflower, effects of pocketgophers,environmentalcharacteristicsof theGFMrelative toadjacent forests,andsoildevelopment.
Bracken Fern, Western Coneflower, Pocket Gopher, and Environmental Research
There isabundant researchonbracken fern fromaround theworlddealingwithallelopathy,competition,encroachmentrates,andharmtocrops,livestock,
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andhumans.Theallelopathicpotentialofbrackenfernhasbeendemonstratedbyseveralresearchers,includingStewart(1975)andGliessman(1976).TheallelopathicpotentialofbrackenfernintheGFMwasdemonstratedbyFergusonandBoyd(1988),whofoundthatmostoftheseedsthatgerminatedonsoildominatedbybrackenferndiedbeforetheseedcoatwasshed.Ferguson(1991)demonstratedallelopathicpotential forwesternconeflowerinlaboratorytests.Volatilecom-pounds(vapors)fromwesternconeflowerreducedordelayedseedgermination,andwaterextractsreducedgrowthoftheseedlingradicle.
GrowthandmortalityofplantedconifersatGFMsiteswasreportedbyFergusonand Adams (1994) and Ferguson (1999). Hand weeding of bracken fern andwesternconeflowerfromplantingsitesincreasedheightgrowthofplantedconiferseedlings.Pocketgopherskilledfrom24to59percentoftheseedlings,dependingonspecies.Oftheseedlingskilledbypocketgophers,77percentwerekilledthefirstsummer(followingspringplanting)andthefirstorsecondwinter,butfewseedlingswerekilledthesecondorthirdsummers.
EnvironmentalconditionswerestudiedbyFergusonandByrne(2000)toseeiftheydifferedbetweenGFMandnon-GFMsitesinthesamevicinity.RemotemonitoringstationswereusedtosampleharvestedareasataGFMsiteandthreeadjacenthabitattypes(non-GFMgrandfir,subalpinefir,andwesternredcedar).Variablessampledwerewindspeedandwinddirectionat9 ftabove thesoilsurface;precipitation;solarradiation;relativehumidityat4.5ft;airtemperatureat4.5ft;soiltemperatureonthesoilsurface,1inch,and8inchesdepth;soilwaterpotentialat1inchand8inches;andsoilpHat1inch.
Comparisonof theGFMsite tonon-GFMsites in thesamevicinityshowedthattheGFMsitehadashortergrowingseason,eventhoughoneofthesiteswasasubalpinefirhabitattype140fthigherinelevationthantheGFMsite.SnowmeltedattheGFMsiteanaverageof9dayslaterthanatthesubalpinefirhabitattype,24dayslaterthanatthenon-GFMgrandfirhabitattype,and52dayslaterthanatthewesternredcedarhabitattype.
AverageGFMsoiltemperaturesat1and8incheswerecoolerthanthenon-GFMsitesinAprilandMaybecauseoflatesnowpacksattheGFMsite.Duringtherestofthegrowingseason,theGFMsitewaswarmerthanthesubalpinefirhabitattype,butcoolerthanthegrandfirandwesternredcedarhabitattypes.
Summersoilmoistureat theGFMsitedidnotdrytothepermanentwiltingpointasoftenasthenon-GFMsites.Soilsat8inchesdriedtoawaterpotentialof–15barsinonly2of6yearsofmonitoringattheGFMsite,while–15barswasreachedduring4ofthe6monitoringyearsatthenon-GFMgrandfirhabitattype,4of5yearsatthewesternredcedarhabitattype,and5of5yearsatthesubalpinefirhabitattype.
ThemostinsightfulvariablemeasuredwassoilpHat1-inchdepth.TheGFMsitewasdifferentfromtheotherthreesitesbecausesoilpHcycledfromabout6.0inthespringto4.0inthesummerandbackto6.0inthefall(fig.1).Eachyearfor7years,soilpHwaslowerthan5.0forseveralweekstoafewmonths.AsoilpHbelow5.0isacommonlycitedthresholdwhereAltoxicityiscom-montomanycrops(Shojiandothers1993).AlaboratorystudyhasshownthatexchangeableAlincreasesexponentiallyinGFMsoilsaspHdecreasesbelow5.0(Page-Dumroeseandothers,thisproceedings).
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Ash-cap Soil Relationships _______________________________________
Allophanic and Nonallophanic Andisols
The Andisol soil order includes soils that are characterized by andic soilpropertiesthatarisefromthepresenceofsignificantamountsofnoncrystallinealuminosilicatessuchasallophaneandimogolite,Al-humuscomplexes,and/orpoorlycrystallineFeoxides(SoilSurveyStaff2003).AlackofilluvialBhorizonsindicates that theprocessof translocation isnotsignificantwithin theAndisolorder(Ugoliniandothers1988;Dahlgrenandothers1991)andclearlyseparatesAndisolsfromothersoilorderswithsimilarmineralogicalcomponents.
Andisolsarecommonlydescribedasbeingallophanicornonallophanic,de-pendingonthenatureofthemineralspresent.AllophanicAndisolsaredominatedbyallophane,imogolite,andclayminerals;areweaklytomoderatelyacid;andhavelowKCl-extractableAlandlowAlsaturation(table1)(Shojiandothers1985;Nanzyoandothers1993).NonallophanicAndisolshaveAl-humuscomplexesandcrystallineclaymineralsastheirdominantmineralogicalcomponents,andcontain
Figure 1—Average daily soil pH at 1 inch for a GFM site, 19�9 through 199� (Ferguson and Byrne 2000). Each line is a different year of data, and discontinuous lines are periods of time when soils were too dry to collect pH measurements. The horizontal line at pH � shows a commonly cited threshold where plants start to experience Al toxicity.
Table 1—Comparative characteristics of allophanic and nonallophanic Andisols.
Characteristic Allophanic NonallophanicMineralogy More allophane and imogolite; Less allophane and imogolite: less Al-humus complexes more Al-humus complexes
Soil acidity Weakly to moderately acid Strongly acid
Exchangeable Al Low High
Al toxicity Rare Common
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asubstantiallysmallerproportionofallophaneandimogoliteascomparedtoal-lophanicAndisols.Inaddition,nonallophanicsoilsarestronglytoverystronglyacid,havehighKCl-extractableAl,andcommonlyexhibitAl toxicity (table1)(Shoji and others 1985; Nanzyo and others 1993). Al-humus complexes andhighconcentrationsofexchangeableAlinnonallophanicAndisolsresultinrapiddissolutionandequilibriumbetweenAlinsolidandsolutionphases.AllophanicAndisolsaredominatedbyallophaneandimogolite,whichhaveslowerdissolu-tionratesand,therefore,resultinslowerreleaseofAlintosoilsolution(DahlgrenandSaigusa1994;Dahlgrenandothers2004).TherapidreleaseratesofAlinnonallophanicAndisolsprovideasourceofAlforplantuptake.Duetothepos-sibilityofAltoxicity,thedistinctionofallophanicandnonallophanicAndisolsisimportantformanagementpurposes.
BecauseoftheimpactofAndisolmineralogyonplantproductivity(Dahlgrenandothers2004),itisimportanttounderstandthefactorsthatcontrolmineralformationandweatheringwithintheorder.Differencesinparentmaterialsuchas tephraage,geochemistry,hydraulicproperties,andadditionsofexogenousmaterialssuchasloess(InoueandNaruse1987;Vaccaandothers2003)havebeenreportedtoinfluencethedevelopmentofcertainmineralogicalcomponentswithinash-influencedsoils.Otherfactorsthataremoreinfluencedbymanage-mentincludeorganicmatterandpH(ShojiandFugiwara1984;Johnson-Maynardandothers1997).TheformationofallophanicAndisolstendstobefavoredinenvironmentswherepHisgreaterthan5.Incontrast,nonallophanicAndisolsarepredominatelyfoundinmoreacidic(pH<5)environmentswithhigherconcentra-tionsoforganicmatter(ShojiandFujiwara1984;Shojiandothers1993).
Therelationshipbetweenorganicmatter,pH,andAlavailabilityindicatesthatplantcommunitiesmayplaya role in influencingAndisolproperties. Specificexamples of the impact of vegetation and vegetation conversion on Andisolmorphologyandchemistryhavebeenreported.Japanesepampasgrass(Miscan-thus sinensis),forexample,isassociatedwiththeformationofdark,humus-rich,surfacehorizonsknownasmelanicepipedons(Shojiandothers1990).BiomassproductionbyJapanesepampasgrasswasestimatedtobe4,840lbsperacreabovegroundand15,500lbsperacrebelowground.Withalloftheabove-groundandone-quarterofthebelow-groundpartsaddedtothesoileachyear,Japanesepam-pasgrasscreatesconditionsthatpromoteaccumulationandhumificationofsoilorganicmatterresultingintheformationofmelanicepipedons(Shojiandothers1993).Dahlgrenandothers(1991)reportedloweringofsoilsolutionpHwithacorrespondingincreaseinAlconcentrationsinAhorizonsofAlicMelanudandswhereJapaneseoak(Quercus serrata)replacedJapanesepampasgrass.Theac-cumulationoforganicmatterwasadistinguishingfeaturebetweensoilsunderthetwovegetationtypes.AnotherexampleoftheeffectofplantsonAndisolscanbefoundontheNorthIslandofNewZealandwhereAndisolsrarelydisplaythickdarkhumushorizonsexceptwherenativepodocarpforesthasbeenconvertedtobrackenfern(Pteridium aquilinum var. esculentum)(Leamyandothers1980).
Andisols in the Grand Fir Mosaic
Sommer (1991) sampled soilsand foliage in threeGFMplantcommunities:matureforest,naturalbrackenfernglade,andbracken-invadedclearcut.SoilpHwaslowerandexchangeableAlwashigherinbracken-dominatedplantcommuni-tiesthaninthematureforest.Soilandfoliarnutrientswereadequateforconifer
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growth,althoughAlwasapproaching levelsknown tobe toxic tosomeplantspecies.Smallsamplesizeandhighvariabilitypreventedconclusiveresults,butevidencesuggestedthatdisturbedforestsitesintheGFMareinvadedbybrackenfernplantcommunitiesandbecomemorelikebrackenfernglades.
TheimportantdocumentationofbothallophanicandnonallophanicAndisolsin theGFMwasreportedby Johnson-Maynardandothers (1997).Soilchemi-calandmineralogicalpropertieswerestudiedinadjacentmatureforest,naturalbrackenfernglade,andbracken-invadedclearcut.Retrospectivecomparisonofthe30-year-oldclearcuttothematureforestandbrackenferngladeshowedaconversionfromallophanictononallophanicsoils(fig.2).Soilsintheforestweredominatedbyshort-range-orderAl-Feminerals,hadlowexchangeableAl,andhadpH>5,allofwhichareconsistentwithcharacteristicsofallophanicsoils(table1).Soilsinthebracken-invadedclearcutandbrackenferngladeweredominatedbyAl-humuscomplexes,hadhighexchangeableAl,andpH<5,whichisconsistentwithnonallophanicsoils. Johnson-Maynardandothers (1997)werethefirst toreportnonallophanicAndisolsinnorthernIdaho.Also,theywerethefirst,toourknowledge,toreportaconversionfromallophanictononallophanicmineralogy.Allophanicandnonallophanicsoilsexistside-by-sideintheGFM,theirexpressionbeingdependentuponthedominantplantcommunity.
ThechemistryofsoilwatermovingthroughsoilsoftheGFMhasalsobeenstudiedintheGFM(Johnson-Maynardandothers1998),usingthesamestudysitesasJohnson-Maynardandothers(1997).SoilwaterchemistrywasconsistentwiththepreferentialformationofAl-humuscomplexesinbracken-dominatedsitesthathadoncebeenforested.Soilsolutionwasalsocollectedfromaweededareainabrackenferngladewherebrackenfernandwesternconeflowerwerehandweededfor6yearspriortosampling(Ferguson1999).SoilwaterpH,Al,anddissolvedorganiccarbonintheweededareaweremoresimilartotheforestthantosoilwatercollectedfromunderthebrackenfernglade.Weedingappearedtoresultinsoilwaterwithchemicalcompositionmoresimilartothatmeasuredin
Figure 2—Depth distribution of Al in soil fractions as determined by selective dissolution techniques (adapted from Johnson-Maynard 199�).
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theundisturbedforest,suggestingthatthegrowthofbrackenfernandwesternconeflowerplayanimportantroleintheconversionfromallophanictononal-lophanicsoils.
AlthoughsoilwaterAlconcentrationswerehighestinbracken-dominatedplantcommunities, theywere lower thanpublished toxicity levels forother coniferspecies.MoreworkisindicatedtodeterminetoxiclevelsforplantspeciesintheGFMandtodeterminethedifferentformsandtoxicityofAlinsoilsolution.
Discussion ______________________________________________________ResearchontheGFMecosystemhasidentifiedfourfactorsthat,individually
andcollectively,mayaccountfortheslowrateofsecondarysuccessiontowoodyvegetationfollowingdisturbancesthatcreateopeningsintheforestcanopy.Thefirst factor iscompetitionamongplants forsite resourcessuchas light,water,nutrients,andgrowingspace.Competitioncanbeintensebecauseforbcommu-nitiesdominatedbybrackenfernandwesternconeflowerexpandrapidly intopreviouslyforestedopenings.
The second factor is allelopathy. Direct and indirect effects of phytotoxinsreleasedbyplantscanreducethesuccessfulestablishmentandgrowthofotherspecies.Theallelopathicpotentialofbrackenfernandwesternconeflowerhasbeendemonstrated(Stewart1975;Gliessman1976;Ferguson1991).Thequantificationof the individualeffectsattributable toallelopathyandcompetition isdifficultbecauseremovalofaplantfromitsnaturalenvironmentsimultaneouslyremovesthesourceofallelopathyandcompetition.Ecologistsusetheterm“interference”torefertothecombinedeffectsofallelopathyandcompetition(Muller1969).
The third factor is largepopulationsofpocketgophers.GopherscancauseasubstantialamountofmortalitytoplantedandnaturalseedlingsintheGFM.Mostgopher-causedmortalitytoplantedseedlingstakesplacethefirstsummerafterplantingandduringthefirstandsecondwinters(Ferguson1999;Fergusonandothers2005).Partialremovaloftheoverstorycanopyallowsenoughlighttoreachplantedseedlingssotheycansurviveandgrow—albeitslowerthaninfullsunlight—andalsoreducesabundanceofpocketgophers,brackenfern,andwesternconeflower(Fergusonandothers2005).
Thefourthfactorisanonallophanicsoilformingprocess.ThedatacollectedbyJohnson-Maynardandothers(1997,1998)demonstratetheconversionofal-lophanictononallophanicmineralogybasedonthecriteriasummarizedintable1.Intheundisturbedforest,thedominantsecondarymineralogicalcomponentofsoilsisinorganic,short-rangeorderminerals,whichisconsistentwithallophanictypeAndisols.Inbracken/coneflowerdominatedareas,Al-humuscomplexesarethedominantcomponentofsoils,consistentwithwhathasbeendescribedinnonallophanicsoils.
Allophanicandnonallophanicsoilsexistside-by-sideintheGFM,withmineral-ogydependentuponthedominantvegetation(fig.2).Allophanicconditionsoccurwhenvegetationisdominatedbyconiferoustrees,butnonallophanicconditionsoccurwhensitesaredominatedbybrackenfernandwesternconeflower(John-son-Maynardandothers1997).Whenbrackenfernandwesternconeflowerareremoved,soilwaterchemistryissimilartothatunderallophanicGFMsoils(Johnson-Maynardandothers1998),indicatingthatbrackenfernandwesternconeflowerareamechanisminpromotingnonallophanicsoils.Itislikelythatbrackenfernandwesternconeflowerarenotonlysourcesoflargeannualadditionsofcarbon
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tothesoil,thusfavoringtheformationofAl-humuscomplexes,butalsosourcesoforganicacidsthatlowersoilpH(Johnson-Maynardandothers1998).
Reforesting GFM Sites____________________________________________Inthissection,wediscussmanagementstrategiesforreforestingGFMsitesas
theyrelatetothenonallophanicsoilformingprocess.ThemostimportantpointtorememberisthatnaturalregenerationofwoodyplantspecieswillbeaslowandunreliableprocesswithintheGFM.WeknowofmanyexamplesofcutoverGFMforeststhathavelittlewoodyvegetationafter20to30years.Seedsthatgerminateinopenings in theGFMforestcanopyaresubject tocompetition,allelopathy,pocketgophers,andAltoxicity.Thesefourfactorscancombinetovirtuallyelimi-natethenaturalestablishmentoftreesandotherwoodyplantspecies.
Promptplanting followingadisturbancewill help seedlingsbecomeestab-lishedbeforethesitehasabundantbrackenfern,westernconeflower,andpocketgophers.Plantinglargervs.smallerseedlingshelpsincreasesurvivalandgrowthrates.Plantedseedlingsinclearcutsneedtobeprotectedfrompocketgophersuntilthethirdspringaftertheyareplanted.
Partialcuttings,whereonlyaportionoftheoverstorytreesareremoved,re-taintheshrubcomponentbetterthanclearcuts,andresultinlessbrackenfern,westernconeflower,andgopher-causeddamagetoseedlings(Fergusonandoth-ers2005).Plantedtreesdonotneedprotectionfrompocketgophersinpartialcuttings;however,theywillnotgrowasfastasinclearcuts.Afterseedlingsareestablished(5to10years),allorpartof theremainingoverstorytreescanberemovedtoimprovegrowthofseedlings.
Theoverallperformanceofsomeplantedconiferspecieswasbetter in trialplantingsonGFMsites(Ferguson1999;Fergusonandothers2005).Engelmannspruceandwesternwhitepinegrewwell,hadlittlemortalityfromnon-gophercauses,andhadlittletopdamagefromsnoworsenescingbrackenfernfronds.Douglas-firalsodidquitewell,especiallyiflargerseedlingswereplanted.Lodge-polepinegrewrapidly,butthisspeciesoftensufferedseveresnowdamagetotops,limbs,andstems.Westernlarchhadveryhighoverallmortality,bothfromgopherandnon-gophercauses,butsurvivingtreesgrewrapidly.AnotherconcernwithwesternlarchistopdamageandsevereleancausedbysnowloadsintheGFM.
Research Questions _____________________________________________Muchhasbeenlearnedaboutash-capsoilsandmanagementoptionsforthe
GFM,andadditionalresearchwouldhelpfillthegapsinourknowledge.Researchstudiesshowthatallophanicandnonallophanicsoilformingprocessesexistside-by-sideintheGFM.Allophanicprocessesoccurwhereconifersdominatethesite,andnonallophanicprocessesoccurwherebrackenfernandwesternconeflowerdominate.Itwouldbehelpfultostudyallophanicvs.nonallophanicmineralogyacross a range of overstory densities, and determine how quickly allophanicprocessesturnintononallophanicprocessesfollowingharvestorotheractivitiesthatreducethedensityoftheforestcanopy.
Anotherkey research topic is tounderstandwhypHiscyclic inGFMsitesdominatedbybracken/coneflowersuccessionalplantcommunities(fig.1).Com-parisonsofseasonalpatternsinpHunderbrackenferngladestoundisturbedgrandfirforestsmayshedlightonthemechanismsbehindthisobservation.
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SoilpHvaluescyclebelow5.0duringpartofthegrowingseason,whichcouldresult in Al toxicity (Page-Dumroese and others, this proceedings). However,littleisknownaboutAltoxicitythresholdsforplantspeciesandtheirmychor-rhizalassociationsintheGFM.WewouldexpectthatAltoxicityvarieswithAlconcentration,thevariousAlcompoundsthatexistinash-capsoils,andsize/ageofplantspecies.ThecyclicnatureofsoilpHintheGFMmayalsointerferewithnutrientavailability(seePage-Dumroeseandothers,theseproceedings).Moreinformation isneededonavailabilityofnutrientsother thanAl, especiallyni-trogen.RecentworkhassuggestedthatadditionsoflimeareeffectiveinraisingpHandreducinglevelsofbioavailableAlinnonallophanicAndisols(Takahashiandothers2006).Limingexperimentscouldthereforebeusedtoprovidevalu-ableinformationabouttheroleofpHandactiveformsofAlintreeregenerationproblemsobservedintheGFM.
Theallelopathicpotentialofbrackenfernhasbeendemonstratedbyseveralresearchersaroundtheworld,butweonlyhaverudimentaryknowledgeofal-lelopathyinwesternconeflower.Ferguson(1991)demonstratedtheallelopathicpotential ofwestern coneflower in laboratory tests, but additional research isneededunderfieldconditions.
TheanswerstotheseresearchquestionswouldimproveourknowledgeofthemechanismsthatdelaysecondarysuccessiontowoodyplantspeciesintheGFM,therebyhelpingrefinemanagementrecommendationsforGFMash-capsoils.
References ______________________________________________________Cooper,S.V.;Neiman,K.E.;Roberts,D.W.1991(revised).ForesthabitattypesofnorthernIdaho:
asecondapproximation.Gen.Tech.Rep.INT-236.Ogden,UT:U.S.DepartmentofAgriculture,ForestService,IntermountainResearchStation.143p.
Dahlgren,R.A.;Saigusa,M.1994.AluminumreleaseratesfromallophanicandnonallophanicAndosols.SoilScienceandPlantNutrition.40:125-136.
Dahlgren,R.A.;Saigusa,M.;Ugolini,F.C.2004.Thenature,propertiesandmanagementofvolcanicsoils.AdvancesinAgronomy.82:113-182.
Dahlgren,R.A.;Ugolini,F.C.;Shoji,S.;Ito,I.;Sletten,R.S.1991.Soil-formingprocessesinAlicMelanudandsunderJapanesepampasgrassandoak.SoilScienceSocietyofAmericaJournal.55:1049-1056.
Ferguson, D. E. 1991. Allelopathic potential of western coneflower (Rudbeckia occidentalis).CanadianJournalofBotany.69:2806-2808.
Ferguson,D.E.1999.Effectsofpocketgophers,brackenfern,andwesternconefloweronplantedconifersinnorthernIdaho—anupdateandtwomorespecies.NewForests.18:199-217.
Ferguson,D.E.;Adams,D.L.1994.Effectsofpocketgophers,brackenfern,andwesterncone-floweronsurvivalandgrowthofplantedconifers.NorthwestScience.68:241-249.
Ferguson,D.E.;Boyd,R.J.1988.BrackenferninhibitionofconiferregenerationinnorthernIdaho.Res.Pap.INT-388.Ogden,UT:U.S.DepartmentofAgriculture,ForestService,IntermountainResearchStation.11p.
Ferguson,D.E.;Byrne,J.C.2000.EnvironmentalcharacteristicsoftheGrandFirMosaicandad-jacenthabitattypes.Res.Pap.RMRS-RP-24.FortCollins,CO:U.S.DepartmentofAgriculture,ForestService,RockyMountainResearchStation.20p.
Ferguson,D.E.;Byrne,J.C.;Coffen,D.O.2005.ReforestationtrialsandsecondarysuccessionwiththreelevelsofoverstoryshadeintheGrandFirMosaicecosystem.Res.Pap.RMRS-RP-53.FortCollins,CO:U.S.DepartmentofAgriculture,ForestService,RockyMountainResearchStation.16p.
Ferguson,D. E.; Johnson, F.D.1996.ClassificationofGrandFirMosaichabitats.Gen.Tech.Rep.INT-GTR-337.Ogden,UT:U.S.DepartmentofAgriculture,ForestService,IntermountainResearchStation.16p.
Gliessman,S.R.1976.Allelopathyinabroadspectrumofenvironmentsasillustratedbybracken.LinneanSocietyBotanicalJournal.73:95-104.
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Inoue,K.;Naruse,T.1987.Physical,chemicalandmineralogicalcharacteristicsofmoderneoliandustinJapanandrateofdustdeposition.SoilScienceandPlantNutrition.33:327-345.
Johnson-Maynard,J.L.1995.AlterationofAndisolsintheGrandFirMosaicecosystemfollowinginvasionbybrackenfernsuccessionalplantcommunities.Moscow:UniversityofIdaho.91p.Thesis.
Johnson-Maynard,J.L.;McDaniel,P.A.;Ferguson,D.E.;Falen,A.L.1997.Chemicalandmin-eralogicalconversionofAndisolsfollowinginvasionbybrackenfern.SoilScienceSocietyofAmericaJournal.61:549-555.
Johnson-Maynard,J.L.;McDaniel,P.A.;Ferguson,D.E.;Falen,A.L.1998.Changesinsoilsolu-tionchemistryofAndisolsfollowinginvasionbybrackenfern.SoilScience.163:814-821.
Jimenez,J.2005.BrackenferncommunitiesoftheGrandFirMosaic:biomassallocationandinflu-enceonselectedsoilproperties.Moscow,ID:UniversityofIdaho.209p.Thesis.
Leamy,M.L.;Smith,G.D.;Colmet-Daage,F.;Otowa,M.1980.ThemorphologicalcharacteristicsofAndisols.In:Theng,B.K.B.,ed.Soilswithvariablecharge.PalmerstonNorth,NewZealand:OffsetPublications:17-34.
Muller,C.H.1969.Allelopathyasafactorinecologicalprocess.Vegetatio.18:348-357.Nanzyo,M.;Dahlgren,R.;Shoji,S.1993.Chemicalcharacteristicsofvolcanicashsoils.In:Shoji,
S.;Nanzyo,M.;Dahlgren,R.,eds.Volcanicashsoils:genesis,properties,andutilization.Am-sterdam,TheNetherlands:ElsevierSciencePublishers:145-187.
Shoji,S.;Fugiwara,T.1984.ActivealuminumandironinthehumushorizonsofAndosolsfromnortheasternJapan:theirforms,properties,andsignificanceinclayweathering.SoilScience.137:216-226.
Shoji,S.;Ito,T.;Saigusa,M.;Yamada,I.1985.PropertiesofnonallophanicAndisolsfromJapan.SoilScience.140:264-277.
Shoji,S.;Kurebayashi,T.;Yamada,I.1990.GrowthandchemicalcompositionofJapanesepampasgrass(Miscanthus sinensis)withspecialreferencetotheformationofdark-coloredAndisolsinnortheasternJapan.SoilScienceandPlantNutrition.36:105-120.
Shoji,S.;Nanzyo,M.;Dahlgren,R.A.1993.Volcanicashsoils:genesis,properties,andutiliza-tion.Amsterdam,TheNetherlands:ElsevierSciencePublishers:288p.
SoilSurveyStaff.2003.KeystoSoilTaxonomy.9thed.U.S.DepartmentofAgriculture,NaturalResourcesConservationService.U.S.Government.PrintingOffice,Washington,DC:331p.
Sommer, M. R. 1991. Soils of the Grand Fir Mosaic. Moscow, ID: University of Idaho. 97 p.Thesis.
Stewart,R.E.1975.Allelopathicpotentialofwesternbracken.JournalofChemicalEcology.1:161-169.
Takahashi,T.;Ikeda,Y.;Fujita,K.;Nanzyo,M.2006.EffectoflimingonorganicallycomplexedaluminumofnonallophanicAndosolsfromnortheasternJapan.Geoderma.130:26-34.
Ugolini,F.C.;Dahlgren,R.A.;Shoji,S.;Ito,T.1988.Anexampleofandosolizationandpodzoliza-tionasrevealedbysoilsolutionstudies,S.Hakkoda,N.E.Japan.SoilScience.145:111-125.
Vacca,A.;Aamo,P.;Pigna,M.;Violante,P.2003.Genesisoftephra-derivedsoilsfromtheRoc-camonfinavolcano,southcentralItaly.SoilScienceSocietyofAmericaJournal.67:198-207.
Zdanowicz,C.M.;Zielinski,G.A.;Germani,M.S.1999.MountMazamaeruption:calendricalageverifiedandatmosphericimpactassessed.Geology.27:621-624.
Znerold,R.M.1979.Westernbrackencontrolwithasulam.Pullman,WA:WashingtonStateUniversity.36p.Thesis.
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In: Page-Dumroese, Deborah; Miller, Richard; Mital, Jim; McDaniel, Paul; Miller, Dan, tech. eds. 2007. Volcanic-Ash-Derived Forest Soils of the Inland Northwest: Properties and Implications for Management and Restoration. 9-10 November 2005; Coeur d’Alene, ID. Proceedings RMRS-P-44; Fort Collins, CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station.
Deborah Page-Dumroese and Dennis Ferguson are Research Scientists at the Rocky Mountain Research Station, U.S. Forest Service in Moscow, ID; Paul McDaniel and Jodi Johnson-Maynard are faculty in the Department of Plant, Soil, and Entomological Sciences, University of Idaho, Moscow, ID.
Abstract Datafromvolcanicash-influencedsoilsindicatesthatsoilpHmaychangebyasmuchas3unitsdur-ingayear.Theeffectsofthesechangesonsoilchemicalpropertiesarenotwellunderstood.OurstudyexaminedsoilchemicalchangesafterartificiallyalteringsoilpHofash-influencedsoilsinalaboratory.Soilfromthesurface(0-5cm)andsubsurface(10-15cm)mineralhorizonswerecollectedfromtwoNationalForestsinnorthernIdaho.Soilcollectionsweremadefromtwoundisturbedforeststands,apartialcut,anaturalbrackenfern(Pteridium aquilinum[L.]Kuhn)glade,anapproximately30-year-oldclearcutinvadedwithbrackenfern,anda21-year-oldclearcutinvadedwithwesternconeflower(Rudbeckia occidentalisNutt.).Eitherelementalsulfur(S)orcalciumhydroxide(Ca(OH)2)wereaddedtothesoiltomanipulatepH.After90daysofincubation,pHrangedfrom3.6to6.1forbothNationalForestsandallstandconditions.TotalC,totalN,andextractablebasecations(Ca,Mg,andK)weregenerallyunaffectedbypHchange.AvailablePincreasedaspHdroppedbelow4.5forbothdepthsandallsoiltypes.NitratewashighestatpHvaluesgreaterthan5.0anddecreasedaspHdecreasedindicatingthatnitrificationisinhibitedatlowerpH.Contrarytonitrate,potentiallymineralizableNincreasedaspHdeclined.TotalacidityandexchangeablealuminumincreasedexponentiallyaspHdecreased,especially intheuncutandpartialcutstands. Datafromthis laboratorystudyprovidesinformationontheroleofpHindeterminingtheavailabilityofnutrientsinash-capsoils.
Chemical Changes Induced by pH Manipulations of Volcanic
Ash-Influenced SoilsDeborah Page-Dumroese, Dennis Ferguson, Paul McDaniel, and
Jodi Johnson-Maynard
Introduction
Innorth-centralIdaho,someforestsarecharacterizedbyconiferregenerationproblemsdespitefavorableclimaticconditions(udicmoistureandfrigidsoiltemperatureregimes).Foreststandsatmid-elevationsaremostatriskaftertimberharvestorotherdisturbancebecausetheyarequicklyinvadedbybrackenfern(Pteridium aquilinum[L.]Kuhn),westernconeflower(Rudbeckia occidentalisNutt.),andpocketgophers(Thomomys talpoides).ThesesitesarecollectivelyknownastheGrandFirMosaic(GFM)andarenamedforthedominantconifer,grandfir(Abies grandis[Dougl.exD.Don]Lindl.),thatoccursinamosaicpatternwithshrubandforbcommunities(Ferguson1991a;Fergusonandothers,thisproceedings).
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Page-Dumroese, Ferguson, McDaniel, and Johnson-Maynard Chemical Changes Induced by pH Manipulations of Volcanic Ash-Influenced Soils
TimberharvestingbeganintheGFMinthe1960sanditsoonbecameevidentthatregenerationproblemsexisted.Woodyvegetationisstillinfrequentonmanyofthesesites30yearsafterclearcutting,evenwithrepeatedplantings(FergusonandAdams1994).Clearcutstandswerequicklyinvadedbyforbs(predominatelybrackenfernandwesternconeflower)androdents.Theallelopathicpotentialofbothbrackenfernandwesternconeflowerhasbeenwelldocumented(Stewart1975;FergusonandBoyd1988;Ferguson1991b).Inadditiontoinvadingforbs,pocketgophersalsocausesubstantialseedlingmortality (Fergusonandothers2005).Competition for light,moisture, andnutrientswithin theGFM ishigh.Whilethecombinationofcompetition,pocketgophers,andallelopathycontributetothearrestedstateofsecondarysuccession(FergusonandAdams1994),thesefactorsdonotappeartoentirelyexplainreforestationfailures.
Soils throughout the GFM are strongly influenced by volcanic ash in thesurfacehorizons.Theashwasdepositedapproximately7,700yearsagowhenMt.Mazama erupted (Zdanowicz 1999). Volcanic ash-influenced soils haveuniqueparentmaterialsandsecondarymineralassemblagesthat,ingeneral,arenotaswellunderstoodasthoseinothermineralsoils.Volcanicash-influencedsoilsareclassifiedaseitherallophanicornonallophanic,dependingontherela-tiveabundanceoforganicmatterandinorganicshort-range-orderminerals(Shojiand others 1993). Nonallophanic soils have more organic matter, lower pH,higherlevelsofKCl-extractablealuminum(Al),andlowerlevelsofcalcium(Ca)relative toallophanicsoils (Shojiandothers1993).LowsoilpHmay increaseconcentrationsofextractable(potentiallyplantavailable)Al,leadingtoAltoxic-itytowoodyvegetation(Dahlgrenandothers1991).Clearcuttingandintensiveutilization(wholetreeharvesting)offorestbiomassmayacceleratesoilacidifica-tionprocesses(Ulrichandothers1980;NoskoandKershaw1992).Inadditiontoacidificationfromharvestactivities,vegetation-inducedacidificationappearstooccurunderbrackenfernandwesternconeflowerplantcommunities(Johnson-Maynardandothers1997).Theseacidifiedvolcanicash-influencedsoils,whicharehighinexchangeableAl,mayreleaseAlintosoilsolutionatlevelstoxictowoodyvegetation(AndereggandNaylor1988).
Twosoil factorshavebecomeaconcerninGFMforestopenings.First,soilpH drops below 5.0 after harvest operations and the subsequent invasion ofbrackenfernandwesternconeflower(figs.1and2).AtthispH,AlcanreachtoxiclevelsandlowsoilpHcaninhibitgrowthofsomeseedlingspecies(NoskoandKershaw1992).Second,thereareseasonalpHfluctuationsof2-3pHunitsthatarenottypicallyfoundinbulkmineralsoilunlessheavilyimpactedbyacidrainor,occasionally,harvestactivities(Mrozandothers1985;Braisandothers1995;Alewellandothers1997).WinterpHvaluesaveragearound6,butdropbelow4duringthegrowingseason.TheseseasonalpHfluxescouldbecorrelatedwithinputsofacidlitterfrombrackenfernandwesternconeflower,increasingrootrespirationduringthegrowingseason,ordecreasesinsoilmoisturecontent.Inaddition,thesetwospecieslikelytakeuphighamountsofnutrientsfromthesoil,whichmayalsocontributetoacidconditions(Gilliam1991).ManyfactorsinfluenceforestsoilpH(forexample,precipitation,nutrientexchange,andsoilage),butharvestactivitycanparticularlyinfluenceit (StaafandOlsson1991).AlthoughforestharvestingcanlowerpH,subsequentinvasionbybrackenfernandwesternconeflowerappearstocontributetoandmaintainlowpHrelativetoundisturbedforestsoils.
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Chemical Changes Induced by pH Manipulations of Volcanic Ash-Influenced Soils Page-Dumroese, Ferguson, McDaniel, and Johnson-Maynard
Figure 2—Average soil pH at 2.� cm for the Clearwater National Forest fern-invaded clearcut (unpublished data collected as described in Ferguson and Byrne 2000). The bold line is 1997 and the thin line is 199�.
Figure 1—Average soil pH at 2.� cm for the Nez Perce National Forest coneflower-invaded clearcut (from Ferguson and Byrne 2000). The bold line is 1994, which was a dry growing season. The thin line is 199�, which was a wet growing season. Dis-continuous parts of the line are from removal of the pH probe during the driest part of the growing season. Soil pH at this site was assessed in situ using pH probes (model �1�, IC controls Orangeville, Ontario, Canada) buried 2.� cm below the mineral soil surface.
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TheslowforestregenerationprocessintheGFMhasdecreasedmanagementoptionsforfuelreductionsandbiomassproduction,biodiversityofnativefloraandfauna,andaestheticvaluesinandneartheseareas.LowsoilpHanditscyclicnatureover a growing seasonmaybealtering soil chemistry, nutrient cyclingprocesses, and preventing establishment of woody vegetation. Consequently,ourobjectivewastoartificiallyalterpHofash-influencedforestsoilsfromtheGFMbyadditionsofsulfur(S)orcalciumhydroxide(Ca(OH)2)tobetterevaluatepotentialin situ chemicalchangeswithinthesesoils.
Study Site Description ___________________________________________Twostudysites,oneontheClearwaterNationalForestandoneontheNez
PerceNationalForestofnorth-centralIdaho,wereselectedtoprovideanorth/southrangeofplantcommunitycovertypesforsoilcollection.TherearethickerdepositsofvolcanicashinthenorthernpartoftheGFMwherethesesoilsareclassifiedasAndisols.InceptisolsdominateinthesouthernpartoftheGFMwhereashdepositsare thinnerandmorehighlymixed.Bracken ferndominates forbcommunitiesinthenorthernpartoftheGFMandwesternconeflowerdominatesinthesouthernpart,althoughbothspeciesoccurtogetherthroughouttheGFM.Table1listsstudysitelocations,vegetationtypes,andsoilclassifications.
ClearwaterNational Forest soil sampleswere collected in 1994near EaglePoint(elevation1,400m,easternaspect,20percentslope,T40N,R7E,S35).Thedominantsoilfeatureofthisstudyareaisapproximately60cmofMt.Mazamavolcanic ashunderlainwith colluviumor residuumderived from fine-grainedigneousrock.Toassesstheimportanceofvegetationcommunitystructure,soilsampleswerecollectedfromadjacentareaswithsimilarslope,aspect,andpar-entmaterial, butdifferent vegetationcover. Soil sampleswere collected fromtheundisturbed forest (46m2ha–1basal areaofoverstory), apartial cut (ap-proximately30m2ha–1ofoverstoryremaining),anaturallyoccurringbrackenfernglade(presentwhentheadjacentareaswereharvested),anda~30-year-oldbrackenfern-invadedclearcut(invadedbybrackenfernandwesternconeflowerafterharvestingbetween1965and1968).
NezPerceNationalForestsoilsampleswerecollectedin1994atDogleg(eleva-tion1,740m,southernaspect,5percentslope,T31N,R6E,S34).Thedominantsoilfeatureisapproximately40cmofMt.Mazamavolcanicashunderlainwithdeeplyweatheredmicaschist(Sommer1991).Vegetationtypesatthissitewereundisturbedforest(45m2ha–1basalareaofoverstory)anda21-year-oldwestern
Table 1—Location, vegetation type, and soil classification of study sites.
National Forest Vegetation type Soil classification‡
Clearwater Undisturbed forest Typic HapludandNez Perce Undisturbed forest Vitrandic CryumbreptClearwater Partial cut Typic HapludandClearwater Natural bracken fern glade Alic FulvudandClearwater �0-year-old bracken fern-invaded clearcut Alic HapludandNez Perce 21-year-old western coneflower-invaded clearcut Vitrandic Cryumbrept‡ Clearwater National Forest soil classifications from Johnson-Maynard and others (1997)Nez Perce National Forest soil classifications from Sommer (1991).
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coneflower-invadedclearcut(invadedbywesternconeflowerandbrackenfernafterharvestingin1973).Vegetationtypeswereadjacenttoeachother,havingsimilarslope,aspect,andparentmaterial.Therewerenonaturalwesternconeflowergladesdatingtopre-harvestactivitiesandnopartialcutstandsinthevicinity.
Methods _______________________________________________________
Field Collection Methods
Ineachforestandvegetationtype,mineralsoilwascollectedfromthe0-5cmand10-15cmdepths.Soilsampleswerebrought to theUSDAForestService,MoscowLaboratory,airdried,andpassedthrougha2-mmsieve.InitialpHwasmeasuredelectrometricallyina2:1water:soilsuspension.
Laboratory Methods
DependingoninitialsoilpH,wechosefivetreatmentstoraiseorlowersoilpHinanattempttoestablisharangeofpHvaluesfrom3.5to6.0.Foreachvegeta-tiontypeanddepth,Satratesof0.45,0.90,1.80,2.70,or3.6gkg–1orCa(OH)2atratesof0.45,0.90,or1.80gkg –1wereaddedtoprovidearangeofpHvalues.Inaddition,therewasacontrol(nochemicaladded)foreachvegetationtypeandsoildepth.EachSorCa(OH)2soiladditionrateandthecontrolfromeachvegetationtypewasreplicatedthreetimes.Soilwasplacedin655cm3plastictubeswithnylonscreenoverthebottomopeningstopreventsoilloss.
Soilwaterpotentialwasbroughtto–0.033MPabytheadditionofdeionizedwater.Thetubeswererandomlylocatedonagreenhousebenchandincubatedatadaytimetemperatureof25°Candanighttimetemperatureof18to20°CuntilthepHstabilized(90days).Whensoilwaterpotentialdroppedbelow–0.10MPa,additionaldeionizedwaterwasaddeduntilthesoilreachedfieldcapacity.AfterpHstabilized(unchangedfor5days),soilwasairdriedforchemicalanalyses.FinalpHwasmeasuredasdescribedaboveaftertheincubationperiod.
Totalcarbon(C)andnitrogen(N)wereanalyzedinaLECOinductionfurnaceoperatedat1050°C(LECOCorp,St.Joseph,MI).Totalacidityandexchange-ableAlwereextractedwith1NKCl (BertschandBloom1986).Exchangeablecalcium(Ca),magnesium(Mg),andpotassium(K)wereextractedusing1NNH4Cl(Palmerandothers2001).CalciumandMgwereanalyzedbyatomicabsorptionspectroscopy,andKwasanalyzedbyflameemission.Nitrate-N(NO3-N)wasdeterminedonmoistsamplesusing1NKClextractandanAlpkemRapidFlowAnalyzer(Mulvaney1996).PotentiallymineralizableN(PMN)wasestimatedus-ingthe7-dayanaerobicincubationtechniqueonmoistsamples(Powers1980).Extractablephosphorus(P)wasdeterminedusingeithertheBray1method(forsampleswithapH<6.0)ortheOlsenmethod(forsampleswithapH>6.0)(Kuo1996).Organicmatterwasdeterminedbyweightlossaftercombustionat375°Cfor16h(Ball1964).
Statistical Analyses
RegressionequationsweredevelopedusingPROCMIXEDinSAS(Littellandothers1996),atthe0.05significancelevel,andLSMEANSwasusedtocomparevegetationtypeswithinsoildepths.WhenanalyzingresultsforCa,weexcluded
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treatmentstoraisesoilpHbecausetheCa(OH)2wouldhaveartificiallyelevatedCalevels.Transformationsofvariableswereexploredtoachievehomogeneityoferrorvariance,normalityandindependenceoferrorandblockeffects,andtoobtainadditivityofeffects(Littellandothers1996).
Results and Discussion ___________________________________________
Soil pH Changes
FieldstudiesintheGFMindicatethatsubstantialpHfluxesoccurthroughouttheyear(figs.1and2)(Fergusonandothers,thisproceedings).ResultsofourcontrolledstudyconfirmourinitialobservationthatchangesinvegetationtypeinfluenceforestsoilpH(table2).BeforetreatmentwithSorCa(OH)2,the0-5cmsoilpHwaslowestinthenaturalbrackenfernglade(5.0)andfern-invadedclearcut(4.7)ontheClearwaterNationalForest,intermediateontheNezPerceNationalForestundisturbedarea(5.4)andconeflower-invadedclearcut(5.4),andhighestontheClearwaterNationalForestundisturbedforest(6.3)andpartialcut(6.4)(table2).SoilpHatthe10-15cmdepthfollowedthesametrends.AftertreatmentwithSorCa(OH)2and90daysofincubation,finalpHvaluesrangedfrom3.6to6.1(table2).MostpHchangesoccurredwithin45daysofstartingtheincubationperiod,butthelowestpHvalueswereachievedafter85days.
Interestingly,untreatedsoilsfromtheClearwaterNationalForestundisturbedandpartialcuttreatmentsexhibitedadeclineinsoilpHduringincubationinthegreenhouse.Forexample, theinitialaveragepHintheundisturbedforestwas6.3,butattheendoftheincubationperiod,thehighestpHvaluewas5.4.This“natural”decreaseintheabsenceofvegetationandbioticprocessesissimilartothepHdecreasesshowninfigures1and2.Inthesetwofigures,winterpHvaluesaveragearound6,butdropbelow4duringthegrowingseason.TheseseasonalpHfluxesmaybedrivenbyinputsofacidlitterfrombrackenfernandwesternconeflower.Inaddition,thesetwospecieslikelytakeuphighratesofnutrientsfrom
Table 2—Initial and final soil pH ranges after treatment with S or Ca(OH)2.
National Forest Vegetation type Initial pH Final pH range - - - - - -0-5 cm depth- - - - - - - -Clearwater Undisturbed forest �.� �.7 - �.4Nez Perce Undisturbed forest �.4 �.� - �.�Clearwater Partial cut �.4 �.� - �.0Clearwater Natural bracken fern glade �.0 �.7 - �.0Clearwater �0-year-old bracken fern-invaded clearcut 4.7 �.7 - �.�Nez Perce 21-year-old coneflower-invaded clearcut �.4 �.� - �.� - - - - - - 10-15 cm depth - - - - - -Clearwater Undisturbed forest �.� �.� - �.�Nez Perce Undisturbed forest �.� �.� - �.�Clearwater Partial cut �.2 �.� - �.2Clearwater Natural bracken fern glade 4.9 �.9 - �.1Clearwater �0-year-old bracken fern-invaded clearcut 4.� �.7 - �.1Nez Perce 21-year-old coneflower-invaded clearcut �.� �.� - �.1
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thesoil,whichmayalsocontributetoacidconditions(Gilliam1991).AlthoughforestharvestingcanlowerpH,subsequentinvasionbybrackenfernorwesternconeflowerappearstocontributetoandmaintainlowpHrelativetoundisturbedforestsoils.However,thelaboratorydataindicatesthatsomepHchangeswithinthesesoiltypesarepossibleevenwithoutvegetationfacilitatingthechange.
Carbon and Nitrogen
ThereweresignificantdifferencesintotalCconcentrationamongthevegetationtypes(table3).SoilCconcentrationwashighestunderthefern-invadedclearcutatbothdepths (11.27percent0-5cmdepth;10.00percent10-15cmdepth).TotalCwas lowestat the10-15cmdepthwhereconiferswerepresent (bothundisturbedforestsandpartialcut).Thesoilsthatsupportthehighestvegetationturnoverrates(brackenfernandwesternconeflower)hadsimilarCconcentrationsatbothdepths,whilevegetationtypeswithconiferspresenthadabouttwiceasmuchCinthesurfacesoilcomparedtothe10-15cmdepth.
Thefern-invadedclearcuthasapproximately390g/m2ofbrackenfrondbiomassaddedtothesoilannually(Znerold1979).OntheClearwaterNationalForest,rhizome and fine root biomass in the fern-invaded communities averaged4000g/m2(Jimenez2005);inthenaturalglade,rhizomeandfinerootbiomassaveraged3200g/m2.ItisnotsurprisingthatthisvegetationtypehashigherCcon-centrations.WeexpectedthatthenaturalbrackenferngladewouldhaveasmuchCasthefern-invadedclearcut,butthiswasnotthecase.Thenaturalbrackenferngladesoilappearstobeatanintermediatepointbetweentheundisturbedforestandthefern-invadedclearcut.TheseresultsaresimilartoCandNdatacollectedfromnearbysiteswithintheGFM(Johnson-Maynardandothers1997).Oneex-planationmaybethatthenaturalbrackenferngladehasreachedasteadystate.
Table 3—Mean C, N, Ca, Mg, and K in the control treatment, by vegetation type and depth. Each mean is an average of three replications.
National Vegetation Forest type Carbon Nitrogen Calcium Magnesium Potassium
- - - - - - percent - - - - - - - - - mg/kg - - - 0-5 cm depthClearwater Undisturbed forest �.�0 a‡ 0.40 a 12.21 d 1.12 b 1.�4 bNez Perce Undisturbed forest 7.�7 b 0.74 c 14.1� e 1.14 b 0.99 aClearwater Partial cut �.2� a 0.�� a 7.�� b 0.74 a 0.99 aClearwater Natural bracken fern glade 7.9� b 0.�1 b �.�� a �.29 d 2.77 cClearwater Bracken fern-invaded clearcut 11.27 c 0.�9 bc �.70 a 2.�4 c 2.�9 cNez Perce Coneflower-invaded clearcut �.17 a 0.�� a 9.1� c 0.92 a 1.02 a 10-15 cm depthClearwater Undisturbed forest �.17 a 0.24 a �.41 c 0.74 d 1.22 cNez Perce Undisturbed forest �.90 b 0.22 a �.�� c 0.41 a 0.71 bClearwater Partial cut �.�� ab 0.2� a �.79 b 0.49 c 0.71 bClearwater Natural bracken fern glade �.90 c 0.4� c 4.2� b 1.�� e 2.20 eClearwater Bracken fern-invaded clearcut 10.00 d 0.�7 d 2.72 a 0.77 d 1.�0 dNez Perce Coneflower-invaded clearcut �.27 c 0.�4 b �.�� c 0.4� b 0.4� a‡ Within soil depth, means followed by different letters are significantly different (p = 0.05) using LSMEANS.
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Becausebrackenfernproduceshighlevelsofallelopathicchemicals(FergusonandBoyd1988),itisperhapsbecomingautotoxic(GliessmanandMuller1978),whichresultsinlessfrondbiomass(naturalglade678g/m2;fern-invadedclearcut916g/m2(Jimenez2005))andlessorganicCincorporatedintothesoil.Thesetwotypesofbrackenfernstands(naturalgladeandinvadedclearcut)mayalsobeatdifferentlifecyclestages(Atkinson1986).
HighersoilCconcentrationsinthefern-invadedclearcutareconsistentwiththedevelopmentofnonallophanicsoilcharacteristicsfollowinginvasion(Nanzyoandothers1993;Johnson-Maynardandothers1997;Dahlgrenandothers2004).IncreasedlevelsofCinthebrackenfernsites,ascomparedtoundisturbedsoils,may increase the potential for preferential formation of Al-humus complexes(Dahlgrenandothers1993).
ForestsitesinvadedbywesternconeflowermaintainedmoderatelevelsofCthroughoutthesamplingdepths.Atthe10-15cmdepththeconeflower-invadedclearcuthadnearlytwiceasmuchCastheundisturbedforestsoil(table3).Car-bonwasdistributeddeeperinthesoilprofileintheconeflower-invadedclearcutthanonthebrackenfernsites.Thismaybebecausetheconeflower-invadedsitehadgreatersurfaceandsubsoilmixingcausedbypocketgophers(FergusonandAdams1994)orbecauseofslightlylesssurfacevolcanicashdeposition(Sommer1991).
Foreachvegetationtype,therewasgenerallymoreNinthe0-5cmdepththaninthe10-15cmdepth,withtwonotableexceptions.Boththefern-invadedclearcutandtheconeflower-invadedclearcutsoilshadasmuchNinthe10-15cmdepthasthesurfacesoil.Thisislikelycausedbythelargeannualinputsofforbbiomassthatusuallyoccurinnewlyinvadedclearcuts(Attiwillandothers1985).
RegressionanalysesshowedthattotalCandNwereunchangedafteralteringpH.Thisresultwasnotunexpectedsincewedidnotaddorganicmatter.
Base Cation Concentrations
Basedonthecontrolsamples,vegetationtypedoesinfluencesoilCa,Mg,andKconcentrationsinthesevolcanicashsoils(table3).Forbothsoildepths,theferngladeandthefern-invadedclearcuthadsignificantlymoreKandMgthansoilsfromundertheothervegetationtypes.Incontrast,Cacontentwasgreatestinsoilsunderbothundisturbedforests.
Regressionanalysisshowedthatbasecationconcentrations(Ca,Mg,andK)didnotchangeasaresultofpHchanges(datanotshown).OurresultsdifferfromthoseofMohebbiandMahler(1988)whofoundastrongcorrelationbetweenpHandcationconcentrationafterartificiallychangingpHinaloessalsoil.Intheirstudy,aspHincreased,bothKandMgdecreased;however,CasharplyincreasedfrompH5to7.ItalsoincreasedafterpHdroppedbelow3.5.Itisunusualthatsoilconsistingofvolcanic-ashinfluencedmaterials,whichhaveavariablecharge,didnotshowamarkedreductionintheretentionofexchangeablebaseswithdecreasingpH.Thisindicatestheremaybeenoughpermanentchargemineralstomaintainbaseconcentrations.Intheferngladeandthefern-invadedclearcut,soilsmaybedevelopingpropertiestypicalofnonallophanicAndisols(Johnson-Maynardandothers1997).
LackofpH-drivenchangesincationconcentrationinourstudymayberelatedto high organic C content of the ash-influenced soil (Shoji and others 1993).Theoretically,oncethesesitesareharvested,substantiallossesofbasiccationsare
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possible.Bothlossofnutrientsfromabovegroundpools(Boyleandothers1973;Federerandothers1989)andincreasedleachinglosseshavebeenreportedafterharvesting(Hendricksonandothers1989).However,cationsmayberedistrib-utedintonew,immediateregrowthofbrackenfernorwesternconeflowerafterharvestingandnotlostfromthesite(Johnsonandothers1997).
Available Phosphorus
Phosphorus(P)amountsvariedsignificantlyamongvegetationtypesandsoildepths.ThemeanvaluesforPinthecontroltreatmentareshownintable4.ThelargestPmeansareinthe0-5cmdepthundertheundisturbedforests(NezPerceNationalForest3.17μg/gandClearwaterNationalForest3.03μg/g).Thefernglade(2.73μg/g)andfern-invadedclearcut(2.20μg/g)wereintermediateinP,andthelowestmeanswereintheconeflower-invadedclearcut(1.87μg/g)andpartialcut(1.70μg/g).
RegressionanalysesshowedthatPincreasedwithdecreasingpH.ResponseofsoilPwassimilaratbothsoildepths;therefore,regressionequationsareshownonlyforthe0-5cmdepth(table5).Thevegetationtypeshadsimilarresponse
Table 4—Mean P, potentially mineralizable N (PMN), nitrate (NO�-N), aluminum (Al), and total acidity in the control treat-ment, by vegetation type and soil depth. Each mean is the average of three replications.
National Vegetation Forest type P PMN NO3-N Al Total acidity
µg/g - - - - - - mg/kg - - - - - - - - - - - -cmol/kg - - - - - 0-5 cm depthClearwater Undisturbed forest �.0� c‡ 100.41 b �7.7� a 0.17 a 0.2� aNez Perce Undisturbed forest �.17 c �0.1� ab 172.01 b 0.22 a 0.41 abClearwater Partial cut 1.70 a 14.9� a 10�.1� a 0.�4 ab 0.�� bcClearwater Natural bracken fern glade 2.7� c 7.�� a 2�0.07 bc 0.�4 b 0.7� cClearwater Bracken fern-invaded clearcut 2.20 b ��.�2 ab 24�.99 c 1.14 c 1.77 dNez Perce Coneflower-invaded clearcut 1.�7 ab 2.14 a 97.�1 a 0.2� a 0.�4 ab 10-15 cm depthClearwater Undisturbed forest 1.�0 c �.�� a 24.0� a 0.1� a 0.�1 aNez Perce Undisturbed forest 2.10 d ��.�� a ��.�1 a 0.�1 ab 0.9� abClearwater Partial cut 1.40 b 2�.04 a �1.�� ab 0.�0 a 0.�1 aClearwater Natural bracken fern glade 1.�0 b �.97 a 1��.94 c 1.�� b 1.70 bClearwater Bracken fern-invaded clearcut 2.�� e 192.�0 b 127.4� bc �.�� c 4.22 cNez Perce Coneflower-invaded clearcut 0.9� a 29.�1 a 47.�1 ab 0.21 a 0.�1 a‡ Within each soil depth, means followed by different letters are significantly different (p = 0.05) using LSMEANS.
Table 5—Regression equations for 0-� cm depth (bold lines on figs. �, �, and �).
Y= exp (βo +β1*pH) and Y, βo, and β1 take on the following values:
Definition Dependent(Y) βo β1
P concentration PHOS 2.�7�9 –0.��12Potentially mineralizable N PMN 10.449� –1.44�7NO�-N concentration NO�-N –7.14�2 2.2212KCl-extractable Al ALUM 10.�40� –2.2�14Total acidity ACID 9.9�7� –2.0�2�
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surfaces(fig.3).SoilfromtheClearwaterNationalForestundisturbedforesthadthehighestavailablePwhenpHdroppedbelow4.0.Bothhumusandallophanecontentinvolcanicash-influencedsoilsaffectPavailabilityandthehighlevelofCinthefern-invadedclearcutsoilmaybesorbingP(Wada1985).Theseresultsarequitedifferentfromtheloessalsoilsthathaveastronglinearincreaseinavail-ablePaspHincreases(MohebbiandMahler1988).Forvolcanicash-influencedsoils,thepHdependencyofphosphatesorptionishighestbetweenpH3and4,andgenerallydecreaseswithincreasingpH(Nanzyo1987).Thisisespeciallytrueforallophanicash-influencedsoilsascomparedtononallophanicash-influencedsoils(Nanzyoandothers1993).
Insoilsconsistingofweatheredvolcanicash,Psorptionisamajorsoilfertilityproblem(AndreggandNaylor1988).Inmostmineralsoils,organicmatterisanimportantreservoirforP.However,inmanyvolcanicash-influencedsoils,organicmatterprotectsPfromsorption(Moshiandothers1974).Thisappearstobethecaseforthesesoilsaswell.
Figure 3—Regression equations for available P concentration (µg/g) of the 0-� cm depth as affected by pH manipulation by vegetation type. The bold line is the regression for all vegetation types.
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Potentially Mineralizable N and Nitrate-N
PotentiallymineralizableN(PMN)concentrationsvariedwidelyamongveg-etationtypesandsoildepths(table4).Forexample,inthecontrolsoilforthe0-5cmdepth,PMNrangedfromalowof2.14mg/kgintheconeflower-invadedclearcutto100.41mg/kgintheundisturbedforestontheClearwaterNationalForest.AmountsofPMNatthe0-5cmsoildepthwaslowinthefernglade,butintermediateinthefern-invadedclearcut.
Nitrate-N(NO3-N)alsovariedamongvegetationandsoildepths.Thelargestmeansatthe0-5cmdepthforthecontrolsoil(table4)wereinthefern-invadedclearcut(246.99mg/kg)andfernglade(230.07mg/kg),andthelowestmeanwas87.73mg/kgintheundisturbedforestsoilfromtheClearwaterNationalForest.MeansforNO3-Natthe10-15cmdepthwerelowerthanthe0-5cmdepth,butthetrendsweresimilar.
AnalysesshowedthatPMNconcentrationsdeclinedrapidlyassoilpHincreasedabove5.0and,incontrast,soilNO3-NconcentrationincreasedrapidlyabovepH5.0,exceptintheferngladeandfern-invadedclearcutwherethischangeinNformoccurredbelowpH4.5(fig.4a-f).WhilethesoilsinbothundisturbedforestsandthepartialcutforestsexhibitedathresholdlevelofpH5.0forsub-stantialchangesinthequantityofavailableN,thetwositeswithbrackenfernvegetationtypesandtheconeflower-invadedclearcuthadsteadychangesinNaspHincreased.Bothsoildepthshavesimilarregressioncurvesforeachvegetationtype;therefore,onlythe0-5cmsoildepthisshown(table5).
The sharpdecline inPMN from theseash-influenced sites isdifferent fromthenorthernIdaholoessalsoils,whichhadasignificantincreaseinPMNaspHincreasedfrom3.0to7.0(MohebbiandMahler1988).Thismayindicateadiffer-enceinorganicmatterconcentrationfromloess-grasslandareastoash-forestedareas,andsuggeststhatorganicNinvolcanicash-influencedsoilsmaybefairlyresistanttomicrobialdecompositionbecauseoftheAl-organiccomplexesthatareformed(Shojiandothers1993).
Whilesoilfrommostofthevegetationtypesshowacrossoverinrelativeabun-danceofPMNandNO3-NaroundpH5.0,thebracken-ferndominatedvegetationtypeschangebelowpH4.5.IncreasedNO3
-NanddecreasedPMNathigherpHvaluesisconsistentwithresultsofacidrainandsoilnutritionstudies(Schier1986;Marx1990).NitrogenmineralizationoftenincreaseswhensoilpHisraised(MontesandChristensen1979),butoccasionallyhasbeenshowntodecrease(AdamsandCornforth1973).NitrificationisalsopHsensitiveandgenerallyincreasesaspHisraisedfromveryacidtomoderatelyacid(Robertson1982).Inthisstudy,theclearcutsinvadedwitheitherbrackenfernorwesternconeflowerlikelyexhibitthisNchangeeachyearaspHchanges(BinkleyandRichter1987).
Aluminum and Total Acidity
KCl-extractableAl (whichreflectsexchangeableAl)and totalacidityvariedsignificantlyamongvegetationtypesandsoildepths.Meanvaluesinthecontroltreatments are shown in table4.Aluminumand total acidity are significantlyhigherintheferngladeandfern-invadedclearcut,forbothdepths.MeanAlandacidvaluesaregenerallyhigherinthe10-15cmdepthsoilascomparedtothe0-5cmdepth.
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Figure 4—Soil NO�-N and PMN concentration (mg/kg) in the 0-� cm depth as affected by pH manipulation, by vegetation type (a) Clearwater National Forest, undisturbed, (b) Nez Perce National Forest, undisturbed, (c) Clearwater National Forest, partial cut, (d) Clearwater National Forest, bracken fern glade, (e) Clearwater National Forest, bracken fern-invaded clearcut, (f) Nez Perce National Forest, coneflower-invaded clearcut.
(a) (b)
(c) (d)
(e) (f)
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RegressionanalysesshowedthatAlwashighlycorrelatedwithchangesinpH(table5)inallvegetationtypes.AluminumincreasedexponentiallywhenthepHdecreasedbelow4.5(fig.5).Both0-5cmand10-15cmdepthshadsimilarcurves;therefore,onlythe0-5cmsoildepthregressionlinesareshown.Volcanicash-influencedsoilscontainhighlevelsofAl-containingmaterialsthatcanundergodissolutionunderacidic(lessthatpH5.0)conditions(Tisdaleandothers1993).Inthesesoils,verylittleexchangeableAlwasdetectedabovepH5.0.BasedoncontinuoussoilmeasurementsofpH(figs.1and2),soilsunderbrackenfernandconeflowervegetationhaveapHbelow5.0eachgrowingseason.SoilpH5.0isgenerallyconsideredtobethecriticalpointforAltoxicitytowoodyvegetation(Wolt1994).
Ingeneral,woodyplantspeciesappeartobemoretolerantofAlthanagricul-turecrops(McCormickandSteiner1978;Ryanandothers1986),andthereisconsiderablevariationinAltoleranceamongtreespecies(McCormickandSteiner1978;Steinerandothers1984;ArpandOuimet1986;Hutchinsonandothers1986;Schaedleandothers1989;Raynalandothers1990).Aluminumtoxicityalterstreerootanatomy,whichfirstoccursintheroots(Hutchinsonandothers1986;Schaedleandothers1989;McQuattieandSchier1990;NoskoandKer-shaw1992;Schier1996).TheresultofAltoxicityisimpairedrootdevelopment,resultinginreducedrootlengthandformationofashallowrootsystem.Athigh
Figure 5—Exchangeable Al concentration (cmol/ kg) in the 0-� cm depth as affected by pH, by vegetation type. The bold line is the regression for all vegetation types.
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Allevels,mitosisisalmostcompletelyinhibited.Leamy(1988)notedthatinvol-canicash-influencedsoils,Altoxicitymayoccuratconcentrationsof2cmol/kgsoil,andthisvalueisusedasathresholdinSoilTaxonomyforidentifyingthoseAndisolsinwhichAlphytotoxicitymayoccur(SoilSurveyStaff2003).Aluminumlevelsfoundinthislaboratorystudyaremuchhigherthan2cmol/kgwhenpHdecreasedbelow5.0andindicatesastrongpotentialforAltoxicityintheseash-influencedsoilsaspHvaluesdecline.
ThevariousstudiesonAltoxicityintreespeciesaredifficulttocomparebecauseofdifferent studymethods,unitsofmeasure,growthmedia, lengthofexperi-ments,andageoftrees(Schaedleandothers1989;NoskoandKershaw1992).However,oneimportantfindingisthatyoungseedlingsaremoresensitivetoAltoxicitythanolderseedlings.Forexample,Schier(1996)foundthatAlconcentra-tionsof0.32mM/linhibitedrootbiomassinnewlygerminatedredspruce(Picea rubens)seedlings,whilethethresholdwas2.1mM/lin1-year-oldseedlings.ItseemsreasonabletoassumethatconiferseedgerminatingonGFMsitescouldbeimpactedbylowconcentrationsofAl.Aluminumtoxicity,allelopathiccom-pounds,andcompetitioncouldcombinetoeliminatethenaturalestablishmentoftreesandotherwoodyplantspeciesonthesesites.
Regressionanalyses for totalacidity followed thesame trendasextractableAl(fig.6),andonlythe0-5cmsoilregressionlinesareshown.Theregressionequationfortotalacidityisshownintable5.Mostoftheacidityinthesesoils
Figure 6—Total acidity (cmol/kg) in the 0-� cm depth as affected by pH manipulation by, vegetation type. The bold line is the regression for all vegetation types.
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occursasAl.TherelationshipbetweenexchangeableAlandtotalacidityisnotunusual sincemost of the exchangeable acidity is derived fromAl andHontheexchangesites(BinkleyandRichter1987).Changesinexchangeableaciditygenerallyoccuroveralongperiodoftimeandareduetoacidificationthroughweathering,leaching,cationuptake,oratmosphericdeposition(Richter1986).RapidchangesinacidityoccuroccasionallybyotherH-ioninputs.IntheGFM,bothbrackenfernandwesternconeflowervegetationhavethepotentialtoinputH-ionsviaorganicacidproductionoradditionsofhighamountsoforganicCthroughyearlyvegetationcycles.
Summary ______________________________________________________Analysis of unaltered soil samples supporting undisturbed grand fir forest
andbrackenfern/westernconeflowerplantcommunitiessuggeststhatchemicalpropertiesofGFMforestsoilarealteredthroughinvasionofsuccessionalplantspeciesaftertimberharvestorotherdisturbance.Changesinsoilconditionsaresimilartoadepthof15cm.SeasonaldecreasesinsoilpHunderbrackenfernandwesternconeflowervegetationtypesmostlikelycauseareleaseofexchangeableAlatlevelstoxictowoodyvegetation.HighlevelsofC,exchangeableAl,andtotalacidityunderthesetwovegetationtypesmayalsobefacilitatingalocalizedconversionoftheseash-influencedsoilsfromallophanictononallophanicAndis-ols.ForestedsoilsintheGFMarecapableofexhibitingthesesamecharacteristicsoncedisturbed.
Resultsofthisstudyalsoprovideinsightsintothechemicalchangesthatmayoccurinvolcanicash-influencedsoilsaspHfluctuates.Mechanismsthatcon-tributetoforb-dominatedsecondarysuccessionalplantcommunitieshavebeenidentified.Forexample, theapparentchangeinNbetweenPMNandNO3-Nhasimplicationsindeterminingwhichspeciescangrowonthesesites,asdoestheexponentialincreaseofAlbelowpH5.0.Clearly,thislaboratorystudypointsoutthepotentialforAltoxicitythatmayaccompanyseasonalpHfluctuations.Theselaboratorystudyfindingsareconsistentwithin situsoilsolutiondata,whichindicate that soils invaded by bracken fern and western coneflower undergoconversionfromallophonictononallophanicproperties(Johnson-Maynardandothers1997).However,alteringthepHofash-influencedsoilsdifferedfromal-teringloessalsoils(MohebbiandMahler1988).Thesesoil-typedifferencesarelikelyattributabletotheuniquephysical,chemical,andbiologicalpropertiesofash-influencedsoilsascomparedtothosederivedfromotherparentmaterials(Dahlgrenandothers2004).
This laboratory study highlights important characteristics of ash-influencedsoilsthatmaycontributetochangesinvegetation.Thistypeofstudy,combinedwithfieldwork,willhelpinthedevelopmentofpracticalmanagementrecom-mendations.
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Kuo,S.1996.Phosphorus.In:Methodsofsoilanalysis.Part3.Chemicalmethods.Madison,WI:SoilScienceSocietyofAmerica:869-919.
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Stewart,R.E.1975.Allelopathicpotentialofwesternbracken.J.Chem.Ecol.1:161-169.Tisdale,S.L.;Beaton,J.D.;Nelson,W.L.;Havlin,J.L.1993.Soilfertilityandfertilizers.New
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University.36p.M.S.thesis.
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In: Page-Dumroese, Deborah; Miller, Richard; Mital, Jim; McDaniel, Paul; Miller, Dan, tech. eds. 2007. Volcanic-Ash-Derived Forest Soils of the Inland Northwest: Properties and Implications for Management and Restoration. 9-10 November 2005; Coeur d’Alene, ID. Proceedings RMRS-P-44; Fort Collins, CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station.
William Elliot is Project Leader, Ina Sue Miller is Hydrologist, and David Hall is IT Specialist, Soil and Water Engineering Research Work Unit, Rocky Mountain Research Station, Moscow, ID.
WEPP FuME Analysis for a North Idaho Site
William Elliot, Ina Sue Miller, and David Hall
Introduction
Acomputerinterfacehasbeendevelopedtoassistwithanalyzingsoilerosionratesassoci-atedwithfuelmanagementactivities.ThisinterfaceusestheWaterErosionPredictionProject(WEPP)modeltopredictsedimentyieldsfromhillslopesandroadsegmentstothestreamnetwork.Thesimple interfacehasa largedatabaseofclimates,vegetationfilesandforestsoilpropertiestosupportthisandotherinterfaces,includingDisturbedWEPPforforestsandWEPP:Roadforroadsegmentanalyses.Thesoildatabasesforroadsanddisturbedforestedhillslopesarebasedonrainfallsimulationandnaturalrainfallstudies. TheWEPPFuMEinterfacecarriesouterosionpredictionrunsforsixforestconditions:
1.Undisturbedmatureforest 2.Wildfire 3.Prescribedfire 4.Thinning 5.Lowtrafficroads 6.Hightrafficroads
Theclimate,soiltexture,topography,roaddensity,wildfirereturninterval,prescribedfirecycleandthinningcyclearespecifiedbytheuser. TheWEPPFuMEinterfacecanbeusedanywherewithintheUnitedStatesusingtheexistingclimatedatabase.Theinterfaceisintendedtoprovideanoverviewofthesourcesofsedimentonagiven fuelmanagement site. Sedimentpredictions fromWEPPFuMEare for surfaceerosiononly.
20� USDA Forest Service Proceedings RMRS-P-44. 2007
Elliot, Miller, and Hall WEPP FuME Analysis for a North Idaho Site
Hillslope Method and Parameters _________________________________The example in this paper is an area within the Yellowpine timber sale in
northernIdaho(fig.1).ThewatershedhillslopeboundariesweredelineatedusingGeoWEPP(ageo-spatialinterfacetoolforWEPP)(fig.2).EachhillslopefromtheexamplewatershedwasexaminedusingtheFuMEmodel.Onlyonehillslopecanberunatatimeandinthisinstance,hillslopenumber22isdisplayed(fig.2).
FuMEwasrunforanindividualhillslope(number22,fig.2).Theconditionsofthemodelweresandyloamsoiltexture,hillslopelengthof708feet,hillslopegradientstartingwiththetopofthehill25,36,and20percent,a40ftbufferlengthandthedefaultroaddensity,fireandthinningcycles.
Figure 1—Unit 4 of the Yellowpine timber sale in northern Idaho.
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WEPP FuME Analysis for a North Idaho Site Elliot, Miller, and Hall
Figure 2—The WEPP-FuME model windows for hillslope 22.
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Elliot, Miller, and Hall WEPP FuME Analysis for a North Idaho Site
Table 1—WEPP FuME summarized results and weighted averages.
Thinning + Rx Background Thinning Rx Fire Thinning + Rx fire fire w/moderate Hill slope sedimentation effects effects w/high severity fire severity fire
- - - - - - - - - - - - - (ton/mi2)- - - - - - - - - - - (ton/mi2)* (ton/mi2)** 22 1�9 141.� 1�2.1 1��.� �2.92 2� 97.2 9�.2 99.1 100.2 �0.�2 �1 92.2 92.� 9�.2 9�.� 2�.4� �2 120.� 122.� 12�.� 129.7 ��.94 �� 11�.� 119.� 120.2 121.� �9.4� 41 104.1 10�.1 10�.1 10�.2 �1.�� 42 144.� 14�.� 144.� 14�.9 4�.�2 4� 9�.� 94.� 94.� 10�.1 29.02
Weighted averagesfor the examplewatershed 11�.7 11�.2 117.9 120.� �9.9* The projected background rate in this column assumes fuel management activities did not reduce the fire hazard by remov-ing excess fuel. The estimated background rate for this column was calculated with a high severity fire value.** The projected background rate in this column assumes fuel management activities reduce the fire hazard by removing excess fuel. Therefore, the estimated background rate for this column was calculated with a moderate severity fire value.
Note: All sedimentation estimates displayed above are calculated from the low end erosion rates of the road network.The high severity fire value was used in the background sedimentation rate calculation unless stated otherwise.
Cumulative Watershed Results ____________________________________AllhillslopesfromtheexamplewatershedwereanalyzedwithWEPPFuME.
Thesummarizedresultsandweightedaveragesfortheexamplewatershedaredisplayedintable1below.
Fromthetablewecanobservethatifamoderatefirescenariooccursevery40yearsforthewatershed,incombinationwiththeprescribedfireandthinningmanagementactivities,includingerosionfromroads,thereisa65percentdecreaseoferosionoccurringwhencomparedtothebackgroundrate.Intheeventofahighseverityfire,incombinationwiththeprescribedfireandthinningmanage-mentactivitiesincludingtheerosionfromroads,thetotalwatershedresultsina6percentincreaseofpredictederosion.Forbothexamples,thebackgroundrateincludeslowimpactroadsandthehighseverityfirescenario.
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WEPP FuME Analysis for a North Idaho Site Elliot, Miller, and Hall
References ______________________________________________________Covert,S.A.;Robichaud,P.R.;Elliot,W.J.;Link,T.E.2005.Evaluationofrunoffpredictionfrom
WEPP-basederosionmodelsforharvestedandburnedforestwatersheds.TransactionsoftheASAE.48(3):1091-1100.
Elliot,W.J.2004.WEPPinternetinterfacesforforesterosionprediction.Jour.oftheAmer.WaterRes.Assoc.40(2):299-309.
Elliot,W.J.;Hall,D.E.1997.WaterErosionPredictionProject(WEPP)forestapplications.GeneralTechnicalReport INT-GTR-365.Ogden,UT:U.S.DepartmentofAgriculture,ForestService,IntermountainResearchStation.11p.
Elliot,W.J.;Hall,D.E.2005.WaterErosionPredictionProject(WEPP)FuelManagement(FuME)tool.Fuelsplanning:sciencesynthesisandintegration;environmentalconsequencesfactsheet12.Res.NoteRMRS-RN-23-12-WWW.FortCollins,CO:U.S.DepartmentofAgriculture,ForestService,RockyMountainResearchStation.2p.
Elliot,W.J.;Robichaud,P.R.2004.Theeffectivenessofpostfiremitigationtreatments.Presentedatthe2004BAERTrainingWorkshop;2004April30;Denver,CO.
Elliot,W.J.;Robichaud,P.R.2004.Evaluatingsedimentrisksassociatedwithfuelmanagement.Fuelsplanning:sciencesynthesisandintegration;environmentalconsequencesfactsheet8.Res.NoteRMRS-RN-23-8-WWW.FortCollins,CO:U.S.DepartmentofAgriculture,ForestService,RockyMountainResearchStation.2p.
Elliot,W.J.;Miller,I.S.2002.EstimatingErosionImpactsfromImplementingtheNationalFirePlan.2002ASAEannualinternationalmeeting/CIGRXVthworldcongress;2002July28-31;Chicago,IL.St.Joseph,MI:ASAE:ASAEmeetingpaperno.02-5011.
Elliot, W. J.; Miller, I. S. 2004. Measuring Low Rates of Erosion from Forest Fuel ReductionOperations,2004ASAE/CSAEAnnualInternationalMeeting;2004August1-4;Ottawa,Ontario,Canada:ASAEpapernumber045018.
Laflen,J.M.;Elliot,W.J.;Flanagan,D.C.;Meyer,C.R.;Nearing,M.A.1997.WEPP–Predictingwatererosionusingaprocess-basedmodel. JournalofSoil andWaterConservation.52(2):96-102.
McDonald,G.I.;Harvey,A.E.;Tonn,J.R.2000.Fire,competitionandforestpests:Landscapetreatmenttosustainecosystemfunction.In:Neuenschwander,L.F.;Ryan,K.C.,eds.Proceed-ingsfromtheJointFireScienceConferenceandWorkshop;1999June15-17;Boise,ID.Onlineat<http://jfsp.nifc.gov/conferenceproc/T-11McDonaldetal.pdf>.AccessedJune,2004:17p.
Spigel, K. M. 2002. First year postfire erosion rates in Bitterroot National Forest, Montana.Madison,WI:UniversityofWisconsin.147p.MSThesis.
211USDA Forest Service Proceedings RMRS-P-44. 2007
In: Page-Dumroese, Deborah; Miller, Richard; Mital, Jim; McDaniel, Paul; Miller, Dan, tech. eds. 2007. Volcanic-Ash-Derived Forest Soils of the Inland Northwest: Properties and Implications for Management and Restoration. 9-10 November 2005; Coeur d’Alene, ID. Proceedings RMRS-P-44; Fort Collins, CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station.
William Elliot is Project Leader, Ina Sue Miller is Hydrologist, and Brandon Glaza is Civil Engineer, Soil and Water Engineering Research Work Unit, Rocky Mountain Research Station, Moscow, ID.
Erosion Risks in Selected Watersheds for the 2005 School Fire Located Near Pomeroy,
Washington on Predominately Ash-Cap Soils
William Elliot, Ina Sue Miller, and Brandon Glaza
Geo-WEPP Spatial Analysis
Alimitederosionpotentialanalysiswascarriedoutonthe50,000acreSchoolFire.ThreeWEPPinterfaceswereusedfor theanalysis,aGISwizard,anonline interfaceandawin-dowsinterface.TenwatershedswithinthefireareaweremodeledwiththeGeoWEPPtool(ageo-spatialinterfaceforWEPP,WaterErosionPredicationProject).Thewatershedscovered18,823acres,orabout38percentofthetotalburnedarea.Hillslopeswerespecifiedhigh,moderateorlowburnseveritybyexaminingtheBAER(BurnedAreaEmergencyResponse)severitymap. ByconsultingwiththeBAERspecialists,watershedsofgreatestinterestwereidentified.OnesetincludedfourwatershedsdischargingintotheTucannonRiverfromthewesternside,in-cludingSchoolCreek,whichflowedintotheTucannonRiverattheTucannonGuardStation.AsecondsetincludedthreewatershedsflowingintotheTucannonRiverfromtheeastside,southoftheTucannonGuardStation.ThethirdsetofwatershedswerelargerandincorporatedDryCreek(atributarytoCummingsCreek),CummingsCreekandPatahaCreek.
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Elliot, Miller, and Glaza Erosion Risks in Selected Watersheds for the 200� School Fire Located Near Pomeroy, Washington…
ERMiT Hillslope Analysis – Online Interface ________________________TheERMiT(ErosionRehabilitationManagementTool;August,2005version)
resultsforasinglestormerosionpredictionaregivenintable1below.Table2providesanoverallaverageofallERMiT runs.Hillslopeswerespecifiedhigh,moderateorlowseverityfromtheBAERseveritymap.Anaverageofabout12randomlyselectedhillslopesor5percentofthehillslopesonlargerwatersheds,wererunwithERMiTforeachwatershed,withtheexceptionofupperPataha.IntheupperPatahawatershed,only10hillslopeswereidentifiedasmoderateorseverelyburned.Themulchingtreatmentassumedanapplicationroleof0.9tons/acrefollowingthefire.Onaverage,thereisa20percentchancethattheerosionrateinthewatershedwillbegreaterthan7tonsperacreifleftuntreated,andonlya10percentprobabilitythaterosionwillexceed10tons/acifleftuntreated.
Table 1—ERMiT single storm erosion predictions – August-200� version.
Untreated Seeded Mulched Year Year Year Drainage Exceedance 1 2 1 2 1 2
- - - - - - - - - - - - - - - - - (tons/ac) - - - - - - - - - - - - - - - - - -
Tucannon West � 10% Mean 12.9� 9.00 12.9� 4.9� 1.�4 �.11 Std Dev �.00 �.97 �.00 �.�2 0.�� 2.1�
20% Mean �.�7 �.7� �.�7 2.27 0.00 0.92 Std Dev �.�� �.9� �.�� 1.7� 0.00 0.79
Tucannon West 2 10% Mean 10.0� 7.24 10.0� �.9� 0.99 2.4� Std Dev �.40 �.�0 �.4 4.0� 1.02 2.�0
20% Mean �.�� 4.�7 �.�� 1.7� 0.00 0.70 Std Dev �.22 4.71 �.22 2.09 0.00 0.��
Tucannon West 1 10% Mean 14.14 9.�1 14.14 �.27 1.�� �.1� Std Dev �.11 �.9� �.11 �.79 1.�� 2.�1
20% Mean 9.2� �.2� 9.2� 2.21 0.00 0.90 Std Dev �.79 4.44 �.79 1.99 0.00 0.�7
School Canyon 10% Mean �.00 4.1� �.00 2.21 0.�� 1.�4 Std Dev 7.00 �.24 7.00 �.�� 0.74 2.04
20% Mean �.77 2.�1 �.77 0.92 0.00 0.�7 Std Dev �.1� �.�4 �.1� 1.�4 0.00 0.�7
Grub Creek 10% Mean 10.71 7.70 10.71 4.�� 1.10 2.�7 Std Dev �.�1 �.2� �.�1 �.�7 0.9� 2.�7
20% Mean 7.�1 �.1� 7.�1 1.9� 0.00 0.7� Std Dev �.02 4.�� �.02 1.9� 0.00 0.�4
Hixon Creek 10% Mean �.71 4.49 �.71 2.0� 0.�� 1.�9 Std Dev �.�1 �.7� �.�1 �.41 1.�4 2.41
20% Mean 4.10 2.4� 4.10 0.9� 0.00 0.�7 Std Dev �.7� 4.0� �.7� 2.00 0.00 0.7�
(continued)
21�USDA Forest Service Proceedings RMRS-P-44. 2007
Erosion Risks in Selected Watersheds for the 200� School Fire Located Near Pomeroy, Washington… Elliot, Miller, and Glaza
Table 2—Average of ERMiT runs.
Untreated Seeded Mulched Year Year Year Drainage Exceedance 1 2 1 2 1 2
- - - - - - - - - - - - - - - - - (tons/ac) - - - - - - - - - - - - - - - - - -
Means of ten sets of 10% Mean 10.�2 7.�� 10.�2 4.�� 1.�1 2.9�ERMiT runs Std Dev 2.�0 1.�� 2.�0 1.24 1.0� 1.24
20% Mean 7.0� 4.�0 7.10 1.99 0.1� 0.�� Std Dev 1.�� 1.11 1.�� 0.72 0.�1 0.40
Tucannon East 10% Mean �.22 �.72 �.22 2.90 0.72 1.�2unnamed Std Dev �.44 �.24 �.44 �.9� 0.�9 2.��
20% Mean �.2� �.44 �.2� 1.22 0.00 0.�1 Std Dev �.94 4.49 �.94 1.97 0.00 0.��
Upper Cummings 10% Mean 10.2� �.94 10.2� �.99 1.04 2.�4Creek Std Dev �.0� 4.42 �.0� 2.�2 1.0� 1.71
20% Mean �.70 4.7� �.70 1.�� 0.00 0.�1 Std Dev 4.1� �.07 4.1� 1.2� 0.00 0.��
Dry Creek 10% Mean 11.�2 7.77 11.�� �.2� �.0� 4.�� Std Dev �.�9 �.0� �.�� 4.2� 2.7� �.�9
20% Mean �.�7 4.�1 7.�0 2.70 0.7� 1.�1 Std Dev �.7� 4.07 �.77 2.71 1.0� 1.�7
Upper Pataha 10% Mean 1�.�� 9.4� 1�.�� �.�4 �.�9 �.�9 Std Dev �.17 4.1� �.17 �.10 1.9� 2.7�
20% Mean 9.02 �.�0 9.02 �.40 0.7� 1.�� Std Dev �.90 2.�� �.90 1.70 0.�4 0.�1
Table 1 (Continued).
Untreated Seeded Mulched Year Year Year Drainage Exceedance 1 2 1 2 1 2
- - - - - - - - - - - - - - - - - (tons/ac) - - - - - - - - - - - - - - - - - -
WEPP Windows Analysis ________________________________________TheWEPPwindowsinterfacewasrunforeachwatershedtoestimatereturn
periodsforpeakrunoffrates.Theseresultswerecombinedwithothermethodstomakefinalrunoffpredictions.
Conclusions _____________________________________________________TheGeoWEPPtoolallowstheuser toquicklyestimatehillslopeparameters
foruseintheERMiTprogram.TheresultsfromtheERMiTprogramshowthatmulchingwillhavemajorbenefits in reducingerosion,especiallyon thehighseverityareas.Ontheotherhand,erosionrisksonlowseverityburnedslopeswereprojectedasbeingminimal.
214 USDA Forest Service Proceedings RMRS-P-44. 2007
Elliot, Miller, and Glaza Erosion Risks in Selected Watersheds for the 200� School Fire Located Near Pomeroy, Washington…
References ______________________________________________________Elliot,W.J.;Cuhaciyan,C.O.;Robichaud,P.R.;Pierson,F.B.;Wohlgemuth,P.M.2001.Modeling
ErosionVariabilityafterFire.Presentationatthe2001ASAEInternationalMeeting;2001July30-August1;Sacramento,CA.
Foltz,R.B.;Elliot,W.J.1999.ForesterosionprobabilityanalysiswiththeWEPPModel.Presentedatthe1999ASAE/CSAEAnnualInternationalMeeting,PaperNo.995047.St.Joseph,MI:ASAE.
Laflen,J.M.;Elliot,W.J.;Flanagan,D.C.;Meyer,C.R.;Nearing,M.A.1997.WEPP–Predictingwatererosionusingaprocess-basedmodel.JournalofSoilandWaterConservation.52(2):96-102.
Renschler,C.S.2004.TheGeo-spatialinterfacefortheWaterErosionPredictionProject(GeoWEPP).Onlineat<http://www.geog.buffalo.edu/~rensch/geowepp/>.AccessedJune,2004.
Robichaud,P.R.;Elliot,W.J.;Pierson,F.B.;Hall,D.E.;Moffet,C.A.2006.ErosionRiskManagementTool(ERMiT)Ver.2006.01.18.Onlineat<http://forest.moscowfsl.wsu.edu/fswepp/>.Moscow,ID:U.S.DepartmentofAgriculture,ForestService,RockyMountainResearchStation.
USDAARSNationalSoilErosionResearchLaboratory.2004.WEPPSoftware.Onlineat<http://topsoil.nserl.purdue.edu/nserlweb/weppmain/wepp.html>.AccessedJune,2004.
21�USDA Forest Service Proceedings RMRS-P-44. 2007
In: Page-Dumroese, Deborah; Miller, Richard; Mital, Jim; McDaniel, Paul; Miller, Dan, tech. eds. 2007. Volcanic-Ash-Derived Forest Soils of the Inland Northwest: Properties and Implications for Management and Restoration. 9-10 November 2005; Coeur d’Alene, ID. Proceedings RMRS-P-44; Fort Collins, CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station.
Richard E. Miller, USDA Forest Service, PNW Research Station (retired), Olympia, WA.
Conference Wrap-upRichard E. Miller
Mypurposeistwofold:toreviewkeymessagesfrompreviousspeakersandtooffersomeconceptsthatmayhelpyoulinkrecentlyacquiredinformation. WhenMt.Mazamaeruptedabout7,000yearsago,itsairborneashandpumicefellonawidevarietyofexistingsoils.ThisMazamatephrawasanewparentmaterialforsoildevelop-ment(fig.1).Atsomelocations,theoriginaldepositionwasredistributedby:gravity,wind,water,plants,oranimalactivities,includingthoseofhumans.SoilatanyspecificlocationintheInlandWestisaresultofthesesoil-formingfactorsandtheirmanypossibleinteractions.
Figure 1—Soil-forming factors (Jenny 1941).
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Major Take-Home Messages _____________________________________ 1.Ash-derivedsoilsareextensive,variable,anddifferentfromsoilsderived
fromotherparentmaterials. 2.Activities(equipment,fire)canchangesoilpropertiesandfunctions. 3.Consequences of soil changes for vegetative growth or soil erosion are
uncertain,becausetheyareseldomquantified. 4.Hence, optimum allocation of preventative or restorative efforts is
uncertain.
What is a Forester to do? ________________________________________Assumingyourintentistoprotectandmanagesoilatspecificlocations,how
willyouuseinformationgainedatthisconference?Canyoustatefactsandex-plainrelationshipsamongthesefacts?Willthisnewinformationchangeoraffectyourfuturedecisionsaboutprescribingorcontrollingactivitiesonash-derivedorash-influencedsoils?
Mostforestersandlandmanagersareconcernedaboutyield…ofwood,forageandprotectivevegetation.Mostrecognizethatyieldataspecificlocationdependsonnumerousfactorsandtheirinteractions(fig.2).Severalspeakersreviewedtheeffectsonsoilpropertiesofeitherheavyequipmentusedinharvestingorofwildandprescribedfire.Youshouldrecognizethatachangeinsoilpropertiesisachangeinoneofseveralfactorsthatcontributestoyield.Despitevisuallyapparentormeasuredchangesinsoilcharacteristics(forexample,bulkdensity,resistance,organicmatter)orfunctions,however,yieldmaynotchange.Otherfactorsthatalsoaffectyieldatagivenlocationcanbeenhancedbyorcompensateforthe
Figure 2—Factors that set productivity or yield (Jenny 1941).
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potentiallynegativeeffectsofsoilchangesonyield.Factorscontrollingyieldalsointeract.Forexample,soildisturbancemayreducevegetativecompetitionfortrees.Consequently, this indirecteffectof soildisturbanceoncompetingvegetationcanenhancetreegrowthorcompensatefordirect,potentiallynegativeeffectsofdisturbanceontreegrowth.
Whenyoupropose toharvest treesorprescribe fire,canyoupredict likelyconsequencesonsoilpropertiesandsubsequentplantyield?Thecomponentsof thispracticaland importantquestionaredisplayed in figure3.You,as theagent,proposetousegroundbasedequipmentatlocationY.Doyourecognizethateachlocationhasauniquecombinationofsoils,climate,andotherfactorsthatdeterminetheseverityofsoildisturbanceandthepracticalconsequencesfortreeorvegetativegrowth?Therefore,donotanticipatethesameeffectsonsoilorgrowthatalllocations.Refertocurrentresearchresultsandexplanations,forexample,Gomezandothers(2002);Powersandothers(2005)forjustificationofyourdecisionsandrememberyourA,B,C’s(fig.4).
Theconceptofecologicalstabilityalsoappliestosoilstability(fig.5).Soilsdifferintheirinitialresistancetoheavyequipmenttraffic.Forexample,comparevisualeffectsoftrafficonasandysoilcontaining70-to90-percentgravelandcobblesbyvolume in the top3 feetwith thatonadeepsilt loamsoil that isstone-free.Thesetwosoilsdifferintheirweight-bearingcapacityandinshearstrength,especiallywhenmoistorwet.Soilsalsodifferintheirresilienceorrateofrecoveryafterdisturbance.Rateofrecoveryofsoilpropertiesandfunctionsdependslargelyoninteractionsamongclimate,above-and-belowgroundorgan-isms,andsoilproperties.Forexample,recoveryishastenedinclimatesthatcausesoiltohavecyclesofthawingandfreezing,wettinganddrying,orclimatesthatpromoterapidgrowthofplantsandotherorganisms.
Figure 3—A general concept of actions and consequences.
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Figure 4—Locations (sites) differ: Remember your A, B, C’s.
Figure 5—Ecological stability: response depends on resistance; recovery depends on resilience.
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Figure 6—Soils and site differ in resistance and resilience.
Amongthemanycombinationsofsoilsandmicro-andmacro-climatesintheInlandWest,weneedtoidentifyourA-,B-,C-locations.Recallasimilarurgingbyourafter-dinnerspeaker,LarryRoss:“goforthandstratifyforestland;”thenfitthepracticetothesoil.
Soilsandclimatesdiffer.Soilsandclimatesinteracttocreatevaryingconsequencesofsoildisturbanceorfireforyield(fig.6).Yourconsideringdifferencesinsoildepthlikedifferencesinbankaccountswillbehelpful:Equateshallowsoilstoa$100accountanddeepsoilstoa$1,000account.Thus,yourprescribingground-basedequipmentorfiretoreducefuelswillmostlikelyresultinreducedgrowthandsubsequentyieldonshallowsoilsorsoilswithshallowashcaps.Moreover,presenceofcoarse,non-weatheredrockfragmentsfurtherreduceeffectivesoildepthorthe“bankaccount.”Finally,rememberinteractions:whereequipmentorfiredegradesoilforplantgrowth,anticipatestrongerreductionsinplantgrowthwhereclimateisharshandlessfavorableforplantgrowth.
Final Take-Home Messages ______________________________________ 1.Donotassumenegative“consequences”forvegetationyieldonallsoils
andlocations(soilsdiffer…climatesdiffer…hence,treeresponsediffers). 2.HelpotherstoidentifyCaseA,B,Clocationsbymeasuringtreeresponse
todisturbance. 3.KnowyourA-,B-,C-soils/sites. 4.AllocatetimeanddollarsatCaseAlocations(whereactivitiesreducegrowth). 5.SavetimeanddollarsatCaseBandClocations(whereactivitieshaveno
effectorimprovegrowth). 6.Inshort,allocateyourprotectiveandrestorativeefforts…toachievefavor-
ablebenefit/costratios.
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Literature Cited __________________________________________________Gomez,A.;Powers,R.F.;Singer,M.J.;Horwath,W.R.2002.Soilcompactioneffectsongrowth
ofyoungponderosapinefollowinglitterremovalinCalifornia’sSierraNevada.SoilSci.Am.J.66:1334-1343.
Jenny,H.1941.FactorsofSoilFormation.ASystemofQuantitativePedology.NewYork,NY:McGraw-Hill.
Powers,R.F.;Scott,D.A.;Sanchez,F.G.;Voldseth,R.A.;Page-Dumroese,D.;Elioff,J.D.;Stone,D.M.2005.TheNorthAmericanlong-termsoilproductivityexperiment:Findingsfromthefirstdecadeofresearch.ForestEcologyandManagement.20:31-50.
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