forests are more than trees s tudforests are more than trees (cont.) s tud en t p a ge fire3 fire is...

project learning tree Exploring Environmental Issues: Focus on Forests Forests Are More Than Trees 17

© AmericAn Forest FoundAtion

Forests are More than treesS

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Nomatterwhereyoulive,youdependonforests.Theyprovidecharcoal,firewood,fruits,lumber,medicines,nuts,paper,turpentine,andotherresourcesthatmakeupmorethan5,000commercialproducts.Manypeopleuseforestsforfishing,hiking,hunting,andotherrecreationalactivities,aswellasfortheirbeautyandsolitude.

Everypersonintheworldalsodependsonforestsforanumberofbeneficialecosystem services.Thoughyoumaynotreceiveamonthlybillorpayforthemdirectly,youusethoseserviceseveryday.Theyincludethefollowing:

• Clean Water. Forestsarecriticaltomaintainingcleanwatersupplies.Forestsabsorbrain,facilitatetherechargeofundergroundaquifers,coolandcleansewater,reduceflooding,andsustainwatersheds.Forestsalsohelptoslowstormrunoff,whichhelpspreventsoilerosionandmoderateswatercyclessothatweexperienceamoreconsistentwatersupply.

• Oxygen. Likeallgreenplants,treesuseenergyfromthesuntomakecarbohydratesthroughphotosynthesis.Intheprocess,treesabsorbcarbondioxide(CO2)fromtheatmosphereandreleaseoxygen,whichhumansandotherorganismsneedtolive.

• Nutrient Cycling.Treesabsorbnutrientsfromthesoilthroughtheirrootsandtransportnutrientstocellsintheirleaves,branches,andtrunk.Whenatreediesorwhenpartsofatreefallanddecay,nutrientsandotherorganicandinorganic materials arereturnedtothesoilandatmosphere.

• Carbon Storage. Astreesgrow,theyhelptoremoveCO2fromtheatmospherebyabsorbingandstoringcarbonintheirtissues.Togrowapoundofwood,anaveragetreetakesinabout1.5pounds(0.68kg)ofCO2andgivesoffabout1.1pounds(0.50kg)ofoxygen.Thewoodcontinuestostorethe

carbon,evenwhenthewoodismadeintolumberorotherproducts.

• Temperature Regulation and Rainfall. Throughtheirrootsandleaves,treesabsorbandreleasethousandsofgallonsofwatereachdayinaprocesscalledtranspiration.Inforests,thislarge-scalemovementofwatercaninfluenceregionaltemperaturesandannualrainfall.

• Wildlife Habitat. Forestsprovideaplaceforthousandsofplantandanimalspeciestolive.Thecomplexstructureofforestscreatesmanynicheswhereanimals,plants,andotherorganismscanfindfood,shelter,andwater.

The changing Forests of north AmericaTothehumaneye,forestsmayseempermanentandtimeless.Treesriseabovetheforestflooranddominatethelandscape.Althoughtheremaybedramaticandcolorfulchangesinforestsfromseasontoseason,theforestsmaynotseemtochangemuchfromyeartoyear.Infact,however,forestsaredynamicecologicalcommunitiesthatundergoconstantchange.Someofthechangesarenaturalprocesses,suchasthegrowthanddeathoftreesandthecyclingofnutrients.Somechangesarecausedbyhumansandtheiractivitiessuchasbuildingroads,cuttingtimber,andexpandingcitiesandcommunities.Somechangeshappenquicklyoverafewhoursordays,suchasawildfireorwindstorm,whileotherchangestakemanyyearsorevendecades,suchasthegradualtransformationofameadowintoaforeststand.

NorthAmericanforestshavechangedsignificantlyinthepasttwocenturies.BeforetheEuropeansettlement,nativepeoplealreadyhadasignificantnegativeimpactonthenaturalforest.Theyregularlyburnedareasofforestlandtoimprovewildlifehabitatandhunting,tomakeiteasiertotravel,toreducenumbersofinsectpests,andtoenhanceconditionsforberriesandotherfoods.Insomeregions,nativepeoplealsoclearedforeststogrowbeans,corn,squash,andothercrops.

18 project learning tree Exploring Environmental Issues: Focus on Forests Forests Are More Than Trees © AmericAn Forest FoundAtion

Forests are More than trees (cont.)S

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WiththeEuropeansettlementandthedramaticincreaseinpopulation,thehumanaffectsonNorthAmericanforestsalsoincreased.Inthe18thand19thcenturiesinparticular,newimmigrantsclearedforestsextensivelyforagriculture,fuelwood,timber,andurbanexpansion.By1900,nearlytwo-thirdsofthepre-settlementforestintheEasternUnitedStateshadbeenremoved,resultinginareductionincleanwater,wildlifehabitat,andotherecosystemservicesprovidedbyforests.

The20thcenturybroughtarangeofconservationlawsandpracticesaimedatprotectingforestsandotherecosystems.Asaresult,theextentofforestedlandremainsrelativelystableinCanadaandisevenincreasingslightlyintheUnitedStates.ThroughoutNorthAmerica,however,forestsarestillfacingsignificantchallengesthatthreatentheirexistenceandtheirabilitytoprovideresourcesandimportantecosystemservices.

changes Facing Our Forests TodayWhenweconsidertheimportanceofforestsandthedemandsthathumansplaceonforestresources,it’snotsurprisingthatforestsfacemanychallenges.Thenatureofthosechallengesshiftsasresearch,newtechnologies,populationgrowth,developmentpatterns,economicconditions,legislation,andpoliticalleadershipcomeintoplay.PressingissuesthatfaceNorthAmericanforeststodayincludefire,climatechange,invasivespecies,andchangesinownershipandlanduse.

Invasive Species1 Invasiveplants,animals,anddiseaseshaveinfestedmillionsofacresofforestlandacrossNorthAmerica,therebycausinglocalandregionaldisruptionsinforestecosystems.Aspeciesisconsideredinvasiveifitiscapableofspreadingrapidlyandcausingeconomicorenvironmentalharm.Many,butnotall,invasivespeciesarenonnativetothelocalecosystem.Invasiveorganismsaffectthehealthofforesttrees,aswellasthehealthofwildlifeandhumanpopulations.

Humanactivitiesrelatedtoincreasedinternationaltrade,travel,andtransporthavecausedasurgeinthenumberofspeciesthatareintroducedtonewareas,particularlyinthepast50years.2Somenewspeciesareharmless,butothersmaydisplacenativespeciesandtriggerarangeofdisturbances.

Insomeregions,invasivespeciesmaybeespeciallyaggressive.Newhabitatsmaylackpredatorsandparasitesthathelpedcontroltheirpopulationsintheirnativelands.ExamplesofinvasivespeciesincludepestssuchasDutchelmdiseasefungus,plantssuchasthekudzuvine,andinsectssuchasthegypsymothandemeraldashborer.

American elm killed by Dutch elm disease. Photo by Joseph O’Brien, USDA Forest Service.

Old kudzo infestation draped on killed trees. Photo by James H. Miller, USDA Forest Service.


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Fire3 Fireisanaturalprocessthatshapesmanyforestecosystems.Firecaninfluencethetypesoftreesandvegetationinaforeststandbyfavoringspeciesadaptedtofire.Thethickbarkofponderosapineandgiantsequoiatrees,forexample,providesinsulationfromafire’sheat.Firemayhelpsomespeciesreproduce,includingtreessuchasthejackpine,whoseconesopenonlywithexcessiveheat.Inaddition,fireisamajorecologicalfactorinfluencingdecompositionandnutrient cycling.Firealsobringsanumberofenvironmentalandsocialcosts.Forestmanagershavetraditionallyattemptedtostoporsuppressallforestfires.Althoughthispolicyseemslikealogicalwaytoreducefiredamage,overseveraldecadessuppressionhashadtheoppositeresultinmanyplaces.Withoutfiretocleardownedbranchesandotherflammablematerialintheforest,thesuppressionpolicycancreateconditionsforevenmoreseverefires.

Thegreaterpossibilityofseverefires,combinedwithrisinghumandevelopmentinandnearforests,putsmanypeopleandlocalcommunitiesatrisk.Thosefactorshavesignificantlyincreasedboththedifficultyandcostofmanagingfireswhentheydooccur.Forexample,theamountthattheU.S.ForestServicespentonfiremanagementrosefrom$300million,or13percentofitsbudgetin1991,tonearly$2billion,or48percentofitsbudgetin2009.

Atechniqueknownasprescribedburningisnowbeingusedtoreintroducethenaturalprocessoffirebackintomanyforestecosystems.Thisprocessallowsacarefullycontrollednaturalorhuman-madefiretoburninaspecificareaunderselectedweatherconditionssothefirecanaccomplishspecificforest managementobjectives.Prescribed burningcanreducethefuelthatcanfeeddangerousfires.

Climate Change4 Forestsandclimatechangearecloselyrelated.From1850to2010,theamountofCO2intheatmosphereroseby35percent,mostlyasaresultofhumanactivitiessuchasdeforestationandburningfossilfuels.5ClimatemodelspredictthatincreasesinCO2andothergreenhouse gaseswillwarmtheEarth’satmosphere,causingchangesinprecipitation,sealevel,andweatherpatterns.Shiftsinthelocation,extent,andstructureoftheworld’secosystems,includingforests,arealsoexpected.Suchchangesmay,inturn,alterthewaythatpeoplemanageforests.

Carbonnaturallycyclesbetweentheanimals,atmosphere,oceans,plants,andsoils.Duringtheprocessofphotosynthesis,treesabsorbCO2fromtheatmosphereandsequesterorstoreitintheirwoodytissues,especiallyintheirbranchesandtrunks.Carbon sequestrationistheprocessthroughwhichCO2fromtheatmosphereisabsorbedbytrees,plantsandcropsthroughphotosynthesis,andstoredascarboninbiomass(treetrunks,branches,foliageandroots)andsoils.

Forestssequestermorecarbonthananyotherland-basedecosystem.Onematurecoastredwoodtree,forexample,mayholdmorethan200tons(181,437kilograms)ofcarboninitstrunkalone—theequivalentofabout800tons(725,748kilograms)ofCO2.ThepotentialofforeststostorecarbonmakesthemacriticalpartofcontrollingandmanagingatmosphericCO2.

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Prescribed fire in 3-year old rough during a dormant season (December) burn. Photo by David J. Moorhead, University of Georgia.



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eChanges in Ownership and Land Use7 In2009,about56percentofthe751millionacres(304millionhectares)offorestlandintheUnitedStateswasprivatelyowned,while44percentwaspubliclyowned.8Privateownersofforestlandincludeclubs,conservationorganizations,corporations,individualfamilies,andNativeAmericantribes.Publiclandownersincludethefederalgovernment;localgovernments;andstateforestry,park,andwildlifeagencies.

Sincetheyear2000,significantchangesinforestownershiphaveoccurredintheUnitedStates.Becauseofrecentchangesintaxlaws,forestproductscompanieshavesoldmillionsofacresofforestlandtoindividualandgroupinvestors.Wherecompaniesusedtoownforestlandandtomanufactureandsellwoodproductsfromit,forestlandownersarenowoftenseparatedfrommanufacturingoperations.

Inadditiontothechangeincommercialforestlandownership,some60millionacres(24,281,138hectares)ofprivateforestlandarecurrentlyownedbypeoplewhoare75yearsofageorolder,orwhoplantosellortransfertheirlandinthenearfuture.Suchsalesandtransferswillmeanfurtherchangesinforestownership.

Whenforestlandchangesownership,changesinmanagementpracticesandlandusemayfollow.Often,ownersgetthemosteconomicgainwhentheforestlandisdividedintosmaller,moredevelopedparcelsorrecreationproperties.Becauseofthisapproach,muchoftheforestlandsoldbyfamiliesandindividualswillbeusedfornewhousingandotherdevelopment.Overthecomingdecades,thistrendisexpectedtoresultinasignificantlossofproductiveforestland.

The Forest ecosystemManypeoplethinkofforestsasawholelotoftrees.Butforestsaremuchmorethantrees.Forestsarecomplexsystemsmadeupofmanydifferentbiotic(living)elements,suchasanimals,bacteria,andplants,aswellasabiotic(nonliving)elementssuchasair,soil,andwater.

Thetermecosystemdescribesacommunityoforganismsinteractingwitheachotherandtheirphysicalenvironment.Aforest ecosystemconsistsofthelivinganddeadorganisms—fromthesmallestbacteriaandalgaetothelargestbirdsandmammals—plustheair,theinorganicmaterialcontainedinthesoil,andthewater,aswellastheinteractionsamongtheseparts.

Thehealthofaforestecosystemcanaffectthelocallandscapeandthelocal,regional,andevencontinentalweather.Therootsoftreesandotherplantstransportwaterandnutrients;theyalsoholdsoilinplace.Whereforestsgrowandmature,theyhelptodrainandstorewater,toreduceerosion,andtomoderatesurfacewind.Inaddition,themoisturegeneratedbyhealthytreescontributestorainfalloccurringmanymilesaway.

Forest ecologyisthestudyofthecomplexinteractionsamongtheelementsofaforestecosystem.Someofthecomponentsoftheforestecosystemexploredthroughforestecologyaredescribedinthefollowingparagraphs.

Forests are More than trees (cont.)


Public - 43.6% Private - 56.3%

Corporations18.4%

Noncorporate private owners37.9%

Federal government33.0%

State agencies9.2%

City and municipal governments1.4%

Forestland Ownership in the United States

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Producers, Consumers, and DecomposersThelivingcomponentsoftheforestecosystemmaybeclassifiedaccordingtohowtheygettheirfood.Producersarethetreesandothergreenplantsthatmanufacturetheirownfoodfromsimplecompoundsandfromenergyobtainedfromsunlight.Consumersareorganismsthateatplantsoranimals.Decomposersarebacteria,fungi,insects,orotherorganismsthatbreakdowntheforest’sorganicmaterialintobasiccompounds.

Thetransferoffoodenergyfromorganismsononenutritionalleveltoorganismsonanotherlevelisreferredtoasafood chain.Forexample,agreenplantmaybeconsumedbyaleaf-eatinginsect;thatinsect,inturn,maybeconsumedbyaninsect-eatingbird.Asinotherecosystems,aforest’sfood webisacomplexandinterlockingseriesoffoodchains.

Nutrient CyclesForestorganismsneednutrientssuchascarbon,nitrogen,phosphorus,potassium,andsulfurforlife,growth,andreproduction.Nutrientcyclesprovideself-regeneratingsuppliesofthoselife-supportingmaterials.Treesabsorbnutrientsfromthesoilbytakinginnutrient-ladenwaterthroughtheirrootsandbytransportingthenutrientstocellsintheirtrunk,branches,andleaves.Whenleavesorneedlesfallanddecay,theyreturnnutrientstothesoil.Asorganicmaterialsaccumulateontheforestfloor,theirmassdecomposesintothesoilandair,andthenutrientcyclebeginsagain.

PhotosynthesisInphotosynthesis,plantsusethesun’senergytoconvertCO2andwater(H2O)intooxygen(O2)andcarbohydrates(predominantlyglucoseandstarch).Initssimplestform,theequationforphotosynthesisis

6CO2+12H2O=C6H12O6+6O2+6H2Ocarbonwaterglucoseoxygenwaterdioxide

Manypartsofaforestecosystemareinvolvedinphotosynthesis.Mineralsabsorbedbytheplantandtreerootsarecarriedbywatertotheleaveswherethemineralsformchlorophyll(thegreenpigmentinleaves).Photons,theelementaryparticlesoflight,passintotheleavesandareabsorbedbychlorophyll.Withphotosynthesis,oxygenisreleasedintotheatmospherethroughtheleaves.Theplantsandtreesusetheresultingcarbohydratesasfood(chemicalenergy)forgrowthandsustenance.

AssociationsWithinaforestecosystem,therearemanydifferenttypesofrelationships—inadditiontothefeedingrelationshipsdescribedearlier—thatinfluencetheinteractionsamongforestplantsandanimals.Symbiotic relationshipsarecloseecologicalassociationsbetweentheindividualsoftwoormoredifferentspecies.Asymbioticrelationshipmaybenefitonespecies,bothspecies,orneitherspecies.

Ecologistsuseadifferenttermforeachtypeofsymbioticrelationship.Mutualismiswhenbothspeciesbenefit.Forexample,oaktreesprovidefood(acorns)forsquirrels,whostoretheacornsbyburyingthem,enablingtheacornstogerminateandgrowintooaktrees.Commensalismiswhenonespeciesbenefits,buttheotherisunaffected.Forexample,mossgrowingontreetrunksallowsthemosstogetlightandcollectmoisturethatrunsdownthetrunk,butmossdoesn’tharmthetree.Parasitismiswhenonespeciesbenefits,buttheotherisharmed.Forexample,gallwaspslaytheireggsinlivingtissuesoftreesandshrubs,causingagrowthtoformthatprotectsandfeedstheyoungwasps,butthatactivitycancausetheplant’sleavestofallorbranchestodieback.


Ingestion

Respiration

Wastes anddead/dying matter

Decomposers

Consumers

Dying/dead matter

Weathering

CO

O

Mineralization bysoil microbes Nutrients

unavailableto plants

Uptake

RockMinerals

Living PlantsProducers

Soil NutrientsN, P, S, K

2

2

Photo-synthesis



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eConnectionsTreesplaydifferentrolesintheforestcommunitydependingontheirage,size,andspecies.Theirbark,fruit,leaves,nuts,roots,andseedsprovidefoodformanykindsofanimalsandmicrobes.Treesofferhomesandrestingorhuntinglocationsfordifferentanimalspecies.Treesalsocreateshadeandshelterforotherplantsandanimals.Treescanbecomehostsformanyorganisms,whichmayormaynotharmthetree.

Insomeinstances,onespeciesoftreecanbebeneficialtoothertreeandplantspecies.Forexample,therootsystemoftheredaldercan“fix,”ortransfer,nitrogenfromtheatmosphereandcandepositnitrogenintothesoil,thusaddingtothesoilinmuchthesamewaythatdirectapplicationsofnitrogen-richfertilizersgreenupalawn.

Biological DiversityBiological diversityofaforestreferstothefullrangeoflivingorganismsthatinhabitaparticularforestecosystem.Biologicaldiversityincludesthemicroorganismsinthesoil;thegrassesandplantsthatmakeupthegroundcover;theamphibians,birds,invertebrates,mammals,andreptilesthatmaketheforesttheirhome;andthetreesthemselves.Anothermeasureofthediversityisthenumberandfrequencyofeachspecies.Anativeforestinanaturalconditionisoftenmorediversethanaforestplantationwithonlyoneortwotreespecies.

Seasonal ChangesSeasonalchangesresultfromtheangleoftheEarth’saxisandtheEarth’smovementaroundthesun.WhentheNorthernHemispherestartstoangleawayfromthesun,thusreceivinglessdirectsunlight,theautumnseasonbeginsandismarkedbyshorterandcoolerdays.(IntheSouthernHemisphere,justtheoppositeisoccurring;thespringseasonbeginsandismarkedbylongerandwarmerdays.)

ThechangingangleofsunlighttriggersavarietyofbiologicalchangesinNorthAmericanforestecosystems.Thechangesincludeanimalhibernation,aslowingofphotosynthesis,anddormancyintreesandotherplants.Sometreeslosetheirleavesasthecoldertemperaturesandshorterdaysofautumncausecellstodieatthebaseoftheirleaves.Inthosedeciduoustrees,alayerofcorkbeginstoform,whichkeepswaterandnutrientsfromtravelingtotheleaf,thuscausingtheleaf’sattachmenttothetwigtoweaken.Chlorophyllstartstobreakdown,whichthenexposesyellowandorangeleafpigments.Atthesametime,scarletandpurplepigmentsarealsoformed.Theblendingofsuchleafpigmentsproducesthemanycolorsofautumnleaves.Eventually,theleafdetachesfromthetreeandfallstotheground.

Withoutitsleaves,thedeciduoustreeislesslikelytosufferdamagefromfreezingtemperaturesandstrongwinds.Butwithoutleaves,photosynthesisisimpossible.Deciduoustreeswillremaindormantinthewinter,untilthelongerdaysandwarmerweatherofthespringtriggersnewgrowth.

Forest Stand Development9 Scientistshavelongdescribedtheprocessofhowaforestgrowsanddevelopsovertimeassuccession.Withsuccession,plantandanimalcommunitiesmovethroughdifferentstages,witheachbeingcharacterizedbythedominanceofcertainspecies.


Time

annualweeds

perennialweeds andgrasses

shrubs

young forestcommunity

mature forest community

Secondary Succession


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Theprocessofsuccessionbeginswithabarrensite.Thefirstplantstogrowarecalledpioneerspeciesandmayincludemosses,ferns,andgrassseeds.Eventually,ifconditionsareright,ahealthyplantcommunityofshrubsandsmallwoodyplantswillbeestablished.Overtime,ayoungforestcommunitymayformanddevelopintoamatureforestcommunitywithasemipermanentmixofspecies.

Althoughsuccessionmaybepicturedasasimple,linear,andpredictableprocess,itisactuallynotanyofthosethings.Itisadynamicprocesswithmanyvariablesandpossibleoutcomes.

Thetermforest stand developmentisusedtodescribethecomplexinterrelationshipsbetweentreesgrowinginaforestovertime.Astandisdefinedasauniformgroupoftreesthatareallaboutthesameageorspecies.Dependingontheirlocation,foreststandsmaybedifferentsizesandshapes.

Foreststanddevelopmentoccursasindividualtreesandgroupsoftrees(calledcohorts)growandcompeteforlightandspace.Whenatreedeclines,dies,orisremovedfromthestand,growingspacebecomesavailabletoothertreesandplants,whichmay,inturn,changetheappearanceofthestand.

Thisnaturalprocessmaybeacceleratedwhenaneventsuchasawildfire,storm,orhuman-causeddisturbancecausestreesinthestandtoberemovedordie.Treespeciesadaptedtothenewenvironmentalconditionsonthesitemayhaveacompetitiveadvantagetogrowinthespace.Afteramajordisturbancewherethemajorityoftreesareremovedorkilled,theopenspacemaybegintore-fillwithnewgrasses,herbs,andtreeseedlings.

Atfirst,mostofthenewtreeswillbeaboutthesamesize.Eventually,though,someofthetreeswillbecomelargerandtherebyincreasethecompetitionfornutrients,sunlight,andwater.Sometreesmayendupgrowingmoreslowlyordie.Overtime,theappearanceandcompositionofthestandwillchangeasdifferenttreesgrowtodominatethestand.

A Tree’s Life cycleTreeshavelife cycles thatincludeseeds,seedlings,youngtrees,maturetrees,anddeath.Astreesgothroughtheirlifecycles,boththeirphysicalformandtheirroleintheforestecosystemwillchange.

Bylookingatthegrowthringsofatree,onecanlearn(a)aboutpastinfluencesontreegrowth;(b)aboutdisturbancessuchasfire,drought,ordisease;and(c)aboutchangesinenvironmentalconditions.Bytakingacoresample,onecanobservegrowthringsinalivingtreewithaminimumofdamagetothetree.


TreeLifecycle

Mature OakDead Tree (“Snag”)

Rotting Log with Plants and Insects

Sapling

SproutSeed



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eStarting as SeedsMosttreesbeginasseeds,andtreesareclassifiedbyhowtheirseedsareproduced.Sometrees,suchasaspen,beech,eucalyptus,redwoods,andwillows,mayreproducewithoutseedsbysproutingfromtherootsofaparenttreeorfromthestumporinjuredportionofapredecessor.Byfar,however,thelargestnumberoftreespeciesareangiosperms.Angiospermshaveflowersandproducetheirseedsinsidefruitorasawoodynutform.Theseedsareusuallypollinatedbyinsectsorotheranimals.Maples,oaks,anddogwoodsareangiosperms.

Incontrast,gymnospermshave“naked”seeds,meaningthattheseedsarenotenclosedinfruit.Gymnospermsproducetheirseedsinsidefleshyorwoodyconesorariels,andtheyarepollinatedbythewind.Gymnospermshavenoflowers.Gymnospermsarealsocalledconifersorcone-bearingtrees,andtheyincludespeciessuchaspines,firs,spruces,andyews.

Ifaseedlandsinasitewithfavorablelight,soil,temperature,moisture,andnutrientconditions,theseedmaygerminateandgrowintoaseedling.Theseedlingmustthencompetewithothergrowingplantsinthearea,anditmustalsosurvivebrowsingbyplant-eatinganimals.Theseedlingmaygrowandmaturequicklyorslowly,dependingonenvironmentalconditions.

Growing from Young to Mature TreesYoungtreesmustcompetewithothertreesandplantsforsunlightandotherresources,suchasnutrientsinthesoil,spaceforroots,andwater.Alltreesneedlight,butcertainspeciesmayrequiremoreorlesslightthanothers.Indenseforests,smalltreesmaygrowslowlyunlessalargertreefallsandcreatesanopeninginthecanopy.

Treesthatcanpersistinthelow-sunconditionsoftheunderstoryarecalledshade-tolerant.Hemlocksareoneexampleofshade-toleranttrees.Treesthatarenotshade-tolerant,suchastheDouglasfir,requirefullsunlightfromtheverybeginningstagesoftheirlives.Somespeciesareshade-tolerantasseedlingsbutbecomelessshade-tolerantastheyage.

Thelengthoftimeittakesatreetoreachmaturitydependsonthespeciesoftreeandtheenvironmentalopportunitiesthatarepresentduringitslife.Treesareconsideredmaturewhentheycanproduceseeds.Dependingonthespecies,reachingmaturitymayrequireafewseasonsorevendecades.

Likealllivingthings,treesaresubjecttodiseaseandinjury.Treesthatareweakenedordamagedbyinjuryanddiseasewilleventuallydie.Decomposers,suchasbacteria,fungi,andinsects,willthenbreakdowntreetissues,returningtheirnutrientstothesoiltoberecycledthroughtheforestecosystem.

north American Forest TypesNorthAmericahasmorethan1.67billionacres(677millionhectares)offorestland—aboutone-thirdofthetotallandareaofthecontinent.10Forestlandincludesmanydifferentforesttypes—fromthechillyevergreenboreal forestsinnorthernCanadatothesteamytropicalrainforestsinsouthernMexico.

Tropical forest in Honduras. Photo by Howard F. Schwartz, Colorado State University.

Subtropical forest in El Hierro.



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Thetypeoftreesorothervegetationthatoccursinanareaisdeterminedlargelybypatternsoftemperatureandprecipitation.TheFoodandAgricultureOrganization(FAO)oftheUnitedNationsclassifiesforestsbasedonthesetwofactors,usingtemperatureasthefirstlevel,andthenusingprecipitationpatternswithinagivenareaasthesecondleveltofurtherdistinguishforesttypes.11

Forthefirstlevel,theFAOusesfivebasicclimategroupingsordomains:Tropical,Subtropical,Temperate,Boreal,andPolar.Thesedomainsaredefinedasfollows:

Tropical: Meanmonthlytemperatureofmorethan64°F(18°C)allmonthsoftheyear

Subtropical: Meanmonthlytemperatureofmorethan50°F(10°C)atleast8monthsoftheyear

Temperate: Meanmonthlytemperatureofmorethan50°F(10°C)between4and8monthsoftheyear

Boreal: Meanmonthlytemperatureofmorethan50°F(10°C)between1and4monthsoftheyear

Polar: Meanmonthlytemperatureoflessthan50°F(10°C)allmonthsoftheyear

BecauseoftherelationshipoftheEarthtotheSun,themeanmonthlytemperatureofanareaisgenerallylowerthefartherthatareaisfromtheequator,withthelowestmeantemperaturesoccurringatornearthepoles.NorthAmericanforestsareprimarilysubtropicalandtropicalinMexico,subtropicalinthesouthernmostUnitedStates,temperateinthebulkoftheUnitedStates,andborealinCanadaandAlaska.

Withineachofthefivedomains,thereareforestswithdifferentlevelsofprecipitationrangingfromdeserttorainforest.Treeswillnotgrowwhereprecipitationistooloworwhereprecipitationdoesn’tcomeintherightseasontosupportthetrees.ThatiswhyNorthAmerica’sinteriorislargelydominatedbygrasslands.12

Temperate forest in Great Smoky Mountains National Park, Tennessee.

Boreal forest in Canada.

Polar domain, Antarctica Peninsula.




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The Urban Forest13 AnotherincreasinglyimportantforesttypeinNorthAmericaistheurbanforest.Anurbanforestisthecollectionoftreesinacity,town,orsuburb.Anurbanforestmayincludestreettrees,aswellastreesandplantsingreenways,naturalareas,parks,privateproperty,publicgardens,andrivercorridors.

Likeotherforests,urbanforestsaredynamicecosystemsthatprovideecosystemservicessuchascleanwaterandair.Urbanforestsimprovewaterqualitybyabsorbingwaterandsofteningtheeffectofrain,therebyreducingsoilerosionandstormwaterrunoff,whichcanpollutewaterwaysandcauseflooding.Astheirtreesgrow,urbanforestsalsoremoveCO2andothergreenhousegasesfromtheatmosphereandsequestertheminthetrees’branches,roots,andtrunks.

Inadditiontoprovidingecosystemservices,strategicallyplacedtreesintheurbanforestmaysaveenergybyshadingbuildingsfromthesummersunandbyblockingthemfromcoldwinterwinds.Theurbanforestmayalsoreducenoise,provideplacesforrecreation,andaddbeautyandopenspacetourbancommunities.Urbanforestsalsoprovidecriticalhabitatformanywildlifespecies.

Urbanforestshavemaintenancecosts,asdootherpublicservicessuchasstreetlightsorsidewalks.14Maintenancecostsmayincludeplanting,pruning,andreplacingthetrees;wateringtreesandremovingstormdebrisandtreelitter;andrepairingdamagetopowercablesandotherproperty.However,

thebenefitsprovidedbyurbanforestsusuallyfaroutweightheircosts,andcommunitiesthroughoutNorthAmericaareworkingtoincreasetheextentoftheirurbanforests.

Forest resource ManagementForestryisthescience,art,andpracticeofunderstanding,managing,andwiselyusingthenaturalresourcesderivedfromforestland.Suchresourcesincludefish,plants,recreation,soil,timber,water,andwildlife.

Peoplehavebeenmanagingforestssinceprehistorictimes.Onemightthinkofforestsonacontinuumofhumaninterventionormanagement.Atoneendofthecontinuumareprimary forests.Primaryforestsareessentiallyintactforestcommunities,composedlargelyofnativespeciesandunmodifiedbyhumanactivity.Attheotherendofthecontinuumareplantations,onwhichtreesareplanted,grown,andharvestedascrops.

Alongthiscontinuumisarangeofforeststhataremanipulatedormanagedbypeopletofillavarietyofneeds.Someofthoseforestsaremanagedmoreintensivelythanothers,andtheymaybepurposelymanipulatedtoservecertainpriorityfunctions.Productionforests,forexample,aremanagedprimarilytoproduceforestproducts.Evenforestsinprotectedareas,suchasnationalparksandnaturereserves,maybemanagedtominimizefirehazardsorthespreadofdisease.



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Forest SustainabilityInthepast100years,humanshavelearnedagreatdealaboutforestecosystems.Evenwiththisnewknowledge,however,wearestillfacedwiththedilemmaofhowtouseourforestsinsustainableways.

Forest sustainabilitymaybedefinedasmanagingforeststomeettheneedsofthepresentwithoutcompromisingtheabilityoffuturegenerationstomeettheirownneeds.Sustainabilitycanbedescribedasabalancebetween(a)society’sincreasingdemandsforforestproductsandbenefitsand(b)theneedforpreservationofforesthealthanddiversity.Thatbalanceiscriticaltothesurvivalofbothforestsandforest-dependentcommunities.

Inpractice,peopleoftenusea“triplebottomline”approachtomeasureprogresstowardsustainabilitybylookingatthethreeelementsofeconomy,environment,andsociety.15OnewaytothinkofthosethreeelementsisshowninFigure1below.Eachoftheelements—economicprosperity,environmentalprotection,andsocialwell-being—isinterdependentwiththeother,andeachelementmaybepresenttoagreaterorlesserdegreeinaparticularsituation.Theultimategoalofforestsustainabilityinvolvesabalanceofallthreespheres,asindicatedbytheshadedareainthemiddle.

Figure 1: The Elements of Sustainability

AnotherwaytothinkaboutthethreeinterrelatedelementsofsustainabilityisshowninFigure2.Asthatdiagramindicates,thehumaneconomydependsonsocietyandsocialinteraction.16Society,inturn,cannotexistwithouttheenvironment,whichprovidesbasicnecessitiessuchasair,energy,food,rawmaterials,andwater.Thus,theeconomyreliesonsociety,which,inturn,reliesonthenaturalenvironment.Figure 2: “Triple Bottom Line” of Sustainability17

Theessentialideaofforestsustainabilityisthatenvironmental,social,andeconomicissuesandidealsmustbeintegratedintodecisionmakingandactionsthataffectforests,whiletakingintoaccountbothfutureandpresentneeds.

The goal of forest

sustainability is a balance

of these three elements.

Environment Protection

Thehealthyfunctioningoftheforestitself

Social Well-BeingThesocial,cultural,andpoliticalwell-beingofthecommunitiesthatdependontheforest

Economic ProsperityTheeconomicprosperityofthepeoplethatdepend

ontheforest

Economy

Society

Environment





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Monitoring North American ForestsDespiteitsapparentsimplicity,forestsustainabilityisacomplexgoalthatdependsonaccurateassessmentofthepresentandfuturestatusofforests.TheMontrealProcessisaninternationalinitiativethatoutlinesonewayforcountriestomonitorforestsustainability.ThatprocessisacollaborativeeffortamongCanada,Mexico,theUnitedStates,andnineothercountriestobetterunderstandanddefinewhatsustainableforestmanagementmeans.

The12countrieshaveagreedonasetofsevencriteriathatidentifywhatisimportantinsustainableforestmanagementand67indicatorsformeasuringprogresstowardit.TheMontrealProcessincludeseconomic,environmental,andsocial,components,anditprovidesasystematicmethodforperiodicmonitoringofthestateoftheworld’sforests.Moreover,itisanimportanttoolformovingtowardforestsustainability.

In2010,theU.S.DepartmentofAgriculturecompletedthe2010 National Report on Sustainable Forests,whichdocumentsthestateofU.S.forestsandprogresstowardthegoalofsustainableforestmanagement,byusingtheMontrealProcesscriteriaasitsbasisofanalysis.

The Future of ForestsAsscientificandtechnologicaladvancesincreaseourknowledgeaboutthewaysforestsworkandthebenefitstheyprovide,wecontinuetolearnmoreabouthowtoensurethelong-termhealthofforestsandtheavailabilityofforestresourcesforfuturegenerations.

Ourgrowingworldpopulationisplacingincreasingdemandsonforestecosystems.Everypersonwhousesforestproducts,whovisitsforests,orwhodesirescleanwaterandairhasastakeinthefutureofforestecosystems.Byhelpingpeopleofallagesunderstandforestecosystemsandtheconceptofsustainability,wewillbebetterpreparedtoaddressforest-relatedissuesinthefuture.

Endnotes 1. For more information about invasive species and forests,

see Activity 7: Forest Invaders, page 115.2. ScienceDaily 2010. 3. For more information about the role of fire in forests, see

Activity 5: The Nature of Fire, page 87.4. For more information about climate change and forests,

see Activity 8: Climate Change and Forests, page 131.5. Matthews, Payne, Rohweder, and Murray 2000. 6. National Park Service and California State Parks 2010.7. For more information about changes in forest ownership,

see Activity 3: Who Owns America’s Forests?, page 67.8. USDA Forest Service 2008.9. Adapted from Oliver 2007.10. Food and Agriculture Organization of the United Nations.

2009.11. Food and Agriculture Organization (FAO) of the United

Nations, Forestry Department. 2001. 12. Perry, Oren, and Hart 2008, p. 42.13. Adapted from USDA Forest Service’s “Urban and

Community Forestry” 2011a.14. Escobedo and Seitz 2009.15. USDA Forest Service 2010a, p. 2.16. Ibid.17. Ibid.


Questions for “Forests are More than trees”S

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1. List6differentecosystemservicesprovidedbyforests,andwriteaone-sentencedescriptionofeach.

2. DescribetheforcesthatchangedNorthAmericanforests:(a)beforeEuropeansettlementand(b)afterEuropeansettlement.

3. Name4pressingissuesthatNorthAmericanforestsfacetoday.Startheoneyouthinkismostimportant,andexplainyourreasonforchoosingit.

4. Whatareinvasivespecies,andwhyaretheyaproblemforforests?

5. Whatare3benefitsand3costsofforestfiresforpeopleandtheenvironment?

6. Explaintherelationshipbetweenforestsandclimatechange.Includewaysthatforestsaffectclimatechangeandthatclimatechangeaffectsforests.

7. HowistheownershipofNorthAmericanforestschanging?Whyisthisaproblem?

8. Describe5differentinteractionsbetweentreesandotherbioticorabioticcomponentsoftheforestecosystem.

9. Explainwhatanurbanforestisandhowitcanbenefitpeople.

10.Whatisforestsustainability?Whyisitaworthwhilegoal?



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Answersto“Questionsfor“ForestsAreMorethanTrees””studentpage(page29)

1.Forestecosystemservicesmayincludethefollowing:• Clean Water.Forestsabsorbrain,coolandcleansewater,rechargeundergroundaquifers,reduceflooding,andsustainwatersheds.

• Oxygen.Forestsabsorbcarbondioxide(CO2)fromtheatmosphereandreleaseoxygen.• Nutrient Cycling.Foresttreesabsorbnutrientsfromthesoilandstorethemintheircells;nutrientsarereturnedtothesoilandatmospherewhentreesdie.

• Carbon Storage.ForestsstoreCO2fromtheatmosphere.• TemperatureRegulationandRainfall.Withtranspiration,forestscaninfluenceregionaltemperaturesandannualrainfall.

• Wildlife Habitat.Forestsprovidefood,shelter,andwaterforthousandsofplantandanimalspecies.• Resources.Forestsprovidecharcoal,firewood,fruits,nuts,lumber,medicines,paper,turpentine,andotherresources.

2.ForcesthatchangedNorthAmericanforestsbothbeforeandafterEuropeansettlementinclude:(a)BeforeEuropeansettlement:Nativepeopleregularlyburnedforestlandforhunting,foreaseoftravel,toreduceinsectpests,andtopromoteberriesandotherfoods.Insomeregions,nativepeoplealsoclearedforeststogrowcrops.

(b)AfterEuropeansettlement:Boththehumanpopulationandtheirrelianceonforestsincreased.Forestswereextensivelyclearedforagriculture,fuelwood,timber,andurbanexpansion.Startinginthe20thcentury,conservationpracticeshavehelpedtostabilizeforests.

3.PressingissuesfacingNorthAmericanforestsincludeclimatechange,fire,invasivespecies,andchangesinownership.

4.Invasivespeciesareplants,animals,ordiseasesthatarecapableofspreadingrapidlyandcausingeconomicorenvironmentalharm.Invasivespeciesareaproblemforforestsbecausetheydisplacenativespeciesandtriggerotherdisturbances.

5.Benefitsoffireincludehelpingsomespeciesreproduce,helpingwithdecomposition,andaidingnutrientcycling.

Costsoffireincludelossofproperty,healthrisks,andthemonetarycostofsuppression.

6.IncreasedlevelsofCO2intheatmospherearecausingchangesintheEarth’sclimate.Climatechangeisexpectedtoaffecttheextent,location,andstructureofforests.BecauseforestsabsorbandsequesterCO2,theyareanimportantwaytoreduceCO2intheatmosphereand,thus,reducetheeffectsofclimatechange.

7.Inrecentyears,forestproductscompanieshavesoldlargetractsoflandtoindividualandgroupinvestors.Also,alargepercentageofprivateforestiscurrentlyheldbyelderlyownersandsoisexpectedtochangehandsinthenearfuture.Bothofthosetrendsarelikelytoresultinasignificantlossofforestland.


8. Interactionsbetweentreesandotherforestecosystemcomponentsmayinclude:• Food Webs.Thesewebsinvolvethetransferoffoodenergyamongforestorganisms,includingconsumers,decomposers,andproducers.

• Nutrient Cycles.Cyclingincludesvitalnutrientssuchascarbon,nitrogen,phosphorus,potassium,andsulfur,whichareabsorbedintothetree,storedinitscells,andthenreturnedtothesoilafterthetreedies.

• Photosynthesis.Treesandotherplantsusethesun’senergytoconvertCO2andwaterintocarbohydratesandoxygen.

• Associations.Theserelationshipsareamongforestorganisms,includingsymbioticrelationshipssuchascommensalism,mutualism,andparasitism.

• Connections.Foresttreesplaydifferentroles,suchasprovidingfood,homes,shade,andshelter,aswellasfixingnitrogen.

• Seasonal Changes.Evolvingchangesinsunlight,temperature,andprecipitationaffectforestplantsandanimalsinanumberofways.

9. Anurbanforestisthecollectionoftreesinacity,town,orsuburb.Benefitsofurbanforestsincludebeauty,cleanwaterandair,energysavings,openspace,reducednoise,placesforrecreation,andwildlifehabitat.

10.Forestsustainabilityismanagingforeststomeettheneedsofthepresentwhileenablingfuturegenerationstomeettheirneeds.Balancingcurrentandfutureneedsiscriticaltothesurvivalofforestsandthepeoplewhodependonthem.

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