current distribution not indicative of underlying …

CURRENTDISTRIBUTIONNOTINDICATIVEOFUNDERLYINGNICHEREQUIREMENTSOFANALPINEFORB:IMPLICATIONSFORPREDICTING

CLIMATE-INDUCEDRANGESHIFTS

EmmaSumner

AthesissubmittedinpartialfulfilmentoftherequirementsforthedegreeofBachelorofScience(WildlifeandConservationBiology)(Hons)

inthe

DepartmentofEcology,Environment&Evolution

LaTrobeUniversityBundoora,Victoria

24thApril2017wordcount:9690

II

Declaration

Icertifythattheattacheddocumentismyoriginalwork.Nootherperson’sworkhasbeen

usedwithoutdueacknowledgement.ExceptwhereIhaveclearlystatedthatIhaveused

someofthismaterialelsewhere,ithasnotbeenpresentedbymeforexaminationinany

othercourseorsubjectatthisoranyotherinstitution.Iunderstandthattheworksubmitted

maybereproducedand/orcommunicatedforthepurposeofdetectingplagiarism.

Noneoftheresearchundertakeninconnectionwiththisthesisrequiredapprovalbya

UniversityEthicsCommittee.

Name:EmmaElizabethSumner

Subject:EEE4HNA/B

Document:Thesis

StudentNumber:17724437

Date:24/4/2017

III

AcknowledgementsIwouldliketoacknowledgethefollowingpeople:Dr.JohnMorganforhissupervision,forprovidingmewithachallengingproject,andforhisguidancethroughoutthewholeprocess.ThePlantEcologyLab,forthethought-provokingweeklymeetingsandsupportthroughouttheyear.ThankstoSueByceson,Dr.PeteGreen,Dr.SusannaVennandDr.DeniseFernandofortheirastutesuggestionsregardingexperimentaldesign.ThanksalsotoZacWalker,GeorgeCollinsandHannaKapuscinski-Evansfortheirsupportandcomradery.MaxBartleyandNickMoorefortheirtechnicalassistanceandhardwork,andtheLaTrobeWildlifeSanctuaryforassistingwithseedpropagation.ThankstovolunteersStephJohnsonandJackTatefortheirassistanceinthefield.BevLawrenceandAPEASkiLodgefortheirhospitality,andMtHothamSkiResortforgraciouslyallowingmetoconductfieldresearchatMtHotham.Dr.SimonWatsonforintroducingmetostatisticalmodellingandguidingmethroughthedataanalysisprocess,andWarwickPapstforhisadviceonworkingonthehighplains.IwouldalsoliketothankandacknowledgetheResearchCentreforAlpineEcologyfortheirgenerousresearchgrant.Finally,thankyoutotheentireDepartmentofEcology,EnvironmentandEvolution.

IV

TableofContents

EXECUTIVESUMMARY.............................................................................................................1

INTRODUCTION.......................................................................................................................2FINGERPRINTSOFCHANGE...........................................................................................................2MODELLINGFUTUREPLANTDISTRIBUTIONS–CORRELATIVEAPPROACHES..............................................3THEROLEOFDISPERSALINDETERMININGRANGELIMITS....................................................................4AMORE‘IN-DEPTH’UNDERSTANDINGOFRANGELIMITS.....................................................................5THEROLEOFBIOTICINTERACTIONSINDETERMININGRANGELIMITS......................................................6THEROLEOFBIOTICINTERACTIONSINDETERMININGFUTUREDISTRIBUTIONS..........................................8

METHODS...............................................................................................................................10STUDYSPECIES........................................................................................................................10STUDYSITE.............................................................................................................................11SITECONDITIONS.....................................................................................................................12FIELDTRANSPLANTEXPERIMENT.................................................................................................14LABORATORYGERMINATIONEXPERIMENT.....................................................................................14LIGHTLIMITATIONEXPERIMENT..................................................................................................15FREEZINGRESISTANCEEXPERIMENT.............................................................................................16DATAANALYSIS.......................................................................................................................17

RESULTS..................................................................................................................................20SITECONDITIONS.....................................................................................................................20FIELDTRANSPLANTRESULTS.......................................................................................................22LABORATORYGERMINATIONRESULTS...........................................................................................24LIGHTLIMITATIONRESULTS........................................................................................................25FREEZINGRESISTANCERESULTS..................................................................................................27

DISCUSSION............................................................................................................................28GERMINATIONCHARACTERISTICS................................................................................................28FROSTTOLERANCEINSEEDLINGS.................................................................................................29EFFECTSOFFACILITATIONALONGANABIOTICSTRESSGRADIENT.........................................................30EFFECTSOFCOMPETITIONONSEEDLINGGROWTH..........................................................................32CONCLUSION..........................................................................................................................34

REFERENCES...........................................................................................................................36

APPENDICES...........................................................................................................................42APPENDIXI............................................................................................................................42APPENDIXII...........................................................................................................................45APPENDIXIII..........................................................................................................................46APPENDIXIV..........................................................................................................................47

V

ListofFiguresFIG1.OCCURRENCERECORDSOFALPINEPODOLEPIS(ATLASOFLIVINGAUSTRALIA)................................11FIG2.PODOLEPISROBUSTAINFLOWER(IMAGE:J.MORGAN).............................................................11FIG3.LOCATIONOFMTHOTHAMINVICTORIA,ANDSTUDYSITELOCATIONSATMTHOTHAM(1-10)REPRESENTINGTHEELEVATIONGRADIENTONSOUTH-EASTANDNORTH-WESTSITES..................................13FIG4.TOTALNUMBEROFFREEZINGDAYS(TEMPERATURES≤0ᵒC)RECORDEDATMTHOTHAM,INRELATIONTOALTITUDEDURINGSTUDYPERIOD(NOV2016–MAR207)ONNORTH-WEST(SOLIDLINE)ANDSOUTH-EAST(DASHEDLINE)EXPOSEDSLOPES......................................................................................................20FIG5.GROWINGDEGREEDAYS(GDD)RECORDEDFORSOUTH-EAST(A)ANDNORTH-WEST(B)EXPOSEDSITESDURINGSTUDYPERIOD(NOV2016–MAR2017)............................................................................21FIG6.EFFECTOFTREATMENTANDALTITUDEONSEEDLINGSURVIVAL.MEANPROBABILITYOFSURVIVAL(±95%

CI)OVERONEGROWINGSEASONFORSEEDLINGSPLANTEDALONGANALTITUDINALGRADIENTINCONTROL(SOLIDGREENLINE)ANDGAP(SOLIDORANGELINE)TREATMENTS...................................................................22FIG7.MEANRELATIVENEIGHBOUREFFECT(RNE)(±1SE)FORPAIREDTRANSPLANTEDSEEDLINGSINGAPANDCONTROLTREATMENTSON(A)NORTH-WESTAND(B)ANDSOUTH-EASTEXPOSEDASPECTSACROSSTHEELEVATIONGRADIENT...................................................................................................................23FIG8.EFFECTOFLIGHTANDTEMPERATUREONGERMINATION.FITTEDVALUESFORPROBABILITYOFGERMINATIONFOR(A)LIGHTCONDITIONSAND(B)DARKCONDITIONS(±95%CI)FORTHEGENERALISEDLINEARMODELAPPLIEDONCABINETGERMINATIONDATA..............................................................................24FIG9.EFFECTOFLIGHTLIMITATIONONNETPHOTOSYNTHESIS.FITTEDMEANRATEOFPHOTOSYNTHESIS(±95%

CI)OFSEEDLINGSGROWNUNDERFULLSUN,48%SHADEAND82%SHADE...........................................26FIG10.EFFECTOFLIGHTLIMITATIONONBIOMASS.FITTEDMEANDRY-WEIGHTOFBIOMASS(±95%CI)OFSEEDLINGSGROWNUNDERFULLSUN,48%SHADEAND82%SHADE.....................................................26FIG11.MEAN(±1SE)VARIABLEFLUORESCENCETOMAXIMUMFLUORESCENCE(FV/FM)RATIOSOFLEAFMATERIALUSEDINFREEZINGRESISTANCESTUDY,ATFOURTEMPERATURES:4,-5,-11,AND-20°C;FORALPINEPODOLEPISLEAVESOF(A)MATUREPLANTSAND(B)SEEDLINGS.............................................................27FIG12.SHADECASTBYRESIDENTVEGETATIONATNORTH-WESTSITESATMTHOTHAM,VICTORIA..............42FIG13.SHADECASTBYRESIDENTVEGETATIONATSOUTH-EASTSITESATMTHOTHAM,VICTORIA...............42FIG14.FREQUENCYOFVEGETATION(HERB,GRAMMINOID,SHRUB)HEIGHTSATMTHOTHAMONSOUTH-EASTEXPOSEDSITES(A-E).....................................................................................................................43FIG.15.FREQUENCYOFVEGETATION(HERB,GRAMMINOID,SHRUB)HEIGHTSATMTHOTHAMONNORTH-WESTEXPOSEDSITES(A-E).............................................................................................................44FIG16.EUCALYPTUSPAUCIFLORAWOODLANDWITHDENSEPODOLOBIUMALPESTREUNDERSTORYDOMINATE

NORTH-WESTEXPOSEDSLOPESATMTHOTHAM(1670-1700M).......................................................45

VI

ListofTablesTABLE1.SUMMARYINFORMATIONFORTHETENSITESALONGTHEMTHOTHAMTRANSECTINCLUDING

LOCATION,ALTITUDEANDASPECTFOREACHSITE...............................................................................13TABLE2.GERMINATIONATTRIBUTESOFALPINEPODOLEPISAT14°CWITHANDWITHOUTAPERIODOFCOLD

STRATIFICATION..........................................................................................................................25TABLE3.ANALYSISOFTHEEFFECTOFTREATMENT,ALTITUDEANDASPECTONSEEDLINGSURVIVAL.............46TABLE4.ANALYSISOFTHEEFFECTOFTREATMENTANDALTITUDEONSEEDLINGSURVIVAL.........................46TABLE5.TABLEOFCOEFFICIENTSFORTHEGLMUSEDTOFITSEEDLINGSURVIVALASAFUNCTIONOF

TREATMENTANDALTITUDE...........................................................................................................46TABLE6.STATISTICALANALYSISOFRELATIVENEIGHBOUREFFECTFORNORTH.......................................47

1

ExecutiveSummary

Astheclimatewarms,plantspeciesarepredictedtomoveupwardandpolewardinorderto

remainwithintheirclimaticenvelopes.Thesepredictionsaremadebyextrapolatingcurrent

distributionstofutureclimatescenariosundertheassumptionthatplantboundariesare

controlledbyclimatealone.However,species-specificresponsestoclimatechangearelikely

morecomplexthancanbeforecastwithsimpleclimatemodelling.Understandingcontrols

onspeciesgeographicalrangelimits,andhowthesemayrespondtorapidenvironmental

changehaspromptedcallsforgreater‘bruteforce’experimentation.Here,Iinvestigate

controlsonthedistributionofamodelalpinespeciesPodolepisrobusta(Asteraceae)by

conductingaseriesoffieldandlaboratoryexperiments.Germinationexperiments

demonstrateawidegerminationniche,withnolimitingdormancycharacteristicsorcold

stratificationrequirements.However,whenseedlingsweresubjectedtofreezing

temperatures,leavessufferedsignificantdamagetophotosyntheticapparatuscomparedto

adultplants.Hence,itislikelythatearlyseedlingestablishmentisstronglytiedto

occurrencesofearlyfrostduringthegrowingseason.Facilitativeinteractionsplayastrong

roleacrossrangeedges.Asdemonstratedbyatransplantexperimentalongatemperature

andmoisturegradient,closeinterspecificneighbourssignificantlyincreasedsurvivaland

growthofplantedseedlings,comparedtoseedlingsplantedincanopygaps.Thispatternwas

consistent,evenbelowthecurrentdistribution,contrarytoexpectationsofstronger

competitiveinteractions.Whilethefieldstudyfindsnoresponsetocompetitiononseedling

survival,experimentalshadingindicatesintoleranceatheavy(82%)lightinterception.This

hasconsequencesforestablishmentwithindensevegetation.Resultsconsistentlyindicate

thatP.robustaisabletooccupyafargreaternichethancanbeobservedcurrently.These

resultshighlighttheimportanceoffacilitativeinteractionsattheseedlingstageinthealpine

zone,demonstratingthatbioticfactorsacttoconstrainorwidenthetheoreticalniche.I

arguethatbioticinteractions,dispersallimitation,andrecruitmentprocessesmayenforce

strongerlimitstogeographicdistributionthanclimatictolerancesperse.Predictionsonhow

plantspeciesmayrespondtoclimatechangewillbenefitfromincorporatingthesefactors.

2

Introduction

Thenicheisafundamentaltenetinecology,andframesourunderstandingofspeciesrange

limits(Holt2009).Climateandotherabioticfactorsareoftendemonstratedashavingstrong

influencesonplantspeciesdistributions(KörnerandPaulsen2004).Hence,responsesto

climatechangeareoftencouchedintermsofclimatictolerances.Inalpineecosystems,

climatewarmingisexpectedtodrivespeciesdistributionstohigheraltitudes(Dullingeretal.

2012).Theserangeshiftshaveimportantconservationimplications,astheupwardmigration

ofmorecompetitive,lower-altitudeplants,andthereductionofsuitablehabitatforhigh-

altitudeplants,couldpotentiallyleadtorangecontractionsandspeciesextinctions(Thuiller

etal.2005;Dullingeretal.2012;Alexanderetal.2015).However,geographicdistributionsof

plantspeciesresultfromacombinationofabiotictolerancesandbioticfactorssuchas

speciesinteractions,dispersalanddemographicprocesses(Holt2009).Thecomplexityand

urgencyofpredictingthepotentialimpactofclimatechangeonspeciesdistributionshas

beenincreasinglymetwithcallsforgreater‘brute-force’experimentation(Holt2009;Munier

etal.2010;HilleRisLambersetal.2013;Alexanderetal.2015;Alexanderetal.2016).

Experimentalassessmentsofspeciesdistributionsprovideadirectapproachinattemptingto

quantifytheniche,andareapowerfultoolformakinginferencesaboutspatialheterogeneity

ofabioticfactorsandspeciesinteractions(Moore2009).

Fingerprintsofchange

Inmountains,duetoanaltitudinaltemperaturegradient,speciesareexpectedtomigrate

upslopeinresponsetoclimaticshiftsinvolvingwarmingtemperaturesandlongergrowing

seasons(Paulietal.1996).Revisitationofhistoricalsitesprovidesoverwhelmingevidencefor

globaltrendsinupwardspeciesmigration(Paulietal.2012),withincreasesinspecies

richnessreportedforsummitsintheEuropeanAlps(ParoloandRossi,2008;Paulietal.

2012),theHimalayas(Telwalaetal.2013),theAndes(Feeleyetal.2011)andtheAustralian

Alps(Vennetal.2012).Inparticular,speciesgainsaremorepronouncedonsummitsof

loweraltitudes,owingtolargernearbyspeciespoolsandsuggestingthatupwardshiftsare

drivenlargelybyleading-edgeexpansionsinresponsetoincreasingtemperature(Paulietal.

3

2012).However,contrastingtrendswerereportedforMediterraneanmountainregions

(Paulietal.2012),andmountainregionswithMediterranean-typeclimates(Crimminsetal.

2011),whereratherthantrackingtemperatures,plantspecieshaverespondedtoa

decreasedwaterdeficitbyshiftingtheiroptimalelevationsdownslope.Crimminsetal.(2011)

alsoreportthatspecies’entireranges–includinglowerboundaries–areshifting,ratherthan

justthroughupper-boundaryextensionsasobservedintemperateregions.Such

contradictoryresponsestoclimatechangeunderminetheassumptionthattemperatureis

theprinciplefactorindeterminingspeciesdistributions,andhighlightstheimportanceof

otherclimaticfactorssuchasenergyandwateravailability(Crimminsetal.2011;Cahilletal.

2012).Ultimately,theupwardtrendinspeciesmigrationsisexpectedtoresultinrange

contractionandextinctionofmountainplantspecies,manyofwhicharerareandendemic

(Dullingeretal.2012).However,long-termrevisitationstudiesarelimitedinspatialand

temporalscope,promptingmanyecologiststoemploycomputermodellinginorderto

predictpotentialresponsestoclimatechange(Brookeretal.2007).

Modellingfutureplantdistributions–correlativeapproaches

Typically,climateenvelopemodellingisemployedtopredictspeciesrangesinthecontextof

climatechange(Brookeretal.2007).Speciesrangelimitsareassumedfromsimple

correlationsofabioticconditionswithincurrentdistributions.These‘climaticenvelopes’are

thenextrapolatedtofutureclimatescenarios(Brookeretal.2007)inordertocreatea

‘statisticalnichemodel’(Holt2009).Frequently,speciesdistributionmodelspredict

substantialimpactsonalpineplantdiversity,owingtohighratesofhabitatloss(Dullingeret

al.2012).InaEuropean-scaleanalysis,aclimate-envelopebasedmodelpredictedhabitat

lossesofapproximately60percentofmountainspecies(Thuilleretal.2005).However,

estimatesofhabitatlossmaydependonthescaleofthemodel.Finescale(local)models

predictedthepersistenceofallhabitatsprojectedtonolongerexistatcoarseresolutions

(Europeanscale)(Randinetal.2009).Thisislikelybecausetopographyandmean

temperaturedatacontainmorevariabilityatfinescalethancanbeexpressedatlargerscales

(Thuilleretal.2005).Indeed,temperaturedatacollectedlocallyindicatesthathigh

topographicvariabilitywillconservetheclimaticnichesofmanyspeciesintheSwissAlps

4

(SherrerandKörner2010).Hence,inconsistenciesinspeciesdistributionmodelling

demonstratethatestimationsofhabitatlossdependupondataresolution.Thishas

implicationsfortheaccuracyofpredictionsofhabitatlossandspeciesextinctions.Further,

predictivemodelsignorecrucialelementsaffectingspeciesdistributionssuchasdispersal

traitsandbioticinteractions,andassuchprovideonlyaroughestimateofpossibleresponses

toclimatechange(Holt2009;Urbanetal.2012).

Manyecologicalassumptionsandtheoriescaninfluencepredictionsofspeciesdistributions

underclimatechange(Austin2002).Brookeretal.(2007)recognisetheshortcomingsof

climate-basedmodelling,andincorporatebioticinteractionssuchascompetitionand

facilitationbetweenplantspecies,andplantdispersalabilityintoaspatialmodelofa

theoreticalcommunity.Here,theinclusionofbioticprocessesprovidedcontrarypredictions

forfuturespeciesdistributionsthanthosebasedpurelyonclimaticcorrelation.However,

whilethisisusefulinhighlightingthequalitativeimportanceofnon-climaticvariablesinplant

distribution,itdoessowiththeuseofartificialdata.Assuch,isnotnecessarilyindicativeof

thepatternsandprocessesfoundinnaturalplantcommunities.Predictivemodelsrequire

greaterunderstandingoftheecologicalprocessesthatinfluencespeciesdistributionsinthe

contextofclimatechange.Whilespeciesdistributionmodelsassumethatrealisednicheswill

beretainedovertime,withspeciesmigratingtoremainwithincurrentclimaticenvelopes

(Thuilleretal.2005;Brookeretal.2007),limitationsofdispersalandestablishmentsuccess

maypreventaspeciesfromshiftingitsrangetokeeppacewithachangingclimate(Urbanet

al.2012).

Theroleofdispersalindeterminingrangelimits

Withongoingclimatechange,certainclimaticfiltersincludingtemperatureandsnow-

durationarerelaxedinalpineenvironments(Alexanderetal.2016).Thesechangeshavethe

potentialtoopenuphabitattoplantspeciesattheirleading-edge(Alexanderetal.2015).

Globally,alpinetree-linesarethoughttobestronglytemperature-controlled(Slatyerand

Noble1992;Harschetal.2009),andthereforepotentiallyresponsivetowarmer

temperatures(HoltmeierandBroll2005).However,ameta-analysisrevealedupward

5

advancementsatonlyhalftheexaminedtree-lines(Harschetal.2009).InAustralia,though

warmertemperatureshaveextendedthefundamentalnicheattheupperboundaryofsnow

gumsby100m,thetree-linehasremainedrelativelystable(Green2009).Evenafter

extensivefiresintheAustralianAlpsprovidedsuitableconditionsforseedlingestablishment,

mostrecruitmentwasseenwithinandbelowthetree-line,indicatingthatupslopemigration

maybelimitedbydispersalability.IntheItalianAlps,speciesthathavemigratedupslopethe

farthestsincethe1950sarethosethatpossessedlight,wind-disperseddiaspores(Paroloand

Rossi2008).

Aspreviouslydiscussed,plantdispersaltraitshavebeenincorporatedintosomespecies

distributionmodels,withwind-dispersaldenotinggreatermigrationsuccess(Austin2002;

Brookeretal.2007).However,thoughprimarilywind-dispersed,tree-linespeciesinthe

northernhemisphereshowlittlesignofupslopemigration,suggestingpost-dispersal

mechanismsmayinfluenceleading-edgeexpansions(HobbieandChapin1998).Similarly,

thoughdispersalhasbeenfoundtobesufficient,therehasbeenlittlesignofupslope

advancementintheScandinavianmountainsbymountainbirch,potentiallyduetothe

interactionofmicro-topography,climateandherbivory(Hofgaardetal.2009;Speedetal.

2010).Specieslimitedbypre-orpost-dispersalprocessesarethereforeatriskoffailingto

remainwithintheircurrentclimate-envelopeswithcontinuedclimatewarming.Certainly,

migrationisaprocessnotonlytiedtotraitssuchasseedsizeanddispersalability,butalso

contingentonpropaguleavailability,germinationniche,andseedlingestablishment.

Amore‘in-depth’understandingofrangelimits

Thereislittledoubtthatclimateunderpinsthelarge-scaledistributionsofmanyplant

species(Körner1999),andthisisindeedamajorassumptioninmostspeciesdistribution

models(Brookeretal.2007;Randinetal.2009;Dullingeretal.2012).Thisisparticularly

evidentformountainplantswheretheupperboundaryofalpineorsubalpinespeciescan

becorrelatedwithmeanseasonaltemperature(Körner1999).However,themechanism

behindtheseboundariesaremorecomplexthancanbeexpressedbyaveragegrowing

seasontemperaturestypicallyusedbyclimate-envelopemodelling(Körneretal.2016).In

6

mountainplants,irregularfreezingtemperaturesduringthegrowingseasonaremore

likelytoresultintissuedeathandplantmortalitythanaverageminimumtemperature

(Larcher1995).Körneretal.(2016)demonstratethatfrostdamageduringbudbreakand

leafemergenceduringthegrowingseasonareinstrumentalinestablishingthecold-edge

rangelimitsoffivetreespeciesinEurope.Freezingresistanceisalsospecies-specificand

relatedtolocation,withhigherfreezingresistancereportedforplantpopulationswith

increasingaltitude(Vennetal.2013).Inaddition,differentlifestagesofplantsexhibit

unequalfrostresistance:whileadultplantsmaybeabletore-sproutfromprotectedbuds,

seedlingsaremuchmoresensitivetofreezingtemperatures(Larcher1995).Indeed,entire

cohortsmaybedevastatedbyoneincidenceofearlyspringfrost(Larcher1995).Hence,

individuallife-historystagesmayresponddifferentlytoabioticconditions,andwill

contributeunequallytopopulationviabilitybeyondcurrentranges(WarrenandBradford

2011).

Theroleofbioticinteractionsindeterminingrangelimits

Competitionandfacilitationalsoplayimportantrolesinthestructureandassemblageof

alpineplantcommunities(Holt2009).Therelativeimportanceofsuchinteractionsmaybe

distinguishedbycomparingplantsurvivalorproductivityinthepresenceorabsenceof

benefactors,orwhenacomponent(suchasthecanopy)ofthebenefactorisaltered

(BertnessandCallaway1994).PositiveassociationswithinvasiveTaraxacumofficinaleand

thecushionplantAzorellamonanthaintheChileanAndeswasconfirmed,asT.officinale

seedlingsplantedwithinthecanopiesofA.monanthaexperiencedhighersurvival,net-

photosynthesisandstomatalconductancethanthoseplantedinbarepatches(Cavieresetal.

2005).Theacquisitionof,anduseofresourcesnecessaryforplantgrowthsuchasnitrogen

andwater,arelinkedtophotosyntheticperformance(Muraoka2002).Hence,amajor

limitationofalpineplantgrowthisphotosyntheticallyactiveradiation(PAR,400-700nm)

duringthegrowingseason(Körner1999).AreductioninincidentPARfromneighbouring

plants,whileconstituting‘resourcecompetition’,canbemitigated,orbalancedbyindirect

(positive)effectsofreducedsolarinsolationontopsoilmoisture(Körner1999).

7

Positivespatialassociationsbetweenmatureadultsofonespeciesandtheseedlingsof

anotherarewidelyreferredtoasthe‘nurseplant’syndrome,andtypicallyoccurinstressful

habitats(Callaway1995;Callawayetal.2002).Athighelevations,ameliorationofstressors

suchasstrongwinds,soilinstabilityanddroughtbystress-tolerantneighbours,facilitatesthe

persistenceoflessstress-tolerantspecies(BertnessandCallaway1994).Whileneighbours

positivelyinfluencedthegrowthoftargetspeciesintheTibetanPlateau,positiveresponses

wererelatedtospeciesdensity,suggestingthatbothcompetitionandfacilitationwere

operatinginparallel(Wangetal.2007).Thisisbecausethemagnitudeofpositiveand

negativeplantinteractionschangesacrossaspeciesrange(BertnessandCallaway1994).

Itisgenerallyacceptedthataspecies’lowerboundaryisconstrainedbycompetitive

interactionsandextendedatupperboundariesbyfacilitationbymorestress-tolerantspecies

(BertnessandCallaway1994).Theapparentinverserelationshipbetweencompetitiveability

andstress-tolerancewaspopularisedbyGrime(1977),andisneatlydemonstratedwith

manipulationsalonganenvironmentalgradient.Plantspeciesrespondedtoneighbour

removalsaccordingtotheirpositionalonganaltitudinalgradientintheFrenchAlps(Choler

etal.2001).Whenneighbourswereremovedfromtargetspeciesattheirtrailing-edge,

biomassincreased,whilebiomassdecreasedwithneighbourremovalattheleadingedge,

wherespeciesaretypicallymoreconstrained(Choleretal.2001).Thisstress-gradient

hypothesisissupportedbyevidencefromneighbourremovalexperimentsconducted

worldwidewheregenerally,interactionsshiftedfromcompetitiontofacilitationaselevation

andabioticstressincreased(Callawayetal.2002).Theselarge-scalemanipulative

experimentshighlighttheunderestimationofplant-plantinteractionsinecologicaltheory

(Choleretal.2001).And,whilethebalancebetweencompetitionandfacilitationshiftsacross

space,itmayalsoshiftacrosstime.

Potentiallypositiveornegativeresponsestoneighboursmaychangedependingonthelife

stagesoftheinteractingspecies(CallawayandWalker1997),ortemporalfluctuationsinthe

environment(Valiente-Banuet2008).Indeed,theaforementionednurse-plantsyndromeis

typicallyfavourableonlyforbeneficiariesduringearlylife-stagesandmayswitchtoa

competitiveinteractionastheseedlingmatures(McAuliffe1988;Callaway1995).

Interactionscanalsoshiftwithvariationinclimateoverthecourseofasinglegrowingseason

8

(Kikvidzeetal.2006),whereabioticstressorsarerelaxedorheightened(Bertnessand

Shumway1993).Furtherchangesinenvironmentalconditionsmayalterthebalanceof

facilitativeandcompetitiveinteractionsbetweenplantspecies.Inalpineenvironments,the

relaxationoralterationofcertainclimaticfilterswithongoingclimatechangeislikelyto

changethedirectionandstrengthofplantinteractions.

Theroleofbioticinteractionsindeterminingfuturedistributions

Aspredicted,specieshavebeguntoshifttheirdistributionsinresponsetoclimatechange.

Thisisespeciallyevidentinalpinesystemswheresteepelevationalgradientsprovideshort-

distanceescapes(Bertrandetal.2011).Transplantexperimentsarevaluableinteasingout

therelativeimportanceofbioticfactorsbeyondaspecies’currentrange.InArctictundra,the

growthandsurvivalofseveralspeciestransplantedabovecurrentelevationlimitswaslimited

bybelow-groundcompetitionfromtundraplants(HobbieandChapin1998).Conversely,

germinationandestablishmentofsugarmaplewaslowestbeyonditscurrentupper-

boundaryduetogranivorybythesouthernred-backedvole(BrownandVellend2014).In

contrast,rootpathogenslimitupwardexpansionofsugarmaple(BrownandVellend,2014),

whilefungalendophytesextendtherangeofBromuslaevipesduetoconferreddrought

resistance(Afkhamietal.2014).

Variationsinestablishmentsuccessbeyondcurrentrangeswilllikelyresultinthe

reorganisationofcommunitymembersintonovelplantassemblages(Urbanetal.2012).

Alexanderetal.(2015)testtheeffectsofasynchronousmigrationontheperformanceof

fourtargetalpineplants.Whenalpineplantsweretransplantedtoloweraltitudestosimulate

migrationfailures,performancewashinderedbynovelcompetitors.Conversely,

performanceofthesamespecieswasenhancedwhentransplantedintonovelhigh-altitude

communities.Thisasymmetryincompetitiveabilitybetweenplantsfromlowerandhigher

altitudessuggeststhatspeciesarelikelytobeaffectedatthetrailingedgeoftheirranges

(Alexanderetal.2015).

9

Currentandfuturedistributionsofplantspeciesarecontrolledbyacombinationofabiotic

andbioticfactors,actinginconcert.Theseforcesaredynamic,shiftingovertemporaland

spatialscalesbutareoftenignoredorminimisedinspeciesdistributionmodelling.

Therelative,andsimultaneousimportanceofclimate,bioticinteractions,andother

constraintsoncurrentandfuturedistributions,canonlybeseparatedbyexperimental

manipulation;however,empiricalstudiesofthistypearerare(Holt2009).Iconducteda

seriesoffieldandlaboratoryexperimentsontheecologyandphysicaltolerancesofamodel

speciesAlpinePodoelpis(Podolepisrobusta,Asteraceae).Iaimedtoinvestigatehowabiotic

andbioticfactorsaffectseedlingsurvival,inordertomakeinferencesonconstraintsto

currentandfuturedistributions.Thetypeandstrengthofplantinteractionswere

determinedwithatransplantexperimentaboveandbelowthecurrentdistributionofAlpine

PodolepisatMtHotham,alongatemperatureandmoisturegradient.Inaddition,laboratory

experimentsassessedgerminationcharacteristics,andfreezingandshadetoleranceof

seedlings.Specifically,Itestedthefollowinghypotheses:

(i)competitionwillreduceseedlingsurvivalandgrowthatloweraltitudes,andfacilitationwill

increasesurvivalandgrowthathigheraltitudes;

(ii)germinationnicheforAlpinePodolepisisnarrow;

(iii)AlpinePodolepissurvivalandgrowthisrestrictedbylightlimitation;and

(iv)earlyseedlingsurvivalisconstrainedbyfreezingtemperatures.

10

Methods

Studyspecies

Podolepisrobusta(Maiden&Betche)J.H.Willis,commonlyknownasAlpinePodolepis,isa

small(20–60cm)erectperennialdaisy(Jeanes1999).AlpinePodolepisisrestrictedto,and

reasonablycommonthroughouttheAustralianAlpsBiogeographicRegion(Frood2015)(Fig.

1).Itgrowslargelyinassociationwithsnowgumwoodlandandalpinemeadowsattheupper

limit,orontheedgeofinvertedtree-linesassociatedwithcoldairdrainage,ataltitudes

between1200–1700m(Jeanes1999;Frood2015).AtMtHotham,plantsarelargely

associatedwiththewarmanddrynorth-westaspect(J.Morgan,unpublisheddata).

TheabundanceofAlpinePodolepiswasoncereducedatleastinpartthroughcattlegrazing

upuntilthe1950s(VanRees1982;Wahrenetal.1994),adisturbancewhichhassince

ceased(Wahrenetal.1994).Theeffectoffireisnotthoughttohavelong-lastinginfluences

ontheabundanceofAlpinePodolepisas,likemanyalpineforbsandgrasses,itrespondsby

resproutingrapidlypost-fire(Wahrenetal.2001).Inearlyspring,multipleshootsarisefrom

abasalrosetteofglabrous,lightgreenleaves(Frood2015).AlpinePodoelpisflowersin

summer(Dec-Mar)andarecharacterisedbybrightyellowcapitula(20-35mmindiameter),

clusteredindensecymes(Jeanes1999)(Fig2.).Comparedtootheralpinedaisies,seedsare

heavy(0.69mg±0.01mg)(Sommervilleetal.2013).Thoughpresumablywinddispersed,

thereiscurrentlynoexperimentalevidenceconcerningtheefficacyofwinddispersalby

AlpinePodolepis.

11

Fig.1.OccurrencerecordsofAlpinePodolepis Fig.2.Podolepisrobustainflower(AtlasofLivingAustralia,2017). (image:J.Morgan)

StudySite

AlllaboratoryandglasshouseexperimentswereconductedatLaTrobeUniversity,Bundoora,

Melbourne,whilefieldexperimentswereconductedatMountHotham

(Fig.3).MtHotham(1860m)isoneofVictoria’shighestmountains.Meanannual

precipitationis~1480mm,mostofwhichfallsaspersistentsnowduringwinter.Mean

minimumandmaximumtemperaturesrangefrom8°Cto16.3°Cmid-summerand-0.1to-

3.6°Cmid-winter(BureauofMeteorology,2017).Frostsarefrequent,evenduringwarmer

months(WilliamsandAshton1987).

TenstudysitesatMtHothamwerechosentorepresentagradientoftemperatureand

moisture.Sitesrangefrom1620m(lowest)to1855m(highest),andincludefivesiteson

eachofsouth-eastandnorth-westfacingslopes(Table.1).Thesehavedifferentexposureto

incidentlight,whicheffectstemperature,evaporationandhence,snowdurationand

growingseasonconditions.

12

Siteconditions

Airtemperatureat5cmabovegroundduringstudyperiod(Nov2016–Mar2017)was

measuredbi-hourlywithThermochroniButtons(MaximIntegrated,California,USA)attached

toawoodenstakeateachsite.Fromthesedata,growingdegreedays(GDDs)were

calculated(McMasterandWilhelm1997)asanindicatorofthermalaccumulation(in°C).

GDDsweresummedforeachsiteinordertorepresentacumulativeindexofavailableenergy

forgrowthanddevelopmentofseedlingsduringthestudyduration,accordingtothe

formula:

GDDs=[(TMAX+TMIN)/2]–TBASE,

whereTMAXandTMINarethedailymaximumandminimumtemperatures,respectively,and

TBASE=thetemperatureabovewhichmetabolicfunctionispossible.0°Cwaschosenasthe

basetemperature,asperBrownetal.(2006)andVennetal.(2013).

Ateachsite,lightinterceptionbydominantvegetationwasmeasuredwithaquantumlight

sensor(LI-COR,Nebraska,USA).Photosyntheticallyactiveradiation(PAR)wasmeasureda

totaloftentimesaboveandbelowthecanopyofvegetationalonga30mtransectat3m

intervals.Alongthesametransect,vegetationstructurewasmeasuredat1mintervals,

wherebycanopyinterceptionofherbs,graminoidsandshrubsalongastructurepolewas

recordedwithinheightclassesof10cmincrements.

13

Fig.3.LocationofMtHothaminVictoria,andstudysitelocationsatMtHotham(1-10)representingtheelevationgradientonsouth-eastandnorth-westsites(seeTable.1).Table1.SummaryinformationforthetensitesalongtheMtHothamtransectincludinglocation,altitudeandaspectforeachsite.(UTM=UniversalTransverseMercatorcoordinatesystem).

Site Location(UTM55H) Altitude(m) Aspect1 511370E,5907898N 1855 NW2 511433E,5907823N 1860 SE3 511218E,5907696N 1820 NW4 511297E,5907589N 1800 SE5 510990E,5907580N 1780 NW6 510924E,5907434N 1690 SE7 510900E,5907495N 1700 NW8 510816E,5907296N 1660 SE9 510792E,5907329N 1670 NW10 510783E,5907128N 1620 SE

14

Fieldtransplantexperiment

TodeterminethecontrolsonAlpinePodolepisseedlingsurvivalandgrowth,beyondthe

boundariesofitscurrentdistribution,atransplantexperimentwasundertakenatMt

Hotham.Theeffectsofaltitude,aspectandcompetitionwereexamined.

SeedwasgerminatedfromseedcollectedatMtHothaminMarch,2016.Seedwassurface

sownontoamixtureofsterilisedperlite,sandandpottingmixinOctober2016ina

glasshouse.Propagatedseedlingswerethenprickedoutintotrayswith4X4cmsoilplugs

andgrownfor6weeksunderglasshouseconditions.PriortoplantingatMtHotham,

seedlingswereplacedoutsidefor7daysatBundoora,andwerethentransportedtoMt

Hotham,acclimatedfor5days,andthenplantedovera3-dayperiod.Seedlingswerekeptin

theirtraysduringtransportationtoeachsite.Inmid-November2016,eachsitereceived26

seedlings,oneintoeachgap(cleared)andcontrolplot,arrangedalonga26mtransectwith

alternatingtreatmentsateachmetreinterval.Clearedplotswerecreatedfor‘gap’treatment

byremovingabove-groundvegetationfromwithin~15cmofthetransplantsitewith

secateursandweremaintainedmonthly.Thegaptreatmentswereprobablyconservative.

Seedlingsplantedintogapswerelikelystillgivensomeshelterfromwindsbyresident

vegetation.Atplanting,thenumberofleaves,andlengthoflongestleafwasrecorded.These

measurementswererecordedagainatthefinalsurveyinMarch2017.Seedlingsurvivalwas

recordedmonthly.

Laboratorygerminationexperiment

TodeterminewhetherseedgerminationofAlpinePodoelpishasanarrowverseswide

germinationniche,seedswereexposedtodifferenttemperatureandlightavailability

regimesinalaboratorygrowthcabinetstudy.

Treatmentsspannedarangeofdiurnaltemperaturesthatrepresentspring/autumn

conditions(14/10°C),earlytomid-summerconditions(20/12°C,24/16°C)andextreme

mid-summerconditions(30/20°C).Eachtreatmentwasconductedwith12hrlight/dark

cycles(ThermolineGrowthCabinets).Withineachtreatment,seedswereeitherexposedto

15

light/darkcyclesorwerekeptinconstantdarkconditionsbywrappingpetridishesintwo

layersofaluminiumfoil.Anadditionaltreatmentat4°Cwasimplementedfortwosetsof

replicatesinconstantdarkconditions.After30days,if0%germinationwasscored,replicates

weremovedintogrowthcabinetat14/10°Candplacedintorespectivelight/darkand

constantdarkconditions.

Foreachtreatment,therewerefivereplicates,eachconsistingof25seedsplacedinto90

mmpetridishesonWhatman#1filterpapermoistenedwithdistilledwaterandsealedwith

Parafilmtopreventlossofmoisture.Thesereplicateswereplaced,stacked,intogrowth

cabinets.Theorderofstackeddisheswasrandomisedafterscoring.

Replicateswerescoredforgerminationapproximatelyevery4daysforlight/darktreatments,

andapproximatelyevery8daysforreplicatesinconstantdarktreatmentsinorderto

minimizelightexposure.Seedwasconsideredgerminatedoncetheradiclehademerged

fromtheseedcoat,andwereremovedafterscoring.Filterpaperwasre-moistenedwhen

required.Once12dayspassedwithnonewgerminationfromwithinatreatment,remaining

seedsweretestedforviabilityusingtetrazoliumtesting(Moore1973).Attheendofthe

experiment,germinationpercentageswereadjustedforviability.

Lightlimitationexperiment

Theeffectoflightavailabilityonseedlinggrowthwasexaminedinaglasshouseexperiment.

Inthisexperiment,netphotosynthesisandbiomassaccumulationwereassessedinrelation

tothreelightregimes.Thetreatmentswere:(i)0%shade(treatedwithoutshadecloth);(ii)

48%shade,(iii)82%shade.PhotosyntheticallyActiveRadiation(PAR)intheglasshouseona

cleardayatmiddaywasapproximately1500µmolm-2s-1.

Treatmentswereconstructedusingcommercialknittedshadeclothattachedtothesidesand

topofarectangularenclosureconstructedof2.5mmfencewireandchickenwirenetting.

Seedwassurfacesownontoamixtureofsterilisedperlite,sandandpottingmix.Propagated

seedlingswerethenprickedoutinto40x100mmpotscontainingsterilisedpottingmixand

16

grownforsevendaysforanacclimationperiodandtocontrolformortalityduetotransplant

shock.Duringtheacclimationperiod,seedlingsweregrownunderfullambientlightinthe

glasshouseandirrigatedatregularintervals.Afterthisperiod,threeseedlingswereallocated

atrandomtoeachtreatmentofwhichtherewerefivereplicates.Thedry-weightofboth

aboveandbelowgroundbiomassof15seedlingswasmeasuredatthecommencementof

experimentaltreatments.Treatmentreplicateswererepositionedweeklytocontrolfor

glasshouseeffects,andseedlingswereirrigatedatregularintervals.

Imeasuredfoliargasexchangewithadifferentialinfraredgasanalyser(IRGA)(PP-Systems,

Massachusetts,USA),70to80daysafterseedlingswereinstalledintheirrespectivelight

regimes.Measurementsweretakenunderambienttemperatureconditions,whileCO2was

controlledforeachreplicateat400ppm.Measurementswererestrictedtothehours

between11:45amand1:45pmoncleardaystoreducetheinfluenceofpassingcloudand

sunposition.Fiverecordingsweretakenmanuallyonthreefullyexpandedleavesfromeach

seedling.EachleafwasinsertedinsidetheleafcuvetteoftheIRGA,whererecordsofnet-

photosynthesis,stomatalconductance,photosyntheticallyactiveradiation(PAR)intensity,

leafhumidityandtemperaturewereobtained.Atthetimeoffinalrecording,allseedlings

wereharvestedforaboveandbelowgroundbiomass,washedtoremoveexcesssubstrate

anddriedat80°Cfor48hinordertoobtainmeasurementsofdry-weightbiomass.

Freezingresistanceexperiment

Toassessthesensitivityofseedlingstoextremecold,theeffectsoffreezingtemperatures

wereassessedinthelaboratoryusingchlorophyllfluorescenceandthefluorescenceyieldof

PhotosystemII.

PlantmaterialforfreezingresistanceanalysiswascollectedfromthepopulationatMt

Hothaminmid-March2017.Duringcollection,15wholerosetteswereharvestedandsealed

inpolyethylenebags,andtransportedtothelaboratoryinMelbourneinachilledportable

cooler.Uponarrivalatthelaboratory,plantmaterialwaswrappedindamppapertowelin

ordertomaintainhydrationofplantmaterial,andstoredat4°Cinthedarkfor24htoallow

17

forcoldacclimation.Followingpre-treatment,threeleavesfromeachindividualwere

subjectedtooneoffourtemperaturetreatments(-5°C,-11°C,-20°C)for8husing

thermostaticallycontrolledfreezers.Similarly,controlsampleswereheldat4°C.Following

thefreezingtreatment,plantmaterialwaswrappedindamppapertowel,sealedin

polyethylenebagsandplacedinthedarkinaconstanttemperaturefacilityat18°C.

Theratioofvariabletomaximumfluorescenceoftheplantmaterial(FV/FM)wasthen

determinedafterthreedaysusingaPAMchlorophyllfluorometer(Walz,Effeltrich,

Germany).FV/FMratiosarereportedalongsidecontrol(4°C)samples,providinganestimate

ofphotosystemIIefficiencyduringtheassayprocedure.

Theaboveprocesswasalsoexecutedforseedlings.SeedcollectedfromMtHothamin2016

wassurfacesownonamixtureofsterilisedperlite,sandandpottingmix.Propagated

seedlingswereprickedoutandtransplantedinto40x100mmpotsfilledwithpottingmix

andgrownforthreeweeksunderglasshouseconditions.Afterthisperiod,seedlingswere

washedtoremoveexcesssubstratefromroots.Seedlingrootswereretainedduringfreezing

resistancetreatments.Ratherthanassessingfreezingdamagetothreeleavesperplant(as

withthematureplants),oneleafwasassessedfrom15replicateseedlingsforeach

treatmentduetothesmallnumberandsizeofleaves.

DataAnalysis


Prediction:Ifthedirectionofplantinteractionchangesamongseedlingsalongatemperature

andmoisturegradient,Iwouldexpecttoseehighersurvivalingapsrelativetocontrolsatlow

altitudeswherecompetitiveprocessesaremorelikely,switchingtohighersurvivalincontrols

relativetogapsathigheraltitudes,wherefacilitativeprocessesbecomemorecommon

(Callaway1995).Additionally,ifthecurrentdistributionofAlpinePodolepisiscontrolledby

climate,Ipredictthattherewouldbelowersurvivalonthesouth-eastaspect.Therefore,in

themodelling,treatment,altitudeandaspectwereconsideredasfixedeffects.Totest

whetherseedlingsurvivaldifferedamongfixedeffects,generalisedlinearmodels(GLM)were

18

fitusingtheLaplaceapproximationinthepackagelme4(Batesetal.2015)inthe‘R’

statisticalpackage(RCoreTeam2013).ModelselectionwasbasedontheAkaikeinformation

criterion(AIC)(Akaike1974).

Similarly,plantperformance(growth)isexpectedtochangeaccordingtotreatment(gapor

control)alonganaltitudinalgradient.Thenetdirectionofpositiveandnegativeinteractions

wascalculatedbetweenpairsoftransplantedseedlingsingapandcontrolplotsusingthe

RelativeNeighbourEffect(RNE)Index(Brookeretal.2005;Vennetal.2009):

RNE=(Gap–Control/MAX(Gap,Control),

whereGapandControlcorrespondtotheperformanceofindividualsingaps(neighbours

removed)andcontrols(neighboursleftintact),respectively,andMAX(Gap,Control)refersto

thehighestperformancevaluebetweenthetwotreatments.Lengthoflongestleafwasthe

indiceusedtoquantifyseedlingperformanceandwascalculatedasfinallength/initial

lengthuponthefinalsurveyinMarch2017.RNEvaluesweremodifiedasperCallawayetal.

(2002)suchthatnegativevaluesindicatenegativeneighboureffectsonperformance

(competition),andpositivevaluesindicatepositiveneighboureffectsonperformance

(facilitation).PresentedaremeanRNEforseedlingsinpaired‘gap’and‘control’plots.Inthe

analysis,adeathinanypairofseedlingswasremovedfromfinalcalculations.Thismeantthat

inonecase,onthesouth-eastaspect,asitewasremovedfromanalysisduetolow

replicationofpairedseedlings.Inaddition,asiteonthenorth-westaspectwascouldnotbe

analysedduetomissingdata.RNEvalueswereanalysedwithone-wayANOVAaccordingto

sitewherebythelowestsiteoneachaspectwassetasthe‘dummy’thatallothersiteson

thatcorrespondingaspectwerecomparedto.North-westandsouth-eastaspectswere

analysedseparatelyinordertoteaseoutthedirectionofplantinteractionbyaltitudealone

withoutpotentialconfoundingfactorofaspect.


Prediction:IfcompetitionforlightisakeyfactorlimitingthedistributionofAlpinePodolepis,

thenIwouldexpecttoseereducedrateofphotosynthesisandreducedbiomasswith

19

decreasinglightavailability.Rateofphotosynthesisanddry-weightbiomasswerefittedin

separategeneralisedlinearmixedeffectsmodels(GLMM)usinglme4(Batesetal.2015)in

the‘R’statisticalpackage(RCoreTeam2013).Inthefirstinstance,shade-housereplicate,

plant,andleafwereusedasrandomfactors,andseedlingwasusedasarandomfactorinthe

latter.


Prediction:Ifspecificgerminationrequirementsarelimitingfactorsinthedistributionof

AlpinePodolepis,Iwouldexpecttoseeanarrowrangeofgermination.

TheinteractionbetweenlightandtemperatureonthegerminationofAlpinePodolepis

seedlingswasanalysedwithageneralisedlinearmodel(GLM)usinglme4(Batesetal.2015)

inthe‘R’statisticalpackage(RCoreTeam2013).Aquasi-binomialerrordistributionwasused

inordertoaccountfortheover-dispersionevidentingerminationdata(clusteringofbinary

outcomeswithintreatments).Finalgerminationofseedsindarkandlighttreatmentsat14°C

werecomparedtothosethatreceivedaperiodofcold-stratificationusingStudent’st-tests.


Theextentoftissuedamageinresponsetofreezingtemperatures(-5°C,-11°C,-20°C)was

analysed.Ifrecruitmentdynamicsareinfluencedbyoccurrencesoffreezingtemperatures,

seedlingtissueisexpectedtoexperiencehigherdamagerelativetocontrol(4°C)andtoadult

tissue.Student’st-testswereusedforsimplecomparisonsbetweenFV/FMratiosofadultand

seedlingleaves,asagreatertemperaturerangeisrequiredinordertocalculatelevelof

‘freezingresistance’bylinearinterpolationasperBannister(2005)andVennetal.(2013).

Lethaltemperaturesareconsideredthoseatwhich50%damageoccurstothe

photosyntheticapparatusofleavesrelativetocontrol(4°C).

20

Results

Siteconditions

South-easternexposedsitesexperiencedmorefreezingdays(days£0ᵒC)thannorth-west

exposedsitesduringstudyperiod(Nov2016–Mar2017).Thenumberoffreezingdays

increasedwithaltitude,andthistrendwassimilarforbothaspects(Fig.4).

Overall,asexpected,north-westernsitesexperiencedgreatercumulativeGGDsduringthe

studyperiodthansitesonthesouth-east(Fig.5).GDDsdecreasedwithincreasingaltitudeon

south-eastexposedsites.ThehighestcumulativeGDDswasrecordedat1780monthe

north-west,andtheredidnotappeartobealineartrendwithGDDsandaltitude.Thisis

possiblyduetotheinfluenceofvegetationcoveratsitesonthenorth-west,asdense

vegetationcoverreducedincidentlightby75–100%at1670mand1820mrespectively(see

AppendicesI&II).

Fig.4.Totalnumberoffreezingdays(temperatures≤0ᵒC)recordedatMtHothaminrelationtoaltitudeduringstudyperiod(Nov2016–Mar207)onnorth-west(solidline)andsouth-east(dashedline)exposedslopes.

21

(a)

(b)

Fig.5.GrowingDegreeDays(GDD)recordedforsouth-east(a)andnorth-west(b)exposedsitesduringstudyperiod(Nov2016–Mar2017).

1350

1450

1550

1650

1750

1670 1700 1780 1820 1855

GDD

Altitude

1350

1450

1550

1650

1750

1620 1660 1690 1800 1860

GDD

Altitude

22


Pooledacrossallsitesandtreatments,totalsurvivalofseedlingsoveronegrowingseason

was82%.Survivalwassignificantlyaffectedbytreatment,withhighermortalityforseedlings

plantedintogapsthancontrols(p<0.001)(Fig.6).Atrendofincreasingmortalitywith

altitudewassignificantforseedlingsinbothgapandcontroltreatments(p<0.05).Seedling

survivalwasnotsignificantlydifferentonnorth-westorsouth-eastexposedsites(p>0.05).

Fig6.Effectoftreatmentandaltitudeonseedlingsurvival.Meanprobabilityofsurvival(±95%CI)overonegrowingseasonforseedlingsplantedalonganaltitudinalgradientincontrol(solidgreenline)andgap(solidorangeline)treatments.

Interactioneffectsonseedlingperformancewerepositiveatsevenofeightplantingsitesthat

variedinaltitudeandaspect;attheremainingsitetheinteractionwasneutral(Fig.7).The

greatestdifferencesinleafgrowthoccurredat1820monthenorth-westaspectwhere

seedlingsplantedintoclearedandcontrolplotsincreasedleafsizeby12and84%

23

respectively,hencethepositiveRNEvalue.Seedlingsat1670mshoweda153%increaseof

leafsizeinclearedplotsanda110%increaseofleafsizeincontrolplots,hencetheneutral

RNEvalue.NostatisticaldifferencesbetweenRNEvaluesweredetectedforplantedseedlings

onthesouth-eastsites;rather,positiveinteractionswithcloseneighbourswereconsistentat

eachsitealongtheelevationgradient.Onthenorth-westaspect,theneutralinteractionat

1670mdifferedsignificantlyto1820m(p<0.01)and1855m(p<0.05)wheregrowthwas

positivelyinfluencedbycloseneighbours(Fig.7a;AppendixIV,Table.6).

(a) (b)

Fig.7.MeanRelativeNeighbourEffect(RNE)(±1SE)forpairedtransplantedseedlingsingapandcontroltreatmentson(a)north-westand(b)andsouth-eastexposedaspectsacrosstheelevationgradient.Positivevaluesindicatefacilitativeinteractions,andnegativevaluesindicatecompetitiveinteractions.Neutralinteractionsareindicatedbyerrorbarscrossingtheyaxisat0.Differentsuperscriptsabovecolumnsdenotesignificantdifferencesbetweensites.NPlabelsindicatethatanalysiswasnotpossible.

24


Temperature-mediateddormancyisweak,withhighgermination(>50%)acrossalldiurnal

temperatureandlightconditions,andonlyconstrainedatthelowesttemperatureinthedark

(Fig.8).Therewasasignificantinteractionbetweenlightanddarktreatmentswith

temperature(p<0.05),asgerminationissuppressedindarkconditions(p<0.01),but

increaseswithtemperature(p<0.001),whilegerminationoccurredequallywellatall

temperatureregimesinlightconditions(14°C–30°C).Timeto50%germination(t50)

occurredwithoutstratificationandwithin30daysforbothlightanddarkconditions³20°C.

At14°Cinthedark,responsetocoldstratificationwaspositive(p<0.05),increasing

germinationby21.8%andreducingT50byatleast42days(Table2).Inthelighttreatment,

T50decreasedonlymarginallyby3daysaftercoldstratification.

(a) (b)

Fig.8.Effectoflightandtemperatureongermination.Fittedvaluesforprobabilityofgerminationfor(a)lightconditionsand(b)darkconditions(±95%CI)forthegeneralisedlinearmodelappliedoncabinetgerminationdata.Germinationpercentagesfromrawdataincludedaspoints.Notethedifferentscalesfortemperatureaxis.

25

Table2.GerminationattributesofAlpinePodolepisat14°Cwithandwithoutaperiodofcoldstratification.LAG(days)=thenumberofdaysfromthestartoftheexperimentuntilgerminationbegan.t50(days)=thenumberofdaysfor50%oftotalgerminationtooccur.Lighttreatment Coldstratification

periodLAG(days) t50(days)

Final%

germinationLight 30days 4-8 8-11 96.8Light 0days 7-10 14-20 99.2Dark 30days 11-14 13-23 83.8Dark 0days 10-13 62-65 62


Bothseedlingdrymass(aboveandbelowgroundbiomass)andnetphotosynthesis

respondedsimilarlytolightlimitationtreatments(Fig9.10.).Valueswerecomparablefor

seedlingsgrowninfullsun(0%shade)andat48%shadeforseedlingbiomass(p>0.05)and

netphotosynthesis(p>0.05).However,plantbiomass(Fig.10)wasreducedsignificantlyin

seedlingsgrownunder82%shadewhencomparedtoseedlingsgrowninfullsun(0%)

(p<0.001)and48%shade(p<0.001).Similarly,netphotosynthesis(Fig.9)wassignificantly

lowerforseedlingsgrownat82%shadewhencomparedtoseedlingsgrowninfullsun

(p<0.01)and48%shade(p<0.05).

26

Fig.9.Effectoflightlimitationonnetphotosynthesis.Fittedmeanrateofphotosynthesis(±95%CI)ofseedlingsgrownunderfullsun,48%shadeand82%shade.

Fig.10.Effectoflightlimitationonbiomass.Fittedmeandry-weightofbiomass(±95%CI)ofseedlingsgrownunderfullsun,48%shadeand82%shade.

27


TheFV/FMratiosofadultandseedlingleavesdeclineddramaticallywithdecreasing

temperaturesinthelaboratoryfreezers(Fig11.),withasubstantialdecreaseevidentfor

seedlingleavesat-5°Candadultleavesat-11°C.At-5°C,seedlingsexperiencedsignificantly

greaterdamagetothephotosyntheticapparatusofleavesrelativetocontrol(4°C)(p<0.001)

andtoadultleavesexposedtothesametreatment(p<0.001).Bothadultandseedlings

experiencedalmostcompletedamageattemperatures£11°C.

Fig.11.Mean(±1SE)variablefluorescencetomaximumfluorescence(Fv/Fm)ratiosofleafmaterialusedinfreezingresistancestudy,atfourtemperatures:4,-5,-11,and-20°C;forAlpinePodolepisleavesofa)matureplantsandb)seedlings.

0

0.2

0.4

0.6

0.8

1

-25 -20 -15 -10 -5 0 5 10

F V/F

M

Treatmenttemperature(°C)

0

0.2

0.4

0.6

0.8

1

-25 -20 -15 -10 -5 0 5 10

F V/F

M

Treatmenttemperature(°C)

(a)

(b)

28

Discussion Facilitative(positive)interactionsinfluencedthesurvivalandgrowthofseedlingsoverone

growingseasonatMtHothamintheVictorianAlps.Seedlingsurvivalwasnotinfluencedby

aspect,butatrendofincreasingmortalitywithaltitudewasdetected.Therateof

photosynthesisandbiomassaccumulationmayalsoberestrictedinthefielddueto

competitionforlightinheavilyshadedsites,assuggestedbyglasshouseexperiments.

Germinationwasobservedinthelaboratorytobebroad,attemperatures³14°Cinlightand

darkconditions.Whilecoldstratificationwasnotrequired,theresponsetostratificationwas

positiveindarkconditions,wherehigherpercentgerminationandfastergerminationrates

likelyreflectssynchronousgerminationinthefieldaftersnowmelt.Youngseedlingssuffered

greaterdamagetofreezingtemperaturesthanadultplants.Asfreezingtemperaturesare

commonandunpredictableinthealpinezone,vulnerabilityattheemergingseedlingsstage

maybealimitingfactorinrecruitmentanddistribution.Resultssuggestthatwhatis

observedtodayastherealisednicheofAlpinePodolepisisnotreflectiveofitspotential

range,andhighlightstheimportanceoffacilitativeinteractionsinalpineenvironments.

Germinationcharacteristics

Germinationisoneofthemostfundamentaldevelopmentalprocessesinthelifecycleof

plants,andvarieswidelyamongspecies(Korner1999).AlpinePodolepisexhibitedhigh

germinationatabroadrangeoftemperatures;however,itwassuppressedinthedarkat

4°C.Responsetocoldstratificationwaspositive,increasingrateofgerminationandfinal

germinationinthedark.Thoughlong-termdormancyisconsideredrareinalpinelandscapes,

somealpinespeciesrequiretheexperienceoflowtemperaturesoverwinterinorderto

germinate(BaskinandBaskin2003).ThisisthecasewithAustralianalpinespeciesAciphylla

glacialis(VennandMorgan2009),Euphrasiacollinassp.(Sommervilleetal.2013),and

Eucalyptuspauciflora(BeardsellandMullett1984),whereunlessseedsaresubjectedtoa

periodofcold-wetstratification,germinationispoorornotpossible.Alackofdormancy

(excludingafterripening),andawidegerminationrangeindicatesthatAlpinePodolepisare

29

notdependentuponaspecifictemperatureregimeforgermination,acommontrait

throughoutAsteraceae(BaskinandBaskin2003;Sommervilleetal.2013).

Positiveresponsestocoldstratificationhavebeenreportedforawidearrayofalpinespecies,

andinsomecaseswidensthegerminationrangeandimprovesfinalgermination

(Sommervilleetal.2013).Hence,thoughgerminationwasreducedindarkconditions,thisis

likelyovercomeinsitubyacoldperiodexperiencedoverwinter.Coldstratificationalso

reducesvariabilityingerminationtime,synchronisingseedlingemergenceaftersnowmelt

(ShimonoandKudo2005).Assuch,itisunlikelythatAlpinePodolepisarecapableofstoring

dormantseedinthesoil.ThiscontrastswithCarexspecieswheregerminationeventsare

spreadovertwoyears,reducingtheriskofcompleterecruitmentfailure(Schütz2002).

Hence,whileitisunlikelythatthedistributionofAlpinePodolepisiscontrolledbynarrow

germinationrequirementsseeninotheralpinespecies,anopportunisticandlikely

synchronousgerminationinearlyspringindicatesthatrecruitmenthingesupontheamount

ofseeddispersedinthepreviousseason,andtheenvironmentalconditionsupon

germination.

Frosttoleranceinseedlings

GivenrequirementsforgerminationarerelativelybroadforAlpinePodolepis,limitstoits

distributionmustbecontrolledbyfactorsotherthananarrowgerminationniche.Indeed,

whilegerminationiscommonintheVictorianalpinezone,halftheamountofnaturally

emergingseedlingsdiesbeforeestablishment(VennandMorgan2009).AlpinePodolepis

seedlingswerefoundtobemoresensitivetofreezingtemperaturesthanadults,suffering

significantdamagetophotosyntheticapparatusat-5°C.Cold-edgeboundariesaresetby

occurrencesoffrostduringthegrowingseason,coupledwithspecies-specificfreezing

resistance(abilitytosurvivefreezingtemperatureswithoutdamage)(Körneretal.2016).

Freezingtemperaturesareanimportantfilterongermination,recruitmentandpersistencein

alpineplantcommunities(KörnerandPaulsen2004)and,assuch,areprincipledeterminants

ofgeographicdistributions(SakaiandWeiser1973).FrostsintheAustralianAlpsare

common,evenduringwarmerseasons(WilliamsandAshton1987).Duringthisstudy,

30

freezingtemperatureswererecordedasbeingmorecommononsouth-easternaspects,and

increasingwithaltitude.Resistancetofreezingtemperaturesofalpineplantsoverthe

growingseasonisreportedlyquitehighinAustralianalpinespecies,withapatternof

increasingtolerancewithaltitude(Vennetal.2013).Whileadultsmaybelesssusceptibleto

springorsummerfrosts,seedlingshavelowertoleranceandlimitedrecuperationability,as

recentlyemergingseedlingsareyettodevelopmeristematicregionsunderground(Korner

1999).However,whileitisunknownwhenthethresholdforfrostresistanceisreachedfor

AlpinePodolepis,occurrencesoffrostduringseedlingemergence,andduringtheearly

stagesofestablishment,arelikelytoreducesurvival.Hence,seedlingestablishmentmay

thereforebelimitedtorelativelyrare,favourableseasons.However,successful

establishmentmaybepossible,givensuitablemicrosites(Vennetal.2009).

Effectsoffacilitationalonganabioticstressgradient

Duringthisstudy,seedlingmortalitywaslow,andwasnotaffectedbyaspect,contraryto

expectations,giventhecurrent,stronglynorth-westerndistributionofAlpinePodolepisatMt

Hotham.Whileseedlingmortalityincreasedslightlywithaltitude,mortalitywaslowacross

theentiregradientofbeyond-rangetransplants.Althoughouraltitudinalgradientwassmall

(235m),thechangesinenvironmentalconditionswerenoticeablewithmorefreezing

temperaturesrecordedonsouth-easternaspect,whichincreasedonbothaspectswith

altitude.Asindicatedbyourfreezingresistanceexperiment,earlyseedlingsurvivalisstrongly

affectedbyfreezingtemperatures.Ourplantedseedlingsweresixweeksoldattimeof

planting,likelyenoughtimeforseedlingstodeveloprootreservesandaleveloffrost

resistance,unlikeinnewlyemergentseedlings(Körner1999).Hence,ifconditionsduringthe

earlygrowingseasonallowforseedlingestablishment,seedlingsaretoleranttoarangeof

conditionsatMtHotham,contrarytowhatthecurrent,stronglynorth-westerndistribution

mightsuggest.Conclusionscanonlybebasedoffofonegrowingseason,andperhapsthe

strengthofaspectandaltitudemaybecomemoreapparentwithtime.

Incontrast,similarstudieshavereportedhighseedlingmortalityduringthefirstgrowing

season(UrbanskaandShutz1986;Vennetal.2009).Indeed,theseedlingstageiscriticalin

31

thelifecycleofplants(ForbisandDoak2004),andpresumably,highsurvivaloverasingle

growingseasonisindicativeofahightolerancetovariedclimaticconditionsthatwouldbe

experiencedalongthealtitudinalgradient.Inalpineenvironments,plantsareexposedto

stressfulabioticconditionsincludingfreezingtemperatures,needleice,andscouringwinds

(Körner1999).However,substantialvariationinmicrohabitatinfluencesthecompositionof

localvegetation(SherrerandKörner2011).Suchvariation,whiledrivenbytopography,

altitude,andslopeorientation(SherrerandKörner2011),isalsodrivenbyvegetation(Körner

1999;Vennetal.2009).

Whileseedlingsurvivalwasgenerallyhighatallsites,survivalwasconsistentlyhigherin

control(uncleared)plotsthaningaps.Numerousstudieshighlightfacilitationasanimportant

factorinseedlingsurvivalinnaturalcommunities(Callawayetal.1997;Brookeretal.2007;

Vennetal.2009:WarrenandBradford2010),asneighbouringplantsamelioratestressful

abioticconditions,creatingamicroclimatesuitableforseedlingestablishment(Callawayetal.

1997).Indeed,whilesomespeciesrequirebarepatchesforgerminationandestablishment,

seedlingsinalpineenvironmentsarecommonlyreportedclumpedtogetherintheleeof

largerneighbours(Callawayetal.2002).Insuchmicrosites,‘nurseplants’bufferestablishing

seedlingsfromscouringwinds,increaselocaltemperatureandsoilmoisture(Callaway1995)

andaidinthereductionofdisturbancessuchassoilfrostheave(Vennetal.2012).However,

unlikemanysimilartransplantstudieswhichtestthestressgradienthypothesis(Choleretal.

2001:Callawayetal.2002;Cavieresetal.2005),aswitchinthetypeofinteraction

(facilitationorcompetition)wasnotevident.Instead,consistentlypositiveinteractionswere

demonstratedatallsites,highlightingtheimportanceofpositiveinteractionsatoneof

Australia’shighestmountains.Perhapsthisisunsurprising,giventhegradientsinvestigated

byotherecologistsareoftengreaterandtransplantsaremonitoredovermorethanone

growingseason(seeCholeretal.2001:Alexanderetal.2015).However,Vennetal.(2009)

andAlexanderetal.(2015)reporteffectsofcompetitionduringthefirstgrowingseason.

Whilecompetitioncertainlyisanimportantfactorinthedistributionofspecies(Callawayet

al.1997;DunnettandGrime1999),itdoesnotappeartobeakeydriverofAlpinePodolepis

establishmentduringthefirstgrowingseason.

32

FacilitativeinteractionspositivelyinfluencedthegrowthofAlpinePodolepisseedlingsat

mostsitesoverthecourseofonegrowingseason,consistentwithseedlingsurvivalresponse.

Thisiscountertoexpectationsthatthedirectionofplantinteractionsshouldshiftalongan

abioticstressgradient(Callaway1995;Choleretal.2001;Callawayetal.2002).One

occurrenceofneutralinteraction(whereseedlinggrowthwasnotaffectedbythepresence

orabsenceofneighbours)wasreportedonthenorth-westaspectatthelowestsite.Here,

abioticconditionsdidnotnegativelyaffectseedlingsinclearedsitesasitdidelsewhere,a

signalofrelativelybenignconditions,whichissupportedbylocaltemperaturedata.Here,no

freezingtemperatureswererecordedduringthestudyperiod.Hadsitesextendedtoeven

loweraltitudes,competitiveinteractionsmayhavebecometheprevailinginteractionas

reportedelsewhere(Callawayetal.2002;Alexanderetal.2015).Thelackofcompetitive

interactionsatMtHothammaybeindicativeofabioticstressorsotherthantemperature.

Facilitativeinteractionsareoftenreportedduetolowavailablemoistureondryaspects

(Hillier1990)andheatstress(Korner1999).

PositiveinteractionsmaydominateforAlpinePodolepisduringearlylifestage.Indeed,the

patternsandphenomenaof‘nurseplant’syndromeareoftenstrongestduringearlylife

stages(Callaway1995).Competitiveinteractionsmaydominateoncetheplantreaches

maturity(Callaway1995)orduringmildseasonswhereabioticstressisreduced(Kikvidzeet

al.2006).Alongasimilaraltitudinalgradient,positiveinteractionsinfluencedthegrowthof

Brachyschomeridigulaseedlings,butthestrengthandbalanceofinteractionsshifted

temporally(Vennetal.2009).Withenvironmentalvariationoverthecourseofone,ormany

growingseasons,thedirectionandstrengthoffacilitationandcompetitionislikelytochange

inapredictablemanner(BertnessandCallaway1994;BrookerandCallaghan1998).Nurse-

plantsmaybecomeout-competedbybenefactorsorthereverse(Callaway1995;Kikvidzeet

al.2006),whilefavourableseasonalconditionsmaytipotherwisefacilitativeinteractionsinto

competitiveones(TielborgerandKadmon2000;Valiente-Banuet2008).Hence,while

positiveinteractionspredominatethegrowthandsurvivalofAlpinePodolepis,overthefirst

growingseason,thistrajectorymaychangethroughsubsequentseasons.

Effectsofcompetitiononseedlinggrowth

33

Themechanismsbywhichseedlingsinteractwithnaturalcommunitiesarenumerous,and

canonlybeseparatedbyexperimentalmanipulation(Brunoetal.2003).Theresultssuggest

thata“suitable”environmentforAlpinePodolepisdependsonlightavailability,andindicates

thatmoderateshadeisnotnecessarilynegativeforseedlinggrowth.Thelow-light

environmentthatoccursbeneaththestandofdominantPodolobiumalpestreatlow-altitude,

north-westernsitesforexample,wouldleadtodecreasednetphotosynthesisandbiomass.

Incontrast,high-lightorpartyshadedenvironmentsareequallyfavourableforgrowth.Such

lightconditionscanbefoundwithintherelativelywell-illuminatedunderstoryoftheupper

limitsofsnow-gumwoodlands,andthroughoutmuchofthetreelessalpinemeadows.

However,insituconditionsareusuallynotoptimal,andnetphotosynthesisisoftenbelowfull

capacityduetocombinationsofwaterstress,temperatureextremesorlowhumiditycausing

partialstomatalclosure(Muraokaetal.2002).Moreover,damagecausedbyextreme

temperatures,drought,orherbivoryalsomustincreasemaintenancecosts,anadded

constraintonnetgrowth(Körner1999).

Whilecertainabioticstressorscanbemediatedbymicrositescreatedintheleeorcanopyof

other,morestress-tolerantplants,astheplantreachesmaturity,competitionforresources

becomesmoreimportantbelow-ground(AguiarandSala1994).Wilson(1988)foundthat

rootcompetitionwasthemoreintenseformofplantinteraction,occurringdirectlythrough

allelochemicalexudates,andindirectlythroughresourcedepletion.IntheTibetanPlateau,

interactionsofrootcompetitionvarybetweenspecies(Songetal.2006).Hence,theeffects

ofcompetitionandmayplayoutinthelongertermforAlpinePodolepisseedlings.Indeed,

competitionmaybeactingalongthegradientinconcertwithfacilitation,suchthatweare

notyetabletoobservetheeffectsofaboveorbelow-groundcompetition.Howthisbalance

ofcompetitionandfacilitationwillplayoutthroughtimewillbeimportantforunderstanding

howinteractionsinfluencetherangeboundariesofalpineplants.

Asdemonstratedwithlaboratorygerminationandfieldtransplants,AlpinePodolepisappear

tohaveatheoreticalnichefargreaterthancanbeobservedatMtHothamcurrently,

indicatingpossiblelimitationofdispersaland/orpropaguleavailability.Itiscommonfor

plantstolose90-100%ofproducedseedtoseedpredation(Louda1989).Pre-and-postseed

34

predatorscandeterminenetfecundityoftheirplanthosts(Mckoneetal.1998),having

consequencesforpopulationdensity(Louda1982)anddistribution(BrownandVellend

2014).Pre-dispersalseedpredationiscommonamongalpineAsteraceaeandhasbeen

reportedforAlpinePodolepisinMtKosciuszko(Pickering,2009).However,theeffectsof

herbivoryandsoilpathogensaredifficulttodetermine.

Thereisapaucityofevidenceregardingtheimportanceofinsectsandpathogensinthe

populationdynamicsandrangelimitsofhostplants.Differentialratesofinsectorpathogen

attackmayalterorreversecompetitiverelationshipsbetweenplants(LeeandBazzaz1980;

RaiandTripathi1985).Indoingso,theyhavethepotentialtoexcludeplantspeciesfrom

communities(Crawley1989),andthereforemayplayamajorroleinthestructuringofplant

boundaries.Inaddition,plantresponsetoherbivoryislikelytovarywithlifestageandmay

interactwithresourceavailability.Seedlingsarelikelytohavelowerdefenseand/ortolerance

toattackthanestablishedplants(BoegeandMarquis2005)andmayalsoplayarolein

definingspeciesdistributions.Futureresearchmightconsiderhowdispersal,seedpredation

and/orherbivoryandpathogensmayinfluencepopulationdynamicsanddistributionof

plants,andhowtheseinteractionsmightchangewithcontinuedclimatewarming.

Conclusion

Typically,facilitativeinteractionsarereportedasoccurringmostlyattheextremelimitsofa

speciesenvironmentaltolerance,leadingtorangeexpansionandalteringtherealisedniche

(Brunoetal.2003).Here,residentplantspositivelyinfluencedsurvivalandgrowthofAlpine

Podolepisseedlingsbeyondthecurrent,observedrange.However,facilitationoccurrednot

onlyattheupperlimitstoitsdistribution,butalsobelowthetrailingedge.Habitat

ameliorationisanimportantstructuringforceinstressfulenvironments(Brunoetal.2003).

Forseedlingsurvivalinthealpinelandscape,thisistrueforAlpinePodolepis,regardlessof

theabioticstressgradient,duringthefirstgrowingseason.Althoughtheconsistenttrendof

positiveinteractionsmaychangeovertime,earlyseedlingestablishmentisacriticalstage

(Körner1999).Highoverallsurvivalindicatesawiderangeofphysiologicaltolerancealongan

abioticstressgradient.Highoverallsurvivalalsohighlightspossiblelimitationsindispersal

35

and/orpropaguleavailability.Inaddition,earlyseedlingsurvivalislikelyrestrictedby

occurrencesoffrostduringtheearlygrowingseason.Whilethereissomeevidenceofshade

intolerance,whichmayacttorestrictdistributionsatloweraltitudes,furtherexperimental

researchwillberequiredinordertobetterunderstandcompetitiveinteractionsinalpine

plants.Simultaneousinvestigationintopropaguleavailability,dispersalabilityandinsitu

recruitmentwillalsoaidinferencesontheroleofpopulationdynamicsondistributionand

migrationrates.Whetherconsistent,positiveinteractionsreportedherewillchangeover

timewillprovidefurtherinsightintothemechanismsofspeciesinteractions,andtheir

influenceonspeciesdistributions.

36

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AppendixI

Fig12.Shadecastbyresidentvegetationatnorth-westsitesatMtHotham,Victoria

Fig13.Shadecastbyresidentvegetationatsouth-eastsitesatMtHotham,Victoria

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(a)

(b) (c) (d) (e)

00.20.40.60.81

0-10 11-20 21-30 31-40 41-50 51-60 61-70

1660m

00.20.40.60.81

0-10 11-20 21-30 31-40 41-50 51-60 61-70

1620m

00.20.40.60.81

0-10 11-20 21-30 31-40 41-50 51-60 61-70

1690m

00.20.40.60.81

0-10 11-20 21-30 31-40 41-50 51-60 61-70

1800m

0

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0.4

0.6

0.8

1

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1860m

Fig.14.Frequencyofcanopyinterceptionofherb,gramminoidandshrublife-formsatMtHothamonsouth-eastexposedsites(a-e).

Freq

uencyofto

uche

s

Heightincrement(cm)

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(a)(b)(c)(d)(e)

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1700m

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1670m

Fig.15.Frequencyofcanopyinterceptionofherb,gramminoidandshrublife-formsatMtHothamonnorth-westexposedsites(a-e).

Freq

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s

Heightincrement(cm)

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AppendixII

Fig.16.EucalyptuspauciflorawoodlandwithdensePodolobiumalpestreunderstorydominatenorth-westexposedslopesatMtHotham(1670-1700m).

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AppendixIIITable3.Analysisoftheeffectoftreatment,altitudeandaspectonseedlingsurvival.

Fixedeffect Chisq Df Pr(>Chisq)

Treatment 11.2621 1 0.000791***Altitude 6.4467 1 0.011116*Aspect 0.3057 1 0.580321

Theeffectsoftreatment,altitudeandaspectonseedlingsurvivalwasassessedwithageneralisedlinearmodel(GLM).SignificantPvaluesindicatedbyasterisks.ShownaretheChisquare,degreesoffreedomandP-valuesofthemodel.(‘***’p<0.001;‘**’p<0.01;‘*’p<0.05;‘.’P<0.1).Table4.Analysisoftheeffectoftreatmentandaltitudeonseedlingsurvival.

Fixedeffect Chisq Df Pr(>Chisq)Treatment 11.2383 1 0.0008013***Altitude 6.1427 1 0.0131952*

Theeffectsoftreatmentandaltitudeonseedlingsurvivalwasassessedwithageneralisedlinearmodel(GLM).SignificantPvaluesindicatedbyasterisks.ShownaretheChisquare,degreesoffreedomandP-valuesofthemodel.(‘***’p<0.001;‘**’p<0.01;‘*’p<0.05;‘.’P<0.1).Table5.TableofcoefficientsfortheGLMusedtofitseedlingsurvivalasafunctionoftreatmentandaltitude.

Estimate S.E zvalue Pr(>|z|)Intercept 11.145130 3.728284 2.989 0.00280**

Treatmentgap -1.151963 0.359530 -3.204 0.00135**Altitude -0.0052086 0.002097 -2.426 0.01527*

ThesurvivalofAlpinePodolepisseedlingswasassessedwithageneralisedlinearmodel(GLM)fittedwithtreatment(gaporcontrol)andaltitudeasadditivefixedeffects.SignificantPvaluesindicatedbyasterisks.Shownarethemodelestimates,standarderrorsandz-values.(‘***’p<0.001;‘**’p<0.01;‘*’p<0.05;‘.’P<0.1).

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AppendixIVTable6.StatisticalanalysisofRelativeNeighbourEffectfornorth-westandsouth-eastsites.

RNEnorth-west coefficients estimate s.e. zvalue Pr(>|t|) 1670m-1700m -0.27689 0.16143 -1.715 0.0954 1670m-1820m -0.45308 0.14534 -3.117 0.0037** 1670m-1855m -0.34817 0.14968 -2.326 0.0261*

RNEsouth-east 1620m-1660m -0.07716 0.17118 -0.451 0.6547 1620m-1690m 0.07056 0.16204 0.435 0.6656 1620m-1800m 0.10457 0.16204 0.645 0.5225

Shownareone-wayANOVAcomparisonsbetweensitesaccordingtoaspect.AsterisksindicatesignificantP-values.(‘***’p<0.001;‘**’p<0.01;‘*’p<0.05;‘.’P<0.1).

current distribution not indicative of underlying …

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