Despite Buffers, Experimental Forest Clearcuts Impact Amphibian Body Size and Biomass

31 Pages·2015·9.85 MB·English

RESEARCHARTICLE
Despite Buffers, Experimental Forest
Clearcuts Impact Amphibian Body Size and
Biomass
JessicaS.VeyseyPowell*,KimberlyJ.Babbitt
DepartmentofNaturalResourcesandtheEnvironment,UniversityofNewHampshire,Durham,New
Hampshire,UnitedStatesofAmerica
*[email protected]
Abstract
Forestbuffersareaprimarytoolusedtoprotectwetland-dependentwildlife.Thoughimple-
mentedwidely,bufferefficacyisuntestedformostamphibianspecies.Consequently,it
OPENACCESS remainsunclearwhetherbuffersaresufficientformaintainingamphibianpopulationsandif
so,howwidebuffersshouldbe.Wepresentevidencefromasix-year,landscape-scale
Citation:VeyseyPowellJS,BabbittKJ(2015)
DespiteBuffers,ExperimentalForestClearcuts experimenttestingtheimpactsofclearcutting,bufferwidth,andhydroperiodonbodysize
ImpactAmphibianBodySizeandBiomass.PLoS andconditionandbiomassofbreedingadultsfortwoamphibianspeciesat11vernalpools
ONE10(11):e0143505.doi:10.1371/journal.
inthenortheasternUnitedStates.Werandomlyassignedtreatments(i.e.,reference,100m
pone.0143505
buffer,30mbuffer)acrosspools,clearcuttocreatebuffers,andcapturedallspottedsala-
Editor:ChristineCooper,CurtinUniversity,
mandersandwoodfrogs.Clearcutsstronglyandnegativelyimpactedsize,condition,and
AUSTRALIA
biomass,butwiderbuffersmitigatedeffectmagnitudeandduration.Amongrecapturedindi-
Received:July13,2015
viduals,forexample,30m-treatmentsalamanderswerepredictedtobeabout9.5mm
Accepted:November5,2015 shorterthan,while100m-treatmentsalamandersdidnotdifferinlengthfrom,reference-
Published:November23,2015 treatmentsalamanders.Similarly,amongrecapturedfrogs,meanlengthinthe30mtreat-
mentwaspredictedtodecreasebyabout1mm/year,whileinthe100mandreferencetreat-
Copyright:©2015VeyseyPowell,Babbitt.Thisis
anopenaccessarticledistributedunderthetermsof ments,lengthwastime-invariant.Some,butnotall,metricsrecoveredwithtime.For
theCreativeCommonsAttributionLicense,which example,femalenew-capturedandrecapturedsalamanderswerepredicted,respectively
permitsunrestricteduse,distribution,and
andonaverage,toweigh4.5and7glessinthe30mversusreferencetreatmentrightafter
reproductioninanymedium,providedtheoriginal
thecut.Whilerecaptured-femalemasswaspredictedtorecoverby9.5yearspost-cut,new-
authorandsourcearecredited.
captured-femalemassdidnotrecover.Hydroperiodwasanimportantmediator:inthe
DataAvailabilityStatement:Thedatausedinthis
100mtreatment,cuttingpredominatelyaffectedpoolsthatwerestressedhydrologically.
studyareavailablefromtheDryaddatabase(http://
dx.doi.org/10.5061/dryad.62ks6). Overall,salamandersandfemalefrogswereimpactedmorethanmalefrogs.Ourresults
highlighttheimportanceofindividualizedmetricslikebodysize,whichcanrevealsublethal
Funding:Theprojectwassupportedbygrantsto
KJBfrom:theNationalResearchInitiativeofthe effectsandilluminatemechanismsbywhichhabitatdisturbanceimpactswildlifepopula-
USDACooperativeStateResearch,Education,and tions.Individualizedmetricsthusprovidecriticalinsightsthatcomplementspeciesoccur-
ExtensionService(http://www.csrees.usda.gov/
renceandabundance-basedpopulationassessments.
funding/rfas/nri_rfa.html),grantnumbers:2003-
35101-12922and2007-35101-18281;andthe
NortheasternStatesResearchCooperative(http://
nsrcforest.org/).Theprojectwasalsosupportedby
fellowshipstoJSVPfrom:theRobertandPatricia
SwitzerFoundation(http://www.switzernetwork.org/),
PLOSONE|DOI:10.1371/journal.pone.0143505 November23,2015 1/31
ForestBuffersandAmphibianSizeandBiomass
theUniversityofNewHampshireGraduateSchool Introduction
(http://www.gradschool.unh.edu/),andtheUniversity
Globally,forestecosystemsareexperiencingintensifyingstressasgrowinghumanpopulations
ofNewHampshireCooperativeExtension(http://
extension.unh.edu/).Partialfundingwasprovidedby demandmoredevelopedandagriculturallandandlargervolumesofforestproducts[1,2].
agranttoKJBfromtheNewHampshireAgricultural Whetherownersdevelop,harvest,orconservetheirforestsisacomplexdecisiondrivenby
ExperimentStation(http://www.colsa.unh.edu/aes). globaleconomictrends[1,3].Overthelasttwodecades,increasingawarenessthatforestspro-
ThisisScientificContributionnumber:2614.This
videcriticalecosystemservicescatalyzedinterestinsustainablemanagementprogramsthat
workwassupportedbytheUSDANationalInstituteof
allowforestownerstoharvesttimberwhilemaintainingecosystemfunctionsandbiodiversity
FoodandAgricultureMcIntire-StennisProject,
accessionnumber:0226124.Thesefundershadno [4–6].Developingsustainableforest-managementplanscanbedifficultevenforcommonspe-
roleinstudydesign,datacollectionandanalysis, cies,however,givenoursometimesrudimentaryunderstandingofthecomplexinteractions
decisiontopublish,orpreparationofthemanuscript. betweenforestcomponentsandabilitytopredictspecies’responsestodisturbance[7].
CompetingInterests:Theauthorshavedeclared Amphibianscanbeparticularlychallengingtoaccommodategiventheircomplexlifecycles
thatnocompetinginterestsexist. anddiversehabitatneeds[8].Intemperateforests,manyamphibianspeciesoccupywetlands
duringtheireggandlarvalstages,butmigratehundredsofmetersintoadjacentforestasjuve-
nilesandadults(e.g.,[9–11]).Forestharvestingcanalterboththewetlandanduplandhabitat
ofthesespecies,withpotentiallynegativeconsequencesforpopulationpersistence[8].Ingen-
eral,timberharvesting,especiallyclearcuts,islocallyassociatedwithreducedabundanceand
survivalofnumerousamphibianspeciesacrossvariousforesttypes(e.g.,[12–14]).Responding
tosuchscientificevidence,publicpressure,economicincentive,andpersonalecologicalethic,
someforestmanagersintemperateecosystemshaveindicatedwillingnesstointegrateamphib-
ianhabitatneedsintoforestmanagementplans[15–17].
Forestedbuffersareaprimarytoolusedtoprotectamphibiansinsuchplans.Thoughbuff-
ersareimplementedwidely,theirefficacyisuntestedformostamphibianspecies.Thus,it
remainsunclearwhetherbuffersaresufficientformaintainingviableamphibianpopulations
inworkingforestsandifso,howwidebuffersshouldbe.Moststudiesthatrecommend
amphibianbuffersarebasedonobservationaldatafromunbufferedlandscapes(e.g.,[18–20]).
Afterreviewingthemovementcharacteristicsof32speciesacrosssuchlandscapes,Semlitsch
andBodie[9]suggestedthata290-mlifezone,centeredlikeabufferaroundawetland,isnec-
essarytoprotectthecorehabitatofmostwetland-dependentamphibianspecies.Scientistsand
conservationplannersfrequentlyreferencetheneedforaprotective290-mlifezone,butpol-
icy-makersareslowtoembracesuchlargeconstraintsonlanduse[21–23].Comparedtodevel-
opmentandintensiveagriculture,however,forestrycanbeatemporarydisturbance.Because
foreststypicallyregenerateforseveraldecadespost-cut,habitatconditionsaredynamicand
amphibiansmaybeabletopersistevenifbuffersconsiderablysmallerthan290mareused[14,
21,24].
Onlyahandfulofstudieshaveintentionallytestedtheimpactsofbuffer-mediatedforest
cuttingonamphibians,however,andthesehavelimitedinference.Mostwererestrictedto
stream-sidehabitats(e.g.,[25,26]),usednarrowbuffers(i.e.,<35m;e.g.,[27–29]),andwere
conductedinnorthwesternNorthAmerica.Forsome,forestryimpactswereconfoundedby
othermanagementtreatmentsortimeofharvest[30,31].Somefocusedsolelyorpartlyon
terrestrialspecies[29,32]oronlysampledinorextremelyclosetostreams[33,34].SSSuch
studieshavelimitedapplicabilityforamphibiansthatbreedinlentichabitats,especiallysince
post-breedingmigrationsforsuchspeciesoftenextendfarbeyond35m.
Tostrengthenthescientificbasisformakingdecisionsaboutbufferwidth,wepresentevi-
dencefromasix-year,landscape-scaleexperimenttestingtheinteractiveimpactsofclearcut-
tingandbufferwidthonbreeding-adultdemographyfortwoamphibianspeciesatnatural
vernalpoolsinanindustrialforestinthenortheasternUnitedStates.Toourknowledge,thisis
thefirstexperimenttoevaluatebufferefficacyforpool-breedingamphibians.Inaprevious
paperissuingfromthisexperiment[35],weshowedthatnarrowbuffersresultinreduced
PLOSONE|DOI:10.1371/journal.pone.0143505 November23,2015 2/31
ForestBuffersandAmphibianSizeandBiomass
recapturesofmaturespottedsalamanders(Ambystomamaculatum)andwoodfrogs(Litho-
batessylvaticus)andalteredsexratiosforspottedsalamanders.Here,weassesshowbodysize
andconditionandpopulationbiomassvaryinresponsetobufferwidthforbreedingadultsof
bothspecies.Notethatcompetitiveandpredaceousinteractionsbetweenlarvaeofthesetwo
speciescaninfluenceindividualbodysizeandconditionandpopulationbiomass[36–38],but
weassumedsuchinfluencewascomparableacrosspools(becausebothspecieswereabundant
atallpools)anddidnotassessinterspeciesinteractionsinthisstudy.
Amphibianbodysizeandconditionarecorrelatedwithandcanbeproxiesformultiplefit-
nessmeasuresincludingfecundity[39,40],survival[41,42],endurance[43,44],andimmunity
[45,46].Biomassmeasuresproductivityandindexesenergeticcontributionsofamphibian
populationstoaquaticandterrestrialcomponentsofforestecosystems[47,48].Understanding
howbufferwidthrelatestobodysizeandconditioncanprovideimportantinsightsintothe
indirectpathwaysbywhichforestryaffectsamphibianpopulations[49].Similarly,knowing
howadultbiomasschangesinresponsetobufferwidthcanhelpclarifyhowcuttinginfluences
ecosystemenergyflows.Previousresearchsuggeststhatforestcuttingisassociatedwith
reducedamphibiansizeandbodycondition,butstudiesexaminingsuchindirectforestry
effectsarerelativelyrare,werenotconductedinbufferedlandscapes,andproducedresultsthat
wereinconsistentacrossspeciesandageclasses(e.g.,[50–52]).Nonetheless,weexpectedthat
clearcuttingwouldexertnegativeeffectsonamphibianbodysizeandconditionandadultbio-
massinourlandscape,butthatbufferswouldmitigatetheseeffects.Becausenarrowbuffers
providelessforesthabitatthanwidebuffers,wespecificallypredictedthatasbufferwidth
decreasedacrossexperimentaltreatments,thefollowingcharacteristicsofspotted-salamander
andwood-frogbreedingpopulationswouldalsodecrease:
1. individual-adultlength,mass,andbodycondition;and
2. totalbreeding-adultbiomass.
Methods
StudySite,Treatments,andSampling
Weconductedthisresearchina700km2areaofHancockandWashingtoncounties,Maine,
USA(45°0’52”N,44°48”32”N;68°28’11”W,67°53’10”W).Ourentirestudysitewaslocatedin
anindustrialforestinMaine’snorthern-interiorclimatezoneandatthenorthernlimitofthe
DowneastEcoregion[53].Whilemicro-climateandmicro-topographicalconditionsvaried
slightlyacrossthesite,allofourstudypoolsweresubjectedtosimilaroverallclimaticand
land-useconditions.Fordetaileddescriptionsofthesite,experimentaldesign,andsampling
methods,see[35].
Allpoolswerefish-free.Amphibianspeciescompositionwassimilaracrosspools,withthe
followingspeciesoccurringatallpools:Ambystomamaculatum,Lithobatessylvaticus,Noto-
phathalmusviridescens,Lithobatesclamitans,Pseudacriscrucifer,Lithobatescatesbeianus,and
Lithobatespalustris.AmbystomalateraleandAnaxyrusamericanuswerepresentatallbuttwo
andoneofthepools,respectively.Threeadditionalspecieswererarelytrappedduringthe
experiment;theseincluded:Desmognathusfuscus(astreamsalamander;oneindividual),Hyla
versicolor(23individualsacrosssevenwetlands),andLithobatesseptentrionalis(11individuals
acrosssixwetlands).Abioticconditionswerealsosimilaracrosspoolsandcomparedtoother
woodlandpoolsintheregion(Table1;[54,55]).Inparticular,specificconductancevalues
wererelativelylowandpHlevelsweresomewhatacidic.
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ForestBuffersandAmphibianSizeandBiomass
Table1. Mean(±SE)ofvernalpoolabioticcharacteristicsbyforestrytreatmenta.
Treatment pHb SpecificConductance(μS) WaterTemperature(°C) Depth(m)c
Reference 5.60±0.10 18.74±1.40 14.12±0.74 0.94±0.18
100m 5.92±0.14 31.34±5.65 15.39±1.25 1.14±0.12
30m 5.92±0.06 23.32±1.05 16.27±0.87 1.12±0.19
aForestrytreatmentswere:reference(i.e.,uncut),100mbuffer,and30mbuffer.SeeFig1.
bpH,specificconductance,andwatertemperatureweremeasuredateachpoolinMayof2007,2008,and2009,usinganOrionmodel230ApHmeter
andaYSImodel85conductivitymeter.
cMeasuredasthesinglegreatestdepthineachpoolacrossMay2007,2008,and2009.
doi:10.1371/journal.pone.0143505.t001
Betweenfall2003andspring2004,thelandownercreatedexperimentalbuffersbyclearcut-
tingforestaroundthestudypools.Werandomlyassignedeachofthe11poolstooneofthree
treatments:reference(i.e.,uncut;N=3),100mbuffer(N=4),or30mbuffer(N=4).Poolsin
thetwobuffertreatmentshad,respectively,a100-mor30-m-wideuplandbufferencirclingthe
poolanda100-m-wideconcentricclearcutaroundthebuffer(Fig1).
Insummerandfall2003,wesurroundedeachofthe11poolswithadriftfence/pitfalltrap
array[56].From2004to2009,weopenedtrapsinthespringafterice-outandclosedtraps
whenapoolwasdryforatleastsevenconsecutivedaysorinthefallwhenhardfrostscurbed
amphibianmovement.Wecheckedpitfalltrapsdailyduringperiodsoffrequentamphibian
movement(i.e.,April-MayandJuly-September)andeveryonetofivedaysduringperiods
whenamphibianswerelessactive(i.e.,JuneandOctober-earlyNovember).For2009,wedid
notopentrapsatone30m-bufferpoolbecausethepoolwasinaccessible.Ouranalysisisrobust
tothismissingdata,however[57].
Usingthepitfalltraps,wecaptured,counted,andsexedalladultspottedsalamandersand
woodfrogsexitingthepools.Foreachindividual,wealsomeasuredsnout-ventorsnout-uro-
stylelength(hereafterSVL)andmass.Todistinguishrecapturesfromnew-capturesandmini-
mizethechancesofcountingthesameindividualmorethanonceayear,wemarkedallexiting
adultswithapool-specifictoe-clip[58].Foranyindividualthatreturnedtoapoolthesame
yearitwastoe-clipped,weonlyanalyzeddatafromitsfirstvisit.Formoreinformationonthe
rationalebehind,andpotentiallimitationsof,thismarkingmethod,see[35].Post-processing,
wereleasedeachanimalontheoppositesideofthefencefromwhichwecapturedit.
Wemeasuredhydroperiodforeachpoolineachyearasthenumberofdaysthepoolheld
waterbetweenice-out(i.e.,<75%ofthepoolwascoveredinice)andthedaythepooldried
completely.Tofacilitateanalyses,weassignedahydroperiodenddateofOctober28thtopools
thatdidnotdryinagivenyear.Weusedthisdatebecausethesepoolsstillheldwateronthis
date,butitwaslateenoughintheyearthatmostamphibiansatourstudypoolswereinactive.
StatisticalAnalyses
Totesttherelativeimpactsofbuffertreatmentandhydroperiodonseveralmeasuresofbreed-
ing-amphibianbodyconditionandbiomass,weconductedlinearmixedeffectsregressions
(LME)usingthe“lme”functioninS-Plus8.0(InsightfulCorporation,Seattle,WA,USA).We
definedourstudypopulationasalladultsthatmigratedtoapoolandattemptedtobreedina
givenyear.Ourresultsthusapplytoasubsetofeachspecies’totallocalpopulationanddonot
accountforadultsalamandersthatskippedbreedinginagivenyearorjuveniles.Fortherestof
thispaper,werefertoourstudypopulationasthe“breeding”population.
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ForestBuffersandAmphibianSizeandBiomass
Fig1.Experimentaldesignimplementedat11naturalvernalpoolsineast-centralMaine,USA.Undisturbedbuffersofeither100m(left;n=4)or30m
(right;n=4)wereleftadjacenttopoolsand100mwideclearcutswerecreatedaroundthebuffers.Forestbeyondtheclearcutwasundisturbed.Nocutting
occurredatreferencevernalpools(notshown;n=3).
doi:10.1371/journal.pone.0143505.g001
Weassessedbodyconditionusingthreesizemetrics:SVL,mass,andabody-condition
index(BCI).WeusedtheBCIasarelativemeasureofenergyreserves.WecalculatedtheBCI
astheresidualsofanordinaryleast-squaresregressionofmassonSVL.Toobtainnormal
residualsfortheBCI,wesquare-roottransformedthemassandSVLdataforsalamandersand
log-transformedmassandSVLforfrogs.WecalculatedseparateBCIsforeachsexwithineach
species.Residual-basedconditionindicesareanappropriatetoolforourstudyforthefollowing
reasons.First,bycalculatingseparateBCIsforeachsexwithineachspecies,weavoidedthe
scalingissuesthatresultwhencomparingBCIsacrossgroupsknowntodifferinsizedueto
heterauxesisandallomorphosis[59].Second,aftertransformation,ourdatadidnotviolatethe
critical,testableassumptionsinherenttoBCIanalysis,namely:massandSVLwerelinearly
related,BCIwasindependentofSVL,andSVLisareliableindicatorofstructuralsize[60–62].
Finally,residual-basedconditionindicesoutperformsimilarmeasuresofconditionandaccu-
ratelyparallelenergyreservesinavarietyofspecies[61–63].
Wecalculatedbiomassasthesumofthemassofallindividuals,withseparatebiomasses
calculatedforeachspeciesandeachsexateachwetlandineachyear.Foreachindividual
counted,butnotweighed(N=328and748[or9%and11%],forspottedsalamandersand
woodfrogs,respectively),weassignedamassequivalenttotheimputedmeanmassforits
respectivecategory.Wecouldnotdeterminethesexof22spottedsalamandersand27wood
frogsthatwefounddeadintraps.Wedidnotusedeadindividualsinthebiomassanalysis.To
meettheassumptionsofLME,weusedln(biomass+0.5)astheyvariableinallbiomassanaly-
ses,exceptforrecapturedmalespottedsalamanders,forwhichweusedtheuntransformed
biomass.
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ForestBuffersandAmphibianSizeandBiomass
Ourpredictorvariableswere:buffertreatment,mean-poolhydroperiod(i.e.,themean
hydroperiodforeachpoolacrossthesixstudyyears),standarddeviationofpoolhydroperiod
(calculatedforeachpoolacrossthesixstudyyears),aninteractionbetweentreatmentand
mean-poolhydroperiod,andapairofnumericdummyvariablesrepresentinganinteraction
betweentreatmentandstudyyear.Weusedthefirstdummyvariable(cut.year)todistinguish
whetherapoolwasclearcutornot.Weusedtheseconddummyvariable(30m.year)toindicate
marginalimpactsto30mbufferpools.ThistreatmentXyearinteractionallowedustoevaluate
whetherimpactstothecuttreatmentsrecoveredwithtime.Wedefined‘recover’as:being
restoredtovaluessimilartothoseinthereferencetreatment,afterdeviatingfromreference-
treatmentvaluesatsomepriortime.
Weperformedseparateregressionsforeachcombinationofcapturestatus(i.e.,new-capture
orrecapture)andsex,withineachspecies,foratotalofeightregressionmodelspersizemetric.
WetreatedyearandpoolIDascrossedrandomeffects[57]inallmodels,exceptwhenthe
modelwouldnotconvergewithcrossedeffects,inwhichcasewesimplifiedthemodelto
includeeitherarandominterceptforyearorforwetland,whicheverprovidedabettermodel
fit,asdeterminedbylikelihoodratiotests(LRTs).Amongthesimplifiedmodels,weusedyear
randominterceptsfortheSVLofnew-capturedandrecapturedmalewoodfrogs,theBCIof
recapturedfemalewoodfrogs,andtheBCIofmaleandfemalerecapturedspottedsalamanders.
Similarly,weusedwetlandrandominterceptsfortheBCIofnew-capturedmalewoodfrogs.
Wealsomodeledthevariance-covariancestructureforeachregressiontoaccountforheteroge-
neousvarianceacrossgroupsandcorrelationamongindividualsfromthesamewetland(S1
Appendix).WeusedLRTstooptimizethevariance-covariancestructureofeachmodel,ANO-
VAstoassesstheoverallsignificanceofeachfixedeffect,andtteststodeterminethesignifi-
canceofdifferenttreatmentlevels(α=0.05).Weusedtreatmentcontraststocomparethe
referencetreatmenttoeachrespectivecuttreatment(i.e.,bydefault,therewasnodirectcom-
parisonbetweenthe100mand30mtreatments;[57]).Basedonanaprioridecision,whenthe
hydroperiodinteractionwasnotsignificant,weremovedthisinteractionfromthemodeland
refitthemodelfortheremainingfixedeffects.Intheirfinalforms,allmodelssatisfiedthe
assumptionsofLME.See[35]forfurtherdetailsonthedummyvariablesusedintheyearX
treatmentinteractionandthemodel-selectionprocess.
EthicsandDataDepositionStatements
WeconductedalloftheresearchinaccordancewiththerulesoftheInstitutionalAnimalCare
andUseCommitteeattheUniversityofNewHampshire(IACUC-UNH).IACUC-UNH
approvedourresearchprotocol,asdetailedinpermits:020601and050604.Noneofthecap-
turedspecieswereprotectedorendangeredunderfederalorstatelaw.Weconductedthe
researchonprivateland,withpermissionfromthelandowner.Forthesereasons,noadditional
permitsorpermissionwereneededtoconductthiswork.Thedatausedinthisstudyareavail-
ablefromtheDryaddatabase(http://dx.doi.org/10.5061/dryad.62ks6).
Results
Overthesixstudyyears,the11vernalpoolsproducedover47kgofbreedingspottedsalaman-
dersand64kgofbreedingwoodfrogs.Thisbiomassrepresented3624breedingspottedsala-
mandersand6521breedingwoodfrogs.DescriptivestatisticsareprovidedinTable2forsize
andbodyconditionandinTable3forbiomass.
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ForestBuffersandAmphibianSizeandBiomass
Table2. Meanandvariabilityofpredictorandamphibiansizevariables,byspecies,capturestatus,sex,andforestrytreatment.
Mean±SE Range
Meanhydroperiod(days) 126.0±6.0 44.8–197.0
SDhydroperioda(days) 31.8±1.6 6.3–48.8
SVL/SULb(mm) Mass(g) BCIc
Mean±SE Range Mean±SE Range Mean±SE Range
SpottedSalamander
recapture F Reference 82.4±1.0 67.0–99.0 18.1±0.5 8.1–26.0 0.204±0.042 -0.637–1.082
100m 82.6±0.5 61.0–100.0 17.4±0.2 7.3–28.0 0.098±0.024 -0.942–0.912
30m 75.0±0.7 55.0–90.0 13.1±0.3 6.5–22.9 -0.096±0.035 -0.794–0.580
M Reference 74.8±0.6 60.0–90.0 14.0±0.3 8.9–21.0 0.242±0.027 -0.514–1.034
100m 73.1±0.4 54.0–98.0 12.8±0.1 7.3–21.0 0.146±0.018 -0.715–1.009
30m 67.1±0.6 51.0–85.0 9.8±0.2 5.5–20.5 -0.040±0.030 -0.685–0.849
new-capture F Reference 82.3±0.6 61.0–101.0 17.3±0.3 7.5–31.0 0.094±0.026 -0.883–1.188
100m 81.7±0.3 53.0–102.0 16.5±0.1 7.1–26.9 0.032±0.015 -0.979–1.939
30m 74.8±0.4 53.0–95.0 12.7±0.2 6.0–25.0 -0.157±0.017 -1.153–0.962
M Reference 73.6±0.5 55.0–96.0 12.3±0.2 5.7–22.2 0.053±0.020 -0.638–0.825
100m 72.5±0.3 52.0–96.0 11.6±0.1 5.3–24.0 -0.013±0.012 -1.589–1.103
30m 65.4±0.3 51.0–95.0 8.9±0.1 4.5–18.9 -0.128±0.011 -0.742–0.719
WoodFrog
recapture F Reference 51.9±0.3 44.0–58.0 13.1±0.2 8.8–18.0 0.031±0.013 -0.318–0.434
100m 51.0±0.4 35.0–59.0 12.8±0.2 6.6–19.3 0.044±0.014 -0.313–0.454
30m 49.8±0.5 35.0–56.0 11.0±0.3 5.3–17.8 -0.045±0.021 -0.243–0.445
M Reference 44.1±0.2 31.0–56.0 9.1±0.1 4.8–14.0 0.020±0.008 -0.462–0.488
100m 44.5±0.2 31.0–54.0 9.2±0.1 4.1–13.4 0.020±0.010 -0.409–0.710
30m 43.4±0.3 31.0–56.0 8.8±0.2 5.5–14.3 0.011±0.015 -0.273–0.542
new-capture F Reference 49.9±0.1 33.0–60.0 12.1±0.1 3.7–20.8 0.011±0.006 -0.915–0.656
100m 49.6±0.2 37.0–60.0 12.1±0.1 5.0–22.0 0.022±0.006 -0.518–0.555
30m 48.6±0.2 35.0–59.0 10.9±0.1 3.8–21.5 -0.043±0.007 -0.958–0.606
M Reference 44.1±0.1 33.0–55.0 9.0±0.1 3.3–19.0 0.014±0.004 -0.777–0.635
100m 43.0±0.1 30.0–61.0 8.7±0.1 4.2–19.6 0.005±0.005 -0.729–0.821
30m 42.6±0.1 27.0–53.0 8.3±0.1 4.1–13.8 -0.033±0.005 -0.638–0.611
aStandarddeviationofpoolhydroperiod.
bSnout-ventorsnout-urodylelength.
cBodyconditionindex.ObtainedviaordinaryleastsquaresregressionofmassonSVL/SUL.MassandSVL/SULweresquare-roottransformedfor
salamandersandlog-transformedforfrogs,priortoregression.BCImeasuresrelativeenergyreserves.BCI>0indicatesbetterbodyconditionthan
BCI<0.MeanBCImaynotequalzerobecauseBCIwascalculatedoverrecapturedandnew-capturedanimalscombined,foreachsex.
doi:10.1371/journal.pone.0143505.t002
SpottedSalamanders
Ingeneral,wefoundthatspottedsalamandersweresmallerandhadworsebodyconditionat
30m,comparedtoreference,pools.Forsome,butnotall,combinationsofcapturestatus,sex,
andsizemetric,weobservedpartialrecoveryofthesizemetricat30m-bufferpoolsoverthesix
studyyears.Wefoundlessconsistentrelationshipsbetweentreatmentandbiomassthan
betweentreatmentandbodysize/condition.Allresultspresentedinthissectionwerestatisti-
callysignificant,unlessotherwiseindicated.
Recapturedfemalesalamanderswere,throughoutthestudyandonaverage,predictedtobe
9.1mmshorterat30mversusreferencepools(Table4;Fig2).(Note:nofemaleswererecap-
turedat30m-bufferpoolsin2009).Similarly,inthefirstrecaptureyear(i.e.,2005),theaverage
PLOSONE|DOI:10.1371/journal.pone.0143505 November23,2015 7/31
ForestBuffersandAmphibianSizeandBiomass
Table3. Meanandvariabilityoftotalannualbreedingamphibianbiomassbyspecies,forestrytreatment,capturestatus,andsex.
AdultBiomass(g)
Species Sex Treatment Mean±SE Range Total
SpottedSalamander
recapture F Reference 71.2±17.2 0–227.2 1068.4
100m 160.0±66.5 0–1273.4 3199.1
30m 52.2±14.6 0–240.5 992.3
M Reference 102.6±23.1 0–286.0 1539.5
100m 171.8±48.8 0–750.8 3435.9
30m 55.7±12.0 0–191.6 1057.8
new-capture F Reference 214.8±26.1 29.6–436.0 3866.9
100m 390.5±108.9 0–2158.6 9373.1
30m 213.9±32.0 27.4–551.5 4920.4
M Reference 179.6±33.1 0–570.9 3232.9
100m 383.1±96.7 0–1493.5 9195.4
30m 210.8±37.2 45.0–819.7 4848.7
WoodFrog
recapture F Reference 99.3±25.7 0–337.8 1489.2
100m 74.9±27.1 0–515.4 1498.8
30m 33.9±11.0 0–175.2 645.0
M Reference 222.1±82.6 26.3–1347.7 3331.4
100m 106.9±25.9 0–421.6 2137.5
30m 55.5±11.5 0–189.8 1054.4
new-capture F Reference 498.2±87.5 109.8–1319.2 8968.2
100m 341.3±55.2 17.8–1049.5 8192.3
30m 329.1±48.9 22.7–897.5 7570.2
M Reference 600.7±139.8 88.2–2765.9 10812.0
100m 385.4±69.6 27.5–1386.3 9249.4
30m 390.1±50.5 51.8–855.2 8972.3
doi:10.1371/journal.pone.0143505.t003
recapturedfemaleatthe30m-bufferpoolswaspredictedtoweigh7gless,andhaveworse
bodycondition,thanherreference-poolcounterpart.However,massandBCIwerebothpre-
dictedtorecovertomeanreferencelevelsbyabout9.5yearspost-cut.Conversely,recaptured-
femalebodyconditionatthe100m-bufferpoolsworsenedwithtime,sothatbythestudy’send,
100m-poolBCIwaspredictedtobeabouttwotimeslowerthanthemeanreferenceBCI.BCI
alsodecreased,inalltreatments,withincreasinghydroperioddurationandvariability.Addi-
tionally,recapturedfemalebiomasswaspredictedtodecreasebyabout58%peryearat30m-
bufferpools,buttendedtoincrease(i.e.,wasmarginallysignificant)byabout2.4%pereach
additionaldayofmeanhydroperiodinalltreatments.Finally,SVL,mass,andbiomassdidnot
differsignificantlybetweenthe100mandreferencetreatments.
New-capturedfemalespottedsalamanderswerepredictedtoweigh,onaverageandforthe
durationofthestudy,4.5glessat30m-bufferpoolsthanatreferencepools(Fig3).Theyalso
tendedtohavepersistentlyworsebodyconditionat30m-bufferpools.Duringthefirstyear
post-cut,new-capturedfemaleswerepredictedtobe,onaverage,7.3mmshorterinthe30m
versusreferencetreatment.SVLat30m-bufferpoolswaspredictedtorecovertomeanrefer-
encelevelsbyabout14yearspost-cut.Fornew-capturedfemalebiomass,the30mandrefer-
encetreatmentsdidnotdiffer,but100m-treatmentbiomassdependedonmeanpool
hydroperiod.Short-hydroperiodpoolswerepredictedtoproducemuchlowerbiomassinthe
PLOSONE|DOI:10.1371/journal.pone.0143505 November23,2015 8/31
ForestBuffersandAmphibianSizeandBiomass
Table4. Linearmixedregressionresultsshowingtherelativeimpactofforestrytreatment,hydroperiod,andstudyyearonsize,bodycondition,
andtotalannualbiomassofbreedingspottedsalamandersandwoodfrogs.
SizeMetric Predictorc Fvalue j tvalue l Coefficient±SE
(df) (df)
SpottedSalamander
RecapturedFemales
SVLa(mm) treatment(30m)d 3.61 * -2.10 * -9.089±4.336
(2,312) (312)
intercept 683.04 *** 26.13 *** 86.708±3.318
(1,312) (312)
mass(g) treatment(30m) 7.90 * -3.89 * -8.938±2.296
(2,6) (6)
30m.yeare 4.28 * 2.07 * 1.049±0.507
(1,300) (300)
intercept 64.15 *** 8.01 *** 20.062±2.505
(1,300) (300)
BCIb treatment(30m) 6.38 * -2.01 * -0.385±0.192
(2,301) (301)
cut.yearf 5.78 * -2.40 * -0.066±0.027
(1,301) (301)
30m.year 4.28 * 2.07 * 0.105±0.051
(1,301) (301)
mean.hydrog 7.91 * -2.81 * -0.002±0.001
(1,301) (301)
sd.hydroh 7.46 * -2.73 * -0.005±0.002
(1,301) (301)
intercept 15.25 ** 3.91 ** 0.530±0.136
(1,301) (301)
biomass(g) 30m.year 16.37 ** -4.05 ** -0.734±0.181
(1,47) (47)
mean.hydro 4.00 (cid:129) 2.00 (cid:129) 0.024±0.012
(1,47) (47)
New-capturedFemales
SVL(mm) treatment(30m) 4.78 * -2.53 * -7.820±3.095
(2,1079) (1079)
30m.year 5.75 * 2.40 * 0.660±0.275
(1,1079) (1079)
intercept 397.14 *** 19.93 *** 84.855±4.258
(1,1079) (1079)
mass(g) treatment(30m) 3.25 * -2.34 * -4.461±1.905
(2,1051) (1051)
intercept 51.52 *** 7.18 *** 19.008±2.648
(1,1051) (1051)
BCI treatment(30m) 2.34 (cid:129) -1.96 (cid:129) -0.229±0.117
(2,1054) (1054)
biomass(g) treatment(100m)i*mean.hydro 7.91 * 3.88 ** 0.040±0.013
(2,45) (45)
treatment(100m) 6.62 * -3.48 * -5.212±1.496
(2,45) (45)
intercept 21.21 *** 4.61 *** 5.564±1.208
(1,45) (45)
RecapturedMales
SVL(mm) treatment(30m) 5.38 * -3.05 * -9.778±3.201
(2,478) (478)
intercept 415.79 *** 20.39 *** 79.218±3.885
(1,478) (478)
mass(g) treatment(30m) 7.31 ** -3.53 ** -4.796±1.359
(2,473) (473)
30m.year 3.05 (cid:129) 1.75 (cid:129) 0.373±0.214
(1,473) (473)
intercept 92.18 *** 9.60 *** 15.321±1.596
(1,473) (473)
BCI treatment(30m) 5.15 * -3.17 * -0.439±0.138
(2,468) (468)
mean.hydro 5.54 * -2.35 * -0.001±<0.001
(1,468) (468)
intercept 6.73 * 2.59 * 0.297±0.114
(1,468) (468)
biomass(g) treatment(100m)*mean.hydro 4.24 * 2.90 * 3.038±1.047
(2,45) (45)
treatment(100m) 3.15 (cid:129) -2.50 * -314.310±125.594
(2,45) (45)
sd.hydro 3.62 (cid:129) -1.90 (cid:129) -3.457±1.818
(1,45) (45)
intercept 4.19 * 2.05 * 251.847±123.053
(1,45) (45)
New-capturedMales
SVL(mm) treatment(30m) 4.36 * -2.73 * -7.820±2.865
(2,1444) (1444)
cut.year 3.15 (cid:129) 1.77 (cid:129) 0.500±0.282
(1,1444) (1444)
30m.year 5.39 * 2.32 * 0.556±0.239
(1,1444) (1444)
intercept 398.02 *** 19.95 *** 77.363±3.878
(1,1444) (1444)
mass(g) treatment(30m) 6.78 * -3.01 * -3.620±1.204
(2,1410) (1410)
30m.year 22.70 *** 4.76 *** 0.409±0.086
(1,1410) (1410)
mean.hydro 3.27 (cid:129) -1.81 (cid:129) -0.015±0.008
(1,1410) (1410)
(Continued)
PLOSONE|DOI:10.1371/journal.pone.0143505 November23,2015 9/31
ForestBuffersandAmphibianSizeandBiomass
Table4. (Continued)
SizeMetric Predictorc Fvalue j tvalue l Coefficient±SE
(df) (df)
intercept 78.92 *** 8.88 *** 14.336±1.614
(1,1410) (1410)
BCI treatment(30m) 11.02 *** -3.22 * -0.274±0.085
(2,1410) (1410)
30m.year 12.03 ** 3.47 ** 0.043±0.012
(1,1410) (1410)
mean.hydro 3.62 (cid:129) -1.90 (cid:129) -0.001±<0.001
(1,1410) (1410)
biomass(g) treatment(100m)*mean.hydro 4.28 * 2.91 * 0.030±0.013
(2,45) (45)
treatment(100m) 4.53 * -2.90 * -4.409±1.522
(2,45) (45)
cut.year 3.79 (cid:129) 1.95 (cid:129) 0.172±0.088
(1,45) (45)
30m.year 9.45 * -3.07 * -0.269±0.088
(1,45) (45)
intercept 16.56 ** 4.07 ** 5.202±1.278
(1,45) (45)
WoodFrogs
RecapturedFemales
SULa(mm) 30m.year 4.21 * -2.05 * -1.284±0.626
(1,284) (284)
intercept 473.14 *** 21.75 *** 53.190±2.445
(1,284) (284)
mass(g) intercept 89.78 *** 9.48 *** 14.303±1.509
(1,236) (236)
BCI treatment(30m) 4.44 * -2.97 * -0.221±0.074
(2,231) (231)
sd.hydro 5.97 * -2.44 * -0.002±0.001
(1,231) (231)
biomass(g) treatment(100m)*mean.hydro 6.10 * 3.49 )* 0.038±0.011
(2,45) (45
treatment(100m) 5.94 * -3.33 * -5.794±1.741
(2,45) (45)
treatment(30m) -1.89 (cid:129) -5.005±2.654
(45)
intercept 14.18 ** 3.77 ** 4.958±1.317
(1,45) (45)
New-capturedFemales
SUL(mm) cut.year 5.50 * 2.34 * 0.349±0.149
(1,2041) (2041)
intercept 1019.22 *** 31.93 *** 50.362±1.577
(1,2040) (2041)
mass(g) cut.year 5.55 * 2.36 * 0.229±0.097
(1,1869) (1869)
intercept 116.32 *** 10.78 *** 12.572±1.166
(1,1869) (1869)
BCI nsk
biomass(g) treatment(100m)*mean.hydro 3.45 * 2.63 * 0.015±0.006
(2,56) (56)
treatment(100m) 5.98 * -3.45 * -2.931±0.850
(2,56) (56)
30m.year 5.58 * -2.36 * -0.268±0.113
(1,56) (56)
intercept 59.07 *** 7.69 *** 5.737±0.746
(1,56) (56)
RecapturedMales
SUL(mm) 30m.year 3.91 * -1.98 * -0.914±0.462
(1,706) (706)
sd.hydro 11.44 ** -3.38 ** -0.045±0.013
(1,706) (706)
intercept 2064.37 *** 45.44 *** 44.803±0.986
(1,706) (706)
mass(g) sd.hydro 6.35 * -2.52 * -0.033±0.013
(1,684) (684)
intercept 202.99 *** 14.25 *** 9.559±0.671
(1,684) (684)
BCI sd.hydro 2.90 (cid:129) -1.70 (cid:129) -0.002±0.001
(1,685) (685)
biomass(g) 30m.year 3.50 (cid:129) -1.87 (cid:129) -0.518±0.277
(1,47) (47)
mean.hydro 7.11 * 2.67 * 0.015±0.006
(1,47) (47)
intercept 5.21 * 2.28 * 2.471±1.083
(1,47) (47)
New-capturedMales
SUL(mm) intercept 5523.34 *** 4.32 *** 44.060±0.593
(1,3082) (3082)
mass(g) sd.hydro 5.86 * -2.42 * -0.022±0.009
(1,2932) (2932)
intercept 432.10 *** 0.79 *** 9.403±0.452
(1,2932) (2932)
BCI sd.hydro 5.60 (cid:129) -2.37 (cid:129) -0.002±0.001
(1,6) (6)
biomass(g) mean.hydro 5.11 * 2.26 * 0.008±0.004
(1,58) (58)
(Continued)
PLOSONE|DOI:10.1371/journal.pone.0143505 November23,2015 10/31