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Natural Areas Journal
. . . to advance the preservation of natural diversity
Volume 29, Number 2 • April 2009
A QUARTERLY
PUBLICATION
OF
THE
NATURAL
AREAS
ASSOCIATION
Natural Areas Journal
. . . to advance the preservation of natural diversity
A publication of the Natural Areas Association - www.naturalarea.org
©2009 Natural Areas Association
Deer Facilitate
Invasive Plant
Success in a
Pennsylvania Forest
Understory
Tiffany M. Knight1,2
Jessica L. Dunn1
Lisa A. Smith3
JoAnn Davis4
Susan Kalisz1,5
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RESEARCH ARTICLE
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Deer Facilitate
Invasive Plant
Success in a
Pennsylvania Forest
Understory
Tiffany M. Knight1,2
Jessica L. Dunn1
Lisa A. Smith3
JoAnn Davis4
Susan Kalisz1,5
$EPARTMENTOF"IOLOGICAL3CIENCES
5NIVERSITYOF0ITTSBURGH
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110 Natural Areas Journal
ABSTRACT )NVASIVE SPECIES IMPOSE SEVERE BIOLOGICAL AND ECONOMIC COSTS WORLDWIDE )N FORESTED
ECOSYSTEMSINVASIVESPECIESSUPPLANTNATIVESPECIESRESULTINGINDECREASEDBIODIVERSITY&URTHERMORE
HUMANMEDIATEDDISTURBANCESMAYSTRESSNATIVEFORESTSPECIESANDBENElTINVASIVESPECIESTHATTHRIVE
INDISTURBEDHABITATS!NTHROPOGENICCHANGESTOTHELANDSCAPEHAVECAUSEDUNPRECEDENTEDINCREASESIN
WHITETAILEDDEER/DOCOILEUSVIRGINIANUSNUMBERSWHICHHASRESULTEDINTHEDEGRADATIONOFUNDERSTORY
NATIVEPLANTCOMMUNITIES7ESUGGESTTHATDEERMEDIATEDDISTURBANCETOUNDERSTORYCOMMUNITIESFACILITATES
THESUCCESSOFINVADERSINFORESTS-ANY.ORTH!MERICANFORESTSEXPERIENCEBOTHEXOTICPLANTINVASION
ANDDEEROVERABUNDANCEBUTTHETWOPROBLEMSHAVENEVERBEENEMPIRICALLYLINKED)NTHISPAPERWE
QUANTIFYDEEREFFECTSONNATIVEANDEXOTICUNDERSTORYHERBSINAWESTERN0ENNSYLVANIAFOREST7ESHOW
THATTHEPERCENTAGEOFBAREGROUNDANDTHERELATIVEABUNDANCESOFTHEINVASIVEHERBS!LLIARIAPETIOLATA
AND-ICROSTEGIUMVIMINEUMARESIGNIlCANTLYGREATERWHILENATIVEPLANTSARESIGNIlCANTLYSMALLERWITH
A LOWER PROPORTION mOWERING IN DEER ACCESS VS DEER EXCLUSION PLOTS /UR DATA SUPPORT THE IDEA THAT
INVADERSUCCESSISDUEINPARTTOBOTHPREFERENTIALFORAGINGBYDEERONNATIVEHERBSTHATREDUCESTHEIR
SIZEANDmOWERINGSTATUSANDTHECREATIONOFOPENPATCHESWHENDEERAREPRESENT7ECONCLUDETHATDEER
OVERABUNDANCEFACILITATESTHESUCCESSOFINVASIVESPECIESINFORESTEDECOSYSTEMSANDTHATMANAGEMENT
WILLBENElTBYCONSIDERINGTHESEFACTORSJOINTLY
)NDEXTERMS!LLIARIAPETIOLATADEEREXCLUSIONEXPERIMENTDEEROVERABUNDANCEINVASIVESPECIE -IC
ROSTEGIUMVIMINEUM
INTRODUCTION
)NVASIVE SPECIES ARE ONE OF THE LARGEST
THREATSTOGLOBALBIODIVERSITY6ITOUSEKET
AL 7ILLIAMSON AND IMPOSE
SEVERE BIOLOGICAL AND ECONOMIC COSTS
WORLDWIDE 0IMENTEL ET AL 4O
MAINTAINBIODIVERSITYANDMANAGENATURAL
RESOURCES IT IS ESSENTIAL TO DISCOVER THE
MECHANISMS THAT ALLOW INVASIVE SPECIES
TOINVADEANDTHENDOMINATESPECIlCHABI
TATSWHILEOTHERHABITATSAREABLETORESIST
INVASION )NVASION RESEARCH TAKES VARIED
APPROACHES 3OME STUDIES CONSIDER HOW
THECHARACTERISTICSOFTHECOMMUNITYMIGHT
INmUENCE THE COMMUNITYS SUSCEPTIBILITY
TO INVASION -AC$OUGALL AND4URKINGTON
ANDWHYSOMEAREPRONETOINVASION
WHILEOTHERSAPPEARTORESISTINVADERS&OR
EXAMPLE COMMUNITIES WITH HIGH SPECIES
DIVERSITYAREPROPOSEDTOBEMOREDIFlCULT
TOINVADEBECAUSETHEINVADERFACESMORE
POTENTIAL COMPETITORS +ENNEDY ET AL
,EVINEETALORBECAUSENATIVE
SPECIESUSETHEAVAILABLERESOURCESINTHE
HABITAT MORE COMPLETELY 3TACHOWICZ ET
AL,EVINEETAL)NADDITION
INVASIVESPECIESAREHYPOTHESIZEDTOINVADE
ANDDOMINATEHABITATSTHATRECEIVEDIFFERENT
LEVELSOFDISTURBANCEIEEITHERHIGHEROR
LOWERTHANTHEYEXPERIENCEDDURINGTHEIR
EVOLUTIONARYPASTEG(OBBS'ROSS
ET AL !DDITIONALLY SOME STUDIES
CONSIDER THE CHARACTERISTICS OF THE EXOTIC
SPECIESTODETERMINEIFTHEKEYTRAITSCAN
BEIDENTIlEDTHATMAKEITAGOODINVADER
EG #RAWLEY ET AL #ALLAWAY AND
2IDENOUR3UTHERLANDORIFTHE
SPECIES HAS EVOLVED IN THE NOVEL HABITAT
EG "LOSSEY AND .OTZOLD &OR
EXAMPLE THE SUCCESS OF THE EXOTIC PLANT
!LLIARIAPETIOLATAIN.ORTH!MERICAISAT
TRIBUTED TO ITS SHORT LIFESPAN ALLELOPATHY
ANDAUTOGAMOUSBREEDINGSYSTEM.UZZO
#LEARLYCOMMUNITYANDEXOTICSPE
CIESCHARACTERISTICSBOTHCANCONTRIBUTETO
THELIKELIHOODOFINVASION
)N ADDITION TO EXOTIC PLANT INVASION THE
INCREASEINTHEABUNDANCEOFWHITETAILED
DEER /DOCOILEUS VIRGINIANUS :IMMER
MANNISABIOTICDISTURBANCECHALLENGING
UNDERSTORY PLANT SPECIES IN MANY FORESTS
THROUGHOUT EASTERN .ORTH!MERICA $EER
INCREASES ARE DIRECTLY LINKED TO HUMAN
ACTIONS 3PECIlCALLY HABITAT FRAGMENTA
TIONAGRICULTUREANDERADICATIONOFLARGE
CARNIVORES HAVE RESULTED IN A FOURFOLD
INCREASEINTHEABUNDANCEOFWHITETAILED
DEER THROUGHOUT EASTERN .ORTH !MERICA
OVERTHEPASTYEARS-C3HEAETAL
2USSELLETAL4HESEUNPRECEDENTED
NUMBERS OF DEER ARE NOW OCCUPYING A
WIDE RANGE OF HABITATS INCLUDING THOSE
NOT HISTORICALLY INHABITED BY DEER AND
ARE RAPIDLY ALTERING MATURE FOREST NATIVE
UNDERSTORYPLANTABUNDANCEBIODIVERSITY
COMMUNITY COMPOSITION !UGUSTINE AND
DE#OLESTA2OONEYAND7ALLER
#ÙTÏETALANDECOSYSTEMFUNCTION
2USSELL ET AL 7ARDLE ET AL #ÙTÏETAL-ANAGINGFORDEERAND
Volume 29 (2), 2009
INVASIVE SPECIES ARE BOTH TOP PRIORITIES
FOR MANAGERS INTERESTED IN PRESERVING
DIVERSITYOFNATURALFORESTS-C3HEAETAL
.ATIONAL )NVASIVE 3PECIES #OUNCIL
HTTPWWWINVASIVESPECIESINFOGOVCOUN
CILNMPSHTML BUT HERETOFORE THE TWO
PROBLEMSHAVENOTBEENLINKED
"ECAUSE INCREASED DEER DENSITIES ARE
EXPECTEDTOIMPACTTHEBIOTICANDABIOTIC
CONDITIONS WITHIN FORESTS -C3HEA AND
2APPOLE#ÙTÏETAL6ARVAET
ALDEERAREALSOSUSPECTINCREATING
CONDITIONSAMENABLETOEXOTICPLANTINVA
SIONS 0UBLISHED DATA ON THE IMPACTS OF
DEEREXCLUSIONDEERACCESSONEXOTICWEEDS
INVASIONARESCARCEDIFlCULTTOCOMPAREDUE
TODIFFERENCESINHABITATSANDINVADERSPE
CIES6AVRAETALANDPROVIDEMIXED
RESULTS)NTWOSTUDIESDEERBROWSINGEF
FECTSONINVADERABUNDANCEWASFOUNDTOBE
INVADERSPECIESSPECIlCBUTHADNOOVERALL
EFFECT ON THE PROPORTION OF INVADERS IN A
COMMUNITY"OWERS;OLDlELD=7EB
STER ET AL ;COVE FOREST= ,IKEWISE
EXOTICPLANTSWEREMOREABUNDANTINDEER
EXCLUSIONPLOTSINONEOLDlELDBUTHADNO
EFFECTINASECONDOLDlELDTHATDIFFEREDIN
TIMESINCEABANDONMENT#ADENASSOETAL
&INALLYDEERBROWSINGHADNOEFFECT
ONTHESPECIESRICHNESSOFEXOTICINVADERS
INABEECHOAK&AGUS1UERCUSFORESTIN
-ARYLANDBUTDECREASEDTHEABUNDANCEOF
ORIENTALBITTERSWEET#ELASTRUSORBICULATUS
2OSSELLETAL
(EREWEADDRESSTHEPOTENTIALINTERACTION
OFELEVATEDDEERDENSITIESANDTHERELATIVE
ABUNDANCEOFINVASIVEHERBSATTHE4RILLIUM
4RAIL 7ILDmOWER 2ESERVE LOCATED IN &OX
#HAPELABOROUGHOF0ITTSBURGH0ENNSYL
VANIA)TSDIVERSESPRINGmOWERINGDISPLAY
HASMADE4RILLIUM4RAILAWILDmOWERHIKE
DESTINATIONSINCETHELANDWASDONATEDTO
&OX #HAPEL IN 4RILLIUM4RAIL IS AN
IDEALSITEFOROURRESEARCHBECAUSEWEKNOW
THEYEARWHENTHELOCALDEERIMPACTINTHE
SITE CHANGED )N AN INmUX OF DEER
INTO THIS AREA RESULTED IN A NEARLY COM
PLETEDEFOLIATIONOFTHESPRINGEPHEMERAL
UNDERSTORYAT4RILLIUM4RAILTHECARPETOF
WILDmOWERSPREFERREDBYDEERDISAPPEARED
LITERALLYOVERNIGHTDUETOBROWSING
3INCE THAT TIME lELD WORK IN THE UNDER
STORYDEMONSTRATESSUSTAINEDLEVELSOFDEER
Volume 29 (2), 2009
BROWSEONTHESPRINGEPHEMERALSDETAILED
BELOW WHILE ANNUAL AERIAL CENSUSES OF
THE DEER HERD SIZE IN &OX #HAPEL REVEAL
SUSTAINEDDEERDENSITIESOFDEERKM
4HESE DEER ABUNDANCE VALUES ARE TWO TO
FOUR TIMES GREATER THAN THEIR HISTORICAL
ABUNDANCEINEASTERN.ORTH!MERICAAND
MORETHANSIXTIMESGREATERTHANTHERECOM
MENDEDDEERKMLIMITFORSUSTAINABLE
FORESTPLANTCOMMUNITYHEALTH7ITMERAND
DE#ALESTA!NDERSON
)NTHISSTUDYWEQUANTIFYTHEPERCENTCOVER
REPRODUCTIVE STATUS AND SIZES OF NATIVE
ANDINVASIVEHERBACEOUSSPECIESGROWING
IN A SET OF PAIRED CONTROL DEER ACCESS
VSFENCEDDEEREXCLUSIONPLOTSANDINA
LARGEFENCEDAREAIN4RILLIUM4RAILTOTEST
THEGENERALHYPOTHESISTHATDEERFACILITATE
EXOTIC PLANT SUCCESS IN FORESTS7E FOCUS
ONCHANGEINABUNDANCEANDAVERAGEPLANT
SIZEACROSSTHETWOTREATMENTS
METHODS
Study site and species
4RILLIUM4RAILISAHAWILDmOWERRESERVE
EMBEDDED IN A LARGE TRACT HA OF
FORESTANDPARKLANDASSOCIATEDWITH3QUAW
2UN IN !LLEGHENY #OUNTY 0ENNSYLVANIA
o g . o 7
3INCETHEPRESERVEHASBEENOWNED
AND STEWARDED BY THE "OROUGH OF &OX
#HAPEL 4HE "OROUGH WAS DEDICATED AS
A WILDLIFE SANCTUARY IN (ABITATS AT
4RILLIUM 4RAIL RANGE FROM THE mOODPLAIN
OF3QUAW2UNTODRYHILLTOPSM
ELEVATIONRANGE4HEOVERSTORYAT4RILLIUM
4RAILCONSISTSOFMATUREREDOAK1UERCUS
RUBRA , WHITE OAK 1UERCUS ALBA ,
BEECH &AGUS AMERICANA %HRH SUGAR
MAPLE!CERSACCHARUM -ARSHANDTU
LIPTREES,IRIODENDRONTULIPIFERA,4HE
HERBACEOUSUNDERSTORYISADIVERSEMIXTURE
OFNATIVESPECIESWHITETRILLIUM4RILLIUM
GRANDImORUMWAKEROBIN4ERECTUM,
TOADSHADE 4 SESSILE , FALSE MERMAID
&LOERKEAPROSERPINACOIDES7ILLDTWO
LEAVEDTOOTHWORT#ARDAMINEDIPHYLLA-I
CHX!LPH7OOD WILD GINGER !SARUM
CANADENSE , TOUCHMENOT )MPATIENS
CAPENSIS -EERB AND ) PALLIDA .UTT
3OLOMONS SEAL 0OLYGONATUM BImORUM
7ALTER%LLIOTTMAYAPPLE0ODOPHYLLUM
PELTATUM,*ACKINTHEPULPIT!RISAEMA
TRIPHYLLUM,6IRGINIAWATERLEAF(YDRO
PHYLLUM VIRGINIANUM , AND BLOODROOT
3ANGUINARIACANADENSIS,ARECOMMON
ATTHESITE
4WOEXOTICANDINVASIVEHERBACEOUSSPECIES
AREALSONOWCOMMONATTHESTUDYSITEGAR
LICMUSTARD!LLIARIAPETIOLATA-"IEB
#AVARA 'RANDE AND!SIAN STILTGRASS
-ICROSTEGIUM VIMINEUM 4RIN ! #A
MUSBUTWERERAREORABSENTBEFORE
! PETIOLATA AND - VIMINEUM
RESPECTIVELY!LLIARIAPETIOLATAISABIENNIAL
NATIVETO%UROPE)TWASlRSTDOCUMENTED
IN .EW 9ORK IN AND HAS RECENTLY
BECOME A RAMPANT INVADER IN WOODLANDS
THROUGHOUTEASTERN.ORTH!MERICA.UZZO
-ICROSTEGIUMVIMINEUMISANANNUAL
GRASSNATIVETO!SIA)TWASlRSTREPORTED
IN+NOXVILLE4ENNESSEEINANDHAS
RECENTLY EXPANDED ITS RANGE EAST OF THE
-ISSISSIPPI2IVERANDINTO4EXAS'IBSON
ETAL
Paired Plots
7E CONDUCTED OUR INITIAL DEER EXCLUSION
EXPERIMENTUSINGTHREEPAIREDM DEER
EXCLUSION AND DEER ACCESS PLOTS &ENCES
ARE M TALL WITH A MESH SIZE OF CM
EFFECTIVELYELIMINATINGACCESSBYDEERBUT
ALLOWINGFREEMOVEMENTOFOTHERINTERACT
INGSPECIESSUCHASBIRDSSMALLMAMMALS
POLLINATORS AND HERBIVOROUS INSECTS 4HE
FENCES WERE ERECTED IN AND DATA
COLLECTION CONTINUED UNTIL WHEN A
LARGE DEER EXCLUSION FENCE WAS ERECTED
SEEBELOW
6EGETATIONCENSUSESWERECONDUCTEDFOUR
TIMES IN EACH GROWING SEASON !PRIL TO
3EPTEMBER EVERY YEAR )N EACH PLOT WE
IDENTIlEDALLHERBACEOUSPLANTSTOSPECIES
VISUALLYESTIMATEDPERCENTCOVERFOREACH
SPECIES AND PERCENT OF BARE GROUND AND
COUNTEDTHENUMBEROFmOWERINGINDIVIDU
ALS FOR EACH SPECIES 4HIS ALLOWED US TO
DOCUMENTTHEMAXIMUMPERCENTCOVERAND
THE NUMBER OF mOWERING INDIVIDUALS FOR
EACHSPECIESSINCESPECIESDIFFERINTHEIR
PHENOLOGY7EALSOCALCULATEDTHESUMOF
THEPERCENTCOVERVALUESFOREACHSPECIES
FOREACHTREATMENT4OCOMPARETHERELATIVE
RANKINGS OF SPECIES PERCENT COVER IN THE
Natural Areas Journal 111
DEEREXCLUSIONVSDEERACCESSTREATMENTS
WE SUMMED THE RELATIVE RANKINGS ACROSS
THETHREEPLOTSANDCALCULATEDTHEAVERAGE
RANKFOREACHTREATMENT7EUSEDA+RUS
KAL7ALLISRANKTESTTOCOMPARETHERELATIVE
RANKINGOFSPECIESWITHRESPECTTOPERCENT
COVERINDEEREXCLUSIONANDCONTROLTREAT
MENTSAFTERlVEYEARSANDAPAIRED
TTESTTOCOMPARETHEAVERAGEPERCENTBARE
GROUNDATTHEBEGINNINGOFTHEEXPERIMENT
ANDNINEYEARSLATER
10-hectare deer exclusion study
4OPROTECTTHEINTEGRITYOFTHEWILDmOWER
PRESERVEFROMTHESUSTAINEDDEERBROWSING
IN4RILLIUM4RAILINTHELATEFALLOFTHE
"OROUGHOF&OX#HAPELENCLOSEDA
HA AREA RANGING FROM mOODPLAIN TO STEEP
HILLSIDEWITHAMTALLFENCETHUSDEER
WEREEXCLUDEDFROMPORTIONSOFALLHABITAT
TYPES FOUND AT THE SITE4HE CONSTRUCTION
OF THIS FENCE PROVIDED US WITH A UNIQUE
OPPORTUNITY TO TEST IF THE PLANT RESPONSES
OBSERVEDINTHESMALLPLOTDEEREXCLUSION
EXPERIMENTWEREREPEATABLEATTHISLARGER
SPATIAL SCALE "ECAUSE THERE IS ONLY ONE
LARGE FENCED AREA THE ISSUE OF STATISTICAL
NONINDEPENDENCE(URLBERTCANBE
RAISEDBUTSEE/KSANEN(OWEVER
WEEXPECTTHATIFDEERAREIMPORTANTDRIVERS
OF INVADER SUCCESS THEN THE OUTCOME OF
THE TWO EXPERIMENTS WILL BE SIMILAR AND
SUPPORTTHESAMECONCLUSIONS4HUSTAKEN
TOGETHERTHERESULTSFROMTHETWOSTUDIES
CAN PROVIDE STRONG EVIDENCE OF THE ROLE
OF DEER IN EXOTIC SPECIES INVASION AND IN
SHAPINGTHEFORESTUNDERSTORYHERBACEOUS
COMMUNITYSTRUCTURE
7EESTABLISHEDlVESAMPLINGTRANSECTSIN
THEHADEEREXCLUSIONAREATHATSPANNED
THE ELEVATION GRADIENT OF 4RILLIUM 4RAIL
4RANSECTSWEREPARALLELTOEACHOTHERAND
ADJACENTTRANSECTSWERESEPARATEDBY^
METERS4ODETERMINEIFTHEREWEREANYPRE
TREATMENTDIFFERENCESINUNDERSTORYSPECIES
COMPOSITION BETWEEN THE DEER EXCLUSION
AND DEER ACCESS SAMPLE PLOTS DESCRIBED
BELOWWESURVEYEDMPLOTSALONG
lVEPARALLELTRANSECTSINEARLYSPRING
%ACHMTRANSECTWASPERPENDICULARTO
THE SOUTHWEST SIDE OF THE FENCE WITH M INSIDE THE FENCE AND M OUTSIDE THE
FENCEANDPLOTSINSIDEANDOUTSIDEOFTHE
112 Natural Areas Journal
FENCE 4RANSECTS WERE M APART ON AN
ELEVATIONGRADIENT)NEACHPLOTWEDOCU
MENTED PRESENCE OR ABSENCE OF ALL PLANT
SPECIES 7E USED A -ANTEL TEST PERMUTATIONS ON THE %UCLIDEAN DISTANCE
ONCOMMUNITYCOMPOSITIONBETWEENEACH
PLOT7EFOUNDTHATTHESIMILARITYOFPLOTS
IN THEIR COMMUNITY COMPOSITION DID NOT
DEPEND ON LOCATION INSIDE OR OUTSIDE THE
LARGEFENCE04HISREMAINSTRUE
EVENWHENWECORRECTFORSPATIALDISTANCES
BETWEENPLOTS04HUSTHEREWERE
NOTANYPRETREATMENTDIFFERENCESINCOM
MUNITYCOMPOSITION
)NALONGEACHOFTHElVETRANSECTS
SIX M SUBPLOTS WERE MARKED THREE OF
WHICHWEREINSIDETHEFENCEANDTHREEOF
WHICHWEREARRANGEDASTHEMIRRORIMAGE
OUTSIDETHEFENCE4HElRSTSUBPLOTWAS
M FROM THE FENCE AND ADJACENT SUBPLOTS
ALONG EACH TRANSECT WERE SEPARATED BY A
DISTANCE OF M 4HE PERCENT COVER OF
EACH HERBACEOUS SPECIES IN THE SUBPLOTS
WAS QUANTIlED IN AFTER lVE YEARS
OFDEEREXCLUSION!SINTHEPAIREDPLOTS
VEGETATIONCENSUSESWERECONDUCTEDFOUR
TIMES IN EACH GROWING SEASON !PRIL TO
3EPTEMBER4HISALLOWEDUSTODOCUMENT
THEMAXIMUMPERCENTCOVERANDREPRODUC
TION THROUGHOUT THE GROWING SEASON FOR
EACHSPECIES4HESUMMEDPERCENTCOVER
FOR EACH SPECIES WAS CALCULATED FOR EACH
TREATMENT AND TRANSECT IN THE lNAL YEAR
FORATOTALOFlVESAMPLEVALUESFOR
EACHTREATMENTONESAMPLEPERTRANSECT
&OREACHSAMPLEWEALSOCALCULATEDPRO
PORTIONALPERCENTCOVEROFINVASIVESPECIES
;COVEROFINVASIVESPECIES3COVER
FORALLSPECIES=)NADDITIONWECOUNTED
THENUMBEROFREPRODUCTIVEINDIVIDUALSFOR
EACHSPECIESATEACHCENSUS4HISALLOWED
USTOCALCULATETHETOTALNUMBEROFREPRO
DUCTIVEHERBACEOUSPLANTSFOREACHSAMPLE
nANDTHEPROPORTIONOFREPRODUCTIVEPLANTS
THAT WERE NATIVE AND INVASIVE SPECIES ;
REPRODUCTIVESTEMSOFINVASIVESPECIES
REPRODUCTIVESTEMSFORALLSPECIES=&INALLY
FORSEVENFOCALSPECIESINTHESAMPLEPLOTS
ALONG THE lVE TRANSECTS n THE INVASIVE
SPECIES !LLIARIA PETIOLATA AND THE NATIVE
SPECIES!RISAEMATRIPHYLLUM,3CHOTT
!SARUM CANADENSE , (YDROPHYLLUM
VIRGINIANUS , 0OLYGONATUM BImORUM
7ALTER %LLIOTT 3ANGUINARIA CANADENSIS
, AND 4RILLIUM GRANDImORUM -ICHX
3ALISB n WE MEASURED INDIVIDUAL PLANT
SIZEANDTHEINCIDENCEOFDEERHERBIVORY
4HESEFOCALSPECIESWERECHOSENBECAUSE
THEY ARE ABUNDANT AND WELL REPRESENTED
ACROSS OUR SAMPLE PLOTS 7E USED TTESTS
TOCOMPARETHEPROPORTIONALPERCENTCOVER
OFHERBACEOUSINVADERSANDTHEPROPORTION
OFHERBACEOUSINVASIVEREPRODUCTIVEPLANTS
INTHETWOTREATMENTS7EUSED7ILCOXON
PAIRED SIGNRANK TESTS TO EXAMINE MEAN
DIFFERENCES BETWEEN DEER EXCLUSION AND
DEERACCESSTREATMENTSINFOCALNATIVEPLANT
SIZEANDPAIREDONETAILEDTTESTTOTESTFOR
FOCALNATIVEREPRODUCTION
RESULTS
Paired plots
! TOTAL OF HERBACEOUS SPECIES WERE
IDENTIlED IN OUR PLOTS !FTER lVE YEARS
OFTHEDEEREXCLUSIONTREATMENTTHEPLANT
COMMUNITY COMPOSITION DIVERGED SIG
NIlCANTLYBETWEENTHEDEEREXCLUSIONAND
DEER ACCESS PLOTS +RUSKAL7ALLIS RANK
TEST 0 &IGURES AND )N THE
DEER EXCLUSION PLOTS SPECIES ABUNDANCES
WERE MORE EVENLY DISTRIBUTED AND THE
NATIVE WILDmOWER 4 GRANDImORUM WAS
DOMINANT#ONVERSELYINDEERACCESSPLOTS
THEMAJORITYOFNATIVESPECIESWERERAREOR
ABSENTANDTHEINVASIVEHERB!PETIOLATA
WASDOMINANT&IGURE&URTHERIN
ONLYSIXINDIVIDUALSOFALLTHENATIVESPE
&IGURE 0HOTO TAKEN AT THE BOUNDARY OF A
FENCED M DEER EXCLUSION AND A M DEER
ACCESSPLOTYEARSAFTERTHEFENCETREATMENTWAS
ESTABLISHED4HEDASHEDWHITELINEHIGHLIGHTSTHE
FENCE BOUNDARY 4HE AREA TO THE LEFT OF THE LINE
IS INSIDE THE FENCE WHERE REPRODUCTIVE 4RILLIUM
GRANDImORUM IS THE MOST ABUNDANT SPECIES 4HE
AREATOTHERIGHTOFTHELINEISPARTOFTHEPAIRED
DEER ACCESS PLOT WHERE !LLIARIA PETIOLATA IS THE
MOSTABUNDANTSPECIES
Volume 29 (2), 2009
DISCUSSION
4AKENTOGETHERTHERESULTSOFTHETWOEX
PERIMENTSSHOWTHATTHEABUNDANCEOFTHE
TWO EXOTIC INVASIVE SPECIES IN THIS FOREST
UNDERSTORYCOMMUNITYISATTRIBUTABLETOTHE
PRESENCEOFDEER4HREEMECHANISMSCOULD
HAVECOMBINEDTOPRODUCETHISRESULT
GREATER TOLERANCE OF INVASIVE SPECIES TO
HERBIVORYDIRECTCONSUMPTIONOFNATIVE
SPECIESANDAVOIDANCEOFINVASIVESPECIES
ANDOR GREATER TOLERANCE OF INVASIVE
SPECIES TO NONBROWSING EFFECTS OF DEER
7EADDRESSEACHOFTHESEINTURN
&IGURE4HERELATIVEPERCENTCOVEROFTHETENMOSTABUNDANTPLANTSPECIESINOURDEEREXCLUSIONAND
CONTROLPLOTS!LLPLANTSPECIESARENATIVEEXCEPTGARLICMUSTARD!FTERlVEYEARSOFDEEREXCLUSIONCOM
MUNITYCOMPOSITIONSIGNIlCANTLYDIVERGEDBETWEENTREATMENTS+RUSKAL7ALLISRANKTEST0
CIESPRESENTmOWEREDACROSSTHETHREEDEER
ACCESSPLOTSWHEREASINTHEDEEREXCLUSION
PLOTSTHEREWEREmOWERINGINDIVIDUALS
COUNTEDFORTHENATIVESPECIES4HISISMORE
THANAFOLDINCREASEINTHENUMBEROF
NATIVEmOWERINGINDIVIDUALSINTHEABSENCE
OFDEER3IMILARLYTHEPERCENTBAREGROUND
DIVERGED SIGNIlCANTLY IN DEER ACCESS VS
DEEREXCLUSIONPLOTS0LOTSDIDNOTDIFFERAT
BEGINNINGOFTHEEXPERIMENTBUTTHE
PERCENTBAREGROUNDDECREASEDSIGNIlCANTLY
INDEEREXCLUSIONPLOTSPTTEST
T&IGURE
10-hectare deer exclusion study
!S WITH THE PAIRED PLOTS WE FOUND THAT
THE PROPORTIONAL ABUNDANCE OF INVASIVE
PLANTS WAS SIGNIlCANTLY GREATER IN DEER
ACCESSSAMPLEPLOTSTHANINDEEREXCLUDED
SAMPLEPLOTSTTESTRESULTSTDF
03IMILARLYTHEPROPORTIONOF
REPRODUCTIVE INVASIVE PLANTS ; INVASIVE
REPRODUCTIVE STEMSTOTAL REPRODUCTIVE
STEMS= WAS SIGNIlCANTLY HIGHER IN THE
DEERACCESSSAMPLEPLOTSTHANINTHEDEER
EXCLUSIONSAMPLEPLOTSTTESTRESULTST
DF0!LLSIXFOCALNA
Volume 29 (2), 2009
TIVESPECIESWERESIGNIlCANTLYSMALLERON
AVERAGEINTHECONTROLSAMPLEPLOTSTHANIN
THEDEEREXCLUDEDSAMPLEPLOTS0
7ILCOXONSIGNRANKANDWERELESSLIKELYTO
BEREPRODUCTIVEINCONTROLRELATIVETODEER
EXCLUDED SAMPLE PLOTS PAIRED ONETAILED
TTESTTDF0!CROSS
ALL SIX NATIVE FOCAL PLANT SPECIES ONLY
NINE INDIVIDUALS mOWERED IN IN THE
CONTROLSAMPLEPLOTSWHILEINDIVIDU
ALSmOWEREDINTHEDEEREXCLUDEDSAMPLE
PLOTS4HEMEANPLANTSIZEOFTHEINVADER
! PETIOLATA DID NOT DIFFER IN SIZE IN THE
PRESENCEORABSENCEOFDEERTTESTNUMBER
OFBRANCHES&0NUMBER
OFLEAVES&0.OTETHE
INVASIVE SPECIES - VIMINEUM WAS FOUND
INTHEDEERACCESSPLOTSBUTDIDNOTOCCUR
INTHEDEEREXCLUSIONPLOTS
/N AVERAGE DEER CONSUMED OF THE
mOWERING STEMS OF THE NATIVE FOCAL PLANT
SPECIESINOURSAMPLEPLOTSSPECIESRANGES
WHILENODEERHERBIVORYWASOB
SERVEDINTHEDEEREXCLUSIONSAMPLEPLOTS
)NCONTRASTNEITHEROFTHEINVASIVEEXOTICS
!PETIOLATANOR-VIMINEUMEXPERIENCED
ANYDEERHERBIVORY
&IRSTOURDATAPROVIDENOSUPPORTFORTHE
IDEA THAT INVASIVE SPECIES TOLERATE HER
BIVORYTHROUGHREGROWTHANDMORERAPID
REPRODUCTION3TOWEETAL.EITHER
INVADER WAS OBSERVED TO EXPERIENCE ANY
DEER HERBIVORY DURING THIS STUDY OR IN
OTHERSTUDIESON!LLIARIAAND-ICROSTEGIUM
CONDUCTEDATTHISSITEFROM3
+ALISZ UNPUBL DATA "OTH INVASIVE SPE
CIES IN OUR STUDY ARE WEEDY SHORTLIVED
HERBS IE - VIMINEUM IS AN ANNUAL
AND!PETIOLATAISABIENNIALWITHRAPID
REPRODUCTIONANDHIGHPOPULATIONGROWTH
RATEEG$AVISETAL-ORRISONETAL
#OLEAND7ELTZIN)NCONTRAST
THE NATIVE HERBACEOUS UNDERSTORY SPECIES
INOURSTUDYARELONGLIVEDANDSLOWGROW
ING PERENNIALS EG "IERZYCHUDEK (ANZAWAAND+ALISZTHATARELIKELY
TOBEMORESENSITIVETOHERBIVORY+NIGHT
THANTHESHORTLIVEDINVADERS
3ECOND WE FOUND STRONG SUPPORT FOR THE
IDEA THAT DEER PREFERENTIALLY CONSUMED
NATIVEPLANTSPECIESWITHNOEVIDENCEOF
HERBIVORY ON EITHER INVASIVE SPECIES !
PETIOLATAOR-VIMENIUM4HEOBSERVEDIN
TENSEHERBIVORYBYDEERONTHENATIVEPEREN
NIALSDRAMATICALLYALTEREDTHEIRPOPULATION
STRUCTURE/URDATASHOWTHATFEWERNATIVE
PLANTSmOWEREDANDTHEYWEREONAVERAGE
SIGNIlCANTLYSMALLERINSIZEINTHEPRESENCE
OFDEERRELATIVETOTHEDEEREXCLUSIONPLOTS
4HECHANGESINPOPULATIONSTRUCTURESEEN
INTHENATIVEHERBSCANSIGNIlCANTLYALTER
POPULATIONDYNAMICSANDLONGTERMSTABIL
ITY &OR EXAMPLE IN THE PERENNIAL NATIVE
SPECIES4RILLIUMGRANDImORUMmOWERING
IS SIZEDEPENDENT (ANZAWA AND +ALISZ
$EER ARE KNOWN TO PREFERENTIALLY
CONSUMEmOWERINGINDIVIDUALSOVERNON
Natural Areas Journal 113
VORETYPESINHERBIVOREEXCLUSIONSFOUND
THATEXOTICSAREINGENERALSUSCEPTIBLETO
NOVEL GENERALIST HERBIVORES 0ARKER ET AL
)NCONTRASTHEREWESHOWTHATTHE
EXOTICSPECIES!PETIOLATAAND-VIMINEUM
APPEARTOBEUNPALATABLETOANATIVEGENER
ALISTHERBIVORE4HISLACKOFHERBIVORYBY
DEERMAYCONTRIBUTETOTHEMAINTENANCEOF
THEIR ABUNDANCE IN THE PRESENCE BUT NOT
ABSENCEOFDEER
&IGURE0ERCENTBAREGROUNDMEAN±3%ISSIGNIlCANTLYGREATERINDEERACCESSVSDEEREXCLUSIONPLOTS
0LOTSDIDNOTDIFFERATBEGINNINGOFTHEEXPERIMENTBUTBAREGROUNDDECREASEDSIGNIlCANTLYIN
DEEREXCLUSIONPLOTSGRANDMEANOFPLOTS
PTTESTT
mOWERING!NDERSON,OSSOFPHO
TOSYNTHETIC BIOMASS TO HERBIVORY CAUSES
INDIVIDUAL PLANTS TO REGRESS TO A SMALLER
NONREPRODUCTIVE STAGE IN THE FOLLOWING
YEAR +NIGHT 2OONEY AND 'ROSS
)N ADDITION THE LOSS OF mOWERING
INDIVIDUALS TO DEER BROWSING REDUCES THE
POTENTIALFORREGENERATIONBYSEED&URTHER
BECAUSE THE POPULATION GROWTH RATE OF 4
GRANDImORUM IS SENSITIVE TO CHANGES IN
THEVITALRATESOFREPRODUCTIVEINDIVIDUALS
+NIGHT HIGH LEVELS OF DEER HER
BIVORYTHREATENPOPULATIONPERSISTENCEFOR
THIS SPECIES +NIGHT +NIGHT ET AL
IN PRESS )T IS UNKNOWN BUT LIKELY THAT
THEDEMOGRAPHICRESPONSESOFOTHERNATIVE
PLANTSPECIESBROWSEDBYDEERARESIMILARTO
THATOF4GRANDImORUMANDTHEREDUCTIONIN
PLANTSIZEOFALLNATIVESPECIESSUGGESTSTHAT
THIS WILL BE THE CASE 3IGNIlCANTLY LOWER
PERCENTCOVERANDGREATERPERCENTOFBARE
GROUND SIGNIlCANTLY SMALLER INDIVIDUAL
PLANTSIZESANDSIGNIlCANTLYLOWERNUMBERS
OFREPRODUCTIVEINDIVIDUALSOFNATIVESPE
CIESAREALLEVIDENCEOFTHENEGATIVEEFFECTS
OFCURRENTDEERLEVELSATOURSTUDYSITETHAT
COULDRESULTINREDUCEDCOMPETITIVEABILITY
OFTHENATIVEPLANTS
(ERBIVORY WAS NOT OBSERVED FOR EITHER
INVADERINOURSTUDY!LTHOUGHITISUNCLEAR
114 Natural Areas Journal
WHY DEER DO NOT CONSUME - VIMENIUM
PLANTSTHISSPECIESHASBEENSHOWNTOBE
LESSPALATABLETOINSECTSTHAN!PETIOLATA
-ORRISONETAL !LLIAIRAPETIOLATA
PLANTSAREKNOWNTOPOSSESSCHEMICALSTHAT
LIKELY MAKE THEM LESS PALATABLE TO DEER
(ARIBALAND2ENWICK6AUGHN
AND "ERHOW #IPOLLINI AND 'RUNER
AND THUS AVOIDED 4HEREFORE OUR
RESULTSARESIMILARTOAWETLANDSTUDYWHERE
DEER SELECTIVELY BROWSED NATIVE PLANTS
AND AVOIDED THE INVASIVE GRASS 0HALARIS
ARUNDINACEA +ELLOGG AND "RIDGEMAN
0REFERENTIAL BROWSING ON NATIVES
MAY CONFER A COMPETITIVE ADVANTAGE TO
THESEINVADERS)NDEED!PETIOLATADIDNOT
DIFFERSIGNIlCANTLYINSIZEORFREQUENCYOF
mOWERINGBETWEENTREATMENTSINTHEHA
FENCESTUDY
/NEPROMINENTHYPOTHESISFORWHYMANY
EXOTIC SPECIES BECOME INVASIVE IS THE
@ENEMY RELEASE HYPOTHESIS 7ILLIAMSON
-ITCHELL AND 0OWER WHICH
POSITSTHATINTRODUCEDSPECIESESCAPEFROM
SPECIALIST ENEMIES WHEN THEY COLONIZE A
NEWHABITATANDASARESULTHAVEACOM
PETITIVEADVANTAGEOVERTHENATIVESPECIES
&URTHERARECENTMETAANALYSISEXAMINING
NATIVE AND EXOTIC SPECIES EXPERIENCING A
WIDE RANGE OF NATIVE AND INVASIVE HERBI
&INALLYTHEEFFECTSOFDEERONUNDERSTORY
COMMUNITIES COULD ALSO BE DUE TO NON
BROWSINGEFFECTSOFDEERSUCHASSOILAND
LEAF LITTER DISTURBANCE THAT CREATE BARE
SOILAREASTRAMPLINGORSOILCOMPACTION
WHICHAFFECTPLANTGROWTHRATESORSEEDLING
ESTABLISHMENT7ARDLEETAL)NDEED
ALLNATIVEPLANTSWHETHERBROWSEDORNOT
WERE SMALLER WHEN DEER WERE PRESENT
7HILESOMESIZEREGRESSIONOFTHESPECIES
DEERBROWSEREGULARLYISUNDOUBTEDLYDUE
TO HERBIVORY EVEN *ACKINTHEPULPIT A
NATIVESPECIESTHATRARELYEXPERIENCESDEER
HERBIVORYSHOWEDATRENDTOWARDSSMALLER
VEGETATIVESIZEINTHEPRESENCEOFDEERAFTER
lVEYEARS0PAIREDSAMPLEPLOTS
OF THE LARGE FENCED AREA )N CONTRAST !
PETIOLATA DID NOT DECREASE IN SIZE IN THE
PRESENCEOFDEERINTHESESAMEPLOTSWHICH
SUGGESTSTHATITMAYBEMORETOLERANTOFSOIL
COMPACTION TRAMPLING OR OTHER INDIRECT
EFFECTSOFDEER)NTERESTINGLY-VIMENIUM
WAS ONLY FOUND OUTSIDE THE FENCE WHERE
DEERHADACCESS,EAFLITTERDISTURBANCEHAS
BEENSHOWNTOFACILITATETHESPREADOF-
VIMENIUM/SWALTAND/SWALTAND
DEERACTIVITYINTHEDEERACCESSPORTIONSOF
OURSTUDYSITEHADSIGNIlCANTLYMOREBARE
GROUNDWHICHCOULDFACILITATETHISINVASIVE
SPECIES SUCCESS4HUS NONBROWSING EF
FECTSOFDEERMAYALSOBECONTRIBUTINGTO
NATIVESPECIESDECLINE
4AKEN TOGETHER OUR RESULTS SUGGEST THAT
CURRENTHISTORICALLYUNPRECEDENTEDDENSI
TIESOFNATIVEWHITETAILEDDEERARECAUSING
CHANGES IN THE FOREST UNDERSTORY COM
MUNITY LIKELY THROUGH A COMBINATION OF
BOTHSELECTIVEFORAGINGONPALATABLENATIVE
SPECIESANDTHENONBROWSINGEFFECTSTHAT
FAVORINVADERS)TISWELLKNOWNTHATDEER
CANDRAMATICALLYDIMINISHTHEABUNDANCE
ANDRICHNESSOFNATIVEUNDERSTORYSPECIES
2USSELLETAL#ÙTÏETAL)N
THIS STUDY WE HAVE SHOWN AN ADDITIONAL
Volume 29 (2), 2009
EFFECTˆTHECURRENTEFFECTSOFDEERATTHIS
SITEAPPEARTOMAKETHEFORESTUNDERSTORY
MOREHOSPITABLETOINVADERSOFNONNATIVE
SPECIES4HUSTWOPREVIOUSLYUNCONNECTED
PROBLEMSINLANDMANAGEMENTDEEROVER
ABUNDANCEANDINVASIVESPECIESAPPEARTO
BEINTIMATELYLINKED
3TRAZISARAND25NKSPROVIDEDEXCELLENT
lELDASSISTANCE
7HY SOME SPECIES BECOME INVASIVE AND
SOMECOMMUNITIESAREMOREEASILYINVADED
REMAIN POORLY UNDERSTOOD AND HOTLY DE
BATEDTOPICSINECOLOGY3HEAAND#HESSON
,EVINEETAL7ESUGGESTTHAT
THEMULTITROPHICLEVELDYNAMICSBETWEEN
ANATIVEHERBIVOREANDNATIVEANDINVASIVE
PLANTS CHANGES IN COMPETITION BETWEEN
NATIVEANDINVASIVEPLANTSANDABIOTICDIS
TURBANCEMAYALLPLAYIMPORTANTROLESINTHE
FACILITATIONOFTHESEINVADERS3PECIlCALLY
HERBIVORY BY OVERABUNDANT POPULATIONS
OF WHITETAILED DEER APPEAR TO CREATE AND
SUSTAINCONDITIONSFORINVASIVESPECIESTO
DOMINATE UNDERSTORY COMMUNITIES WHILE
DEER EXCLUSION REVERSES THIS TREND4HESE
RESULTSMAYBEGENERALTOOTHERECOSYSTEMS
WITH OVERABUNDANT UNGULATE BROWSERS
&URTHERSTUDIESTHATLINKCHANGESINABUN
DANCEWITHTHEPOPULATIONGROWTHRATESOF
THE INVADERS ARE REQUIRED TO ASSESS IF THE
INVADERSWILLINFACTDECLINE
4IFFANY+NIGHTWASAGRADUATESTUDENTIN
THE+ALISZLABATTHETIMEOFTHISRESEARCH
ANDISCURRENTLYAN!SSISTANT0ROFESSORIN
THE$EPARTMENTOF"IOLOGICAL3CIENCESAT
7ASHINGTON5NIVERSITYIN3T,OUIS-/
3USAN+ALISZISA0ROFESSORINTHE$EPART
MENTOF"IOLOGICAL3CIENCESATTHE5NIVER
SITYOF0ITTSBURGH0ITTSBURGH0!
*ESSICA,$UNNISASENIORRESEARCHTECHNI
CIANINTHE+ALISZLABATTHE5NIVERSITYOF
0ITTSBURGH0ITTSBURGH0!
,ISA 3MITH WAS A CONSERVATION BIOLOGIST
WITH THE7EST 0ENNSYLVANIA #ONSERVANCY
ATTHETIMEOFTHISRESEARCHANDISCURRENTLY
ANECOLOGICALCONSULTANT
*O!NN$AVISWASANENVIRONMENTALEDUCA
TIONSPECIALISTATTHE7ESTERN0ENNSYLVANIA
!UDUBON3OCIETY"EECHWOOD&ARMS.ATURE
2ESERVE
LITERATURE CITED
CONCLUSION
/UR RESULTS SUGGEST THAT MANAGEMENT
PROGRAMSTOREDUCETHEABUNDANCEOFDEER
ANDTHEIREFFECTSONNATIVEPLANTCOMMUNI
TIESWILLALSOHELPTOCURBTHESPREADAND
DOMINANCEOFINVASIVESPECIES
ACKNOWLEDGMENTS
4HIS RESEARCH WAS SUPPORTED BY A GRANT
FROM THE .ATIONAL 3CIENCE &OUNDATION
$%" AND FUNDS AND LOGISTICAL
SUPPORTFROMTHE"OROUGHOF&OX#HAPEL
TO 3 +ALISZ 4HE 7ESTERN 0ENNSYLVANIA
#ONSERVANCY!UDUBON3OCIETYOF7ESTERN
0ENNSYLVANIAANDTHE5NIVERSITYOF0ITTS
BURGHALSOPROVIDEDSUPPORTTO,3MITH
* $AVIS AND 3 +ALISZ RESPECTIVELY7E
THANK THE 0E%2 DISCUSSION GROUP AT THE
5NIVERSITYOF0ITTSBURGHANDESPECIALLY!
2ANDLEFORCOMMENTSONTHEMANUSCRIPT*
%LLIS!'REENE+(ANLEY3(UDSON4
/$AY30ARKER'3TERBA-3TERN4
Volume 29 (2), 2009
!NDERSON2#(EIGHTOFWHITEmOWERED
TRILLIUM4RILLIUMGRANDImORUMASANINDEX
OFDEERBROWSINGINTENSITY%COLOGICAL!P
PLICATIONS
!UGUSTINE$*AND$$E#ALESTA$ElN
INGDEEROVERABUNDANCEANDTHREATSTOFOREST
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"IERZYCHUDEK 0 4HE DEMOGRAPHY OF
*ACKINTHEPULPIT A FOREST PERENNIAL THAT
CHANGES SEX %COLOGICAL -ONOGRAPHS
"LOSSEY " AND 2 .OTZOLD %VOLUTION
OFINCREASEDCOMPETITIVEABILITYININVASIVE
NONINDIGENOUSPLANTSAHYPOTHESIS*OURNAL
OF%COLOGY
"OWERS-!)NmUENCEOFHERBIVOROUS
MAMMALS ON AN OLDlELD PLANT COMMU
NITY YEARS AFTER DISTURBANCE /IKOS
#ALLAWAY 2- AND 7- 2IDENOUR .OVEL WEAPONS INVASIVE SUCCESS AND THE
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#ADENASSO -, 34! 0ICKETT AND 0*
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(ARIBAL -* AND !! 2ENWICK )SOVITEXIN /”$GLUCOPYRANOSIDE A
FEEDING DETERRENT TO 0IERIS NAPI OLERACEA
FROM !LLIARIA PETIOLATA 0HYTOCHEMISTRY
(ARIBAL -* AND !! 2ENWICK 3EASONALANDPOPULATIONVARIATIONINmAVO
NOID AND ALLIARINOSIDE CONTENT OF !LLIARIA
PETIOLATA *OURNAL OF #HEMICAL %COLOGY
(OBBS4.-ODIlCATIONOFECOSYSTEMS
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AGEMENT
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Natural Areas Journal 115
+ELLOGG#(AND3$"RIDGHAM$IS
TURBANCEHERBIVORYANDPROPAGULEDISPERSAL
CONTROL DOMINANCE OF AN INVASIVE GRASS
"IOLOGICAL)NVASIONS
+ENNEDY4!3.AEEM+-(OWE*-(
+NOPS$4ILMANAND02EICH"IO
DIVERSITYASABARRIERTOECOLOGICALINVASION
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+NIGHT 4- %FFECTS OF HERBIVORY AND
ITS TIMING ACROSS POPULATIONS OF 4RILLIUM
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OF"OTANY
+NIGHT4-4HEEFFECTSOFHERBIVORYAND
POLLENLIMITATIONONADECLININGPOPULATION
OF 4RILLIUM GRANDImORUM %COLOGICAL !P
PLICATIONS
+NIGHT 4- ( #ASWELL AND 3 +ALISZ )N
PRESS0OPULATIONGROWTHRATEOFACOMMON
UNDERSTORY HERB DECREASES NONLINEARLY
ACROSSAGRADIENTOFDEERHERBIVORY&OREST
%COLOGYAND-ANAGEMENT
,EVINE *- - 6ILA #- $!NTONIO *3
$UKES + 'RIGULIS AND 3 ,AVOREL -ECHANISMS UNDERLYING THE IMPACTS OF
EXOTIC PLANT INVASIONS 0ROCEEDINGS OF THE
2OYAL3OCIETYOF,ONDON3ERIES"n"IO
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-AC$OUGALL!3AND24URKINGTON!RE
INVASIVE SPECIES THE DRIVERS OR PASSENGERS
OF CHANGE IN DEGRADED ECOSYSTEMS %COL
OGY
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VORESANDTHEECOLOGYOFFORESTUNDERSTORY
BIRDS 0P IN 7* -C3HEA ("
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OF INVASIVE PLANTS FROM FUNGAL AND VIRAL
PATHOGENS.ATURE
116 Natural Areas Journal
-ORRISON*!(!,UBCHANSKY+%-AUCK
+- -C#ARTNEY AND " $UNN %COLOGICAL COMPARISON OF TWO COINVASIVE
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Volume 29 (2), 2009