Alien Flora in Grass Lands

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Society for Conservation Biology

Alien Flora in Grasslands Adjacent to Road and Trail Corridors in Glacier National Park,Montana (U.S.A.)Author(s): Robin W. Tyser and Christopher A. WorleySource: Conservation Biology, Vol. 6, No. 2 (Jun., 1992), pp. 253-262Published by: Blackwell Publishing for Society for Conservation BiologyStable URL: http://www.jstor.org/stable/2386247 .

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Alien lora nGrasslandsAdjacento Road andTrailCorridorsnGlacierNationalPark,MontanaU.S.A.)ROBIN W. TYSERDepartment of Biology and MicrobiologyUniversityofWisconsin-La CrosseLa Crosse, WI 54601, U.S.A.CHRISTOPHER A. WORLEYDepartment of Biology and MicrobiologyUniversityof Wisconsin-La CrosseLa Crosse, WI 54601, U.S.A.

Abstract: Alien plant specieshave rapidly nvaded and suc-cessfullydisplaced native species in many grasslands ofwesternNorthAmerica Thus,the status of alien species inthenature reserve rasslandsof thisregion warrants pecialattention.This study describesalien flora in nine fescuegrassland studysites adjacent to three ypes f transporta-tion corridors-primaryroads, secondary roads, and back-country rails-in GlacierNational Park, Montana (USA).Parallel transects, laced at varyingdistancesfromthe ad-jacent road or trail, were used to determine lien speciesrichness and frequency at individual study sites. Fifteenalien species were recorded, wo Eurasian grasses,Phleumpratense and Poa pratensis, eing particularly common inmost of the studysites. n sites adjacent to primaryandsecondary roads, alien species richnessdeclined out to themostdistanttransect, uggesting hat alien speciesare suc-cessfully nvading grasslandsfrom the roadside areas. Instudy itesadjacent tobackcountry rails, bsence ofa com-parable declineand unexpectedly igh evelsofalien speciesrichness100 mfrom thetrailside uggestthat alien specieshave been introduced n off-trail reas. The results of thisstudy mplythat n spite of low levels of livestock razingand other nthropogenicdisturbances, escue grasslands innature reserves f thisregionare vulnerableto invasion byalien flora Giventhe rominentrole thatroadsidesplay inthe stablishment nd dispersalof lien flora road construc-tion should be viewed from a biological, ratherthan an

Resumen: Especies de plantas introducidasban invadidorapidamentey desplazado exitosamente species nativas enpraderas del Oeste deAmericadel Norte.Por lo tanto el es-tadode las especies ntroducidas n las reservas epastizalesnaturales de esta region xige especial atencion.Este estudiodescribe a flora introducidaen nuevepastizales naturalesdefestuca las acreas e estudios on adyacentes tres iposdecorredores e transporte-caminosprimarios, caminos se-cundariosy senderos emotos- en elParque Nacional "Gla-cier, Montana (EE.UU).Para determinar iqueza y frecuen-cia de especies introducidas, se trazaron transectasparalelas, localizadas a distancias variables del camino osendero adyacente en las areas de estudio. Se registraronquince especies introducidas. Dos pastos eurasiacticos,Phleumpratensis Poa pratensis, esultaron articularmenteabuntes en la mayoria de las acreasde estudio. En lugaresadyacentes caminosprimariosy secundarios, a riqueza deespecies introducidas disminuyo en la direccion de lastransectasma'sdistantes, ugiriendo que las especies intro-ducidas estan invadiendo exit6samente as praderas desdeareas aledanias a caminos. En las acreasde estudio adya-centes senderosremotosno se encontr6una disminucioncomparable; nesperados ltos nivelesde riqueza de especiesintroducidas 100 m de los senderos, ugieren que las es-pecies foracneasban sido introducidas desde otras areasfuerode los senderos. os resultadosde esteestudio mplicanque a pesar de los bajos niveles depastoreo y otraspertur-baciones antropogenicas, os pastizales de festuca en lasreservasnaturales de esta region on vulnerables a la inva-sion de laflora introducida Dado el rolpreponderantequePaper submitted eptember 5, 1990; revised manuscript cceptedMarch 28, 1991.

253Conservation BiologyVolume 6, No. 2, June 1992


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254 Alien loraAdjacentoRoad and TrailCorridors Tyser Worleyengineeringperspective.Nature reserveman agers shouldestablish effective oadside vegetationmanagementpro-grams that include monitoring quickly treatingkeystonealien speciesupon their nitial occurrence nnaturereserves,and creatingbuffer ones on roadsides leading to naturereserves.

juegan los caminos en el establecimiento dispersionde laflora introducida la construccionde rutas debe ser vistadesde unpunto de vista biol6gico, mas que desde una per-spectivameramentengenieril. os administradores e reser-vas naturales deberi'anestablecerprogramas efectivosdemaneijode vegetacionen los bordes de los caminos. Estosprogramas deberian incluirmonitoreo, ratamiento apidode especies ntroducidasy laves tanprontocomo se detectenen las reservasnaturales,y creacion de zonas de transicionen los caminos que conducen a las reservasnaturales.

IntroductionThe widespreaddisplacement fnativeplant pecies byalien flora n the Intermountainunchgrass ommuni-ties ofwesternNorthAmericahasbeen considered nanumber fstudies Young et al. 1972; Mack& Thomp-son 1982; Mooney et al. 1986; Mack 1986). Mack(1989) notes that this displacement s essentiallyworldwide phenomenon, ccurringn the bunchgrasscommunitiesof California'sCentralValley, southernSouthAmerica, nd southernAustralia. uccessful lienplants in the Intermountain rasslands-grasslandsnthe region between theRockyMountains nd CascadeMountains-include species considered agriculturallyuseful e.g.,Poapratensis) as well as speciesconsiderednoxious e.g.,Centaurea maculosa-Watson & Renney1974).Baker 1986) and Forcella ndHarvey 1983) suggestthathigh light ntensitynd frequentbreaks n plantcovercharacteristicfgrasslandsmayfacilitatenvasionbyalien species. In addition, he success ofalienvege-tation n grasslandss regularly ttributed o anthropo-genic disturbances uch as cultivation,ttempts o re-duce shrub over, and especiallygrazing nd tramplingbydomesticungulates Daubenmire 1970;Younget al.1972; Mack 1981; Mack & Thompson 1982;Mooney etal. 1986). Alien peciesareknown opossessa varietyfadaptations o disturbance, ncludingrapid refoliationand photosynthetic ecovery,prostrategrowthformandground-level uds, high evels ofsclerenchymandlignifiedeaf cells, andphenotypic lasticityShearman& Beard1975; Caldwellet al. 1981;Bazzaz 1986;Hall &Kuss 1989; Buttet al. 1989). Significantly,ejmanek's(1989) simulationmodels suggestthateven competi-tivelynferiorlien species can successfullynvadena-tive ommunities, iven ppropriately igh evels ofdis-turbance.Though nature reserves are presumablyrelativelyprotected from the effects f human-related istur-bance,a number f alienspecieshave been recorded ngrasslands f national arks longthe easternborderofthe Intermountainrea,that s, Banif,Glacier U.S.A.),Jasper,GrandTeton,and WatertonLakes (Koterba &

Habeck 1971; Stringer 973; Weaver & Woods 1985,1986). Because roadsidesare human-disturbed icro-habitats o which alien plants are oftenwell adapted(Frenkel1970; Forcella& Harvey 983), it sreasonableto expect the occurrenceofalienflora nnational arkgrasslands o be correlatedwithadjacentroadside cor-ridors.Trailsideareas are also human-disturbedorri-dors (Dale & Weaver 1974; Bright1986; Hall & Kuss1989) ofpossible mportance o theoccurrenceof lienspecies in these grasslands.Asthe nitial hase of long termmonitoringroject,the presentstudy considersthe alien flora of fescuegrasslands djacent to primary oads,secondaryroads,andbackcountryrailsnGlacierNational ark,Montana(U.S.A.).Dominantnativegrasses nthishabitat ncludeFestuca idahoensis, F. scabrella, and several otherbunchgrass pecies. This studyaddressestwo specificquestions:1) What lienspecieshavemost uccessfullyinvadedgrasslands djacent to road and trail orridorsin thepark? nd 2) To whatextent an this nvasion eattributed o theeffectsfroad and trail orridors?Description fStudy itesNine fescuegrassland tudy ites nfivedifferentrain-age systems fGlacier NationalPark,Montana U.S.A.),were selected forstudy.Total grassland rea in thesedrainageswas ca. 2800 ha. Vegetationwas representa-tive oftheFestuca scabrellaiF. dahoensishabitat ypeofMueggler nd Stewart 1980). In additionto thesetwo species, other nativegrassescommon at variousstudy iteswereAgropyronaninum,KoeleriacristataDanthonia intewnedia and Stipa richardsonii. Com-monforbs ncludedAcbillea millefolium,Galium bo-reale,Cerastium rvense, ndLupinus sericeus Tyser1991). A cryptogam round ayercomposed of smalllichensand mosses coveringundisturbed oil surfaceswas commonly resent n thesegrasslands.Primary oads in Glacier Park are narrow, sphalt-based,two-laneroads occasionallyresurfacedwith oiland rockchip treatments. oadside shoulders re usu-ally mowed once or twice each year.Secondaryroadsareunimproved irt oadsbladedbyroadmaintenance

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Tyser Worley Alien loraAdjacentoRoad and TrailCorridors 255

equipment bout once per year,but otherwise hey e-ceive littlemaintenance.Backcountryrail tudy iteswere >2 kmfromthe nearestprimary r secondaryroad. Onlyhiking ndhorse use are permitted n parktrails.Study iteswere relatively opographically omoge-neous, >1 kmfrom ther study ites, nd bordered aprimary oad, a secondaryroad,or a backcountryrailsegmentwith ess than a 100 curve. Of thenine studysites, three PR1, PR2, PR3) borderedprimary oads,three SRI, SR2, SR3) borderedsecondaryroads,andthree (BT1, BT2, BT3) bordered backcountry rails.Study ite ocationsare indicated nFigure1.Withtheexceptionof sporadichomesteading hat occurred inthe northwest ection of theparknear theSR1and SR2studysites and a short-livedmining operationaban-doned ca. 1900 near theBT1 site Fig. 1), no recordsexist ndicatinghat rasslandsftheparkwere usedforlivestock r agricultural ctivities eforethepark wasestablished in 1910. Mean annual precipitation ndmean dailyJuly emperatures romrecording tationsclosestto the study reas are SRI and SR2-59.2 cm,15.40 C; PR1, PR2, andSR3-67.1 cm,15.80 C; PR3 andBT1-99.1 cm,13.80 C; BT2 andBT3-96.5 cm,14.30 C(Finklin1986).With heexceptionof the BT1 site thatwas adjacentto a trailestablished n ca. 1974 (J.Potter,personalcommunication),ll study iteswereborderedbyroadsor trails hathave existed n theparksince at least the1930s Ruhle 1972). Theroadadjacent o theSR3 studysitehasbeen closed to vehicletrafficnd used as a trailsince the early 1970s,though twas a secondary oadfrom 930 to 1970. Because of ts ongeruse as a road,itwas classified s a secondary oad study ite.

GlacierNationalBT2 Y Parkt ~~~~~~~BT3 MonanSR ~~~~B1*SRI PR36SR2~~~~~~R

N PiW E SR3

0 5 10kilometers ContinentalDivide

~ PrimaryoadSecondaryoad

* Study itePark oundary

Figure1.Map ofGlacier National Park showingstudy ite locations.

MethodsStudy esignStudy iteswere sampled during 5-weekperiodfromlateJune oearlyAugust n 1988 and 1989. Species thatcould notbe reliably ampledthroughout his5-weekinterval, or xample spring phemerals,were notcon-sidered.Withone exception see below), study ite di-mensionswere 100 m X 100 m. In the six road studysites a 100 m transect, esignated s the "R" transect,was placed in the centeroftheroadside area betweentheroadbed andthe grassland order Fig. 2). Typically,roadside areas consisted of a drainage ditch primaryroads) or a ridgeof substrate ushed to the side of theroadbed (secondaryroads).In all nine study ites,three 100 m transectswereplaced at varying istancesfrom he grasslandborderparallelto the road or trail Fig. 2). The firstransect,designated s the "G1" transect, as placed 1-2 mfromthegrassland order.Two other ransects,esignated s

Road Roadside

PrimaryoadandSecondary oad 100mStudy ites

R 01 02 03

BackcountryrailStudy ites 25m25 mm

Trail

Transect GrasslandCorridorypes

Primary Secondary BackcountryRoad Road TrailNumberf tudyites 3 3 3StudyiteAcronyms PRI, R2, R3 SRt, R2, R3 BT1, T2, T3Transectsn ach udyite R,G1,G2,G3 R, G1,G2,G3 G1,G2,G3

Figure2. Location oftheA GI, G2, and G3 transectsforprimaryroad, secondaryroad,and backcountrytrailstudy ites.Note thattransects omparableto roadside "R") transectswerenot usedforsampling thebackcountry railsites.

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256 Alien loraAdjacento Road and TrailCorridors Tyser Worley"G2" and "G3," were located 25 m and 100 m, respec-tively, rom he Gl transect.Because of encroachingforest egetation t the BT3 site, the G3 transectwaspositioned 75 m rather han 100 m from he grasslandedge. Thus, alien vegetationwas sampled along fourtransects R, Gl, G2, G3) in each of the six road studysites and along threetransects Gl, G2, G3) in each ofthe three backcountry trail study sites. Roadsidetransects ere in areasclearly isturbed y road-relatedactivities uch as mowing, lading, oad repair, nd ve-hicle traffic. owever, ther hanoccasional depositsofsoil and smallrocks long everalofthe Gl transects, oindications fhuman-relatedubstrate isturbance ereapparent long any of the G1-G3 transects.Presence of all alien vascular pecies was determinedin 20 cm X 50 cm quadrats t 2 m intervals long eachtransect.Percentagefrequencyof individual species(percentageofquadrats nwhich the species was ob-served)andmean alien species richnessmean numberof alienspecies per quadrat)were determined or achtransect.Use of alien species richness s a simple yeteffectiveway to detect differencesn vegetationpat-terns mongtransectsnthesegrasslands Tyser& Key1988). Species nomenclaturenddeterminationf lienstatus ollowHitchcock ndCronquist 1973). It ispos-sible thatPoa pratensis, or a morphologicallyimilarspecies, s native n remote areas in theIntermountainregion of western NorthAmerica (Cronquist et al.1977). In this study, . pratensis was considered analien species.Data AnalysisThe nine study ites were divided nto three corridortypes: rimaryoadsites, econdary oadsites, nd back-country rail ites.The unit used for tatisticalnalysiswas the number of alien species per 0.1 m2 quadrat,designated s alien species richness. or each corridortype, he effects f transect nd site on alien speciesrichnesswere evaluated using two-wayANOVAs fol-lowed by post hoc Tukey multiple comparisons.Be-cause alienspecies richnessdata from everaltransectswere notnormally istributednd could not be trans-formed ystandardogarithmicr square-rootransfor-mations,lienspeciesrichnesseswererank-transformedfor each corridor type prior to ANOVA. Two-wayANOVA ofranks s a robust,nonparametric pproachdescribedbyConover and Iman 1981 andreferencestherein. YSTATv. 3.2 softwareWilkinson 1987) wasused to performtatisticalomputations.ResultsSpecies ampledFifteen lien plant species were recorded (Table 1),most of which were members of three families:As-

teraceae (fourspecies), Fabaceae (three species), andPoaceae (four pecies). Eight fthesespecies were sam-pled along theG3 transects hatwere located farthestfrom ossible effects f djacentroadand trail ctivities.Three additionalobservations re worth noting boutspecies occurrences ssociatedwith thethreecorridortypes. irst,everal pecies-most notably bleum pra-tense, oa pratensis, nd to a lesserextentTaraxacumofficinale-were commonly recorded (frequency>20% ) along one or more transectswithin all threecorridor ypes. econd, henumber f lienspeciessam-pled along theG1-G3 transects as surprisinglyimilaramongthe threecorridor ypes.For example, the cu-mulativenumbers fspecies sampledalongtheG1-G3transectsntheprimary oadstudy iteswere three, ix,and four pecies per site,respectively. orrespondingnumbersfor the othertwo corridortypes were four,four, nd six speciesper study itefor econdary oadsandthree, our, nd five pecies per study ite forback-country rails. hird, heoccurrenceof Centaureama-culosa was consistently ssociated with the primaryroadstudy ites.Centaureamaculosa frequencieswererelatively igh long theR and Gl transectsnprimaryroad study ites,but thisspecies was not recordedinanyofthesecondary nd backcountryrail tudy ites.Thiswas a typical attern bserved hroughouthepark.Continuityith oadside ndTrailside reasMost occurrencepatterns findividual pecies amongtransectswithin tudy iteswere continuouswith thetransect losest to theadjacent road or trail Table 1).This was exemplified by a " + ---" sampling pattern,for xample,Melilotusofficinalis tthePR1 study ite,where a specieswas recordedalongtheR transect utnot recordedalong theGl, G2, and G3 transects.An-other pattern was " + + - -," for example, Centaureamaculosa at the PR2 study ite,where a species wasrecorded alongtheR and Gl transects, ut notthe G2orG3 transects. hough ome speciesexhibitedgaps ntheirdistributionsutwardfrom heroad or trail pat-terns such as "- + - + " or " + - + -," e.g., Poa com-pressa at theSR2 site), these instanceswere relativelyfew.Ofthe46 speciesoccurrencepatterns, nlynine-two ntheprimaryoadsites, ive nthesecondary oadsites, nd two in thebackcountryrail ites-exhibitedsuchdistribution aps Table 1).Alien peciesRichness atternsALIENSPECIES RICHNESSGRADIENTSWithin ll threecorridor ypes, lien species richness(number of alienspecies/0. m2quadrat)variedsignif-icantly mong transects nd among study ites Table2). Alienspecies richness ypically eclinedmonotoni-



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Tyser Worley Alien lora djacentoRoad ndTrail orridors 257Table1. Percentrequencyf alien speciesby ransect. = 50 quadrats or achtransect.

Tran-Site sect ALY BRO CEN CIR LAP LIN MEL PHL POC POP PRU TAR TRA TRP TRRa. Primary oadsPRI R 100 - - - 54 50 60 -GI 74 - 6 28 -

G2 2 - - - - 4 2 - - -G3PR2 R 88 18 - 6 80 2 48 30 6GI 64 8 - - 60 50 - 12 2G2 74 14 6G3 28 4 6PR3 R 18 - - - 88 58 - - -GI 2 34 38 - 2G2 6 - - -G3 2 - - -b. SecondaryRoadsSR1 R 40 - - 18 32 82 -Gl 18 - - 16 20 26 -G2 16 - - 2 - 22 - - -G3 6 - - 2 4 - - - - - -SR2 R 2 2 2 100 - - - -GI 2 8 84 - - - -G2 2 8 - - - -G3SR3 R 78 22 62 28 2 80GI 98 74 - - 6G2 92 32 - - -G3 - 98 16 2 6 2c. BackcountryrailsBT1 GI 66 34 8G2 12 18 2G3 - 4 20 - - -BT2 Gl 94 64 16 - 2G2 68 6 6G3 68 2 16BT3 Gl 100 74 28 - 14G2 90 24 24 -G3 8 96 12 60 - 4

aSpecies acronyms:ALY (Alyssum lyssoides),BRO (Bromus inermis sp. inermis),CEN (Centaurea maculosa), CIR (Cirsium arvense),LAP(Lappula echinata),LIN (Linaria vulgaris),MEL (Melilotusofficinalis),HL (Phleum pratense), OC (Poa compressa),POP (Poa pratensis), RU(Prunella vulgaris ar.vulgaris),TAR Taraxacum officinale), RA Tragopogondubius), TRP Trifolium ratense),TRR Trifolium epens).callyfrom heRto G3 transectsntheprimaryoadandsecondary oad sites Table 2a, b; Fig.3). However, lienspecies richness n the backcountry rail ites did notshow a G1-G3 decline (Fig. 3). Though alien speciesrichnesswas significantlyreater longthe Gl transectthan along eitherthe G2 or G3 transects n the back-country rail ites, he G2 and G3transects id not differsignificantlyrom ne another Table 2c). Hence, therewas an alien species richness radientnthe backcoun-try tudy ites,but t did not extend as deeply nto thegrassland s was the case for he primary nd secondaryroad sites.AMONG ORRIDORTYPE COMPARISONS F G1-G3 TRANSECTSAlien species richness long the G1-G3 primary oadtransectswas not consistently igher relative to theother two corridor ypes. n fact, verallquadratrich-ness means of the G2 and G3 transects t theprimaryroadsiteswerelowerthan orrespondingmeansofbothsecondary road and backcountry rail sites (Fig. 3).Alien pecies richnesswas relatively igh long all three

grassland ransectsn two backcountry rail ites,par-ticularly heBT3 site.DiscussionAlien peciesRichness atternsOne ofthemoreconsistent atterns ound n this tudywas theR-G3decline in alien species richnessforpri-mary nd secondary oad study ites.Because distribu-tionsof mostalienspecies didnotexhibitgapsin theirdistributionsutward from he R transects, his alienspeciesrichness radient robably epresents moreorless continuousdecline inthefrequencies f ndividualspecies. These patterns re consistentwithmodels ofspecies nvasionsWilliamson& Brown1986; Rejmanek1989;Williamson 989) wherean invadingpecies pro-gressively preads "diffuses")from tspoint of initialintroduction, hich n thiscase would be theroadsidearea.Hence,the alienspecies richnessgradients an beattributedo road-related ffects.Some roadside introductions ave undoubtedlyre-



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258 Alien loraAdjacentoRoad and TrailCorridors Tyser WorleyTable 2. Summaryftwo-way NOVAsftheeffectsf ransectocationndstudyiteon alienspeciesrichnessnumber falienspecies/0.1 2quadrat) or he hree orridorypes. osthocTukeymultipleomparisonsre indicated or hetransectactor.Comidor type Factor SS df F p Tukeyaa. PrimaryRoads TransectLocation 9549961.09 3 43.43 Gl > G2 > G3Study ite 1654988.16 2 111.96 G3Study ite 5302817.59 2 341.04


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Tyser Worley Alien loraAdjacent o Road and TrailCorridors 259

A. PrimaryRoad Sites R Phleum ratense2.8 R Poa pratensismOtherrasse-s2.4 R EJForbs2.0 01

R1.61.2 01I 1 02S0.80.4 02

0 0 3 023 023PR1 PR2 PR32.8 B. Secondary Road Sites SR2.4-2.0- R R1.6-

of1.2 0pi R0.8~~~~~~~~~002 020.4 -G30.0critiono SRt SR2 SR32.8 C. BackcountryTrail Sites2.4- 012.0 GIG1.6 01I 021.2 01I03 G0.8 020230.4 02 30.0 BTI BT2 BT3

Study SitesFigure3. Summaryofalien speciesrichness numberofalien specieslO.t1 2quadrat) along each transectin thenine study ites.Arrows ndicateoveralltransectmeans withineach corridor ype.relativelyittleprecipitation,while the PR3 and BT1sitesreceiverelatively igh evelsofprecipitationseeDescription fStudy ites).Now that horse-relatedbackcountry ctivities aremore carefully estricted nd roadside seedingwithalien species has stoppedin thepark,futurentroduc-tionrates reexpectedto be higher longprimaryoadsthan long secondary oads andbackcountryrails. herelatively ecentdispersalof Centaurea maculosa intoGlacier NationalPark, species first bserved in thepark n themid-1960s R. Wassem,personalcommuni-cation),and itspresent ccurrence long primaryoad-sidesprobably haracterizes olonization atterns obefollowedbyfuturepecies enteringhepark.ThoughCmaculosa and future pecies are undoubtedly apableof colonizingsecondaryroadsides and trailsides,t islikely hat heywill initially ccur along primary oad-sides.Thus,distinctions mong transportationorridortypes hould become morepronounced nfuture earsthantheywere during his tudy.

Prominentlien peciesSeveralspecies, particularly bleum pratense and Poapratensis,were relatively ommon n moststudy ites(Fig. 3). In addition,roadside colonies of Centaureamaculosa monitored ince 1984 are currentlynvadingadjacent grasslands Tyser & Key 1988; Tyser 1991).Whatfactors ontribute o the success ofthesespecies?Mack and Thompson 1982) and others propose thatbecause Eurasian rasseshavehada more extensive v-olutionaryssociationwithungulategrazers han havewesternbunchgrasses, hey re comparatively esistantto grazing nd tramplingffects. or example,followingsimulatedgrazing, n alien grass,Agropyrondeserto-rum, establishes canopy with three to fivetimes thephotosyntheticurface rea of morphologicallyimilarnativespecies, Agropyron picatum (Caldwell et al.1981). The selective ole ofdomestic ivestock s a com-monly itedfactor nderlyinghereplacement fnativespecies byaliengrasses nd forbs n the ntermountainwest and elsewhere Young et al. 1972; Mack 1989).Likewise, hewidespread success of noxious forbs nthisregion, uch as C maculosa, is typically ttributedto overgrazing y livestock and other anthropogenicsubstrate isturbancesWatson & Renney 1974; Laceyet al. 1986).However, he overall evelofdomestic ivestock raz-ingandotherhumandisturbancesnthe park has beenrelativelyow, and Mack 1986) notes nstanceswherealienspecieshave nvadedgrasslands ot known ohavebeen disturbed yhumans.While domesticgrazing ndanthropogenicdisturbancesmay hasten invasion byalien species, our resultssuggestthatdispersalfromroadand trail orridorsntoadjacent natural reas canoccur even f evels of hesefactors re ow,andperhapseven ifthey re absent.Otherfactors, ncluding oler-ance to grazing nd trampling y elk,reduced bioticcontrols, nd preadaptation o steppe environments,mayaccountfor hesuccess ofalien species in naturalarea grasslands f thisregion.Mechanismsunderlyingthe success of alien species in agro-systemsmayalsooperate n natural ystems. orexample,the success ofC. maculosa in rangelandsmaybe increasedbybitter-tasting nicin,a sesquiterpene actone found in highconcentrationsn this pecies (Locken & Kelsey1987).Cnicinmayalso renderthisspecies unpalatableto na-tivemammal nd insectherbivoresnnaturereserves.After uccessfully nvadingnatural area bunchgrasscommunities,owhatextentdoes alien flora lterhostcommunities? dditional bservations n thepark sug-gest thatPhleum pratense,and especiallyCentaureamaculosa, arecapableofdecreasing overanddiversityof nativespecies (Tyser 1992; see also Tyser& Key1988). In addition, cryptogamground cover, whichplays an important ole in soil stabilization, itrogenfixation, nd water relationships n the Intermountain



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260 Alien loraAdjacent o Road and TrailCorridors Tyser Worleyregion Reddy & Giddens 1975; Anderson t al. 1982;Brotherson Rushforth983), was lower n areas dom-inated by C. maculosa and P. pratense than n areasdominated by native graminoids Tyser 1992). Mackand Thompson 1982) suggest hatrhizome-tiller atsformedby alien grassesrestrict ryptogam overage.Though additional tudy s clearlyrequired, he poten-tialeffect f alien vegetation n nativebunchgrass om-munities s a legitimate oncern to nature eserveman-agers.In conclusion,our study hows that everal species,especiallyEurasiangrasses, ow widely occurinfescuegrasslands djacent to road and backcountry rail orri-dors n GlacierNationalPark, nd thatdispersal fthesespecies from oadsides nto adjacent grasslands as oc-curred.These resultshighlight hree ssues of generalconcern to the management f nature reserves.First,commonlycited anthropogenicdisturbances uch aslivestock razing o not sufficientlyccount for he oc-currence of alien species in these grasslands.t seemsclear thatnatural rea bunchgrass ommunities re notimmune rom lien species nvasions. econd,most lienintroductions robably ccurred after heparkwas es-tablished.This underscoresthe need foralien vegeta-tion management rograms hat are proactive,ratherthanreactive.Third, hough oadsand other ine corri-dors can benefit he migrationf native pecieswithinlandscapesfragmentedy humandisturbanceSaunderset al. 1991), our observations how that uchcorridorsnegativelynfluence atural rea grasslands.ManagementmplicationsSeveral management ecommendations re proposed.These and other management ctions shouldbe care-fully nd expeditiously onsidered,giventhe apparentvulnerabilityf nature eservegrasslandsn thisregionto invasionbyalienflora.1. This study provides yet another reason to avoidroad-buildingn naturereserves.Where road con-struction n bunchgrasscommunities s unavoid-able, the original opsoil should be redeposited n

roadsideditches. n addition, oad construction ro-jects should not be consideredcompleteuntil na-tive roadside vegetation s fully stablished.Prop-erly viewed,road constructionn naturereservesshould be treated, nd appropriately unded,s 10-20-year biological projects,rather han 1-2-yearengineering rojects.Thus,biologists ndresourcemanagers hould overseeroad construction,atherthanengineers.2. Given the success ofaliengrassesthatwere inten-tionally eeded in thepark, n obvious recommen-dation s to eliminate ll ntentionalntroductionsfalien species, even in developed areas (e.g., road-

sides), withinnaturereserves. n addition o beinginvasive, lien species used for revegetationhavebeen shown osuppress stablishmentfnative pe-cies (Wilson 1989).3. Because roadsides are especiallyvulnerable o col-onization yalien flora ndthenfunction s sitesofprolific eed production,vegetation managementprograms houldbe established hat ntensively,utsensitively, anage nature eserveroadsides.Road-side vegetationmanagement rograms hould (i)monitor he status festablished lienspecies pop-ulations and the arrival f new alien species, (ii)minimize eed productionof keystone lien plantspecies-those having ecosystem-level effects(Macdonald et al. 1989), and iii) rehabilitateoad-sides using ffectiveative eedmixes nd substratepreparation.With the cooperation of local weedcontrol agencies, managementprograms shouldalso create buffer ones on roadsides eadingintonature eserves. ven relativelyimple ctions, uchas mowing oadsidestowardrather han way frompotential ources of lien seeds-for example,mow-ing outwardto reserveboundaries-can be effec-tivepartsof cohesive roadside management ro-grams.4. Specific reatments,ncluding ossibleuse ofherbi-cides, forkeystone lien plant species should beestablished nd approved priorto immigrationfsuch species into naturereserves.Quick and deci-siveproactive oliciescanyieldextremely ffectiveresults, ven over large areas, as in the control ofCentaurea maculosa in the province of Alberta,Canada (Ali 1989).5. Becausehayand manuremaycontain eeds of alienspecies, ivestock-relatedctivities hould be care-fullyreevaluated.To allow seeds to be expelledprior to use on trails, ffective uarantineproce-dures should be established. limination fprivatelivestocknnature eserves houldbe seriously on-templated.

AcknowledgmentsWe are gratefulo GlacierNationalPark'sresearch ndresourcemanagement taff ho supportedthisstudy,especiallyKathy imont,CarlKey,Dave Lang,CliffMar-tinka, ack otter,nd RachelPotter. rank orcella,CarlKey,MarcelRejmanek, nd two anonymous eviewersreviewed arlier rafts f thismanuscriptndwereveryhelpful n clarifying numberof our ideas. We alsothankAndyMatchett or tatistical dvice andAndyTy-ser forassistingwith fieldwork. Financial upportforthis tudywasprovidedbyGlacierNationalPark ndtheUniversityfWyoming-NationalParkResearch Cen-ter,Laramie,Wyoming.



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Literature itedAli, . 1989. Knapweed eradication rogramnAlberta. ages105-106 in P. K Fay and J.R. Lacey, editors.Proceedings ftheknapweed ymposium, pril -5, 1989. Extension ervice,Montana tateUniversity, ozeman,Montana, B 45.Anderson, . C., K T. Harper, nd R. C. Holmgren. 982. Fac-tors nfluencinghedevelopment fcryptogamicoil crusts nUtah deserts.Journal f Range Management 5:180-185.Baker,H. G. 1986. Patterns fplant nvasionnNorthAmerica.Pages 44-57 in H. A. Mooney and J.A. Drake, ditors. cologyofbiological nvasions fNorthAmerica nd Hawaii.Springer-Verlag,New York.Bazzaz,F. A. 1986. Lifehistory fcolonizingplants: ome de-mographic, enetic, ndphysiological eatures. ages 96-110in H.A. Mooney and J.A.Drake, ditors. cologyofbiologicalinvasions fNorthAmerica ndHawaii. Springer-Verlag,ewYork.Bright, .A. 1986. Hiker impact on herbaceous vegetationalong trails n an evergreenwoodland of centralTexas. Bio-logical Conservation 6:53-69.Brotherson, .D., andS. R.Rushforth.983. Influence fcryp-togamiccrustson moisturerelationships f soils in NavajoNationalMonument, rizona.GreatBasinNaturalist3:73-78.Butt, .,J.Lacey, nd G.Kennett. 989.Variation nbiomassofspottedknapweedunder three evels of defoliation nd threelevels of competition. ages 95-99 in P. K Fay ndJ.R.Lacey,editors.Proceedings f theknapweed symposium, pril4-5,1989. Extension ervice,MontanaStateUniversity, ozeman,Montana, B 45.Caldwell,M.M.,J.H. Richards, . A.Johnson, . S.Nowak, ndR.S. Dzurek.1981. Copingwithherbivory: hotosynthetica-pacity and resource allocation in two semiaridAgropyronbunchgrasses. ecologia 50:14-24.Cole, D. N. 1987. Effects f three seasons of experimentaltramplingn fivemontane orest ommunitiesnd a grasslandin westernMontana,USA. Biological Conservation 0:219-244.Conover,W.J., ndR.L. man.1981. Rank ransformationss abridge between parametric and nonparametric tatistics.American tatistician5:124-129.Cronquist, .,A.H.Holmgren, .H.Holmgren, .L.Reveal, ndP.K Holmgren. 977. Intermountainlora.Volume6, Mono-cotyledons.ColumbiaUniversity ress,New York.Dale, D., and T. Weaver.1974. Tramplingffects n vegetationofthe trail orridors f northRockyMountain orests. ournalofApplied Ecology 11:767-772.Daubenmire, . 1970. Steppevegetation fWashington.Wash-ingtonAgricultural xperimental tation Technical Bulletin62:1-131.Finklin, . . 1986. A climatichandbook forGlacierNationalPark-with data forWaterton akes NationalPark.USDA For-est Service ntermountainesearch tationGeneralTechnicalReport NT-204, Ogden, Utah.

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Alien Flora in Grass Lands