1.IntroductionAlien species are acknowledged as a majorthreat to the c - PDF document

13 1.IntroductionAlien species are acknowledged as a majorthreat to the conservation ofglobal biodi-versity (e.g.Sala et al.2000;McNeely et al.2001;Cronk & Fuller 2001;Sukopp 2002;Cox 2004).While detailed case studies ofalien species are necessary to understand In:Nentwig,W.et al.(Eds.):Biological Invasions … From Ecology to Control.NEOBIOTA 6 (2005):13-25 Diversity (CBD),ratified by Austria in1994,underlines the urgent need for well-designed studies examining patterns andprocesses associated with species loss atall scales around the world.To help accomplishing this task,theAustrian Ministry ofAgriculture andForestry,Environment and WaterManagement,in cooperation with theAustrian Federal Environment Agency,commissioned a national inventory ofalien species (Essl & Rabitsch 2002;Rabitsch & Essl 2004).The present con-tribution uses the compiled data and casestudies to analyse patterns within vascularneophytic plants.This taxonomic group isbest suited for such an approach becauseit is well studied and rich in neophytes.The questions addressed in this paper are(1) which habitats are colonized and (2)which ecological effects are provoked byneophytic vascular plant species inAustria.2.Material and Methods2.1 Definitions and DataAlien plant species have been defined vari-ously,with substantially different meanings(e.g.Richardson et al.2000;Schröder 2000;Pyek et al.2004).We use the definitionsprovided in Table 1 to determine whichspecies to include in our lists.The present paper deals with alien vascu-lar plant species which arrived in Austriaafter 1492 by direct or indirect human sup- J.Walter,F.Essl,T.Englisch & M.Kiehn 14 Table 1:Terminology and definitions pertaining to non-indigenous vascular plant species in thispaper (after Scholz 1995,Schroeder 1974,2000). terminologydefinitionreferencealienplant taxa in a given area whose presence there is due Pyek et al.2004to intentional or unintentional human involvement,or which have arrived there without the help ofpeople from an area in which they are alienarchaeophytesplant taxa introduced intentionally or unintentionally Schroeder 1974,2000by humans before 1492 and occurring or having occurred in the wildneophytesplant / fungi / animal taxa introduced intentionally Schroeder 1974,2000or unintentionally by humans following 1492 and occurring or having occurred in the wildanecophytesplant taxa having evolved under intentional or Scholz 1995unintentional human selection from wild-growing non-indigenous ancestors and growing or having grown in the wildnaturalizedalien taxa that reproduce consistently in the wild Kowarik 2003(at least two spontaneous generations within at least casualalien taxa which do not form self-replacing popula-Kowarik 2003tions in the wild (less than two generations within invasiveposing a threat to indigenous biodiversity at the gene-IUCN 2003tic,species or ecosystem levelpotentially expected to fulfil above criterion ifcurrent spreadEssl & Rabitsch 2002invasivecontinues Neophytes in Austria 15 port and which grow or have grown in thewild (neophytes).Plant species that haveevolved under human selection (anecophy-tesŽ) are included (Scholz 1995).A species is defined as invasiveŽifitposes a threat to indigenous biodiversity atthe genetic,species or ecosystem level(IUCN 2001).We are aware that the terminvasiveŽis also used with different mea-nings (Rejmánek et al.2002;Pyek et al.2004).For the present study,however,itsmeaning is restricted to conservationalconcerns and delimited by expert judge-ment.Those taxa that threaten indigenousbiodiversity in adjacent countries but arestill rare in Austria were classified aspotentially invasiveŽ.Furthermore,thespecies were classified according to theirstatus (naturalized or casual).Taxonomyand nomenclature follow Adler et al.(1994),recent taxonomic changes wereincorporated.The national inventory ofalien speciesin Austria provided an annotated list ofneophytic vascular plants with additionalinformation on their distribution and habi-tat requirements (Walter et al.2002).Additionally,case studies ofthe invasionhistory of20 invasive or currently rapidlyspreading neophytes were published (Essl& Walter 2004).Here,we use the compileddata and case studies for further analyses.2.2 Study areaAustria is a landlocked country in CentralEurope covering an area of83,858 kmThe population comprises slightly morethan 8 million inhabitants (97 inhabitants),most ofthem living in the low-lands and in the major valleys ofthe Alps.66% ofthe population live in urbanareas,34% in rural areas.Two-thirds ofAustria are dominated by mountainousregions,and 10% ofthe total areabelongs to the alpine zone (StatistikAustria 2003).The country is covered to43% by forests and to 31% by agricultu-ral land.Whereas the lowlands are shapedby agriculture,the sparsely populatedmountains are dominated by forests oralpine vegetation.In the eastern lowlands,the intersection oftwo biogeographicregions (Pannonic and Central-Europeanregion) promotes a high biodiversity(Adler et al.1994;Ellmauer 1994).3.Results3.1 Habitat preferencesRuderal and segetal vegetationIn ruderal and segetal vegetation,792 ofthe 1110 neophytes recorded for Austriawere documented.Favorable import rou-tes and habitat conditions,as given inlarge cities (Pyek 1998;Sukopp 2002),promote a high diversity ofneophytes inthese habitat types.In Austria,railway sta-tions (e.g.Brandes 1993;Zidorn &Dobner 1999;Hohla et al.1998,2000),motorways (Oppermann 1998;Gerstber-ger 2001),large industrial areas (Geissel-brecht-Taferner & Mucina 1995) and rub-bish dumps (Walter 1992) serve as focalpoints for neophytic ruderal species.Certain species that prefer ruderal andsegetal habitats have recently spread con-spicuously.One ofthem is the South,having spreadmainly along railways over the past 20years.The Mediterranean Geranium purpu-reumwas first recorded for Austria in1990;it has since spread rapidly along rail-ways and is now found in seven ofAustrias nine federal states.Duchesnea indi-,native to South- and Southeast Asia,was a rare casual in Austria up to the1970s;it spread rapidly in the 1990s andhas become widespread in the last years.Several neophytes,e.g.grass species ofthe families PoaceaeandPaniceae,have spread prominently in the last decades.The North American Panicum capillarewasfirst recorded in Austria in 1855 but hasspread remarkably since the 1970s.Morerecently,P. dichotomiflorumP. gattingeri, P. hill-P. schinzii,recorded since the1950s,1980s or 1990s,have spread mainlyin maize cultures (Schröck et al.2004).Since the mid-1990s,Sorghum halepensebeen increasing in frequency and range inAustria (Essl in press).In Austrian zonal forests,138 neophyticspecies were recorded,most ofthem beingonly locally established or casual.parviflorais the only widespread herbaceousspecies.A few others are locally naturalized(e.g.Doronicum pardalianches, Galeobdolonargentatum, Scutellaria altissima).Certain rareneophytic woody species (spp.,Mahonia aquifolium,Prunus serotina, Pseudo-tsuga menziesii, Quercus rubra, Spiraea japonicaare currently spreading.Some ofthese spe-cies are planted for timber productionPseudotsuga menziesii, Quercusrubra) and are therefore ofhigh economicvalue.In the Pannonic region ofeasternAustria the zonal xerothermic mixed oakforests are strongly affected by invasiveneophytes (Robinia pseudacacia, AilanthusFig.1).The most widespread neo-phytic tree is Robinia pseudacacia,compri-sing 0.2% ofthe standing crop offoresttrees (Kirchmeir et al.2001).In Austria,floodplain forests are stronglyinvaded by neophytes:a high proportionofthe 49 neophytes recorded here arewidespread.Ofparticular conservationalconcern is Acer negundo,which forms adense understorey in willow forests ofeastern Austria,e.g.in the national park J.Walter,F.Essl,T.Englisch & M.Kiehn 16 Fig.1:woodlands in Austria (Essl et al.2002 and sup-plementary unpublished data). Donau-Auen (Drescher et al.2004).Fraxinus pennsylvanicaspreads in floodplainforests ofthe March and Danube riverseast ofVienna and outcompetes the rarenative Fraxinus angustifolia(Lazowski 1999;Drescher et al.2004).Furthermore,per-ennial tall herbs (Aster lanceolatus, Fallopiajaponica, Helianthus tuberosus, Solidago gigan-) and the annual Impatiens glanduliferaheavily invaded Austrian floodplainforests (e.g.Feráková 1994;Drescher &Prots 2000;Drescher et al.2004).Riparian areasRiparian areas (banks ofrivers,edges oflakes and ponds) are strongly affected byneophytes in Austria,containing 88 suchspecies.Several neophytes (Fallopia japonicaHelianthus tuberosus) form dense standsmostly by clonal growth.Recently,frondosamantegazzianum spread rapidly,whereasEchinocystis lobatais invading the riparianvegetation ofthe March River (Feráková1994).Several ruderal species frequentlygrow on gravel banks (e.g.ConyzacanadensisErigeron annuus).Somerare naturalized neophytes (e.g.Acoruscalamus, Mimulusguttatus, Typha laxmanniimainly occur in reeds ofstanding waterbodies.Only the riparian vegetation ofthe upper reaches ofundammed rivers inthe Alps (e.g.Lech in Tyrol) lack neophy-tes (Müller & Bürger 1990).Water vegetationAquatic habitats were invaded by 20 neo-phytes in Austria.In nutrient-poor open-water ecosystems,hardly any neophyteswere recorded.In nutrient-rich waterbodies,one invasive neophyte () occurs.There is evidence thatanother species ofthe genus (E. nuttalliiis now becoming naturalized.Certainneophytes with a restricted distributionare casuals (e.g.Azolla filiculoidesA thermal spring in Carinthia nearVillach provides a habitat for some (sub)-tropical aquatic plants (e.g.Myriophyllumaquaticum, Sagittaria latifolia, Salvinia natans,Shinnersia rivularis, Vallisneria spiralis,Hydrilla verticillata, Lagarosiphon major).Thisis the only site where frost-sensitive aqua-tic species are able to survive the harshAustrian winter.Bogs,fens and moist-soil meadowsOnly five neophytes were recorded in bogs,fens and moist-soil meadows.Euthamia gra-) grows in fensand moist meadows ofthe Rhine Delta inVorarlberg.In raised bogs and transitionbogs,only the North American Kalmiaangu-is naturalized (at one site in UpperAustria),and was found recent-ly in Salzburg and Upper Austria.Fertilized meadows and pasturesIn these nutrient-rich grasslands,32 neo-phytes were recorded,two ofthem beingLoliummultiflorumis widespreadin lowland regions and also cultivated as avaluable forage crop in fodder meadows.Veronica filiformisoccurs in nutrient-richmeadows and lawns.The invasion processofthis species started in humid areas ofAustria,but the plant has since invaded alllowlands except for the Pannonic region.Dry,semi-dry grassland and nutrient-poor meadowsThese habitats contain 32 neophytes inAustria.Especially in Pannonic easternAustria,however,dry and semi-dry grass-land is invaded by (Fig.1).Only one otherspecies (Phedimus spurius Phedimus spurius Sedum spurium])is rather widespread and naturalized. Neophytes in Austria 17 More neophytes regularly invade ruderali-zed semi-dry grassland (e.g.Erigeron annu-us, Solidago canadensisRocks and screesIn rocks and screes at high altitudes,neo-phytes are absent in Austria.In sites neigh-bouring settlements at lower altitudes,some ofthe 61 neophytes recorded occurregularly.A few taxa (e.g.cia, Cymbalaria muralis) are naturalized atmany sites,whereas a larger number (e.g.Syringa vulgaris, ThujaorientalisAntirrhinummajus, Erysimum cheiriPhedimus spurius,,Corydalis lutea]) arecasuals or locally naturalized.Alpine grasslands and dwarfshrub communitiesIn the alpine zone ofAustria,only onetaxon has been recorded as persisting forone site (3.2.Ecological effects Ofthe total 1110 neophytes recorded inAustria,17 taxa are considered to be inva-sive and another 18 species have beenclassified as potentially invasive (Table 2).These species are causing detrimentalecological effects for the conservation ofbiodiversity.Change in species composition ofvegetation types is thought to be the mostimportant effect ofplant invasions inAustria.All invasive and potentially inva-sive neophytes are reported to fulfil thiscriterion.Changes in succession patternshave been recorded for 17 invasive andpotentially invasive species.These chan-ges include the formation ofnew vegeta-tion types and altered succession velocitybecause dense stands ofneophytic tallherbs impede the regeneration oftrees(Kowarik 2003).Altered nutrient cycles were recordedfor two species.Lupinus polyphyllus(Fig.2) J.Walter,F.Essl,T.Englisch & M.Kiehn 18 Fig.2:Lupinus polyphyllusin Austria (unpublished data from Mapping theFlora ofAustriaŽ,database kept at Inst.ofBotany,Univ.ofVienna). Neophytes in Austria 19 Table 2:Habitat preferences and ecological effects ofinvasive and potentially invasive neophy-tes in Austria.+ = main occurrence;(+) = accessory occurrence;data taken from Essl &Rabitsch (2002).Invasiveness:* = invasive,° = potentially invasive;Family:Ace.= Aceraceae,Api.= Apiaceae,Ast.= Asteraceae,Bal.= Balsaminaceae,Ber.= Berberidaceae,Ela.=Elaeagnaceae,Fab.= Fabaceae,Hyd.= Hydrocharitaceae,Ole.= Oleaceae,Ona.= Onagraceae,Pin.= Pinaceae,Pol.= Polygonaceae,Ros.= Rosaceae,Sal.= Salicaceae,Sim.= Simaroubaceae.Ecological Effects:1 = changes in species composition,2) changes in succession pattern,3)changes ofnutrient cycles,4) hybridization (based on literature and field experience ofthe Acer negundo*Ace.1,2(+)+(+)*Sim.1+++Ambrosia artemisiifolia°Ast.1+Amorpha fruticosa°Fab.1,2++Asclepias syriaca°Asc.1++*Ast.1,2(+)++(+)*Ast.1,2(+)++Bidens frondosa*Ast.1+Buddleja davidii°Bud.1++(+)Duchesnea indica°Ros.1(+)+(+)Elaeagnus angustifolia°Ela.1(+)+Elodea canadensis*Hyd.1,2+Elodea nuttallii°Hyd.1,2+*Ona.1,4(+)+(+)Fallopia japonica*Pol.1,2(+)++(+)Fallopia x bohemica°Pol.1,2(+)+(+)Fallopia sachalinensis°Pol.1,2(+)+(+)Fraxinus pennsylvanica*Ole.1+Glyceria striata°Poa.1+(+)Helianthus tuberosus*Ast.1,2(+)++mantegazzianum°Api.1(+)(+)+(+)Impatiens glandulifera*Bal.1(+)++(+)Impatiens parviflora*Bal.1(+)+Lupinus polyphyllus°Fab.1,3(+)+°Ber.1+Pinus strobus°Pin.1+(+)Populus x canadensis*Sal.1,2,4(+)++Prunus serotina°Ros.1+Pseudotsuga menziesii°Pin.1,2+*Fab.1,2,3++(+)Rudbeckia laciniata*Ast.1,2(+)++°Ast.1+(+)*Ast.1,2+(+)+Solidago gigantea*Ast.1,2(+)++Syringa vulgaris°Ole.1,2++ Invasiveness Family Ecological effects Segetal,ruderal vegetation Zonal formation Flood-plain formation Riparian areas Open water habitats Bogs,fens,moist meadows Fertilized grassland Dry,nutrient-poor grassland Rocks,screes Alpine meadows,dwarfshrub vegetation Species Robiniapseudacacialive in symbiosiswith nodule bacteria.Both species there-fore severely alter nutrient cycles andincrease the productivity ofthe nutrient-poor habitats they primarily invade(Kowarik 1995;Neuhauser 2001).Hybridization events involve two inva-sive or potentially invasive neophytes.InAustria,crosses ofthe naturalized Northwith six rela-ted native species have been recordeduntil now.Populus various hybrids ofa North American () and a European (P. nigraspecies,cultivated for their fast growth(Heinze 1998a,1998b).Molecular studiesshow that up to 10% ofpoplar regenera-tion in Austria consists ofback crossesbetween P. P.nigra1998b),threatening the native poplar spe-cies (Niklfeld 1999).4.Discussion4.1 Habitat preferencesIn general,invasion success in CentralEurope seems to be associated withstrong anthropogenic or natural distur-bance regimes along with an abundantsupply ofnutrients and a warm climate(Lohmeyer & Sukopp 1992;Pyek 1998;Kowarik 1999;Pyek et al.2002a).Ourdata seem to confirm this hypothesis forAustria.Accordingly,neophytes are distri-buted unevenly in Austria.Lowlandregions and habitats centered in lowlands(riparian vegetation,floodplain forests,ruderal and segetal vegetation) are stron-gly affected by invading neophytes,whereas the vegetation ofthe montaneand alpine zone ofthe Alps (e.g.rocksand screes,alpine grasslands) harbourslow numbers ofneophytes.The habitat preferences ofneophytesin Austria show the same pattern as inneighbouring countries ofCentral Eu-rope.Most neophytes in Germany (Kühn& Klotz 2003) and the Czech Republic(Pyek et al.2002b,2003) also occur inruderal and segetal vegetation.High levelsofanthropogenic disturbance seem topromote the spread ofneophytes in thesehabitats (Kowarik 1999,2003).Humansettlements serve as focal points for plantinvasions,and there is a clear positive cor-relation between size and age oftownsand the number ofneophytes (Sukopp1976;Pyek & Pyek 1991;Pyek 1998).Floodplain forests are characterized bynatural disturbances,regularly creatingopen gravel and sand banks.Moreover,most large rivers in Austria were stronglyaltered by human disturbance (e.g.eutro-phication,damming,water management).River valleys therefore generally serve asimportant corridors for neophytes(Sukopp 1976;Kowarik 1992,1999;Mül-ler 1995,1997) and are also strongly affec-ted by neophytes in Austria.In Central Europe,riparian areas showthe highest number ofneophytes ofallnatural and semi-natural vegetation types(Lohmeyer & Sukopp 1992,2001;Pyeket al.2002b).This finding also holds truefor Austria:floodplain forests and ripari-an areas are the natural vegetation typesmost prone to invasions.Although aquatic habitats in warmerclimates are heavily invaded by neophytes(e.g.Bossard et al.2000;Cronk & Fuller2001),only few neophytes have invadedthese habitats in Austria.This finding istrue for other temperate Central Euro-pean countries as well (Pysek et al.2002b;Kühn & Klotz 2003).This may indicatethat climate strongly influences invasive-ness in aquatic habitats.In Central European dry and semi-drygrassland and nutrient-poor meadows,few neophytes were recorded (Lohmeyer& Sukopp 1992;Kowarik 2003).Although the number ofneophytes in dry J.Walter,F.Essl,T.Englisch & M.Kiehn 20 habitats in Austria is low as well,dry mea-dows and forests in Eastern Austria areheavily invaded by (Wendelberger 1955).This is similar tothe situation in adjacent Hungary,wherethis species is one ofthe most problema-tic neophytes for nature conservation(Török et al.2003).Rocks and screes ofthe montane andalpine zone,alpine grasslands and dwarfshrub communities are not colonized byneophytes.Climate change … e.g.annual mean tem-perature in Austria increased by 0.5°Csince 1980 (Lexer et al.2002),leading toprolonged growing seasons and less severewinters (Walther 2002) … may be decisivefor the rapid spread ofseveral late-flowe-ring species,which are probably limitedby climatic factors in Austria:Ambrosiaartemisiifolia,native in North America,wasa rare casual in the early decades ofthecentury but became naturalized main-ly in the lowlands ofthe Pannonic regionin the second halfofthe 20century.Several American taxa (e.g.Amaranthus hybridus, Amaranthus blitum ssp.emarginatus) are currently becoming natu-ralized in the climatically most favourablesouthern and eastern regions ofAustria(Walter & Dobe 2004).4.2 Ecological effects ofneophytesTaking country size and varying defini-tions ofthe term invasiveŽinto account,our results correspond well with datafrom other European countries:Ger-many:35 invasive neophytes (Kowarik2002);Hungary:approx.35 invasive neo-phytes (Török et al.2003).In Switzerland,11 species are classified as invasive and 16as potentially invasive (SKEW 2002).Onthe British Isles,39 species are consideredpestsŽ,11 ofwhich have severe ecologi-Several case studies demonstrate thatinvasive vascular plant species can changenative ecosystems in different ways:Competitive tall herbs (e.g.Fallopia japoni-ca, Helianthus tuberosus) in nutrient-rich,well-watered sites form dense stands,out-compete native taxa (Walser 1995;Kowarik 1999),change succession pat-terns,and form new vegetation types(Sukopp & Sukopp 1994;Hartmann &Konold 1995;Walser 1995,Wadsworth etal.2000;Bimova et al.2004).Most ofthese species show vegetative growth andare able to store nutrients in tubers or rhi-zomes in winter,allowing fast growth inthe subsequent vegetation period.Inva-sion ofthe neophytic Acer negundostands ofchanges successionpatterns and species composition infloodplain forests ofthe lowlands ofeastern Austria (Drescher et al.2004).This impedes the regeneration ofnativewillow species by creating a second tree-layer (Kunstler 1999).Invasion ofchangesdry grasslands in multiple ways:Speciesnumbers decrease,and the spatial structu-re and microclimatic situation are chan-ged by the formation ofa tree-layer (Bö-cker et al.1995;Kowarik 1995,2003;severely alters nutrient cycles and increa-ses productivity (Kowarik 1995).Densestands ofare currentlywidespread in eastern Austria (Fig.1).Thespecies also invades areas ofhigh conser-vation value,e.g.the National parksThayatal and Donau-Auen (Essl & Hau-ser 2003;Drescher et al.2004).Hybridization between native and alienspecies is one ofthe most importantaspects ofbiotic homogenisation world-wide (Vila et al.2000,Daehler & Carino2001).Ofspecial concern for nature con-servation are crosses involving neophytesand native parental taxa,especially ifthe Neophytes in Austria 21 offspring is viable and hybridizationevents are frequent (Daehler & Carino2001).In Austria,few taxa (Populus ,probably crosses ofwith native taxa) fulfil these criteria,which may have serious consequences forthe native taxa involved (e.g.Ellstrand etal.1996;Heinze 1998a;Vila et al.2000).In the neighbouring Czech Republic,crosses between native taxa ofdifferent sections weredocumented (Krahulec 1999).AcknowledgementsThe underlying study for this paper benefitedfrom contributions by more than 50 experts.As we can not cite all their (and other collea-gues) papers due to limited space,the reader isreferred to Essl & Rabitsch (2002) and Essl &Walter (2004),where all original referencescan be found.We wish to thank P.Schöns-wetter,A.Tribsch (both Institute ofBotany,University ofVienna),W.Rabitsch,M.Sta-chowitsch (both Institute ofZoology,Univer-sity ofVienna) and R.Kribala for valuablecomments on earlier drafts ofthe manuscriptand for linguistic revision ofthe paper.We arealso obliged to T.Kucher for producing thewood-lands,and to H.Niklfeld and L.Schratt-Ehrendorfer for the consent to use the distri-bution data for Lupinus polyphylluscreated bynumerous contributors to the project Map-ping the Flora ofAustriaŽ.We thank the Austrian Federal Ministry ofAgriculture,Forestry,Environment and WaterManagement and the Austrian FederalEnvironment Agency for initiating and com-missioning this study.ReferencesAdler,W.,Oswald,K.& Fischer,R.(1994):Exkursionsflora von Österreich.… Ulmer,Stuttgart-Wien,1180 pp.Bimova,K.,Mandak,B.& Kaparova,I.(2004):How does invasion fitthe various theories ofinvasibility? …Journal ofVegetation Science 15:495-Böcker,R.,Gebhardt,H.,Konold,W.&Schmidt-Fischer,S.(Eds.) 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