Invasion dynamics of three allergenic invasive Asteraceae Ambrosia

21 Pages·2013·3.29 MB·English

Preslia85:41–61,2013 41
Invasion dynamics of three allergenic invasive Asteraceae (Ambrosia
trifida,Artemisiaannua,Ivaxanthiifolia)incentralandeasternEurope
Invaznídynamikatřiallergeníchhvězdnicovitýchdruhů(Ambrosiatrifida,Artemisiaannua,Ivaxanthiifolia)
ve střední a východní Evropě
SwenFollak1, StefanDullinger2,3, IngridKleinbauer3, DietmarMoser4
& FranzEssl4
1AustrianAgencyofHealthandFoodSafety,Spargelfeldstraße191,A-1220Vienna,Austria,
e-mail:[email protected];2UniversityofVienna,Rennweg14,A-1030Vienna,Austria,
e-mail: [email protected]; 3Vienna Institute for Nature Conservation and
Analyses,Giessergasse6/7,A-1090Vienna,Austria,e-mail:[email protected];
4Environment Agency Austria, Spittelauer Lände 5, A-1090 Vienna, Austria, e-mail:
[email protected], [email protected]
FollakS.,DullingerS.,KleinbauerI.,MoserD.&EsslF.(2013):Invasiondynamicsofthreealler-
genicinvasiveAsteraceae(Ambrosiatrifida,Artemisiaannua,Ivaxanthiifolia)incentralandeast-
ern Europe. – Preslia 85: 41–61.
Weanalyzedthehistoryoftheinvasion,spreaddynamicsandhabitataffiliationofthreeallergenic
wind-pollinatedspecies(Ambrosiatrifida,Artemisiaannua,Ivaxanthiifolia;tribeHeliantheae,
Asteraceae) incentralandeasternEurope(CEE)usingdistributiondatafroma widerangeof
sources.Inaddition,weusedniche-basedensemblemodellingtechniquestoassesscurrentinvasion
riskoftheregionstudied.Wecollated1804recordsofA.annua,1063ofI.xanthiifoliaand324ofA.
trifida.Allspecieswerefirstrecordedinthe19thcentury,remainedrareuntilthemiddleofthe20th
century,buthavespreadrapidlyinrecentdecades.IvaxanthiifoliaspreadthefastestfollowedbyA.
annua.ThelatterspeciesisnowabundantinnorthernItaly,alongtheElberiverinGermanyandthe
DanubianLowlandinSlovakiaandHungary,whileI.xanthiifoliaoccursmostfrequentlyinthe
warmandcontinentalpartsofCEE.Ambrosiatrifidaspreadslowlyanditscurrentdistributioncon-
sistsofrelativelyfewandmostlyisolatedlocalitiesinCEE.AmbrosiatrifidaandI.xanthiifolia
occurprimarilyinruderalhabitats,whereasI.xanthiifoliahasalsoincreasinglyinvadedfields.Ini-
tiallyconfinedtoruderalhabitats,A.annuahasexpandeditshabitatnicheduringtheinvasionand
hasinvadedriverinevegetationand(semi-)naturalhabitats.Ensemblespecies-distributionmodels
showthatthecurrentdistributionofA.trifidaandA.annuainCEEiscloselyrelatedtotemperature
andprecipitation,whereaslanduseisonlyimportantforI.xanthiifolia.Underthecurrentclimate,
substantialfractionsofthestudyareaprovidesuitablehabitatforthesespecies:A.trifida(16%of
CEE),A.annua(28%)andI.xanthiifolia(26%).Becauseoftheirsignificantpotentialimpacton
publichealth,futurespreadofthesespeciesshouldbemonitoredandmanagementstrategies(e.g.
raising awareness, early control) should urgently be implemented.
Keywords:allergy,distribution,habitats,humanhealth,impact,invasionhistory,invasivealien
species, species distribution models, spread
Introduction
Plant invasions are a significant component of global change with far-reaching conse-
quencesforbiodiversity,landuseandhumanwell-being(Lambdonetal.2008,Vilàetal.
2011). Some alienplant species are of particular concern for human health due to their
allergenicpollen.InEurope, Ambrosia artemisiifoliaL.(common ragweed) isthemost
42 Preslia85:41–61,2013
widespread allergenic alien plant species that has attracted considerable interest from
European ecologists and immunologists (Taramarcaz et al. 2005, Dullinger et al. 2009,
Smoliketal.2010,Richteretal.2013).Recently,theannualcostoftheinvasionofthis
species in Germany was estimated to be 32 million €, which is almost entirely due to
increasedcostsinthehumanhealthsector(Reinhardtetal.2003).However,severalspe-
cieswithhighallergenicpotentialinthesamegenus(AmbrosiatrifidaL.,giantragweed)
andcloselyrelatedgenera(IvaxanthiifoliaNutt.,burweedmarshelder;Artemisiaannua
L.,annualwormwood)withinthesametribe(Heliantheae)arenotnativeinEurope.Their
invasionhasreceivedmuchlessattentionandhassofarnotbeeninvestigatedsystemati-
cally. However, evidence suggests that A. trifida, A. annua and I. xanthiifolia have
increased in abundance and range in some parts of central and eastern Europe (CEE)
(Follak2009,Medveckáetal.2012,Pyšeketal.2012).Giventhistrend,itseemslikely
thatthesespeciesmaycreatesignificantproblemsforhumanhealthinthemediumterm.
Comprehensive retrospective analyses of invasion histories provide a better under-
standingofpatternsandprocessesaffectingthespreadofaspeciesandmayprovideways
oftestinghypothesesininvasionecology.Forinstance,byanalysingspatio-temporaldis-
tributionpatternsitispossibletoassesstheimportanceofintroductionpathways,toiden-
tifyinvasionfociandwhetherthespeedandnatureoftheinvasionprocesshaschanged
overtime(Pyšek&Prach1993,Mandáketal.2004,Follak&Essl2013).Informationon
habitatpreferences andhabitatshiftsprovidesfurther dataonspreaddynamicsanddis-
persal vectors (Lavoie et al. 2007, Essl et al. 2009). Distribution and rates of spread of
invasive plants are controlled by the interplay of environmental, climaticand anthropo-
genicfactors.Inthisrespect,niche-baseddistributionmodelling(e.g.speciesdistribution
models,SDMs,Guisan&Thuiller2005,Elithetal.2006)hasbecomeanimportanttool
foridentifyingenvironmentalfactorsaffectingaspecies’distributionandforassessingthe
species’ potential range under current and potential future environmental and climatic
conditions(e.g.Thuilleretal.2005,Essletal.2009,Kleinbaueretal.2010,Gallienetal.
2012).Inaddition,aproperunderstandingofaspecies’behaviourinitsnewrangeisapre-
requisitefortheevaluationofmanagementoptionstohaltorslowdownitsfuturespread
(Richter et al. 2013).
Inthisstudy,weextracteddistributionrecordsofA.trifida,A.annuaandI.xanthiifoliain
CEEuptotheyear2011fromawiderangeofdatasourcestoanalysetheirinvasiondynam-
ics.Inparticular,weaddressthefollowingquestions:(1)Whatisthespatio-temporalpattern
intheirspread?(2)Whichhabitatsarepredominatelycolonizedanddidhabitatpreferences
changeduringtheinvasion?(3)Whichpartsoftheregionarecurrentlymostatriskofbeing
invaded?(4)Whataretheimplicationsforfuturespread,impactandmanagement?
Material and methods
Study region
Theregionstudiedisalargecontiguousareaencompassingmostoftheareaswherethe
studyspeciesarecurrentlyfoundincentralandeasternEurope.ItincludesAustria,Czech
Republic,Germany,Hungary,Slovakia,Slovenia,Switzerlandandnorthernpartsofmore
southerlycountrieslikeCroatia,Italy(i.e.theregionsAostaValley,Friuli-VeneziaGiulia,
Liguria,Lombardy,Piedmont,Trentino–AltoAdige,Veneto)andSerbia(Vojvodina,parts
Follaketal.:InvasiondynamicsofallergenicAsteraceaespecies 43
ofcentralSerbia).Theclimateismostlytemperatetosubmediterraneaninthesouthernmost
parts(northernItaly),withapronouncedgradienttowardsamorecontinentalclimatein
theeasternpartoftheregion.Lowlandsaredominatedbyagricultureandthemajorcen-
tresofpopulationarelocatedthere.Coolermountainousregionsdominatedbyforestsand
grasslandsareprominentintheAlpsandCarpathianMountains(e.g.inpartsofAustria,
Czech Republic, Slovakia, Switzerland).
Study species
Besidesbeingphylogeneticallycloselyrelated,thestudyspeciessharearangeoftraits(wind-
pollinatedherbaceousplantsofopenhabitatswithvigorousgrowth)andintroductioncharac-
teristics(e.g.accidentalintroductionintoCEE,invasionstartedinthe19thcentury).
Ambrosiatrifidaisasummerannualspecies30–150(–400)cminheight.Thisspecies
ischaracterizedbyrapidgrowthandrelativelylowseedproduction(Abul-Fatih&Bazzaz
1979a,b).AmbrosiatrifidaisanativeoftheUnitedStateswhereitoccursonriverbanks
andlakeshoresnorthoftheOhioRiver(Basset&Crompton1982).Currently,thisspecies
occursmainlyinNewEnglandandfurthersouth,theOhioandMississippiRivervalleys
and in southern Canada (Basset & Crompton 1982, FNA Editorial Committee 2006).
Artemisiaannuaisanannualspecies30–200(–250)cminheight.Ithasapioneerstrat-
egycharacterizedbyahighdegreeofmorphologicalandreproductiveplasticityandmas-
siveseedproduction(Brandes&Müller2004).ThisspeciesisanativeofEastAsia,most
probablyInnerMongoliainChina,whereitispartofthegrasslandandsteppevegetation
(Ferreira et al. 1997). Artemisia annua has become widespread in temperate regions
worldwide (FNA Editorial Committee 2006).
Ivaxanthiifoliaisalsoanannualspecies30–200(–300)cminheight.Itischaracterized
byrapidgrowthandhighseedproduction(Hunyadietal.1998,Hodi&Torma2002).Iva
xanthiifoliaisanativeoftheNorthAmericanprairies(Jackson1960)whereitoccurson
sandyandsiltyriveralluvials,inriverandstreambedsandoccasionallyasaweedinmoist
places.Thespecies’rangehasbeenincreasedbyhumanmeansandcurrentlycoverslarge
fractions of the lower United States and parts of southernmost Canada (Jackson 1960,
FNAEditorialCommittee2006).Further,ithasbeenintroducedintoEuropeandwestern
Asia (Pruski 2005).
Distribution data and data analyses
WecollectedalltherecordsofA.trifida,A.annuaandI.xanthiifoliainCEEupto2011
from a wide range of sources (Electronic Appendix 1). We searched global (Global
BiodiversityInformation Facility;http//.www.gbif.org), national(floristicmapping pro-
jects of Austria, Croatia, Czech Republic, Germany, Switzerland) and subnational
(floristic mapping projects of Trentino, South Tyrol, Bergamo, Brescia, Friuli-Venezia
Giulia)databasesandimportantnationalherbaria(BP,FR,GZU,LI,SAV,SLO,STU,W,
WU).Thesedataweresupplementedbyanexhaustivesearchoftheliteratureusingappro-
priatekeywordsinindexed(WebofScience,CABAbstracts,Agris,AGRICOLA)aswell
asinnon-indexedjournals,monographs andtheinternet.Additionally,wecontacted38
keycountryandregionalexpertsforfurtherrecords(seeAcknowledgements).Giventhe
strongtraditionoffloristicresearchincountriesofCEE,theinclusionoffloristicliterature
and unpublished data of key experts proved to be particularly important. Further, the
44 Preslia85:41–61,2013
integrationofdifferentdatasetsshouldatleastmitigatespatio-temporalvariationinthe
effort put into sampling underlying each specific source.
Wecross-checkedallrecords toavoiddouble entriesofidenticalrecords indifferent
datasources.Allrecordswereassignedtoagridcell(5×3geographicminutes,~33km2)
oftheFloristicMappingProjectofCentralEurope(=FMCE;Niklfeld1998).Thedate(=
year) of the records was extracted from the original source. If a time period of several
yearswasgiven,weusedthearithmeticmean.Todocumenttheearlyphaseoftheinva-
sion,weidentifiedandmappedthefirstthreerecordsforeachspeciesineachcountryin
CEE (Electronic Appendix 2). For each record the status of the respective population,
whetherestablishedorcasual,wasassessedeitherbytheobserverorbyusinginformation
intheoriginaldatasource.Ourpost-hocclassificationwasmainlybasedonthesizeofthe
population,usingathresholdof100reproductiveindividuals.Smallerpopulationswere
only classifiedasestablishedif atleasttwo records in consecutiveyears were reported.
Populations that observers had not explicitly rated as either established or casual and
which we could not classify unambiguously based on the information in the original
sourcewerealsoclassifiedascasual.DataonthetypesofhabitatscolonizedinCEEwere
extractedfromoriginaldatasourcesandwereassignedtothefollowingcategories:ruderal
habitats,ruderalhabitatsassociatedwithtransportinfrastructurelikeroadsandrailways,
riverinevegetation,fieldsand(semi-)naturalhabitats(incl.urbanparksandgardens,wood
edges,drygrassland).WeanalyzedtheinvasionofthethreespeciesovertimeinCEEand
of the different habitats. We constructed invasion curves by calculating the cumulative
numberofrecordsplottedagainsttime(sensuPyšek&Prach1993).Tocomparetherate
of spread of the three species the regression slopes b of the cumulative number of all
records over time were tested for the period 1950 to 2011, i.e. the beginning of rapid
spreadofeachspecies.Thedatawasanalyzedusingagenerallinearmodelwithspeciesas
afactorandyearasacovariate(Mandáketal.2004).Statisticalanalyseswereperformed
using IBM® SPSS® Version 20.
Species distribution models
Spatially explicit data on climatic conditions (selected bioclimatic variables from
WorldClim,http://www.worldclim.org/bioclim),majorinfrastructure(highways)andnat-
ural(rivers)networks,whichrepresentpotentialinvasioncorridors,andlandusewerecol-
lectedfromvarioussources(Table1).AllGISdatawerepre-processedtomatchthereso-
lutionoftherasteroftheFMCE,i.e.aggregationbymeansofaveraging(topographical
data)orsummarizing(streetandriverlength).ForcalibratingtheSDMs,recordsofthe
species studied were partitioned into those of established and casual populations
(Dullingeretal.2009,Essletal.2009).Thiswasmotivatedbytheassumptionthatthedis-
tributionofestablishedpopulationsismorelikelytoreflectthehabitatrequirementsofthe
species(Richardsonetal.2000).Indeed,modelsthatonlyincludeestablishedpopulations
are more accurate than those that include all the records (Dullinger et al. 2009).
We used SDMs (Guisan & Zimmermann 2000) to identify the factors governing the
currentdistributionofthespeciesstudied.Theproliferationofstatisticalmodellingtools
hasledtotheavailabilityofvariousmethods,eachwithstrengthsandcaveats(Elithetal.
2006). Hence, the use of several modelling techniques (ensemble forecasts) is recom-
mended(Araújo&New2007).WeusedtheBIOMOD-frameworkimplementedintheR
Follaketal.:InvasiondynamicsofallergenicAsteraceaespecies 45
Table1.–EnvironmentalvariablesusedtocalibratethedistributionmodelsofAmbrosiatrifida,Artemisiaannua
andIva xanthifoliiain central and eastern Europe.
Category Variable Source Original scale
Land use Proportional area of human CORINE Land cover map with min. 25 ha
settlementsandagriculturalfields polygons
Highway Length of major streets Tele Atlas N. V. (© 2005) –
River Length of major rivers Various sources –
Temperature Temperature seasonality(BIO4), WorldClim(www.worldclim.org) 2.5 × 2–5 arc minutes
minimumtemperatureofcoldest (Hijmans et al. 2005)
month(BIO6),meansummer
temperature (BIO10)
Precipitation Precipitation seasonality Selected bioclimatic variables 2.5 × 2–5 arc minutes
(BIO15), mean summer from WorldClim
precipitation (BIO18) (www.worldclim.org)
(Hijmans et al. 2005)
software(RDevelopmentCoreTeam2012)forfittingSDMs.BIOMODallowscombina-
tionsofseveralmodellingtechniquesinanensembleforecast(Thuilleretal.2009).Here,
we used a combination that included generalized linear models (GLM, McCullagh &
Nelder1989),generalizedboostingmodels(GBM,Friedman2001),generalizedadditive
models (GAM, Hastie & Tibshirani 1990) and multiple adaptive regression splines
(MARS, Friedman 1991). Different models were evaluated separately and combined in
theensembleforecastusingaweightedapproachthatranksthemodelsusingtheirevalua-
tionscore,i.e.modelswithbetterevaluationstatisticswereregardedasmorereliableand
got higher weights intheensemble procedure (Thuiller etal.2009). Weused arandom
subset(70%)ofthedistributiondataforfittingthemodelsandtheremaindertoevaluate
themodels.Moreover,pseudo-absenceswerecreatedusingarandomsampleof1000data
pointsinasquaredneighbourhoodaroundthepresences.Weusedtheaverageof10repeti-
tionsofeachmodel.IntheGLMs,weusedordinarypolynominaltermsandintheGAMs
thedegreesoffreedomweresettothree.InGBMsweusedamaximumof3000trees.We
performedatenfoldcross-validationusingtheareaunderthecurve(AUC)ofareceiver-
operating characteristiccurvefor modelaccuracyevaluation.AUCisacompositemea-
sureofmodelperformance,withvaluesrangingfrom0to1,where1isaperfectfit.Useful
modelsproduce AUCvaluesof 0.7–0.9, and modelswith“good discriminatingability”
produce AUC values > 0.9 (Swets 1998).
Followingtherecommendations ofLiuetal.(2005), prevalence(=ratioofoccupied
grid cellsvs totalnumber of grid cells)waschosen asathreshold for presence/absence
predictions. Projected occurrence probabilities were transformed into presence/absence
predictionspergridcell,basedonthethresholdthatmaximizesmodelaccuracy.Toassess
theimportanceofvariablesinexplainingthecurrentdistributionofastudyspeciesandto
assure comparability among models, BIOMOD provides a permutation procedure to
extractameasureofrelativeimportanceforeachpredictorvariablethatisindependentof
the model. High values imply high importance of the predictor variable (Thuiller et al.
2009).
46 Preslia85:41–61,2013
Results
Introduction and invasion history
Intotal,wecollated324recordsofA.trifidainCEE(Fig.1A,ElectronicAppendix3).The
firstrecordsarefor1877(Hamburg,Germany),1899(Atzwang,SouthTyrol)and1900
(Basel,Switzerland).IntheothercountriesA.trifidawasfirstrecordedsubstantiallylater.
First record for Austria is 1948 (Graz), the Czech Republic 1960 (Brno) and Slovakia
1980(ČiernanadTisou).InSerbia,A.trifidawasfirstfoundin1982atVojvodina(Čoka)
andinthelate1980sinSlovenia.TherearecurrentlynorecordsforHungaryandCroatia.
Intotal,wecollected1804recordsofA.annuainCEE(Fig.1B,ElectronicAppendix
3). The presence of Artemisia annua was noted in Rochel’s “Plantae Banatus rariores,
iconibus et descriptionibus illustratae” published in 1828, but no definite records were
provided. Firsttangiblerecords arefor 1852 (StaraGradiška, Croatia)and 1871 (Bački
Petrovac,Serbia).Subsequently,thespecieswasfirstrecordedinAustria(1867,Vienna)
and Switzerland (1871, Zurich), followed by Germany (1882, Wandersleben), Hungary
(1882,Budapest),theCzechRepublic(1891,Znojmo)andSlovakia(1916,Komárno).In
the south-western CEE, A. annua was intentionally introduced as an ornamental and
medicinalplantinthe18thcentury.Thus,thisspeciesmighthavealreadyescapedbefore
thefirstrecords.InnorthernItaly,thefirstrecordofA.annuawasfor1909(Bozen,South
Tyrol) and for Slovenia it was 1928 (Ljubljana).
Thereareatotalof1063recordsofI.xanthiifoliainCEE(Fig.1C,ElectronicAppen-
dix3).ThisspecieswasrecordedforthefirsttimeinGermanynearabotanicalgardenin
1858(Potsdam).Intheothercountriesitwasrecordedsubstantiallylater.Thefirstrecord
A
Follaketal.:InvasiondynamicsofallergenicAsteraceaespecies 47
B
C
Fig.1.–DistributionofAmbrosiatrifida(A),Artemisiaannua(B)andIvaxanthiifolia(C)incentralandeastern
EuropebasedonthegridoftheFloristicMappingofCentralEurope(cellsize:5×3geographicminutes,~33km2).
The earliest three records for each country (in their contemporary borders) are in red.
48 Preslia85:41–61,2013
for Switzerland was 1902 (Basel). In Slovakia, this species was first collected in 1934
(Šurany&Čiky),inAustriain1942(Vienna),theCzechRepublicin1948(Prague),Hun-
gary in 1950 (Mezőhegyes), Serbia in 1966 (Novi Sad) and Slovenia as late as 1970
(Škofije). The most recent first national record was for 1976 in Croatia (Đurđancima).
Distribution
AmbrosiatrifidaisrecordedatmarkedlyfewerlocalitiesthanA.annuaandI.xanthiifolia
(Fig.1A).ItismostwidespreadinnorthernpartsofCEE,inparticularGermany,Switzer-
landandtheCzechRepublic,whereitismainlyrecordedinlargecitiesalongtherivers
RhineandElbe(i.e.Basel,Dresden,Hamburg,MannheimRuhr;Fig.1A).Therearecur-
rentlyafewestablishedpopulations,e.g.inSerbia(SouthBačkadistrict,Vojvodina),Italy
(Pavia, Lombardy) and the Czech Republic (Kolín district).
Artemisiaannuaispresentinallthecountriesoftheregionstudied,butthedistributionis
veryunevenwithseveralregionswhereitisveryabundant(Fig.1B).Theinvasionhotspots
are mostly associated with large river valleys. In Germany, the species forms extensive
standsalongtheriversElbeandSaale,andinSlovakiaandHungaryitiswidespreadalong
theDanuberiver.Artemisiaannuaisalsocommonontheplainsandinrivervalleysofnorth-
ernItaly,inparticularintheregionsLombardy,PiedmontandTrentino–AltoAdige.How-
ever,thisspeciesisrareorabsentalongtheAustrianandGermansectionoftheDanuberiver
andotherriverssystems(i.e.Oder,Tisza,Rhine).Populationscanbefoundinlargecities
and their vicinities in the Czech Republic (Olomouc, Prague), Germany (Ruhr, Berlin,
Erfurt),Hungary(Budapest)andnorthernItaly(e.g.Torino),buttherearefewrecordsfor
therestofCEE(westernGermany,Hungary,northernSerbia,Croatia).
Ivaxanthiifoliaismostwidespreadinwarmcontinentallowlandsintheeasternpartof
theregionstudied(Fig.1C).Here,I.xanthiifoliahasspreadfrompointsofintroduction
into the Danubian Lowland and the Pannonian Basin. Invasion hotspots are in southern
and eastern Slovakia (districts Bratislava, Nitra, Košice), northern Serbia (Vojvodina),
south-eastern Hungary (counties Csongrád and Békés), the easternmost part of Austria
(Burgenland, Lower Austria) and eastern Germany (e.g. Dresden Basin). Throughout
mostoftheotherpartsofCEE,I.xanthiifoliaisuncommonexceptforsomelargecities
andareasalongtheriversRhine(Ruhr,Mainz,andMannheim)andElbe(Hamburg).In
mountainousregionsintheAlps(Switzerland,westernAustria)andCarpathiansthethree
species studied are rare to absent.
Spread dynamics
ThecumulativenumberofrecordsofA.trifida,A.annuaandI.xanthiifoliahasincreased
overtimesincetheirintroductionintoCEE(Fig.2).TherateofspreadofA.trifidawas
moderate. The number of records peaked in the periods 1951–1970 (104 records) and
1971–1990(98records)andthereafterdecreasedstronglyto33records.Thefirstestab-
lishedpopulationwasrecordedattheendofthe19thcenturyinGermany.Sincethen,the
percentageofestablishedpopulationshasnotincreased(Fig.2A).Casualpopulationspre-
vail, whereas only 27% of all records are currently classified as established (A. annua:
58%;I.xanthiifolia:35%).ForA.annua,therewasaconstantbutslowincreaseofrecords
fromthe1890suptothe1970s.Thentherewasamarkedincreaseinthenumberofrecords
andrateofspreadbecameparticularlypronouncedafter1995whenthenumberofrecords
Follaketal.:InvasiondynamicsofallergenicAsteraceaespecies 49
Fig.2.–Curvesofthecolonization(i.e.cumulativenumberofrecords)byAmbrosiatrifida(A),Artemisiaannua
(B)andIvaxanthiifolia(C)ofcentralandeasternEurope.Sumofallrecords(solidline)andrecordsofcasual
(dashed line) and established populations (dotted line) are shown.
50 Preslia85:41–61,2013
morethandoubledfrom872(1995)to1804(2011)(Fig.2B).Themajorityoftheearly
recordsofA.annuawereforpopulationscategorizedasofcasualstatus,butthepercent-
ageofestablishedpopulationsincreasedafter1960.Recently,thenumberofestablished
populationshasincreasedmuchfasterthanthatofcasualpopulations(Fig.2B).Ourdata
indicateadistinctlagphaseforI.xanthiifolia,sincerecordswerescarceuntil1950,but
havesharplyincreasedsincethen(>80%ofalltherecordsareforafter1950)(Fig.2C).
Thefirstestablishedpopulationwasrecordedinthemid-1920s,nearly50yearsafterthe
firstrecordofacasualpopulation.Sincethencasualpopulationshaveoutnumberedestab-
lished ones, but from 1991–2011 the number of established populations have doubled
whereasthatofcasualpopulationsincreasedbylessthanoneandahalf.Thecumulative
number of all records over time for each species was best fitted by linear models that
explained93%ofthevariance(F=527.647,df=5;P<0.001).Theslopesforthedifferent
speciesdifferedsignificantly(F=82.945,df=2,P<0.05).Therateofspread(expressed
astheregressionslopeb)duringtheperiod1950to2011(i.e.thebeginningoftherapid
spreadofeachspecies)washighestforI.xanthiifolia(b=0.0245)followedbyA.annua
(b = 0.0145) andA. trifida(b = 0.0095).
Habitat preference
Ambrosiatrifidaoccursonlyinalimitedrangeofhabitats(Table2,Fig.3).Thisspeciespri-
marilycolonizesruderalhabitatsasofthetotalnumberofrecordsmorethantwo-thirdsare
forthishabitat.Recordsinruderalhabitatsassociatedwithrailwayareasincreasedmarkedly
since the 1950s and peaked in the 1990s. Less than 10% of all records for which habitat
informationisavailablewerefornon-ruderalhabitats(i.e.fields,riverinevegetation).
Incontrast,A.annuahasabroaderhabitatniche(Table2,Fig.3).Itregularlyoccursin
ruderalhabitatsassociatedwithtransportinfrastructurelikeroadsandrailways.Sincethe
1990s,andespeciallyinthelastfewyears,recordsforthesetwohabitatsgreatlyincreased
andbecamedominant.Moreover,A.annuaisnowatypicalelementoftheriverinevegeta-
tion of several river systems in CEE (Table 2, Fig. 3), which has led Burkart (2001) to
denote this species ‘a river corridor plant’. Indeed, almost one fifth of all records were
associatedwithriverinevegetation,mostlythatoftheriversElbe,Danube,Adigeandto
a lesser extent the Sava and Drava. Whereas A. annua rarely occurs in fields, there are
severalrecordsin(semi-)naturalhabitats.Earlyrecordsareforurbanparksandgardens,
whichindicateitmostlikelyescapedfromcultivation.Since1990,ithasbeenrecordedin
woodlands, shrubberies and semi-dry grasslands. Such records are mainly for northern
Italy.
Table2.–HabitatpreferencesofAmbrosiatrifida,ArtemisiaannuaandIvaxanthiifoliaincentralandeastern
Europe.Givenarethenumberofrecordsforwhichhabitatinformationwasavailableandthepercentageofoccur-
rences per habitat. See text for information on the different habitats.
Species Roads Railway Ruderal Riverine Fields (Semi-)natu-
habitats vegetation ral habitats
no. % no. % no. % no. % no. % no. %
A. trifida(n = 144) – – 33 22.9 93 64.6 14 9.7 4 2.7 – –
A. annua(n = 1152) 292 25.4 78 6.8 452 25.4 220 19.1 24 2.1 86 7.4
I. xanthiifolia(n = 555) 45 8.1 96 17.3 349 62.9 9 1.6 56 10.1 – –