Ambrosia artemisiifolia in the Czech Republic

16 Pages·2017·1.47 MB·English

Preslia89:1–16,2017 1
AmbrosiaartemisiifoliaintheCzechRepublic:historyofinvasion,
currentdistributionandpredictionoffuturespread
AmbrosiaartemisiifoliavČeskérepublice–historieinvaze,současnérozšířeníapredikcedalšíhošíření
Hana Skálová1,Wen-Yong Guo1,Jan Wild1,2&Petr Pyšek1,3
1Institute of Botany, The Czech Academy of Sciences, Zámek 1, CZ-252 43 Průhonice,
Czech Republic, e-mail: [email protected], [email protected], jan.wild@
ibot.cas.cz,[email protected];2FacultyofEnvironmentalSciences,CzechUniversityof
Life Sciences Prague, Kamýcká 129, Praha 6 – Suchdol, CZ-165 21, Czech Republic;
3DepartmentofEcology,FacultyofScience,CharlesUniversity,Viničná7,CZ-12844
Prague,CzechRepublic
SkálováH.,GuoW.-Y.,WildJ.&PyšekP.(2017):AmbrosiaartemisiifoliaintheCzechRepub-
lic:historyofinvasion,currentdistributionandpredictionoffuturespread.–Preslia89:1–16.
WeanalysethedynamicsofinvasionofAmbrosiaartemisiifolia(commonragweed),oneofthe
mostnoxiousinvasivespeciesinEuropewithagreatimpactonhumanhealth.Weinvestigatethe
habitatsandfactorsthatshapeitscurrentdistributionandspecifyareasintheCzechRepublic
endangeredbythefurtherspreadofthisspecies.Theanalysisisbasedonatotalof281recordsin
164gridcells,recordedupto2016,ofwhich37harbournaturalizedpopulationsand127casual
populations.Themajorityofrecords(49%)wasfromrailwaycorridors,followedbyhumanset-
tlements(11%),andtherewasarecentincreaseinrecordsfromroadsides.Aconditionalinfer-
encetreerevealedfactorsshapingthespeciesdistributionwiththeeffectoftheproportionalarea
ofindustrial,commercialandtransportunitsasthemostimportant,highlysignificantvariable,
further fine-tuned by factors related to human-related dispersal and climate, such as density
of railway network and temperature, respectively. The prediction model indicated that many
suitablegridcellsareunoccupied.Manyofthesegridcellsareintheproximityofcurrentlyoccu-
piedonesbuttherearealsosomecellsratherfarfromcurrentpopulations.Furtherspreadof
A.artemisiifoliaintheCzechRepublicisthushighlyprobable.
Keywords:commonragweed,CzechRepublic,environmentalfactors,plantinvasion,pre-
dictedspread,speciesdistributionmodelling(SDM)
Introduction
Predictingthefuturedistributionofalienplantsandtherolethatspecificpathwaysand
drivers are likely to play in this process in the context of the ongoing global climate
changeareamongthehighestprioritiesofinvasionbiologistsandmanagers(e.g.Thuiller
etal.2005,Gallienetal.2010,Essletal.2015a,Udenetal.2015).Understandingthe
drivers that influence the spatiotemporal patterns in plant invasions is a crucial step in
limitingtheirspreadandminimizingtheirnegativeimpact(Eweletal.1999,Sakaietal.
2001, Pyšek & Hulme 2005). This is especially true for rapidly spreading species that
haveagreatimpactonnativebiodiversityandhumanhealth(Pyšek&Richardson2010,
Essletal.2015b,Pergletal.2016).However,therelativeinfluenceofindividualdrivers,
suchashuman-mediateddisturbanceandchangingclimate,isunknownformostinvasive
doi:10.23855/preslia.2017.001
2 Preslia89:1–16,2017
plantsandhencelimitstheeffectivenessofriskassessmentsandadaptivemanagement
(Udenetal.2015).
Ambrosia artemisiifolia L. (common ragweed) is an annual herbaceous plant that
originatesfromNorthAmericaandisoneofthemostnoxiousinvasivespeciesinEurope
(Lambdonetal.2008,DAISIE2009)mainlybecauseitproduceslargequantitiesofaller-
genicpollen(Kazinczietal.2008)andcausesupto80%lossintheyieldofcertaincrops
(Essletal.2015b).Itisstronglyself-incompatiblewithhighoutcrossingrates(seeEsslet
al.2015bandthereferencesherein).Thespeciesonlyreproducesbyseed,withanaver-
ageof1213seedsperplantreportedfortheCzechRepublic(Moravcováetal.2010),and
between18,000and48,000(withanextremevalueof94,900)forHungary(Essletal.
2015b).Mostseedfallswithin1mofthemotherplant(Essletal.2015b).Seeddispersal
bymammalsandbirdsisreportedinitsnativerange(Rosasetal.2008),butthereislittle
evidenceofseeddispersalbyanimalsinEurope(Bullocketal.2012).Dispersalofseeds
bywaterisuncommon(Fumanaletal.2007).Thelong-distanceseeddispersalisprimar-
ilythroughhumanactivities;eitherdirectlybythetransportofcontaminatedlitterorsoil,
orindirectlyasacontaminantofagriculturalproducts(e.g.cropsandbirdfeed)oragri-
culturalandconstructionmachinerythatistheninadvertentlydistributedalongtransport
corridors (see Bullock et al. 2012 and the references herein). Ambrosia artemisiifolia
formsapersistentseedbankinsoilandisabletogerminateafter40years(Darlington
1922). Seed dormancy is broken by low (winter) temperatures under wet conditions
(Willemsen1975,Baskin&Baskin1987,Fumanaletal.2006).
Ambrosia artemisiifolia was originally introduced into Europe in the 18th century
through botanical gardens (DAISIE 2009, Bullock et al. 2012), and then repeatedly as
acontaminantofagriculturalproductsfromNorthAmerica(Brandes&Nitzsche2006,
Chauveletal.2006).ThespeciesbegantospreadandnaturalizewithinEuropefromthe
1930s, these processes accelerated from the 1960s and since the 1990s there has been
arapidspreadandincreaseinabundanceoflocalinvasivepopulations(Essletal.2015b).
Thelargest,recently-recordedEuropeanpopulationsareonthePannonianPlainsofHun-
garyandinCroatia,SerbiaandUkraine(Essletal.2015b).InRussia,naturalizedpopula-
tionsarerecordedin10regionsintheGloNAFglobaldatabaseofnaturalizedalienfloras
(van Kleunen et al. 2015), ranging from the western part of the country eastwards to
Khabarovsk.Aconsiderableincreaseinabundanceisalsorecordedinsouthernandcen-
tral France, in particular along the Rhône valley and on the plains of northern Italy
(Chauveletal.2006,Essletal.2015b).ItispredictedthatitwillspreadfurtherinEurope,
favoured by ongoing global warming; the species is assumed to benefit from warmer
summersandabsenceoflateautumnfrosts(Cunzeetal.2013,Richteretal.2013a,Chap-
manetal.2014,Storkeyetal.2014,Leiblein-Wildetal.2016).Incontrast,someregions,
especially in the south, are predicted to become unsuitable due to the increase in the
incidenceofsummerdroughtsandtemperature(Jacobetal.2013).
Aslocalscalevariationinsoilcharacteristicsandanthropogenicfactorsarethoughtto
interact with the effect of climate change on the distributions of plant species
(Stratonovitchetal.2012,Guoetal.2013),notonlyclimateneedstobetakenintoaccount
whenpredictingthefuturespreadofA.artemisiifolia.However,factorsotherthanclimate
areinvestigatedonlyoccasionallyandoveralimitedareainanalysesofA.artemisiifolia
distribution.Besidesclimaticfactors,landscapevariablesexplainthecurrentdistribution
Skálováetal.:AmbrosiaartemisiifoliaintheCzechRepublic 3
ofA.artemisiifoliainAustria(Essletal.2009)andsoilcharacteristics,positionwithin
afieldandcroptypeandcoverinarablefieldsinHungary(Pinkeetal.2011,2013).
ToextendtheknowledgeabouttheoccurrenceanddistributionofA.artemisiifoliain
Europe,anddemonstratethatsuchinformationcanbeusedtopredictfuturetrends,we
analyserecordsfromtheCzechRepublic.Inthiscountrythespecieswasfirstreportedin
1883(seePyšeketal.2012a,b),withearlyrecordsoriginatingfromagriculturalfieldsin
thesouthernandwesternpartofthecountrywhereitwasprobablyintroducedwithcon-
taminated seeds. The first record from Moravia, the eastern part of the country, was
reported in 1948. The species was sometimes cultivated in botanical gardens (Jehlík
1998).Thenumberofrecords(seePyšeketal.2012aforadetailedaccountofthesitua-
tionintheCzechRepublic)hasbeenrapidlyincreasingsincethesecondhalfofthe20th
century(Williamsonetal.2005).However,thefactorsthathavefacilitateditsinvasionin
theCzechRepublicareunknownandneedtobeunderstoodiffuturerisksaretobeiden-
tifiedandeffectivemanagementstrategiesdevelopedtoreducethespreadandimpactof
thisspecies.
Inthispaperweaddressthefollowingquestions:(i)Whatwerethepathwaysofinva-
sion by A. artemisiifolia in the Czech Republic and do the invasion dynamics of this
speciesdifferindifferenthabitats?(ii)Whatistheproportionofsiteswithcasualversus
naturalizedpopulations,andunderwhatconditionsaretheformerlikelytoprogressinto
the latter? (iii) Which climatic and landscape factors shape the current distribution
of this species? (iv) Which parts of the Czech Republic are likely to be colonized by
A.artemisiifoliainthefuture?
Materialsandmethods
Studyarea
TheCzechRepublic,acentral-Europeancountrywithanareaof78,864km2andpopula-
tionof10.6million,ispronetoinvasionsbyplantsduetoitspositiononthecrossroadsof
manynaturalandhuman-createdmigrationroutes,whichprovidedispersalopportunities
andpathways.Inaddition,aheterogeneouslandscapeandlonghistoryofhumaninflu-
enceprovidesavarietyofdisturbedsitesthataresuitableforestablishmentofalienplants
(seePyšeketal.2012afordetails).Thesefeatures,togetherwithastrongbotanicaltradi-
tion,makethecountryasuitablemodelforstudyingandpredictingregionalpatternsin
plantinvasions(Pyšeketal.2002,2012a,b,Chytrýetal.2005,2009).
Datacollection
Botanicalrecords of A. artemisiifolia in theCzech Republicup to July 2016 werecol-
lected from various sources: Czech National Phytosociological Database (Chytrý &
Rafajová2003);SpeciesOccurrenceDatabaseheldbytheNatureConservationAgency
oftheCzechRepublic(http://www.ochranaprirody.cz);adatabaseofthedistributionof
vascular plants in the Czech Republic (FLDOK, Štepánek unpubl.); public and private
herbaria;otherliteraturesourcesandunpublishedrecords(e.g.Williamsonetal.2005).
Therecords(281intotal)were,basedontheirlocation,assignedtoninetypesofhabitat:
arablefields;countryside(unmanagedsitesinopenlandscapewherethespeciesoccurs,
4 Preslia89:1–16,2017
suchaspondsandriverbanks,pedestrianpaths,seminaturalgrasslands);industrialareas;
otheragriculturalareas;railways;riverharbours;roads;settlements;andothers)andto5'
× 3' grid cells (longitude × latitude, ~32 km2 at 50° northern latitude) of KFME
(KartierungderFloraMitteleuropasof2551cellsfortheCzechRepublic;Schönfelder
1999).Cellswerefurthercategorizedaccordingtothestageintheinvasionprocessthat
bestrepresentedtheA.artemisiifoliarecord(s)(Richardsonetal.2000,Blackburnetal.
2011): (i) naturalized, for grid cells with a population of more than 50 individuals or
recordsforatleast5yearsoratleast5sites,orrecordsfor3–4yearsand3–4sites,(ii)
casual,forgridcellsthatdidnotmeettheabovecriteria,orthepopulationsizeandother
details are unknown, (iii) absence. Each cell was characterized by climatic data and
anthropogenicvariablessuchasdensityoftransportcorridorsandlanduse(Electronic
Appendix1).
Dataanalysis
Analysis of covariance (ANCOVA) was used to test the difference in the cumulative
numberofA.artemisiifoliarecordsforparticularhabitats,withyearasacovariate.The
datawaslog-transformedtomeettheassumptionsoftheanalysisandthemodelswere
furthercheckedandconfirmedbydiagnosticplots.
Decision tree models, which are also known as classification and regression trees
(Breimanetal.1984,De’ath&Fabricius2000),wereusedtoidentifythemostimportant
predictorsforthepresenceofA.artemisiifoliainindividual5'×3'gridcellswithinthe
CzechRepublic.Asanon-parametricstatisticalmethod,decisiontreemodelscanhandle
datawithanon-normaldistribution,mixedtypesofdataandnon-linearrelationships,and
theresultsfromthemodelsareeasytointerpret(Breimanetal.1984,De’ath&Fabricius
2000, Pinke et al. 2011). To compensate for the overfitting of traditional decision tree
models,theconditionalinferencetreeimplementsapermutationtestateachsplittosta-
tisticallydeterminewhenthemodelshouldstop(Hothornetal.2006,Strobletal.2009).
Theconditionalinferencetreewasconstructedwiththectreefunctioninthepartypack-
age(Strobletal.2009)inR(version3.2.5,RCoreTeam2016).
Speciesdistributionmodelling(SDM)wasusedtoassessthelikelihoodofA.artemisii-
foliaoccurringintheCzechRepublicundercurrentconditions.SDMsdevelopstatistical
connections between known presence of the species and environmental variables, and
they can then map the connections to geographical space (Elith & Leathwick 2009).
SDMsarefrequentlyusedinpredictinghotspotsofrareandendangeredspeciesandthe
potentialspreadofinvasivespecies(Thuilleretal.2005).Gridcellsharbouringpopula-
tionsclassifiedascasualand/ornaturalizedwerecountedaspresence.Weusedpseudo-
absencedatarandomlyselectedfromallabsencegridcells.Twopseudo-absencedatasets
with200absencesforeachdatasetweregenerated.Weusedanensemblemethodtoover-
comethevariabilityinSDMmodelsandmaximizetheusefulnessofthemultiplemodels
(Araújo & New 2007). Seven modelling algorithms were used in the ensemble proce-
dure: artificial neutral network (ANN), classification tree analysis (CTA), generalized
boostingmodel(GBM),generalizedlinearmodel(GLM),maximumentropy(Maxent),
multipleadaptiveregressionsplines(MARS)andrandomforest(RF).Allmodelswere
calibrated via 10-fold cross-validation by randomly splitting the data into two subsets:
trainingdata(70%)andtestdata(30%).Thedefaultsettingsofeachmodelwereused.
Skálováetal.:AmbrosiaartemisiifoliaintheCzechRepublic 5
Two evaluate measures, TSS (Allouche et al. 2006) and AUC (Fielding & Bell 1997,
Phillips & Dudík 2008), were calculated. Models with TSS greater than 0.5 and ROC
largerthan0.8wereincludedintheensemblemodels(Alloucheetal.2006,Phillips&
Dudík 2008, Thuiller et al. 2009). All SDMs and ensemble models were constructed
usingtheBIOMOD2package(Thuilleretal.2009,2012)inR(RCoreTeam2016).The
suitablehabitatmapswerepresentedinArcGIS10.3(EnvironmentalSystemsResearch
Institute,Redlands,CA).
Results
Totalnumberofrecordsandfrequencyindifferenthabitats
ThefirsttworecordsofA.artemisiifoliaintheCzechRepublic(bothin1883)werefol-
lowedbyalagphase.Itwasnotuntilthe1950sthatarathersharpincreaseinthenumber
ofrecordsandoccupiedgridcellsoccurred(Fig.1).Thefirstgridcellwithanaturalized
populationwasrecordedin1962,andthenumberofsuchgridsincreaseddramatically
after2005.Upto2016therewereatotalof281recordsin164gridcells.Ofthesegrid
cells,37harbourednaturalizedpopulationsand127harbouredcasualpopulations.
Despitethefirstrecordscomingfromarablefields,thenumberofrecordsinthistype
ofhabitatincreasedratherslowly(Fig.2).Abouthalfoftherecordsarefromrailwaycor-
ridors, both historically and currently (49% of all records). Human settlements are the
secondmostfrequentlycolonizedhabitat(11%ofallrecords).Anothertrendisthevery
recentincreaseinthecumulativenumberofrecordsfromroadsides(Fig.2).However,
theregressionslopesofthecumulativerecordsbyyearforrailwaycorridors,settlements
androadsidesdonotdiffersignificantly(ElectronicAppendix2),indicatingthattherate
ofspreadofA.artemisiifoliaovertimeinthesehabitatswassimilar.
300
250
er
mb 200
u
n
e
v 150
ati
ul
m
u 100
C
50
0
1875 1900 1925 1950 1975 2000 2025
Year
(cid:2) (cid:2)(cid:3) (cid:3)
Fig.1.–Cumulativenumberof records, occupiedgridcellsand gridcellswithnaturalizedpopulations
(i.e.withpopulationsofmorethan50individualsorrecordsfor5ormoreyears;orrecordsfrom5sitesormore
withinthecell;orrecordsfrom3–4yearsandfrom3–4siteswithinacell)ofAmbrosiaartemisiifoliainthe
CzechRepublicsincethefirstrecordupto2016.
6 Preslia89:1–16,2017
140
Industrialareas
Agriculturalareas
Countryside
120
Roads
Fields
Riverharbours
s 100 Railway
d
r Settlements
o
c
e
r
of 80
er
b
m
u
n 60
e
v
ati
ul
m
u 40
C
20
0
1875 1900 1925 1950 1975 2000 2025
Year
Fig. 2. – Cumulative number of records of Ambrosia artemisiifolia from particular habitats in the Czech
Republicupto2016.
FactorsshapingthedistributionofAmbrosiaartemisiifolia
Aconditionalinferencetreeidentifiedtheproportionofindustrial,commercialandtrans-
port areas within cells as the strongest predictor of A. artemisiifolia presence (Fig. 3,
Electronic Appendix 3). Ambrosia artemisiifolia is highly likely to be present in grid
cellswithmorethan3.1%oftheirareacoveredbythistypeofhabitat.Thepatternisfine-
tunedbytherelativeinfluenceofothercovariates;regardlessoftheproportionofindus-
trial,commercialandtransportareas,gridcellswithahighdensityofrailwaynetworkare
more likely to harbour A. artemisiifolia populations than those with fewer railways.
Anotherimportantinfluenceonwhetherpopulationsremainascasualorbecomenatural-
izedistheannualtemperature.Populationsingridcellswithameanannualtemperature
above9.4°Canddenserailwaynetworks,ormeantemperaturesabove9.1°Candmoder-
atelydenserailnetworksinareaswithlessthan30%ofagriculturallandscapes,arelikely
tobecomenaturalized.Populationsingridcellsbelowthesethresholdsarelikelytobe
casualoccurrence(s)(Fig.3).
Withingridcellswheretheproportionalareaofindustrial,commercialandtransport
unitsarebelow3.1%andtherailwaynetworkissparse,thereisanextremelylowproba-
bility of the occurrence of Ambrosia if the total length of water streams and January
Skálováetal.:AmbrosiaartemisiifoliaintheCzechRepublic 7
novalssplitthegridni-correctedsignifi-occurrence,andthe
ablesinferrooryof
hevarimaBoncategnodes.
misiifoliaintheCzechRepublic,identifiedusingaconditionalinterferencetree.T1–casualoccurrence;and2–naturalizedpopulations).P-valueswerederivedfrochterminalnode.Theyaxisistheprobabilityofagridcellbelongingtothegiveindividualoccurrencecategories.Thenumbersinsquaresindicatetheorderof
artence;ateanthe
–AmbrosiaFig.3.Factorsshapingthedistributionofcellswithdifferentcategoriesofoccurrence(0–absecancetest;thenumbersofobservations(n)aregiveninsidebarsindicatetheproportionsofobservationsi
8 Preslia89:1–16,2017
temperature are low (Fig. 3). Moreover, the proportion of industrial, commercial and
transportareabelow10.2%,incombinationwithlowdensityofrailways,resultsinzero
probabilityofharbouringnaturalizedpopulations(ElectronicAppendix3).Asaresult,
most A. artemisiifolia populations, especially naturalized ones, are recorded along the
Laberiver(eastern,northernandcentralBohemia),south-eastofBrno(southernMoravia)
andclosetothetownofOstrava(north-easternMoraviaandSilesia)(Fig.4).
PotentialdistributionofAmbrosiaartemisiifoliaintheCzechRepublic
Thepredictionmodel(Fig.5)revealedmorethanhalfofthecountry(56%ofgridcells;
Table1)isofverylowsuitabilityforA.artemisiifolia.However,themodelalsoindicates
thatmanygridcellswithsuitableconditionsarecurrentlyunoccupied;morethanhalfof
thosewiththemostsuitableconditionsarenotcolonized,andonlyaboutonequarterof
thesecellshostnaturalizedpopulations.Manyunoccupiedgridcellsincloseproximityto
occupiedcellswereassessedashavingahighsuitability(Fig.5).Thissuitabilityisespe-
ciallytrueforcellsinnorthern,centralandeasternBohemiaalongtheLaberiver,ineast-
ernMoraviaalongMoravaandOdrarivers,innorthernandcentralBohemiainthesur-
roundingsofbigcitiessuchasÚstínadLabemandPrague,respectively,andinnorth-
easternandsouthernMoraviainthesurroundingsofOstravaandBrno.However,some
highlysuitablecellsareratherfarfromcurrentlyoccurringpopulations,especiallythose
inwesternBohemiaalongtheOhřeriverandwestofthecityofPlzeň,andalsoinsouth-
ernBohemiaclosetoČeskéBudějovice.Incontrast,suitablecellsthatarefarfromcur-
rentlyoccurringpopulationsareratherrareinMoravia.
Table1.–PercentageofgridcellsintheCzechRepublicwithinindividualprobabilitycategoriesasrevealedby
thepredictionmodel,percentageofcellswithinthecategoriesthatareoccupiedbyAmbrosiaartemisiifolia
andpercentageofcellswithnaturalizedpopulations.
Occurrence %totalcells %occupied %withanaturalized
probabilitycategory population
0.04–0.2 56.3 0.3 0.1
0.2–0.4 17.1 3.9 0.0
0.4–0.6 14.1 8.1 0.6
0.6–0.8 5.0 24.6 6.4
0.8–0.94 7.5 43.5 15.7
Discussion
Totalnumberofrecordsandfrequencyinparticularhabitats
Ambrosia artemisiifolia was first recorded in the territory of the present-day Czech
Republicinthesameyearasitwasintheterritoryofthepresent-dayAustria(Essletal.
2009).However,therateofspreadintheCzechRepublicwasconsiderablyslowerthanin
Austria.Despitethecountriesbeingofcomparablesize,thecurrentnumberofrecords
and occupied grid cells in the Czech Republic is only about 40% of those recorded
in Austria up to 2009 (Essl et al. 2009). Although it is not possible to make a detailed
Skálováetal.:AmbrosiaartemisiifoliaintheCzechRepublic 9
Fig.4.–MapshowingthedistributionofAmbrosiaartemisiifoliaintheCzechRepublicdisplayedtogether
with(A)distributionofmeanannualtemperaturein5'×3'gridcellsandrivernetworks,and(B)distributionof
proportionalareaofindustrial,commercialandtransportunitsin5'×3'gridcellsandrailwaynetworks.
10 Preslia89:1–16,2017
Fig.5.–PotentialdistributionofAmbrosiaartemisiifoliaingridcells(5'×3')intheCzechRepublicbasedon
factorsrevealedbytheconditionalinterferencetreeasshapingthespeciesdistributionwithuptonowrecorded
occurrencesrepresentedbydots.
comparison with other countries due to the absence of detailed data, it is clear that the
extentoftheareacolonizedintheCzechRepublicisconsiderablylessthaninHungary,
CroatiaandSerbia(Kazinczietal.2008).
Thehighnumberofrecordsassociatedwithtransportcorridors,railwaysandroads,is
typicaloftheoccurrenceofA.artemisiifoliaintheCzechRepublic,SlovakiaandAustria.
TheCzechRepublichasmorerecordsfromrailwaycorridorsandtherewasabouta10-
yeardelayinthestartoftherapidspreadalongroads.Theseroutesseemtohavebecome
themaintransportpathwayofA.artemisiifoliaintheCzechRepublicjustasinothercen-
tral-Europeancountries(Vitalos&Karrer2009,Jollyetal.2011,Medveckáetal.2012,
Milakovic et al. 2014, Essl et al. 2015b, Hrabovský et al. 2016, Milakovic & Karrer
2016). The situation may be similar to Slovakia where the number of ragweed records
started to increase markedly around 2010, namely along highways and main roads
(Hrabovskýetal.2016).ThespatiotemporalpatternintheCzechRepublicalsosupports
theviewofreportedlong-distancedispersalasacontaminantofcropsorbirdfeed,direct
transportofcontaminatedlitterorsoilorattachedtoconstruction-oragriculturalmachin-
ery(Bullocketal.2012).Populationsinarablefieldsarenowratherscarce.Thiscouldbe
aresultofratherlowpropagulepressureduetotheexistenceofalimitednumberofreally
extensivepopulationsintheCzechRepublic,lowerseedproductioncomparedtoother
countries(Moravcováetal.2010,Essletal.2015b)andstilllowabundancealongroads
thatmayserveasasteppingstonefortheinvasionoffields.However,thesituationmay
soonchangeduetotheongoingspreadofA.artemisiifoliaalongroadsthataremanaged