Ecologicalassessmentofphragmitesabstractwetlandusi

EcologicalassessmentofPhragmitesaustraliswetlandsusingmulti-seasonSPOT-5scenesBrigittePoulina,⁎,AurélieDavranchea,b,GaëtanLefebvreaaTourduValatResearchCenter,LeSambuc,13200Arles,FrancebInstitutfürGeographie,Friedrich-AlexanderUniversitätErlangen-Nürnberg,Kochstraße4/4,91054Erlangen,GermanyabstractarticleinfoArticlehistory:Received13October2009Receivedinrevisedform13February2010Accepted21February2010Keywords:CamargueEcosystemhealthGLMmodellingMultispectralindicesMultitemporalimageryPhragmitesaustralisVegetationstructureSPOT-5satelliteStateindicatorsWetlandmonitoringEcologistsandconservationistsneedaccurateandreplicabletoolsformonitoringwetlandconditionsinordertodevelopandimplementadaptivemanagementstrategiesefficiently.TheRhoneDelta(Camargue)insouthernFranceencloses9200haoffragmentedreedmarshesactivelymanagedforreedharvesting,waterfowlhuntingorcattlegrazing,andholdingsignificantnumbersofvulnerableEuropeanbirds.Weusedmulti-seasonSPOT-5datainconjunctionwithgroundsurveytoassessthepredictivepowerofsatelliteimageryinmodellingindicatorsofreedstructure(height,diameter,densityandcoverofgreen/drystems)relevanttoecosystemmanagementandbirdecology.Allindicatorscouldbepredictedaccuratelywithacombinationofbands(SWIR,NIR)andindices(SAVI,OSAVI,NDWI,DVI,DVW,MSI)issuedfromscenesofMarch,June,July,SeptemberorDecemberandsubtractionbetweenthese.Allmodelswererobustwhenvalidatedwithanindependentsetofsatelliteandfielddata.ThehighspatialresolutionofSPOT-5scenes(pixelof10×10m)permitsthemonitoringofdetailedattributescharacterizingthereedecosystemacrossalargespatialextent,providingascientifically-based,replicabletoolformanagers,stakeholdersanddecision-makerstofollowwetlandconditionsintheshortandlong-term.Combinedwithmodelsontheecologicalrequirementsofvulnerablebirdspecies,thesetoolscanprovidemapsofpotentialspeciesrangesatspatialextentsthatarerelevanttoecosystemfunctioningandbirdpopulations.©2010ElsevierInc.Allrightsreserved.1.IntroductionAlthoughwetlandssupporthighbiodiversityandprovideanextensiverangeofpublicgoodsandservicestohumankind,theyareamongthemostthreatenedhabitatsintheworld(Williams,1993;Dudgeonetal.,2006).Theirhighrateofdisappearancehaspromptedthedevelopmentofremotely-sensedtechniquesformappingtheirdistribution,butlittlehasbeendoneformonitoringtheirstateofhealth,especiallyatextensivespatialextentsthatarerelevanttoecosystemfunctioningandspeciespopulations.Ecologistsandconservationistsneedaccurateandreplicabletoolsformonitoringwetlandconditionsinordertodevelopandimplementadaptive-managementstrategiesefficiently(Ostendorpetal.,1995;Kerr&Ostrovsky,2003).CommonreedPhragmitesaustralis(Cav.Trin.exSteudel)isthemostwidelydistributedfloweringplantonearth(Marksetal.,1994;Güsewell&Klötzli,2000).Ittypicallygrowsinornearfreshwater,brackish,andalkalinewetlandsalongagradientfromdeepwater(N2m)toterrestrial(b1mbelowsubstrate)conditions(Clevering,1998).Itoftendominatestheareaitoccupiestoformdensestandsinfloodplains,lowlandshallowlakesandalongnaturalriverchannelsorirrigationcanals.ReedstandsareconsideredasundesirableinvadersinsomeareasofNorthAmericawherenon-endemicgenotypesareproliferating,buthavehighconservationandsocio-economicvaluethroughoutinEuropeduetospecificvulnerablebirdspeciesandvarioustraditional,recreationalandcommercialactivities(Güsewell&Klötzli,2000;Ludwigetal.,2003;Valkamaaetal.,2008).Commonreedcanresistfire,frost,highpH,waterdeficitandsalt,buthasalowtoleranceforwaveandcurrentaction(Marksetal.,1994;Pagteretal.,2005).Eachspring,annualshootsemergefromperennialundergroundrhizomes,growingupto3–4mtallinoptimalconditions.Theseverticalstemsproduceleaves,flower,andeventu-allysetseed.Thestemsdieinearlywinterbutstandasrigidcanesforseveralmonths(Burgess&Evans,1989).Densitymayreach200(wetstands)or300(drystands)shootspermetersquare(Haraetal.,1993),leadingtoarapidaccumulationofdecayingmatter,whichcontributestodryingoutofthereedbedthateventuallyevolvestowardsscrubandwoodland(Granéli,1989;Cowieetal.,1992).Commonreedisrelativelyintolerantofsummermowingandcattlegrazing(vanDeursen&Drost,1990),butcuttingorburningthedrystemsinwinterwillslowdownthishydroseralprocess(Burgess&Evans,1989;Bedford,2005).Commonreedcantolerateaconstantsalinityofupto22.5g/L,butshootheight,diameteranddensitywillstartdecreasingabove5g/L(Lissner&Schierup,1997).Decreasedreeddensityandheightalsoresultfromwaterdeficit(Engloner,RemoteSensingofEnvironment114(2010)1602–1609⁎Correspondingauthor.Tel.:[phone];fax:[phone].E-mailaddress:[e-mail](B.Poulin).0034-4257/$–seefrontmatter©2010ElsevierInc.Allrightsreserved.doi:10.1016/j.rse.2010.02.014ContentslistsavailableatScienceDirectRemoteSensingofEnvironmentjournalhomepage:).Optimalconditionsforreedgrowtharefreshwaterbodiesexhibitingaseasonalfluctuationsof30-cminwaterlevels(Deeganetal.,2007).Avigourousreedbedwillhavehomogeneousvegetationcover,tallgreenstemsanda2:1ratioofdrytogreenstems.Permanentfloodingwithoutwaterrenewalwillresultinlowershoots,ahigherdry-to-green-stemratio,andeventuallyaclumpydistribu