Long-Term Changes in Wetland Area and Composition in the Netherlands Affecting the Carrying Capacity for Wintering Waterbirds

[摘要] InTheNetherlands,arisingingeologicaltimeasthedeltaoftheriversRhine,MeuseandScheldt,aconsiderablechangeinlandscapeoccurredduringtheHoloceneperiodduetosealevelrise.Inmorerecenttimesthischangewasdramaticallyenforcedbyhumanactions.Thisstartedwiththeopeningupofthelargewoodsonhighersoils,some4500yearsBP.Itisestimatedthatthecountrywasonlypopulatedthenbyafewthousandpeople.Duringthenext2000years,theextensiveforestclearingcontinued,anduptoapproximately60%oftheuplandareachangedintograzedwoodland.Over-exploitationduringtheMiddleAgesresultedinextendedheathlands,whichcoveredupto40%ofthetotalareaofuplandsandsby1500AD.Todaywoodlandscoveronly1promilleofthesurfaceareaitcovered7000yearsago.Wetlandsremainedundisturbedforalongperiod,buttheyhavebecomeseriouslyaffectedsincethelateMiddleAges;theconstructionofdikes,embankmentsanddrainagehavecausedtheareaofwetlandstoshrinkdramatically.Especiallywheninthe19thand20thcenturies,asaresultoftheintroductionofsteamandlaterdieselandelectricengines,large-scaleprojectscouldberealised.Thisledtothedisappearanceofmanyfreshwaterlakesandthealmostcompletelossoftheareaofbrackishwater,thenaturallinkbetweenseawaterandfreshwater.AlthoughtheinfluenceofManupontheDutchlandscapecommencedsome4500yearsago,itisonlyduringthelast600yearsthatwetlandshavebeenaffected.Particularlythelast100yearshavebeencrucialwithrespecttodrainageandcultivation.Byreconstructingancientlandscapes,anattempthasbeenmadetodescribethespeciescompositionandnumericalabundanceofwaterbirds,starting7000yearsBP.Twospecieshavebecomeextinctintheterritory,manyothersshowchangesinabundance.Thestartofagriculturehascausedamajorchangeinthefoodprovisioningofmanyherbivorouswaterbirds.Overthelast7000years,asevenfoldincreaseofthenumberofherbivorouswaterfowlisestimated.Ontheotherhandthenumberoffish-eaters,benthos-eatersandplanktivorouswaterbirdshasdeclined,theiravailablehabitatnowhavingdiminishedby45%,36%and55%respectivelywithrespecttotheLateSubatlanticperiod,c.850–1350AD.

[学科分类] 动物科学

[关键词] Cultivation