W.Shuwenetal./EcologicalEngineering18(2001)115–120117

phenomenonoftransientclimaxinsuccession,whenobservedfromlocalecosystems.Asimplecaseofatransientclimaxwouldbethedevelop-mentofcommunitiesinseasonalponds.Ifthekindoforiginalsystem(probablyinasmallerscale)isobservedtobeatransientclimaxelse-where,thesitemaybeagoodchoicebecauseenvironmentalconditionsofthetwosystemsarealike;and(3)closenessofthetwokindsofsys-tems,whichensuresspeciestransportationbyanimals,windor ooding,alsorawmaterialsfornaturedesign.Afterthesiteischosen,theprocessofsuccessionisinitiatedbychangingen-vironmentalconditions,especiallywater.Al-thoughspeciesintroductionisnotindispensable(Mitschetal.,1998),introductionofthespeciesthatcannotbebroughtinbynaturalprocessescanmakeupde cienciesincommunitystructureandthusacceleratethesystem’smaturingpro-cess.Thenwejustneedtokeepthesystemfreeofinterferencefromhumanactivitiesandleavemostofthedesignworktonature.IllustratedhereisaprojectinChinadesignedaccordingtotheprinciplesofecologicalsuccession.

3.Casestudy—awetlandcreationprojectforrarewaterfowlconservationinChina

YanchengBiosphereReserve,the rstandlargestseabeachnaturereserveinChina,islo-catedonthewesternbankofthePaci cOceaninJiangsuProvince.Itisoneoftheworld’smajorwinterhabitatsofred-crownedcranes(Grusjaponensis).EveryNovembertoMarch,a

largenumberofred-crownedcraneswinterinthereserve.Inrecentyears,thenumberhassur-passed1000,nearlyhalfofthetotalwildred-crownedcranesintheworld.YanchengBiosphereReserveisalsooneoftherestingplacesformigratorybirdsfromnortheastAsiaandAustralia.Morethan200speciesofbirdspassbyhere.Therearemorethan200000birdsthatwinterinthereserve,includingtheSaun-der’sGull(Larussaundersi)whichbreedsandwintersthere.Becauseofhumanpopulationgrowthandeconomicdevelopment,alargeareaoftheoriginalcoastalbeachwetlandswasdevel-opedinYanchenginthelate1980s.Oilextrac-tionandshell shcollectionhavealsohelpeddestroythehabitatsofred-crownedcranes.Al-thoughthecoastalbeachareaisnowincreasing,itisnotincreasingasfastaslandreclamationfordevelopment.Inlessthan10years,red-crownedcraneshavelostnearly60%oftheirhabitat,especiallyinthenorthofYanchengBiosphereReserve.Moreandmorered-crownedcraneswereobservedtoenterthefarmlandsandarti cial shpondsto ndfoodandwater,andtheywereconfrontedwithmanydangers.Forexample,theutilizationofagrochemicalfertiliz-ersandpesticidesthreatenedtheirsafety.About10red-crownedcraneswerepoisonedeachyearintheearly1990s.Therefore,awetlandmitiga-tionprojectwasbegunin1994.A240-hareedwetlandwascreatedfromthevastareasoflalanggrasslandtoprovidehabitatsforthered-crownedcranesandotherrarebirdsattheedgeofcorezoneinYanchengBiosphereReserve.

Fig.1.TheplantcommunitysuccessionsereofYanchengcoastalbeachecosystems.