国外关于湿地研究的论文

EcologicalEngineering18(2001)115–120

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Wetlandcreationforrarewaterfowlconservation:Aprojectdesignedaccordingtotheprinciplesofecologicalsuccession

WanShuwena,1,QinPeia,*,LiYanga,LiuXi-Pingb

a

DepartmentofBiology,NanjingUni6ersity,Nanjing210093,People’sRepublicofChina

b

YanchengBiosphereReser6e,Yancheng224001,People’sRepublicofChina

Received20June2000;receivedinrevisedform29December2000;accepted2January2001

Abstract

Thepracticesofwetlandcreationandrestorationformitigatingwetlandlosshavebeenfrequentlycarriedoutthroughouttheworld;however,manyoftheseprojectsdonotworkwell.Inthispaper,theauthorsanalyzewetlandcreationfromtheaspectofwhole-ecosystemdevelopment,andexplaintheextremedif cultyofhumandesigninwetlandcreationbythetheoriesofecologicalsuccession.Morespaceshouldbegiventoself-designthanhumandesigninwetlandcreation,andtheprinciplesofecologicalsuccessionenableustobetterusethegreatdesignabilityofnatureinjustthewaywewish.AwetlandcreationprojectforrarewaterfowlconservationinChinaYanchengBiosphereReservewaschosenasademonstration,designedtotallyaccordingtotheprinciplesofecologicalsuccessionandallowedtoself-designfreeofinterferencefromhumanactivities.A240hareedwetlandwascreatedfromthelalanggrasslandafter4yearsofself-design.Successwasprovedbyitsplantcompositionandagoodhabitatvalueformanymorebirdsthaninthesamearea4yearsbefore.©2001ElsevierScienceB.V.Allrightsreserved.

Keywords:Wetland;Wetlandcreation;Naturalconservation;YanchengBiosphereReserve

1.Introduction

Thepracticesofwetlandcreationandrestora-tiontoreplacewetlandslostordestroyedelse-where,aprocessknownaswetlandmitigation,arecarriedoutfrequentlyintheworld(Mitschetal.,

*Correspondingauthor.

E-mailaddress:qinpeinc@(Q.Pei).1

Presentaddress:SchoolofNaturalResources,TheOhioStateUniversity,Columbus,OH43210,USA.

1998).Disappointingly,manymitigationprojects,thevastmajorityofwhichhavebeenattemptedinwetlands,donotwork,oratleastdonotworkwell(Roberts,1993;Malakoff,1998).Anattempttocreatea12hasaltmarshinSouthernCalifor-nia(Zedler,1996)wasrecentlydeclaredafailurebecauseitdidnotprovidehabitatforlight-footedclapperrail(Malakoff,1998).InOregon,onestudyfoundnearlyallwetlandprojectsarefunda-mentallydifferentfromthewetlandstheyareintendedtoreplace(Kentulaetal.,1992).What

0925-8574/01/$-seefrontmatter©2001ElsevierScienceB.V.Allrightsreserved.PII:S0925-8574(01)00062-3

116W.Shuwenetal./EcologicalEngineering18(2001)115–120

causedsuchfailures?Thecommonanswerisun-certaintyaboutwhatisnecessarytocreateandrestoretheseimportantecosystems(Roberts,1993;MitschandWilson,1996;Young,1996;Zedler,1996;Malakoff,1998;Mitschetal.,1998).Peoplespendmuchtimestudyingthecomplexinteractionsamongcomponentsofanecosystem,butstillfeelagapintheunderstandingofsuchinteractions.Ifthegoalofwetlandmitigationistomimiccloselythefunctionsoftheoriginalsystem,asmanyecologistsbelieveitshouldbe,thejobisstilldif cult(Roberts,1993).

Inwetlandcreation,wedesignthecommunitystructureandsomeoftheenvironmentalcondi-tions,andanticipatethatthesystemwilldevelopintoanexpectedone.Itisaprocessofsecondarysuccession.Whyisitsodif culttoacheive nalsuccess?Maybeweshould ndtheanswerfromthewhole-ecosystemdevelopmentratherthantheinteractionsinasystem.Thestructureofthecommunity,especiallytheplantcommunity,canbeusedasoneindicatorofmaturityofanecosys-tem.Accordingtothepolyclimaxviewpoint,theclimaxcommunityisthelocalend-pointofasere,andisdeterminedbylocalenvironmentalcondi-tions.Sowhetherwecandesigntheenvironmen-talconditionstobejustthesameastheoriginalsystemisofgreatimportancetoensurethechar-acterofthecommunity,andthusadesiredma-tureecosystem.Indeedwemaydoalotofworktomimiccloselytheenvironmentalconditionsoftheoriginalsystem.Butitseemsverydif cultbecausetheenvironmentalconditionsarecom-prisedofsomanyfactors,suchasclimate,soilnutrients,moisture,slope,exposure, re,etc.Forexample,theprobleminacreatedcoastalwetlandinSanDiegoBaywasinadequatenitrogensup-pliesbecauseofsandysoils,whichpreventedcordgrassfromreachingitsfullheight;thusthecreatedwetlandfailedtoduplicatethefunctionsofanaturalone(Roberts,1993).InIllinois,7-year-oldcreateddeepwatermarsheslackedsimi-laritytonaturalmarshesbecauseofarti ciallydeepwaterandlackofsoilcarboninthecreatedwetlands(MitschandFlanagan,1997).

Moreover,designingthecommunitystructurecompletelyliketheoriginalonealsoseemsimpos-sible.Whittaker(1967)emphasizedinhisclimax-

patterntheorythattheconstituentpopulationsinaclimaxcommunityareindynamicbalancewiththewholepatternofenvironmentalfactorsinwhichitexists—‘climate,soil, re,bioticfactors,andwind’.Thecommunitystructureisacontin-uumofoverlappingsetsofspecieseachrespond-ingtosubtlydifferentenvironmentalcues,andthusnode nitepatternoftheoriginalsystemcanbeimitated.‘‘Whileitiseasyto gureoutwhichplantstobringin,wheretoputthem‘speci cally,atwhatelevation’isnotsoclear.Plantingthemafewinchestoohighortoolow,inrelationtothetidalregime,canspelldeathtoanewlyintroducedplantpopulation,’’saysZedler(Roberts,1993).

2.Designwetlandcreationaccordingtothe

principlesofecologicalsuccessionandleavemorespacetoself-design

Humansstillcannotdesignanecosystemasdelicatelyasnaturedoes.Whentoomanyhumanstandardsdonotseemtowork,weshouldleavemorespacetonatureandgiveherachancetoexpressherself(Mitsch,1993).Peoplehavebeguntopaymoreattentiontothenaturedesignthanhumandesign.Awhole-ecosystemexperimentconductedinTheOlentangyRiverWetlandRe-searchParkatTheOhioStateUniversityalsocon rmedthegreatself-designabilityofnature,andthetheoryofself-designforwetlandcreationandrestorationwasbroughtout(Mitschetal.,1998).However,howcanweletnaturedevelopinthewaywedesirefromthebeginning?Naturecannotconsiderallofourrequests,andsheworksindependentlyaccordingtoherrules,theprinci-plesofecologicalsuccession.Soifwewanttoworkwithnaturetowardthesamegoal,wemustobeytheprinciplesofecologicalsuccessionindesigningourprojects,andleavemorespaceforself-design.

Comparedwiththetraditionalway,moreef-fortsareputtochoosingapropersitetoensurethesystem’sdevelopingdirection.Atleastthreeaspectsshouldbeconsideredwhenchoosingasite:(1)abilitytochangeintotheintendedsystem,whenanalyzedfromsuccessionhistory;(2)the

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.

118W.Shuwenetal./EcologicalEngineering18(2001)115–120

3.1.Designandmanagement

3.1.1.Choosingasite

Investigationsontheplantcommunitysucces-sionsereofYanchengcoastalbeachecosystemsweredonebeforechoosingthemitigationsite(Fig.1).Thedominantplantcommunitiesinthetidalzonecanbeclassi edintothreecategories:(1)theprimarytypesofplantationinsuccessiondominatedbysaltlivingwornwood(Suaedasalsa);(2)thexerarchclimaxwherelalanggrass(Imper-atacylindrica)isdominant;and(3)themarshcommunitywherereed(Phragmitescommunis)prevails.Thesuccessionalseresofreedandlalanggrasspartiallyoverlapanddivergemainlybecauseofwaterconditionsintheirecosystems.Wecanconcludefromthesuccessionhistorythattheenvironmentalconditionsofreedmarshandlalanggrasslandaresimilarexceptforwater;thisisalsocon rmedbytheinterestingphenomenonoftransientclimaxobservedinYanchengtidalland.Insomelowerplacesofthelalanggrassland,reedgrowswhenthewaterisamplebecauseof ooding.Insomeplacesencircledbydikesandshortofwatersupply,thereediseventuallyre-placedbylalangandothergrassesandthereedwetlandecosystemturnsintoagrasslandecosystem.

Analyzedfromsuccessionhistory,wateristhemajorfactorforcreatingareedmarshecosysteminYanchengtidallands.Thewornwoodgrasslandorlalanggrasslandbothhavetheabilitytoturn

intoamarsh.However,alalanggrasslandisbetterforitsclosenesstoreedinasuccessionsere,whichensuresarelativelyshortertimeforcreat-ingareedwetland.Nextcomesthestepofchoos-ingalalanggrassland.Severalaspectswereconsidered.First,thesiteshouldbebetweenthecorezoneofthereserveandhumanareas(farm-landsandarti cial shponds),servingasabridgeforbirdsgatheringtothecorezonefromhumanareas.Second,thereshouldbeacertainareaofreedmarshnearorinthechosenlalanggrassland,whichensuresthepropagulesourcesforcreatingareedwetland.Third,thereshouldbeasourceoffreshwaterforcreatingawetlandonthesite.Takingallofthesefactorsintoconsideration,a240halalanggrasslandattheedgeofthecorezonewaschosentocreateareedwetland.

3.1.2.Creatingawetland

InMarch1994,a240-hagrasslandwasencir-cledanddikeswerebuiltaroundthegrassland.Freshwaterwaspumpedintothegrassland.Theaveragewaterlevelwasabout0.5mandtheconstantwaterlevelwasmaintainedaroundtheyear.Somesmall shandshrimpwereputintothewetlandtoprovidefoodforwaterfowl.Whenwintercame,somewaterwasdischargedtokeepashallowlevelofabout0.3m,providingmoreconvenienceforwaterfowlstoplayandforage.Aftertheprojectwasconstructed,thewetlandwasstrictlymanagedtoavoidinterferencefromhumanactivities.

Table1

PlantprimaryproductivityandpercentcoverofcommunitiesinthelalanggrasslandandreedwetlandatthecreatedwetlandsiteatYanchengBiosphereReserveLalanggrassland(priortocreation)PlantLalangChineseaeluropusReed

Average,entiresiteTotal

Primaryproduction(gm 2yr 1)116032514869982971

100Cover(%)75214

Reedwetland(4yearsaftercreation)PlantAlgaeCattailReed

Primaryproduction(gm 2yr 1)53241453294743399724

100Cover(%)681517

W.Shuwenetal./EcologicalEngineering18(2001)115–120119

3.2.Results

After4yearsofself-design,the240halalanggrasslandturnedintoareedwetland,asindicatedbytheplantcommunitycompositionofthetwoecosystems.Weevaluatedthisprojectbystudyingthefunctiontheecosystem,whichisprovidinghabitatforrarewaterfowl.Thenumbersandkindsofbirdsthatwinteredin1993and1998justinthis240halandwerecompared.

3.2.1.PlantcompositionandprimaryproductionFouryearsafterthewetlandwascreatedin1994,largeareasofreedgrewupinthewetland.Theplantcompositionchangedfromlalang,Chi-neseaeluropus(Aeluropussinensis)andreedtoalgae,cattail(Typhaangustifolia)andreed(Table1).TheplantcoverandprimaryproductionarealsolistedinTable1.Thetotalprimaryproduc-tionofthesystemincreasedby3.34timesasthegrasslandturnedintoareedwetland.

3.2.2.Winteringbirds

Manymorebirdswereobservedtowinterinthereedwetlandin1998thanthoseinlalanggrasslandin1993(Table2):thespeciesrichnessofwaterfowlincreasedfrom16to37;speciesunderChina’skeyprotectionincreasedfrom3to11.Thenumberofwaterfowlindividualsincreasedfrom3459to97747.Red-crownedcranesin-creasedby82%to545individuals,aboutonequarterofthetotalintheworld.

4.Conclusions

Inthisprojectofcreatinga240-hareedwet-land,wechoseapropersite,pumpedthewater,andgavenatureaworkingenvironmentwithoutanyfurtherhumanin uences.Allthatwedidwasintendedtomakegoodpreparationfornature’sself-design.Everystepwetookwasjudgedbytheprinciplesofecologicalsuccessiontoensurethedirectionofnature’swork.Wedidnotspendmuchtimeandfundsonimitatingtheenviron-mentalconditionsandcommunitystructureoftheoriginalkindofsystem.Weleftthisworktonaturewhilewefocusedonallowingnaturetodo

herwork.Theapplicabilityofsuchamethodforwetlandcreationwascon rmedbytheprojectinYanchengBiosphereReserve.Naturesurprisedusagainbyhergreatdesignability,suggestingweshouldpaymorerespecttoself-designthantohumandesigninourprojects.The

Table2

Birdswinteringinthe240halalanggrasslandin1993andinthereedwetlandin1998Speciesofbirds

Number1993

1998Grusjaponensis300545Grusgruslilfordi216Grusleucogeranus272Larussaundersi2410Larusargentatus0154Larusridibundus201300

Larusrelictus02Ardeacinerea

15145Mycticoraxnyticorax62Podicepsru collis6180Podicepscristatus024Podicepsnigricollis02Platalealeucorodia016Podicepsminor032Anseralbifrons02Ansererythropus011Ansercygnoides0754Anserfabalis983600Anseranser01750Othergeese

42400Cygnusc.cygnus04Phalacrocoraxcarbo0238Phalacrocoraxpelagicus020Anaspoecilorhyncha12005800Anasplatyrhynchos03600Anascrecca32012270Anaspenelope1002620Anasacuta04000Anasfalcata205400Tadornatadorna0800Mergusmerganser11100Mergussquamatus018Mergusalbellus02900Otherducks

30027000Numeniusarquata1120Tringaerythropus220Calidrisalpina

06700Recur6irostraa6osetta0120Otherbirds106012300Total

3459

96447

120W.Shuwenetal./EcologicalEngineering18(2001)115–120

theoriesofecosystemdevelopment,alsocalledecologicalsuccession,enabledustousethegreatpowerofnatureaswewished.

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