生态景观设计的原则Principles of Ecological LandscapeDesign学部（院）：建筑与艺术学院专业：艺术设计（环境艺术设计）学生姓名：学号：指导教师：完成日期：4ComplexCreations:Designing and ManagingEcosystemsA dragonflyflitsoverthesun-mirroredsurfaceofapond,snappingathatchingmosquitoesbeforecom- ing to rest on an overhanging rush. This is an ecosystem: animals, plants, and theirphysicalenviron- mentlinked together in the exchange of energy and materials. If this were our pond,ourecosystem,wewouldhaveitall:abeautifullandscapefeature,enlivenedbycreaturesweneve rhadto carefor,andhassle-freepestcontrol.Ecosystemslikethisponddoquiet,crucialwork,keepingalivethebiosphereofwhichweareapart.W heresuchanaturalpond,oraforestorfloodplain,exists,itbehoovesustoprotectit.Whereonehasbeen degraded,wewouldbewellservedtorestoreit(seechap.10).Butwheresuchecosystemshavebeenplo wedunderorpavedover,wecanendeavortoreplacethembyfillingthebuiltenvironmentnot justwithlaw nsandplazasandfountainsbutwithecosystems.Anecosystemconsistsofallofthelivingorganismsinanareaalongwiththeirphysicalenviron-ment,anditspropertiesarisefromtheinteractionsbetweenthesecomponents.Anoceanbayisanecos ystem,asisanalpinemeadoworagreenroof.Perhapsbecauseoftheirclearboundaries,lakes andstreams wereimportantobjectsofstudyinthedevelopmentofecosystemecology.Wherebound- ariesarelessdistinct,thelimitsofanecosystemcanbe defined,evenarbitrarily,basedonthequestionanecol ogistisstudyingortheboundariesofa designer’s site.Designedlandscapesalreadybringtogetheramanipulatedphysicalenvironmentandlivingor-ganisms.Theydonotnecessarilyfunctionasnaturalecosystemsdo,however.Theyaredisconnect-ed,toooftenwastefulanddemanding,orelsetheysimplyfailtothrive.Whenwesucceedincreat-ingintegratedecosystems,theresultscanberemarkable.Lifecanspringforth,almostunbidden.Waste scanbetransformedintoresources.Thevariousmembersofalivingcommunitycanreacha tentativebalance.Thebuiltenvironmentcanpurifywater,protectusfromfloods,andstrengthenour sense ofwell-being.T.Beck,PrinciplesofEcologicalLandscapeDesign,DOI10.5822/978-1-61091-199-3_4,©2013TravisBeckComplex Creations: Designing and ManagingTHE ECOSYSTEMCONCEPTTheideathatplantsandanimalsandtheirenvironmentformanintegratedwholeisattherootofthedi sciplineofecology,althoughittookdecadestoarticulateinitsmodernform.In1887,inanaddresstothe Peoria ScientificAssociation,StephenForbesdescribedthelakeas“amicrocosm.”In orderforascientisttounderstandanyonespecies,heargued,Hemustevidentlystudyalsothespeciesuponwhichitdependsforitsexistence,andthevariouscondi tions upon which these depend. He must likewise study the species with which it comesincompetition,andtheentiresystemofconditionsaffectingtheirprosperity;andbythetimehe has studiedallthese sufficiently hewillfindthathehasrunthroughthewholecomplicatedmechanismofthe aquaticlifeofthelocality,bothanimalandvegetable,ofwhichhisspeciesformsbutasingleelement. (Forbes 1887:537)Theterm microcosm didnotenterintowiderecologicaluse.However,theideaofmanyorganisms formi ngalargerentitygainedexpressionintheturn-of-the-centuryconceptoftheclimaxcommu-nity(seechap.2).ThisconceptwassingledoutbyBritishecologistArthurTansleyina1935articleprovoca tively titled“TheUseandAbuseof VegetationalConceptsand Terms.”Theabusetowhichhereferredwas theinsistenceofClementsandotherecologistsonapplyingtheterm organism tothe climaxcommunity.“Thereisnoneedtowear ythe reader,”hewrote,“withalistofthepointsinwhichthebiotic communitydoes n ot resemblethesingleanimal orplant”(Tansley1935:290).However,hedidnot holdbackfrommentioningtha ta community’sprocessofdevelopmentisverydifferentfromthelife cycle of animals and plants. At best, Tansley offered, vegetation might resemble a“quasi-organism,”thoughonenotnearlysowellintegratedasahumansocietyorahiveofbees.Thisacceptance ofa quasi-organismalstatusforcommunitiesdifferentiatesTansley’s criticismofClementsianecology fromGleason’s purelyindividualisticfocus.Thereisacertaintruthtotheideaoftheclimaxcommunitybeing wellintegrateda ndself-regulating,Tansleyargued,butitcouldbestatedmoreaccuratelyanotherway.Tansleypreferredtothinkintermsofintegratedsystems.Hisnotionofsystemswasborrowedfrom thephysical sciences.“These ecosystems,aswemaycall them,”hewrote,“areofthemost variouskinds andsizes.Theyformonecategoryofthemultitudinousphysicalsystemsoftheuniverse,whichrange from the universe as a whole down to the atom” (Tansley1935: 299). An essential partof T ansley’sdescriptionoftheecosystemisthatheincludedinitnotonlyalloftheplantsandanimalsandoth erlivingthingsinagiven“weboflife”butalsothe entiretyofthephysicalcomponentsoftheir environmen t,suchassoil,sunlight,andwater.CREATEECOSYSTEMSBuiltlandscapesalsohavephysicalandbiologicalcomponents:crudely,inindustryterms, hardscapeandsoftscape.Toooften,thesecomponentsarefarfromintegrated.Thehardscapeissetin respo nse to programmatic needs, and plants are tucked into the remaining spaces. If thephysicalenvironmentisnotrightforthebiologicalcomponents,thenitisaltered,byprovidingirrigati on,forinstance (seechap.1).Complex Creations: Designing and Managing Consideratypicallandscapepond.Anestateownermightpayacontractortoclearanarea,ex-cavateahole,lineit,fillitfullofwaterfromawell,andtrimthewholesetupneatlywithrocksorlawnandpe rhapsafewaquaticplantsonaplantingshelf.Aswaterevaporatesfromtheunshadedpond,thewellpum pkicksinandtopsoffthepond.Evensuburbanhomeownerswanttheirownpondsandwaterfalls,fullofmunicipalwaterandlinedwithdwarfconifersorJapaneseiris(Irisensata)sittinglike rockyp uzzlepiecesontheirlawns.Thesesystemsare fullyartificial,rely onsupplementalwater,and often require filtration or even sterilization to remain aesthetically acceptable. Physical andbiological elements are divorced from each other and from theirsurroundings.Bycontrast,apondthatisconceivedofasanecosystemfusesphysicalandbiologicalelements intoawholethatintegrateswith,ratherthansitsapartfrom,ndscapearchitectsAndropogonAssociatescreatedsuchapondonapropertyinGreenwich,Co nnecticut.Naturally,throughout NewEngland’s forests,inthespringsmalldepressionsintheland-scapefillwithwater,which infiltrates asgroundwaterlevelsdropinthesummer.Thesevernalpoolsprovid eimportanthabitatforamphibianssuchassalamandersandfrogs.Onthispropertysuchadepressionexi sted,setagainstagraniticoutcrop,onlyithadlongbeenfilledwithbranches,leaves,andothergreenwast ebygenerationsofgardeners.WhenColinFranklin,foundingprincipalatAndro-pogon,discoveredtherockydellandthesmallspringatitsbase,hesawanopportunity.AndropogonAssoci ates’design philosophy haslongbeentobuild“d ynamic,holisticsystems,”thatis,ecosystems.Franklin’s approachwastolinethecenterofthedepressioninordertomaintainaminimumwaterlevelbutleavethe edgesunlined.Waterfromthespringiscollectedinasumpbeneaththepondandpumpedviaaslenderw aterfallofftherockoutcropandintothepond.Inspringthepond overflows,recharginggroundwaterinthe area(fig.4.1).Themarginsareplantedwithtreesandotherplantsthatareadaptedtothisseasonalflooding.Betweentheopenwater,theplantedwetlandatthepond’sedge,a ndtheseasonalwetlandbeyond,thedesignprovidesdiversehabitat(seechap.7).When waterlevelsdroptotheleveloftheliner,thewettedmarginsdry,mimickingthecycleofvernalpools.Ifwa terlevelsdropfurther,thesumppumpandwaterfallcanmakeupthedifferencefromthe rechargedgroundwater.Becausethepondisintheforest,however,evaporationandthe needformakeupwaterareminimal.Thisforestedpondisnowahuboflifeandthecenteroftheentirelandscape.Ratherthancreatea sterilewaterfeatureofdissociatedelements,Andropogoncreatedanecosystem,withnaturalphysicalcycle sandplantsandanimalsadaptedtothem. ECOSYSTEMSARECOMPLEXADAPTIVESYSTEMSEcologists’ understanding of the multitudinous systems of the universe has evolved since Tansleywrote hiscritiqueofClementsin1935.Mostrecently,ecosystemshavebeenregardedascomplex adap-tivesystems.SimonLevin(1998,1999),abiologistatPrinceton,isachiefproponentofthisview.Incompl exadaptivesystems,asexplainedbyLevin,heterogeneousindividualagentsinteractlocallytocreatelar gerpatterns,andtheoutcomeofthoselocalinteractionsaffectsthefurtherdevelopmentofthesystem(fig.4.2).Itiseasytoseehowthisappliestoecosystems.Theplantsandanimals,rocks andwateranddetrit usthatmakeupapondarealldifferent,yettheyinteracttocreatearecognizableComplex Creations: Designing and ManagingFigure4.1SchematicdesignoftheAndropogon-designedpondecosystem.Duringnormaldryweatherconditions(a)alinerandgroundwaterpumpmaintainaper manentwaterlevel.Duringnormalwetseasonconditions (b) overflow enters peripheral seasonal wetlands and recharges groundwater. (Drawing byColinFranklin.)systemwithpropertiesofitsown.Ifaplantthatproducesmorebiomasscompetitivelyexcludesothe rs alongthe pond’s margins,thentheaccumulationofdetritusinthepond,thepopulationsof bottomfeeders,andotherecosystempropertieswillallbeaffected.Levinfurtherdescribedfourcharacteristicsofcomplexadaptivesystems.Theyarediverse,ag-gregated,nonlinear,andconnected byflows.Ecosystemsincludeindividualorganismswithdiversechar acteristics.Throughtheirinteractions,theindividualagentsinanecosystembecomegrouped intolargerorganizationalentities.Forexample,populationsaregroupsofinteractingindividualsofthe sames pecies(seechap.2).Themostaccuratewaytoviewaggregationisthroughthecompositionofahierarchy (seechap.9).Nonlinearitymeansthatsmallchangesinanecosystemcanleadtooutsizedeffects.Remov alofasinglekeystonespecies,forinstance,canchangethecompositionofanentire community(seechap.7).Nonlinearityalsoreferstothefactthatecosystemsareaffectedbyhistoryas muchasbypresentconditio ns.Finally,asweshallseeinthefollowingsections,ecosystemsclearly exhibitflowsofenergyandmaterial sthatconnectalltheirindividualparts.LET CONSTRUCTED ECOSYSTEMSSELF-DESIGNIf ecosystems are complex adaptive systems that develop from the interaction oftheir componentsandtheeventsofhistory,thensuccessfulecosystemsareunlikelytospringforthfromour headsfullyformedbutshouldemergeinsteadthroughaprocesswemightcallself-design.Complex Creations: Designing and ManagingFigure4.2Turingpatterns,likethisone,areanexampleofacomplexsystemformedfromlocalinteractions.Inthisc ase,each pixel’s colorisdeterminedbythecolorofthesurroundingpixelsaccordingtoacomputer algorithm.Startingfromarandomi nitialstate,thepatterncontinuestoevolve.(ImagebyJonathanMcCabe,underCreativeCommons2.0GenericLicense.) BillMitschandhiscolleaguesexploredself-designattheWilmaH.SchiermeierOlentangyRiver WetlandResearchParkinColumbus,Ohio(Mitschetal.1998).Theyintentionallyleftoneoftwobasinsintheir newlycreatedexperimentaloxbowunvegetated.Theyknewthatwind,water,andanimalswould bringinne wplantssoonenough,andtheywantedtoseehowcloselytheunplantedwetlandwouldresembletheon etheyplanted.Within3years,thetwowetlandswereremarkablysimilarintermsofvegetativecover,dive rsityofplants,waterchemistry,andseveralothermeasuresofecologicalfunc-tion(fig.4.3).Thiscongruenceresultsnotsimplyfromtheunplantedwetlandcomingtoresemblethepla ntedonebutfrombothwetlandschangingto reflect siteconditionsandmigrations.Ofthethirteenorigin alspeciesintheplantedwetland,fourdiedoff.Thesurvivingspecieswerejoinedbyanaddi-tionalfifty-twounplantedspecies.BecausethewetlandswereconnectedhydrologicallytothenearbyOlentangyRi ver,thenatural inflow ofspecieshadamuchgreater influence onthemakeupoftheplant communitiesinthetwowetlandsthandidtheinitialplantingofonebasin.Thesuccessofthetwobasinsasself-designedecosystemsisindicatedbytheOlentangyRiver Wetland’s designation under the RamsarConvention as a Wetland of International Importance.Complex Creations: Designing and ManagingFigure4.3AerialviewofthetwoOlentangyRiverWetlands.(CourtesyofWilliamJ.Mitsch,WilmaH.Schierm eierOlentangy River Wetland ResearchPark.)ECOSYSTEMSAREORGANIZEDINTROPHICLEVELSAs complex adaptive systems, ecosystems are animated by the interactions betweentheirconstituentpartsandtheflowsthatconnectthem.Inthe1940sayoungAmericanecologi st,RaymondLindeman, suggestedawayofanalyzingecosystemsintermsofenergyflow.AswithForbesbeforehim,Linde-man’s focuswasonlakes.After5yearsoffieldworkonthesmallCedarBogLakeneartheUniversityofMin nesota,LindemansignedupforapostdoctoralyearatYaleUniversitywithG.EvelynHutchinson (wholateradvisedRobertMacArthuronhisstudyofresourcepartitioninginwarblers)(seechap.3).Duri ngthatyearheandHutchinsonworkedonthearticlethatwas tobecome“The Trophic–DynamicAspectof Ecology”(Lindeman1942).Tragically,Lindemandiedattheageof27,afewmonthsbe forehisarticle,whichwasinitiallyrejectedasbeingtootheoretical,wasfinallypublishedintheflagshipj ournaloftheEcologicalSocietyofAmerica.Theideasheputforthhavehadalastingimpactonthefieldofecosystemecology.Lindeman’s focus was on the trophic, or “energ y-availing,” relationships within an ecosystem.Bor- rowingfromGermanlimnologistAugustThienemann,heabstractedthefamiliarfoodwebsthatnatural-istsandecologistshadproducedforlakesandothersystemsintotrophiclevels:Producersareorgan-ismssuchasplantsandphytoplanktonthatobtaintheirenergyfromthesun,consumersareorganisms suchaszooplanktonandfishthatobtaintheirenergyfromeatingproducers,anddecomposersarethe bacteriaandfungithatobtaintheirenergyfrombreakingdowntheorganicsubstancesinthewastes and remainsofotherorganisms.Byabstractinganecosystemtotrophiclevels,Lindeman sacrificed aComplex Creations: Designing and Managingcertainamountofbiologicalreality.Healsocreatedtheproblemofhowtoclassifyorganismsthateat both producers and consumers. There can be several levels of consumers in anecosystem,although earlier ecologists had noted that rarely are there more than five trophic levels intotal.Lindeman’s analysisexplainedthisphenomenon.Unlikethechemicalelements,whichcan cycleindefinitely inanecosystem(seechap.6),energy flow sthroughanecosysteminonedirectiononly:fromthesuntoproducerstoconsumerstosecond-aryconsumerstodecomposers.Ateachtransferofenergybetweentrophiclevels,Lindemannoted,a certainamountislost (fig.4.4).Primaryconsumerssuchasbrowsingsnailsexpendacertainamountofenergyjustlivingand findingproducerstoeat.Someofthemdiebeforetheyareeatenbybenthic predat ors.SomeoftheenergycontainedinthebodiesofthosethatareeatenistiedupintissuessuchFigure4.4Lindeman’s diagramofthefoodwebanddifferenttrophiclevelsinageneralizedlake.Energyandnu trientsenterthesystemfromtheoutside.Thesearecapturedandtransformedbybothmicroscopicand macrosco pic producers (phytoplanktersand pondweeds, A 1). Primary consumers (zooplankters and browsers, A 2)eattheproducersandinturnareeatenbysecondaryconsumers(planktonpredatorsandbenthicpre dators,A 3).Tertiaryconsumers(planktonpredatorsandbenthicpredators,A 4)areatthetopofthe foodchain.Alltheorganicmatterinthesystemultimatelycyclesthroughthebacterialdecomposersintheoozeatthebottomofthelake,whichinturnfeedszooplanktersandbrowsers.(FromLindeman,R.L.Copyright©1942,Ecolo gicalSocietyofAmerica.Thetrophic –dynamicaspectofecology.Ecology 23:399–417.WithpermissionfromtheEcologicalSocietyofAmerica.)Complex Creations: Designing and Managingλasshellsthatare difficult todigestandwhoseenergyisnotpassedalong.Theavailableenergyineacht rophiclevel,then,islessthanthatintheprecedinglevel.Lindemanexpressedthisrelationship usingthep roductivitysymbollambda(λ):0 >λ1 >λ2 . . . >λn .Aswemovetohigherandhighertrophiclevels,lessandlessenergyisavailable.Becausehigher-orderconsumersalsoneedever-greaterlevelsofenergytoseekouttheirprey,atsomepointin everyecosystem,thereisnolonger sufficientenergy tosupportanothertrophiclevel.Lindemancalculatedtheproductivityand efficiency ofenergytransferbetweentrophiclevelsforse verallakesforwhichhehaddataanddrewsomepreliminaryconclusions.This prefigured themore precisemodelingofecosystemsthatwastocomeinthenextphaseofecosystemecology.INTEGRATEPRODUCERS,CONSUMERS,ANDDECOMPOSERSAllecosystemsaregovernedbytherulesofenergy flowthatLindemanoutlined.Aswemanageexisti ngecosystemsandstrivetocreatefunctioningecosystemsofourown,weneedtobesurethedifferenttr ophiclevelsarerepresentedintheirproperratios.Ifalevelismissingortherearetoofeworganismsattha tlevel,energy,intheformoforganicmatter,willaccumulateaswaste,orundesirableorganismsmaytakea dvantageofthebounty.Iftherearetoomanylevelsortoomanyorganisms,theywill need supplemental inputs to survive, or else they will die or move away. Using anecosystemapproach,wecancreateamorebalanceddesignedlandscapeinwhichvariouscomponen tssupport eachotherandproducelittlewaste.AtElMonteSagrado,anecologicallymindedluxuryresortinTaos,NewMexico,alinkedseriesofcaref ullydesignedaquaticecosystemsprovidewastewatertreatmentandanessentialpartofthelandscape.The systems’ability to filterwaterdependsontheintegrationofdifferenttrophiclevels.Attheheartofth ewastewater filtrationprocessisaLivingMachine.LivingMachineswereoriginallydeveloped by ecological designer John Todd in the 1970s and 1980s (Todd and Todd 1993).Theyhavesincebeen refined andarenowdesignedandsoldbyLivingMachineSystems.Inthewor dsofgeneralmanagerEricLohan,oneofthedesignersofthesystematElMonteSagrado,theyworkby tak ingnaturalecosystemprocessesand “turbo -charging”them.Inthewastewater system,muchoftheinitialenergycomesnotfromsunlightbutfromthewa steproductsthemselves,whichareconsumedby bacterialdecomposers.Thusfartheprocessresembles aconventionalsepticsystem,inwhichexcessbacterialbiomasssettlesoutassludgethateventuallyhast oberemoved.IntheLivingMachine,the bacteriathatperformtheinitialdecompositionarecentraltoanen tireecosystem(justasbacteriaarein Lindeman’s diagramofalakeecosystem),inwhichtheyareconsumed byprotozoans,microcrusta-ceans,andsnails.Plants floatingabovethewastewaterasitistreatedtakeupaportionofthenewly availa blenutrientsandprovideintheirrootsalivingsubstrateforthisdiversecommunity.Afterdisinfectionand finalpolishinginanoutdoorwetland,thenowclearwaterentersindoordis-playpondsandanotheraquaticecosystem.Hereproducersincludeavarietyoftropicalplants,phyto-plankton,andalgae,and fishplaytheroleofconsumers.Resortguestsalsoserveasconsumerswhen they enjoystarfruit(Averrhoacarambola )andkumquatfromtheplantsthatareirrigatedbythetreatedwastewa ter.Byincludingallthetrophiclevels,thissystemfullyusestheenergyandnutrientspresentComplex Creations: Designing and Managing inthewastewatergeneratedbyresortguests,resultinginclearwaterandvaluableendproductsrath erthanmurkygraywaterandsewagesludge.Ontopofthis,thankstothe efficient reuseofwater thatthea quaticecosystemsallowandtheircentralitytotheoveralldesignoftheresort,eveninthehigh desertElMont eSagradohasalushambiencethatinvitesgueststorelaxandfeelthemselvesapartof living processes (fig.4.5).Figure4.5TreatedwaterfromtheLivingMachineentersanindoordisplaypondatElMonteSagrado resortinTao s,NewMexico.(PhotocourtesyofWorrellWaterTechnologies.)NEGATIVEFEEDBACKLOOPSHELPECOSYSTEMSMAINTAINSTABILITYOne of the aspects of ecosystems that fascinated the early ecologists who studied themwas that ecosystems can demonstrate, in Arthur Tansley’swords, a “relatively stabledynamic equilibrium.”Fifteenyears afterthepublicationofLindeman’sarticleontrophic dynamics,HowardOdum(1957)am assedlargeamountsofdataintoamuchmoreexactpictureofthesurgingdynamics behind such apparentstability.TheecosystemOdumstudiedwastheheadwatersofSilverSprings,Florida.Sincethenineteenth cen turySilverSpringshasbeenatouristattractiontowhichvisitorsflocktoadmirethecrystalclearwa-ter,schoolsoffish,andwavingfreshwatereelgrass(Sagittariasubulata)(fig.4.6).Theglass-bottomed boatwasinventedatSilverSprings,infact,andtothisdayonecantakeaboatridearoundthethr ee quartermilesofwateryattractionswithfolksynamessuchasFishReceptionHall.SilverSpringsmadeComplex Creations: Designing and ManagingFigure4.6ResearchdiversinmainboilofSilverSpringsholdherbivorousturtlesamidalgae-coveredeelgrass.(FromOdum,H.T.Copyright©1957,EcologicalSocietyofAmerica.Trophicstructureandproducti vityofSilver Springs,Florida.EcologicalMonographs27:55–112.WithpermissionfromtheEcologicalSocietyofAmerica.)an excellent natural laboratory for Odum because of the constancy of its flow, temperature,and chemi-calproperties.Odumnotedthatthesprings’“hydrographicclimate”wasata steadystateand thatalong-standingclimaxcommunityhadresulted.Odumandhisteamofresearcherswenttoremarkablelengthstocapturedataoneveryaspectofthe SilverSpringsecosystem.Bendingoverthebowofamotoringboat,theymeasuredthetempera-turechangesinwaterasitflowedoutofthemainboilanddownstream.Byharvestingandweighingsampl esofeelgrassandthealgaethatcoveredit,theydeterminedthebiomassoftheseproducers.Theygrews nailsincagesonthebottomofthestreamandmeasuredtheirincreaseinweight.Theysnuckuponquadr atsmarkedintheeelgrassandpartedtheleavestocountatypeof sunfishcalled stumpknockers(Lepomisp unctatus)wheretheyhid.Cleverly,Odumandhisteamwereabletomeasuretheoverallmetabolismofthecommunitybycomparingoxygen levels in the water during the day and at night. The regular flow of SilverSprings carried all the “waste products” of the ecosystem past the measuring station three quarters of amiledownstreamfromtheboil.Atnightalltheorganismsinthecommunityrespired,loweringoxygenlevelsto apoint that reflected their cumulative metabolism. During the day, respiration continued, butthe photosyntheticproducersalsogaveoffoxygen.Thedifferencebetweendaytimeandnighttimeoxygenlevel s,multipliedbythevolumeofthecurrent,thereforeprovidedameasureofthedifferencebetweenphotosynthesisand respiration, which is the ecosystem’s net primaryproduction.Combiningallthesemeasurements,Odumwasabletocreateadetaileddescriptionoftheflowofenergyin the entire ecosystem. This analysis also allowed him to explain how Silver Springs maintained itself inaseeminglyunchangingstate.Basedontheratioofcommunityproductivitytostandingbio-mass,Odum estimatedthattheentirecommunityturnedover(diedandwasreplaced)eighttimesperyear.Clearly,smaller organi smsturnedovermanytimesmorethantheaverageandlargerlonger-livedorganismsless.Becauseofthedifferentamountofsunlightreachingtheprimaryproducersinwinterands ummer,therewasanaturalpulseinproductioninthesystem.Onemightexpectthisburstofproductivitytober eflected inaflushofnewgrowthintheeelgrassoranincreaseinthepopulationofprimaryconsumers.Infact,sta ndingbiomassandpopulationlevelswerestablethroughouttheyear.Odumevenreportedanoldboatcaptain askinghim whethertheeelgrassevergrew.Seasonalspikesinconsumer reproduction seemedto betimedto matchtheincreasedproductivity,andtheextrayounginonetrophiclevelwerequicklyeatenbytheextrayounginthenext,so thatalthoughmoreenergymayhavebeenflowingthrough,standingbiomassintheecosystemremained const ant.Negativefeedbackloopssuchasanincreaseinconsumptionthatabsorbsanincreaseinproduction helpecosystemsre-mainstable.Wherenegativefeedbackloopsmeetaconstantenvironment,asatSilver Springs,overall stabilitycanbemaintainedforanextendedperiod.第4章复杂的作品:生态景观设计的原则Principles of Ecological LandscapeDesign设计和管理生态系统一只蜻蜓掠过波光粼粼的池塘表面,抓住孵化后的蚊子之前在一个悬臂冲旁休息。