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WetlandvegetationofinlandAustralia
ForAustralianvegetation,ed.D.A.Keith,3rdedn.
JaneA.Catford1,2,3*,JaneRoberts4,SamanthaJ.Capon5,RayH.Froend6andSarasM.
Windecker1andMichaelM.Douglas7
1SchoolofBioSciences,TheUniversityofMelbourne,Vic3010
2FennerSchoolofEnvironment&Society,TheAustralianNationalUniversity,ACT
2601
3DepartmentofEcology,Evolution&Behavior,UniversityofMinnesota,StPaul,MN
55108,USA
4InstituteofAppliedEcology,UniversityofCanberra,ACT2617
5AustralianRiversInstitute,GriffithUniversity,Nathan,QLD4111
6SchoolofNaturalSciences,EdithCowanUniversity,Joondalup,WA6027
7SchoolofEarthandEnvironment,UniversityofWesternAustralia,Perth,WA6009,
*AddressfromJuly2016:CentreforBiologicalSciences,UniversityofSouthampton,
UniversityRoad,Southampton,SO171BJ,UK([email protected])
This is the final author-version (not type-set or copy-edited) of the following book chapter:
Catford, J.A., Roberts, J., Capon, S.J., Froend, R.H., *Windecker, S.M. & Douglas, M.M. (2017) Wetland vegetation of inland Australia. Australian Vegetation (ed. D.A. Keith). Cambridge University Press.p. 490-515. DOi: 10.1017/9781316339701
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Abstract
Wetlandsfedbyrainwater,surfaceflowsandgroundwateroccurthroughoutAustralia,even
inaridareas.Thischapterfocusesontemporarywetlandsandpermanentlywetsystems
thataredominatedbynon-woodymacrophytes,andusesninecasestudiesthatspan
Australiatoillustratetheirbiogeography,dynamicsandkeythreats.Thetypeand
distributionofwetlandvegetationreflectshydrology,climateandgeomorphology,fromthe
annuallyfloodedwetlandsofnorthernAustralia,tosalinelakesofaridandsemi-arid
Australia,togroundwater-dependentsystemsofthesouthwest,tobogsandfensoftheAlps
andTasmania.Wetlandplantshavedevelopedarangeofadaptationsandlifehistoriesto
toleratethedynamicwaterregimescharacteristicofAustralianwetlands,andcanbe
groupedintosevencategoriesthatreflecttheseadaptations.Waterbirdsandwatercan
connectspatiallyisolatedsystems,andseedbanksthatlastfordecadesallowspeciesto
dispersethroughtime.Waterregimeisastrongdriverofspeciescompositionand
abundance,thushydrologicalmodificationthroughwaterextraction,flowregulationor
reductionsinrainfallisasignificantthreattowetlandflora,andarguablytheprincipalthreat
forAustralianwetlandvegetation.Thedisplacementofnativemacrophytesbyexoticand
terrestrialspeciesisbothasymptomandcauseofecologicalchange,withexoticplants
oftenbeingbetteradaptedtomodifiedfloodingandfireregimes,livestockgrazingand
eutrophicationthannatives.Introducedlivestockandferalfaunaeat,trampleanduproot
nativeplants,anddegradetheirhabitat.Thesetypesofthreatsareexpectedtointensify,
increasingthechallengeforwetlandmanagementandpolicy.
Introduction
WetlandsareamongthemostvariableandproductiveofEarth’secosystems.Theyare
highlyvaluabletohumansandofcrucialimportanceforecosystemhealth.Beingatthe
interfaceoflandandwater,wetlandsarehomeandhosttonumeroustaxa,from
phytoplanktontomacroinvertebrates,tobirdsandmammals.Wetlandsoccurthroughout
Australia,varyingfrompermanentlywettoalmostpermanentlydry.Fedbyrainwater,
rivers,surfaceflowsandgroundwater,theboundariesofmanywetlandsshiftseasonally,or
inresponsetolongerclimaticcycles,asinundationvaries.Waterbirdsandwatercan
connectseeminglyisolatedsystems,allowingplantsandtheirpropagulestodispersewidely.
Thediversityofthesesystemsismirroredbythediversityoftheflorathatinhabitsthem.
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ThischapterexploresthetypesofwetlandsthatoccurinAustralia,usingcasestudiesto
illustratetheirbiogeographyanddynamics,andthekeydriversthatshapetheirvegetation.
OverhalfofAustralia’swetlandshavebeendestroyedsinceEuropeansettlement(Bennett
1997);weoutlinethemaindriversofthisloss,aswellassomemanagementandpolicy
initiativesdesignedtoarrestandameliorateit.Weprovideanoverviewofthemajorfactors
andprocessesaffectingwetlandvegetation,andgiveexamplesofwetlandplant
adaptations.
Wefocusontemporaryandpermanentwetlandsthataredominatedbynon-woody
macrophytes(orhydrophytes,i.e.plantsadaptedtolivinginwater,saturatedsoilorvery
moistsoil)andcanbecharacterisedbywaterregimesinvolvingperiodicorpermanent
inundationorwaterlogging.ThehighvariabilityofrainfallandrunoffinAustraliameansthat
someAustralianwetlandsmayonlyfloodonceeveryseveralyears,andpossiblylessoftenin
ephemeralaridzoneriversystems(Capon2003).Wetlandsfedbygroundwaterarebuffered
againstthisvariabilitybutbeingusuallyquitesmallandrelativelyfewaccountforonlya
smallpercentageofAustralia’swetland.Althoughmuchofthematerialdiscussedinthis
chaptercanapplytovegetationinflowingwaters,wefocusonvegetationoflentic(standing
orslowflowingwater)systems.
Driversofwetlandvegetation
Numerousabiotic,bioticandhumanfactorsaffecttheenvironmentalconditions,dispersal
opportunitiesandbioticinteractionsthatshapewetlandvegetation(Boultonetal.2014).
Theinfluenceoftheseinteractingfactorsdeterminesthebiogeographyandecologyof
wetlandvegetation(Fig.1).
Hydrologyisthekeyforcestructuringwetlandandriparianvegetation.Hydrologyrefersto
thedistributionandquantityofwaterinthelandscape.Hydrologyatthewetlandlevelis
characterisedbythewaterregime,whichencapsulatestheduration,frequency,magnitude,
timing(seasonality),rateofchange,andvariabilityofwettinganddrying.Wetlandsmay
experienceextremesinphysico-chemicalconditionsasaresultofchangingflooding
conditions.Becauseofdifferenthydrologicalconditionsassociatedwithwetlandbathymetry
(underwatertopography),wetlandvegetationtypicallyformszones(ormosaics)
demarcatedbysubtlechangesinwaterdepthorinundationduration(Fig.2).Thespecies
thatoccurineachzoneusuallyhavephysiological,morphologicalorlifehistoryadaptations
forthoseparticularhydrologicalandenvironmentalconditions(BrockandCasanova
1997).
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Wetlandhydrologyisintegrallylinkedwithgeomorphology(thephysicalformofthe
catchment,wetlandandassociatedwaterways)andhydraulics(flowdynamicsandvelocity),
andthesethreefactorsinteractcloselytoaffectotherkeydrivers.Togetherwithwater
quality(includingnutrientfluxes,sedimentloadsandioniccomposition)andsoiland
sedimentcharacteristics(lithology),thesefactorsdeterminethekeyenvironmental
conditionsaffectingwetlandvegetation(Fig.1).Plantsandanimalsmayaffecttheabiotic
characteristicsofasitebyalteringitsphysicalorchemicalcharacteristics.Forexample,
fallentreesaffecthydraulicsandchannelform,andcommoncarpdisturbthesediment,
uprootingplantsandincreasingturbidity.
Wetlandbiotamaytoleratechanginghydrologicalconditions,butmanycompletetheirlife
cyclesduringperiodsinwhichenvironmentalconditionsaresuitable.Theabilitytocolonise,
growandreproducequicklyduringsuchtimes,andpersistinadormantstatewhen
conditionsareunfavourable,isparticularlyimportantunderboom-and-bustconditions
(Bunnetal.2006).Dispersalintimeandspaceisthereforecrucialforspeciespersistence.
Plantscaneffectivelydispersethroughtimebystoringpropagules(ordiaspores:seeds,
sporesandvegetativefragmentsthatcandevelopintoanindividualplant)inseedbanksin
thesoil,litterandheldinplantcanopies.Indesertwetlandsthatmayonlybeinundateda
fewtimesacentury,seedsmustbeabletosurviveinterveningdryperiods,andgerminate
whenappropriatefloodingconditionsarise(Brocketal.2003).Liketerrestrialplants,
wetlandplantsdispersebyarangeofmechanism,includingvariousmeans,includingvia
wind,animalandself-propulsion,andmanyalsospreadclonallythroughaboveground
stolonsandbelowgroundrhizomes.However,alargefractionofwetlandplantsalsouse
waterasameansofdispersal(hydrochory),andsomemaybedispersedbyfruit-eatingfish
(ichtyochory;thoughthereappearstobenoevidenceofichtyochoryinAustralia:Jane
Roberts,pers.comm.2015)(CatfordandJansson2014).Water-bornedispersalenables
propagulestoreachsitesthatarehydrologicallyconnectedandlikelytohavesuitable
environmentalconditions.Hydrologicalconnectivityreferstopermanentandtemporary
connectionsamongwetlandsandother(mostlyaquatic)systems;itincludeslateral,
longitudinal(inthecasesofriverinewetlands)andvertical(surfacetogroundwater)
connections(Fig.1).
Waterbirdsareeffectiveindispersingpropagulesoverlongdistancestohydrologically
disconnectedsystems.Suchlongdistancedispersalfacilitatesspecies-andpopulation-
mixingamongwetlands,andcontributestothewidegeographicdistributions,spanning
continentsandbeyond,ofmanywetlandplantspecies.Wetlandsthatareisolated,likesmall
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dischargespringsfedbygroundwater,offerfeweropportunitiesforlongdistancedispersal
andlevelsofendemismaresubsequentlyhigherthaninmoreconnectedsystems,like
floodplainwetlands.
Likeanyvegetation,wetlandvegetationisaffectedbyinteractionswithothertrophiclevels
andwithothertypesofvegetation.Terrestrialvegetationmaycompetewith(orfacilitate)
wetlandvegetationunderdrierconditions,andherbivoresmaymodifytheabundanceof
certainspecies.Asdiscussedbelow,humansaffectwetlandvegetationdirectlyand
indirectlybyalteringenvironmentalconditions,dispersalopportunitiesandbiotic
interactions.Owingtotheinterplayofsomanyfactors,thedynamicsofwetlandscanbe
quitediverse,yettherearecommonalitiesasthecasestudiesbelowillustrate.
Ecologyandfloristicsofwetlandplants
Adaptationsofwetlandplants
Wetlandplantshaveadaptedtospecificfloodinganddryingcycles,andthisisparticularly
evidentinregenerationanddispersal.
Germinationandrecruitmentdirectlyaffectsplantcommunitycomposition.Waterregimes
caninfluenceplantphenology(thetimingofperiodicevents,suchasfloweringandseedset)
byprovidingcuesforgerminationanddispersal,aswellassuitableconditionsforseedling
growth(PettitandFroend2001).Floodingcanbreakdormancybycausingasuddenincrease
insalinityafterdroughtinaridorsemi-aridsystems(Nielsenetal.2007).
Althoughnotallwetlandplantsdispersebywaterandhydrochorousspeciesrarelydisperse
exclusivelybywater,waterisimportantfordispersalintwomajorways–asavectorandas
atriggerfordispersal.Attributesofpropagulesthatfacilitatehydrochoryinclude:buoyancy;
corkyorspongytissueoflowdensity;waxy,cuticularizedepidermis;andsurfaceswith
furrows,pitsorhairsthatcanenhancefloatingability(CatfordandJansson2014).In
climateswithpredictableseasonalpatterns,someriparianplantstimethereleaseof
propagulestocoincidewithparticularphaseoftheriverhydrograph.Thisadaptation
increasesthelikelihoodthatpropaguleswillbetransportedanddepositedonrecently
floodedsoils,providingconditionsfavourableforgerminationandrecruitment.Ifthe
seasonalflowpatternsarechanged,forexamplebyriverregulation,nativeplantsmayno
longerreleasepropagulesatoptimaltimes.Thesummer-autumntimingofpeakflowsin
regulatedriversinVictoriacoincideswiththeseedreleaseofexoticspecies,whereasnative
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riparianspeciesreleaseseedsinwinter-springwhenflowswerehistoricallyattheirhighest
(Greetetal.2012).
Functionaltypesofwetlandplants
Macrophytescanbeclassified intogroupsbasedontheiradaptationsto,andtoleranceof,
flooding.Themost commonlyusedwetlandplant classification scheme inAustralia is that
developedbyBrockandCasanova(1997).Thishierarchicalschemeclassifieswetlandplant
species into three main groups, Submerged, Amphibious and Terrestrial (with seven
subgroups)basedon their lifehistoryandresponse to flooding (Table1).Casanova (2011)
updatedthescheme,butweprefertherelativesimplicityoftheoriginalone.
TheTerrestrialgroupcomprisestwosub-groups,Terrestrial-dryandTerrestrial-damp.
Terrestrial-dryareunabletotolerateflooding,sooccurabovethehighwatermark
(Terrestrialdryspecies,Table1,Fig.2b).Terrestrial-dampspeciesarefoundaround
wetlands,reflectingtheirneedfordampsoilandtheirtoleranceofinfrequentinundation
(seealsospeciesdescribedinChapterXXonFloodplainforestsandwoodlands).
PlantsintheAmphibiousgroupareeitherTolerators,plantsthattoleratefluctuationsin
waterlevel,orResponders,plantsthatrespondtothem.AmphibiousTolerator-emergent
areoftenthedominantandmostconspicuoustypeofwetlandvegetation(Fig.2b,c).These
speciesareabletotoleratefluctuationsinwaterlevelsbyensuringthatasufficientportion
(roughlytwothirdsoftheirabovegroundbiomass)isabovethewater,allowingfor
respiration.AmphibiousToleratorlowgrowingspeciesgenerallycontributearelativelysmall
fractiontotheplantbiomassinawetland.
TherearetwotypesofAmphibiousResponders:plasticandfloating(Fig.2a,d,e,f).Plastic
specieschangetheirmorphologyandform,andmayhaveheterophyllousleaves,which
differwhethersubmergedoremergent(e.g.Sagittariaplatyphylla,Fig.2f).Waterliliesarea
classicexampleoffloatingresponders,astheirlonginternodesorpetiolesallowleavesto
floattothesurfaceofthewaterevenifitsdepthfluctuates(Brock2003).Floating
respondersincludessomeofthesmallestwetlandplants(Spirodela,LemnaandWolffia
species;seeFig.2e)andinvasiveexoticplants(Fig.2d),includingEichhorniacrassipes(water
hyacinth)andSalviniamolesta(salvinia,seeChapterXXonInvasiveplantsandplant
pathogens).
Submergedplantsgrowbelowthesurfaceofthewaterandhaveadaptationsthatenable
themtogerminate,growandreproduceentirelyunderwater.Submergedplantscannot
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tolerateexposuretoair.AswellasangiospermslikeVallisneriaspecies,manyofthe
submergedtaxaarecharophytes(freshwatergreenalgae),e.g.CharaandNitellaspecies.
TrendsinAustralianwetlandvegetationscience
WetlandplantecologyandwetlandvegetationscienceinAustraliawereintheirinfancy
priortothe1970s,mirroringglobaltrends(Fig.3).EarlystudyofAustralianwetlandplants
wasprincipallyconcernedwithspeciesandhabitatdescriptions(includingtaxonomy),and
aquaticweedmanagementinirrigationchannels.
Themainemphasisonemergentmacrophytesinthe1970sand1980sreflectedscientific
andmanagementprioritiesatthattime.Emergentmacrophyteswererecognisedasdrivers
oflakeecologyandappealedtomanagementinterestsbecauseoftheiruseasa“green”
alternativetotreatingwastewaterinconstructedwetlands(Brix1987).Australianresearch,
onEleocharissphacelataandTyphadomingensisforexample,alsocontributedto
internationalinterestinmacrophyteadaptationstoanoxicandhypoxicsubstrates(e.g.
Sorrelletal.1997).
Researchonsalinityandwaterregimedominatedwetlandvegetationresearchfromthe
1990sonwards.Salinityexperimentsinthe1990sbuiltonresearchfromthe1970sand
1980sbyaskingmorecomplexquestions,suchasidentifyingtolerancesofmacrophytes
usingconcentrationgradientsingrowthtrials.Experimentsinthe2000sconsidered
interactionsbetweensalinityanddrying,exploredgeographicvariabilityandinterpreted
findingsintermsofbiodiversity(Goodmanetal.2011).
Investigationsintowaterregimeshaveprogressedfromassessingtheresponseoffew
speciestoasingle-hydrologicvariable(e.g.emergentmacrophytesalongadepthgradient,
ReaandGanf1994),tocomparingmultiplespecies,totheinteractionofthewholewater
regimewithsalinity,sedimentationorplantcommunitycomposition(e.g.Catfordetal.
2011).Inparallel,perspectivehasshiftedfromshort-termquestions(suchaswithin-year
patternsofgrowth,resourceallocationandreproduction)toestablishingtheroleofwater
regimethroughouttheplantlifecycleandoverlargespatialscales.Yearsofresearchhave
revealedthatwetlandplantsemploymanystrategiestocopewithvariablehydrology.More
recently,scientistshavebuiltonthebodyofknowledgeofalteredwaterregimestotest
theoreticalquestions,forexampleofinvasionbiology(Catfordetal.2011).
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Australiahasmadeasignificantcontributiontowetlandecologythroughseedbankstudies.
Initiallyseedbankstudiesweredescriptive,andintentoncharacterisingseeddensityand
speciesrichness,understandingspatialandtemporalvariability,andestablishingtheroleof
hydrologyasadriverofthisvariability.Theyhavesincebecomeapowerfultoolallowing
comparisonamongwetlands,evaluationofantecedentconditions,scenariotesting,impact
assessment,andameansofestablishingrecoverypotentialandresilience.Oneoutcomeof
seedbankresearchinAustralialedtothedevelopmentofamacrophyteclassificationsystem
(BrockandCasanova1997).
Consistentwithglobaltrendsandterrestrialplantecology,wetlandsciencehasseen
growingemphasisoncharacterisingspeciesbasedontheirmorphology,responsesto
environmentalstimuli(e.g.flooding)andeffectsonecosystemfunctionandservices
(CatfordandJansson2014).Thisshiftismotivatedbythegreatergeneralisationthattrait-
basedclassificationscanoffertoecologyandmanagement:understandingplantresponses
andeffectsbasedonspeciescharacteristicsratherthanspeciesidentityallowsfindings
gatheredinonestudyandoneregiontobeappliedelsewhere.
Thefocusonsalinityandwaterregimehasnecessarilyresultedinfewerstudiesdedicatedto
otherenvironmentalfactors:forexample,effectsoffireandtemperatureonwetland
vegetationarepoorlyunderstoodoutsideofalpineandsub-alpineareas.Theshort-term
effectsofnativeherbivores(mainlywaterbirdssuchasblackswansandmagpiegeese),
exoticlivestock(cattle,horses,pigs)andexoticbenthivorousfish(commoncarp)onwetland
vegetationandseedbanksmaybelocallyknown,butthecumulativeanddifferentiallong-
termeffectsofbiotaonfloristiccompositionandstructureneedfurtherstudy.Plant-plant
interactions,factorsmaintainingdominanceorfacilitatinginvasion,andthenurseryeffects
ofstructurallydominantspecies(Jamesetal.2015),havebeeninvestigatedonlyrarely,and
consequentlytheirimportanceinstructuringwetlandplantcommunitiesislikely
underappreciated.
Casestudiesofwetlandtypes
WetlandsarefoundthroughoutAustralia,withtheirtypeanddistributionreflectingtheir
hydrology,climate(particularlyrainfallandevaporation)andtopographicandmorphological
features(Fig.1,Brock2003).NorthernAustraliahaswetsummers,southerncoastalpartsof
Australiathataretemperatehavewetwinters,andthearidandsemi-aridinterior,which
makesuptwothirdsofthecontinent,hashighlyunpredictablerainfall.Iffedbyrainfall,
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surfacerunofforriverflows,wetlandhydrologyreflectstheseclimaticpatterns.Floodingis
highlypredictableandseasonalinthetropics,whereasthesalineandepisodicwetlandsthat
dominatearidandsemi-aridregionscanbecharacterisedbytheir(wet)boomand(dry)bust
cycles.Seasonalorintermittentwetlandsaremorecommonnearthecoast,andwetlands
thataremorepersistentoftenoccurwhererainfallexceeds1000mmannually(Boultonet
al.2014;Brock2003).Incontrasttowetlandsfedbysurfacewater,manygroundwater-fed
systemsnaturallyhaveapermanentsupplyofwater.Springsfedbygroundwatercan
seeminglyoccurinunlikelyplaces,providingrareoasesinthemiddleofthedesert,buttheir
distributionreflectsthelocationofcracksandfissuresintheaquitardsthatconfine
groundwaterorwheresedimentsthatformtheaquiferprojectabovetheground(Fensham
andFairfax2003).Wetlandsfloodedbyriversarenecessarilyfoundalongriverchannels.The
distributionofwetlandsischangingassurfaceandgroundwaterisusedandregulatedby
humans,asclimaticpatternschange,andaswetlandsareinfilledandtheircatchments
modified.Theninecasestudiespresentedbelowillustratesomeofthisdiversity.
Floodplainwetlandsofthewet-drytropics
OneofthemoststrikingfeaturesofnorthernAustraliaistheextensiveareasoffloodplain
associatedwithmanyofitslargeriversystems(Fig.4a).Wheninflood,thewholeexpanseof
ariverfloodplaincanbeinundated;wetlandsarenotjustrestrictedtolowerelevationareas
ofthefloodplain.Inthelowerrainfallregions,suchastheGulfofCarpentariaandthe
Kimberley,floodplainsmayonlybeinundatedforafewweeksayearandcontainveryfew
vascularplants.Incontrast,wetlandsinthehigherrainfallregionsmaybeinundatedforup
tohalfoftheyearandsupportexpansiveareasofaquaticmacrophytes,grassesandsedges
(Pettitetal.2011).Theselattersystemshavebeenthefocusofmuchofthepastresearch
ontropicalfloodplainwetlands,particularlyintheAlligatorRiversRegioninKakaduNational
Park(Finlayson2005).Formedonly1,500–6,000yearsago,thesetropicalfloodplainsare
relativelyrecentgeomorphologicalfeaturesandcontainaflorathatiscommontomany
othertropicalregionsoftheworldwithlessthan25%oftheplantspeciesendemicto
northernAustralia(Cowieetal.2000).
Thepronouncedseasonalityoftherainfall,andassociatedpatternsofannualfloodingand
drying,istheprimarydriverofvegetationdynamicsintheregion.Localvariationin
vegetationcommunitycompositionreflectsmicrotopographyandlocaldifferencesin
inundation(Finlayson2005).Thepredictabilityofthetimingandmagnitudeoffloodsthat
drivewetlandplantdynamicsispositivelycorrelatedwithfishspeciesrichness,bird
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populationstabilityandriparianforestproductioninbothAustralianandSouthAmerican
floodplains(Jardineetal.2015).AfewspeciesdominatelargeareasofAustraliantropical
floodplains;forexample,Oryzaspecies(wildrice),Eleocharisspecies(spike-rush),
Hymenachneacutigluma(nativehymenachne),Pseudoraphisspinescens(watercouch)and
waterlilies(NymphaeaspeciesandNymphoidesspecies)(Finlayson2005).Althoughthese
systemsarerelativelylowinplantspeciesrichnesscomparedwiththesurroundingsavanna
landscape,theyarehot-spotsofprimaryproductionandsupportanabundanceoffauna,
particularlyfishandwaterbirds(Finlaysonetal.2006).RecentresearchonAustralia’s
tropicalriverecosystemshashighlightedtheimportanceofprimaryproductioninfloodplain
wetlands,particularlybyepiphyticalgae,forsupportingaquaticecosystemsofthe
floodplain,mainriverchannelandestuary(Jardineetal.2012).
Incontrasttomanyfloodplainsystemsinmorepopulatedregions,thehydrologyof
Australia’stropicalfloodplainsremainslargelyintact.However,theyhavebeenlistedasone
ofAustralia’stenmostvulnerablehabitatsduetoexoticplantinvasions,whichtransform
thestructureandfunctionofthesesystemsandtheriskofsealevelrise(Lauranceetal.
2011).InvasiveperennialgrassessuchasUrochloamutica(paragrass,Fig.4d)and
Hymenachneamplexicaulis(olivehymenachne)wereintroducedforcattlegrazingandhave
sincespreadlongdistancesassistedbyfloodsandwaterbirdsandnowcoverincreasingly
largeareasofsomefloodplains,includingthoseinKakaduNationalPark(Setterfieldetal.
2013).AlthoughsuccessfullymanagedinKakadu,theSouthAmericanwoodyshrubMimosa
pigra(Mimosa),isaseriousweedonseveralfloodplainsintheNorthernTerritory
(Setterfieldetal.2013).Theirlowelevation(mostare<2mabovesealevel)makesthese
coastalfloodplainshighlysusceptibletosea-levelrise(Catfordetal.2013),whichhas
alreadytransformedareasoffreshwaterwetlandtosalineswamp,includingmorethan
17,000haontheMaryRiverintheNorthernTerritory(MulrennanandWoodroffe1998).
Desertfloodplainwetlandsinaridandsemi-aridAustralia
DesertfloodplainsoccurthroughoutinlandAustraliabutareparticularlywell-developedin
theChannelCountryoftheeasternLakeEyreBasinand,toaslightlylesserextent,inthe
lowlandsofthewesternMurray-DarlingBasin(Caponetal.2016).Characterisedby
extremelylowtopographicgradientswithmeanannualrainfallbelow250mm,these
easterndesertfloodplainstypicallyencompasscomplexchannelnetworksthatdistribute
floodwatersovervastareasduringperiodsofhighriverflows.Incontrast,theephemeral
floodplainsofAustralia’scentralandwesterndesertsareusuallyassociatedwithpoorly
defineddrainagesystemsandaretypicallyinundatedbyflashyoverlandflows.Ineither
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case,thedefiningcharacteristicofdesertfloodplainsistheirhighlyvariableand
unpredictablepatternsofwettinganddrying,whichhaveanoverridinginfluenceonthe
compositionandstructureoftheirvegetation(Capon2005).
Desertfloodplainwetlandsencompassthewholefloodplainandarenotrestrictedto
depressionswithinthefloodplain.Theysupportadiverserangeofshortgrass,sedgeand
forbassociationsthatshiftincompositionandstructurebothtemporally,inresponseto
wettinganddrying,andspatiallyinrelationtofloodhistory(Capon2005).Plantspecies
inhabitingtheseenvironmentstendtobewidelydistributed,manyhavingcosmopolitan
distributionsextendingbeyondthearidzone(Boxetal.2008).Commonfamilies
representedincludeAsteraceae,Amaranthaceae,Chenopodiaceae,Cyperaceae,
Euphorbiaceae,Fabaceae,Goodeniaceae,Malvaceae,Nyctaginaceae,Poaceaeand
Polygonaceae.Manyspeciesmaintainlarge,persistentsoilseedbanks,whichenableplants
toavoidunfavourableconditions(e.g.drought)andre-establishwhensuitableconditions
arise,typicallyfollowingthedrawdownoffloodwaters(Capon2007).Inthearidzone,
woodyvegetationismostlylimitedtowatercoursesandtheirbanksoralongflood
strandlines.Furthertotheeasthowever,largeareasofsemi-aridfloodplainwoodlandsalso
occur(seeChapterXXXonFloodplainforests).Low-lyingswampyareasalsofrequently
supportwetlandshrublands(e.g.ofDumaflorulenta,Chenopodiumauricomum).
Waterresourcedevelopment,ofbothsurfaceandgroundwaters,probablyrepresentthe
greatestthreattoAustralia’sdesertfloodplains,governedastheyarebyhydrology.Land
useispredominantlylivestockgrazing.Althoughovergrazingmayhavesignificanteffectson
vegetationduringdryperiods(e.g.severevegetationcoverreduction,soilcompaction),
cattlehavelimitedaccesstovegetationwhenitisatitsmostproductiveanddiverse(i.e.
followingflooding)duetosurfaceinstability.Recentintensificationofminingexploration
andextractionalsoposeathreattodesertfloodplainvegetationasaresultofinfrastructure
development,wateruseandthedisposalofexcessgroundwater.Climatechangehasthe
potentialtofurtherinfluencevegetation,especiallywherewaterregimesarealtered.
Inlandsalinelakes
Salinelakesandwetlands,includinglakes,claypansandrain-filleddepressions,areamajor
featureofinlandAustralia,accountingforover80%oftotalwetlandareaonthecontinent
(TimmsandBoulton2001,alsoseeChapterXXonChenopodshrublandsandsaltlakes).
Additionally,manyfreshwaterlakesbecomesalineastheydry.Mostsalinelakesoccurin
WesternAustraliaandSouthAustralia(e.g.LakeEyre)buttherearealsomanyintheeastern
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mainlandstates.Mostareephemeralortemporary,butsomewetlands,especiallyin
southernAustralia,canbeseasonalorpermanent.Salinelakesalsovaryinwaveactionand
turbidity(TimmsandBoulton2001).
Vegetationcompositioninsalinelakesisdrivenbysalinity,waterregimeandturbidity
(Porteretal.2007).Speciesrichnesstypicallydeclineswithincreasingsalinityandisusually
greaterintemporary,ratherthanpermanent,lakes.However,onlyafewalgaland
angiospermspeciesarecapableofpersistingunderbothhighlevelsofsalinityandwidely
fluctuatingwaterlevels.Nevertheless,evenhighlysalinelakescansupportveryproductive
submergedvegetation(Brock1994).Rapidgrowthofsubmergedplantscanoccurunder
conditionsoflowturbiditywhensalinitiesarebelow~60gL-1(TimmsandBoulton2001).
Charophytes(e.g.NitellaspeciesandLamprothamniumspecies)aretypicallywell
representedandaquaticforbsareusuallydominatedbyspeciesofRuppiaandLepilaena.
Lakesareoftenfringedbysalt-tolerantsamphires(e.g.Halosarciaspecies,Tecticornia
species),succulents(e.g.Gunniopsisspecies)andsedges(e.g.Cyperusspecies).Forbsand
grassesmaycolonizesomeephemeralandtemporarysalinelakesduringdryperiods,but
somelakeswillformsaltcrustswhendryandremainfreeofvegetation(Porteretal.2007).
Threatstoinlandsalinelakesincludedrylandsalinization,whichhasbeenawidespread
resultofalteredhydrology(fromwaterextractionandriverregulation)andvegetation
clearinginsouthernAustralia,particularlysouth-westWesternAustralia(Halseetal.2003).
Drylandsalinity,alongwithadryingclimate,hasthepotentialtosignificantlyalterthe
salinityandwaterregimesofinlandsalinelakesinmuchofAustralia’ssouth.Increased
nutrientloadsinrunofffromsurroundingfarmsmayalsoposeathreat(Timms2005).
Extractionofmaterialsfromsalinelakes,aswellasfurtherchangestohydrologyresulting
frommininginfrastructureandwaterresourcedevelopment,arealsolikelytohave
significanteffects(Timms2005).
GroundwaterdependentspringsoftheGreatArtesianBasin
Springwetlandsarepermanentwetlandsfedbygroundwaterfromunderlyingaquifers.
SpringwetlandsoccurthroughoutAustraliabutareparticularlydistinctiveinarid
environmentswhere,asinothercountries,theyareoneofthefewsourcesofpermanent
water(Fig.4b,FenshamandFairfax2003).Springwetlandscanoccurinareaswhere
sedimentsthatformtheaquiferprojectabovetheground(outcropsprings).Theseinclude
springsinaquiferrechargeareaswhereratesofrainfall-derivedinflowexceedthroughflow
andwherewater-bearingsedimentsareclosetothegroundsurface,whichoftenoccursat
13
theedgesofanaquifer.Groundwaterfeedingoutcropspringscanhaveshortresidence
times(i.e.waterhasnotbeenintheaquiferforlong),sothesetypesofspringsmaybe
ephemeral.Dischargespringsoccurwherewaterflowsupwardsthroughconfiningbeds
(aquitard)viafaultsorconduitsintheoverlyingsediments(FenshamandFairfax2003).
Dischargespringsmaysustainsmallpermanentwetlandsbecausegroundwaterfeeding
thesesystemshasalongresidencetimeintheaquiferandthusshowsminimalfluctuations
inflowrates.
TheGreatArtesianBasinisanaquifersystemthatunderlies22%ofnorth-easternAustralia,
extendingoverpartsofQueensland,NSW,SAandNT(Powelletal.2015).Waterpercolates
throughthesandstoneaquifergenerallyinasouth-westerlydirection,withsandstoneintake
bedslocatedmainlyalongtheeasternmargininnorthQueensland(Powelletal.2015).
SpringsintheGreatArtesianBasinareoftenreferredtoasmoundsprings,butonlyasmall
fractionofspringwetlandshavevisiblemoundsassociatedwiththem.Moundsmaybe
formedbyupwellingofsubsoilintheartesianwater,fromvegetation-derivedpeat
accumulation,fromtheexpansionofsurfaceclaysandfromaccretionofaeoliansandor
calciumcarbonate(FenshamandFairfax2003).UnlikespringwetlandsinaridareasofWA
andNT,whicharethoughttohavegreaterconnectivity,thespringwetlandsoftheGreat
ArtesianBasinhavehighlevelsendemisminbothfloraandfaunaandarethusofhigh
conservationvalue.Of325nativevascularplantsrecordedintheGreatArtesianBasinspring
wetlands,atleasteightappeartobeendemic,withpresumablylittleopportunityfor
dispersaloutsideoftheseisolated,andenvironmentallyuniquesystems.Theseinclude
Myriophyllumartesum,Eriocauloncarsoniiandrelatedsubspecies,andSporoboluspamelae,
alongwithdescribedspeciesfromthefamiliesPoaceae,CyperaceaeandScrophulariaceae.
Atleast30exoticplantspecieshavealsobeenrecordedinthesewetlands(Fenshamand
Price2004).
SpringwetlandsintheGreatArtesianBasinareseverelythreatenedbygroundwater
extractionandaquiferdrawdown.Between1880and1990s,waterlevelsweredrawndown
byasmuchas100minpartsofQueensland.Asaresult,89%ofspring-groupshavebecome
inactivethroughoutmuchofQueenslandoverthelastcentury(FenshamandFairfax2003).
Thedischargespringsaremostaffectedbygroundwaterextractionand87%ofspringsinthe
dischargeareahavebecomepartlyorcompletelyinactiveduetogroundwaterdrawdown,as
opposedtoonly8%intherechargearea.Ofthespringsthatarestillactive,26%havebeen
severelydegradedthroughwetlandexcavation,whichisintendedtoincreaseaccessfor
livestock.Otherthreatsincludeexoticspeciesusedforpondedpasture(e.g.Hymenachne
14
amplexicaulis,Urochloamutica,Echinochloapolystachya),livestocktrampling,exotic
animals(e.g.pigrooting)andfire(FenshamandFairfax2003).Toprotecttheremaining
springwetlands,nomoreboresshouldbedevelopednearsprings,boresclosetosprings
shouldbecapped,andspringexcavationanduseofexoticpondedpastureshouldbe
prohibited(FenshamandFairfax2003).Greaterprotectionofspringwetlands,especiallyin
dischargeareas,throughthereservesystemwouldbevaluable.
Freshwaterwetlandsoncoastalfloodplainsofsouth-easternAustralia
CoastalfreshwaterwetlandsoccuraroundthecoastofAustraliaonsandyloamsoilsof
waterloggedorperiodicallyinundatedalluvialflats.Primarilyfedbyrivers,coastal
freshwaterwetlandsaresimilarinvegetationstructuretoinlandfloodplainwetlands,but
tendtobelocatedatelevationslessthan20mabovesea-level,havesandiersoils,higher
rainfall,andperiodicsalinewaterinput(Whiteheadetal.1990).RefertoChapterXXfor
Halophyticvegetation,includingcoastalmangrovesandsaltmarshes.
Vegetationcommunitiesincoastalfloodplainwetlandsarelargelydeterminedbyfrequency,
durationanddepthofinundation,butarebeingincreasinglyaffectedbyhumanactivities
thatincludelivestockgrazing,catchmentlandclearingandpollution(Pressey&Middleton
1982).Freshwaterwetlandsincoastalplainstypicallyhavelowcoverofwoodyspecies,
thoughwilloccasionallyhavescatteredtrees(e.g.Casuarinaglauca,Melaleucaericifolia)
thatarecommoninneighbouringswampfloodplainforests(deJong2000).Wetlandsthat
aredrymostofthetimearetypicallydominatedbydensegrassland,sedgeland,orrushland
under0.5mtall.CommonspeciesincludePaspalumdistichum,Leersiahexandra,
Pseudoraphisspinescens,andCarexappressa.Wetlandswithmoreregularcyclesof
inundationanddryingmaysupporttalleremergentspecies,suchasBolboschoenusspecies
andSchoenoplectusspeciesupto1mtall.CommonherbsintheseareasincludeHydrocharis
dubia,Philydrumlanuginosum,Ludwigiapeploides,Marsileamutica,andMyriophyllum
species.Aswaterlevelsbecomedeeperormorepermanent,thesesystemsbegintodevelop
morefloatingvegetationsuchasAzollaspecies,Lemnaspecies,Hydrillaverticillata,
Ceratophyllumdemersum,Nymphoidesindica,Otteliaovalifolia,andPotamogetonspecies.
Landdevelopmentisaparticularthreatforfreshwaterwetlandsalongthecoastbecauseof
thehighvalueoftheland,andbecausehighorganicmatterinthesedimentsoffreshwater
wetlandsmakethemidealforagriculturaldevelopment,includingexoticpasture.KooWee
RupSwamp,historicallylocatedalongthecoastbetweenMelbourneandGippsland,was
onceoneofthelargestfreshwaterwetlandsinVictoria.Extendingover40,000hectares,this
15
swampwasdrainedforagriculturein1876,destroyingdensestandsofswamppaperbark
(Melaleucaspecies)andgiantbulrush(Typhaspecies)(YugovicandMitchell2006).Coastal
wetlandsfilteroverlandflow,improvingwaterqualitybeforeitenterstheocean.The
degradationandlossofwetlandscanresultinincreasedsedimentandnutrient
concentrationsinrunoff,whichmayleadtoalgalblooms,increasedturbidity,andthe
degradationofmarineecosystems(Johnsonetal.1999).Coastalwetlandsarethemselves
threatenedbyeutrophication,especiallybynitrogenandphosphorusthatoriginatesfrom
urbanandagriculturalareas,whichresultsinthedisplacementofnativespeciesbyexotic
species.
Incoastalareas,wheremostofthepopulationresides,manywetlandswereeither
‘reclaimed’,viadrainageorinfilling,orregulatedbycontrolstructures(e.g.barrages)to
permiturbanandagriculturaldevelopment.Thisledtothefragmentation,degradationand
lossofalargeproportionofAustraliancoastalwetlands,whichcontinuetobeverypoorly
researchedecosystems.Insouth-westernWesternAustralia,around70%ofcoastal
wetlandsareestimatedtohavebeenlostsinceEuropeansettlement(Davisetal.2015).In
manycoastalregions,wetlanddrainageandlandusechangehavealsoledtotheexposure
ofunderlyingsulfidicsediments(i.e.acidsulfatesoils)withawiderangeofdetrimental
outcomesincludingdiminishedplantgrowth(Whiteetal.1997).
BillabongsandlakesofthesouthernMurray-DarlingBasinfloodplain
ThefloodplainsoftheMurray,MurrumbidgeeandGoulburnRiversareinsetwithtwomajor
typesofwetlandsthatdifferingeomorphology–billabongsandlakes(seeChapterXXon
Floodplainforeststhatdescribesthedrierpartsfloodplains).Thesefill,drawdownanddryin
responsetoriverinundation,whichvariesacrossthefloodplainresultinginamosaicof
waterregimes,rangingfromnearpermanenttoepisodic.
Billabongsareformerriverchannels,typicallysmall(surfacearea<10ha),mostlyclay-
based,andveryabundant,numberingthousandsperfloodplain.Thoughbillabongsmaybe
referredtoasoxbowlakes,billabongscantakemanyshapesandforms,andoftensimply
featureasdepressionsinthefloodplain(Fig.4c).Thediversityofwetlandplantswithina
billabongisstronglyinfluencedbywetlandform:deeperwetlandshavelittoralvegetation
ontheirslopesandsubmergedherblandontheirbedwhenflooded,whereasshallower
wetlandsmayhavesedgelandthroughout.Floodplainlakesaredeflationbasinswithaclay
orsandlunetteononemargin,typicallylarge(surfacearea100-600ha),andaregilgai,clay
orsand-based(ifnotin-filledbysediment):theynumbertenstohundredsperriversystem
16
(Pressey1986).Theircompactroundshapeanduniformfloorresultinlowenvironmental
heterogeneity,soindividuallakestypicallyhaveasingledominantvegetationtype.
Themosaicofwaterregimesoccurringacrossafloodplainmeansfloodplainwetlandsmay
carryacompletespectrumofgrowthforms,suchasriverredgum(Eucalyptus
camaldulensis)woodland,lignum(Dumaflorulenta)orchenopodshrubland,sedgeland,
varioustypesofgrassland,andvarioustypesofaquaticherbland,andthenumberofspecies
iscorrespondinglylarge.ThespeciespoolisamixofAustralianfamiliesandspecies
(MyrtaceaeandChenopodiaceaefortreesandshrubs),cosmopolitanorwidely-distributed
species(e.g.Phragmitesaustralis,Potamogetoncrispus),Australianaquaticandamphibious
representativesofcosmopolitanorwidely-distributedfamilies(Cyperaceae,Poaceae,
Typhaceae,Juncaceae,Juncaginaceae,Haloragaceae,Ranunculaceae,Elatinaceae,
Polygonaceae),andafewspecieswithrestricteddistributions(e.g.Amphibromusfluitans,
Myriophyllumporcatum).Althoughthespeciescompositionoffloodplainwetlandsishighly
variable,wetlandswithsimilarwaterregimeshavefunctionallysimilarplantcommunities
(Casanova2011).
Overthelast200years,floodplainsofthesouthernMurray-DarlingBasinhavebeen
dramaticallyalteredthroughvegetationclearing,cultivation,livestockgrazing,sediment
fluxes,alteredwaterquality,riverregulation,salinizationandacidification.Thewidespread
declineofsubmergedmacrophytesandhighabundanceandrichnessofexoticspecies
exemplifythis(Catfordetal.2011).Riverregulationisamajor(butnotsole)factor
determiningtheabundanceofexoticspecies.Inbillabongs,20-40%ofspeciesmaybeexotic,
andmostoftheseareshort-livedterrestrialspeciessuchaspasturegrassesoragricultural
weeds.Theirpresenceisalegacyofpastagriculturalenterprises(Luntetal.2012)buttheir
abundanceisboostedbythegenerallydrierconditionsthatriverregulationimposes.These
conditionshavethedualeffectofdisadvantagingthealreadyestablishednativeamphibious
speciesandofprovidingconditionssuitableforexoticterrestrialspecies,butnotnative
terrestrialspecies(Catfordetal.2011).Regulationdisruptsthematchbetweennative
speciesphenologyandfloods,andseasonalflowinversion(highflowsinsummer)favours
thedispersalandestablishmentofexoticspeciesgenerally(Greetetal.2012)thusriver
regulationexacerbatesthethreatofinvasiveexoticssuchasamphibiousNymphaea
mexicanaandSagittariaplatyphylla(Fig.4d&f).
Submergedmacrophyteabundanceanddiversityhasbeenadverselyaffectedbyi)increased
sedimentfluxfromerodeduplands,whichhasincreasedturbidityandreducedphoticdepth;
ii)exoticcommoncarp(Cyprinuscarpio)thatcandislodgemacrophytesthroughtheir
17
benthivorousfeedingstrategy,astrategynotusedbynativefish;andiii)theprolonged
MilleniumDroughtintheearly21stcentury.Tolerancetosuchpressuresrequirescapacityto
growunderlowlight,bulkyrhizomesandrelativelylong-livedseed(6-9years)thatcanaid
recolonisation(Brock2011).Onlytherobustperennial,Vallisneriaaustralis,isknownto
havethesecharacteristics.
BogsandfensoftheAustralianAlpsandTasmania
TheAlpineSphagnumBogsandAssociatedFensecologicalcommunitypredominantlyoccurs
intheAustralianAlpBioregion,whichspans375kmfromMountBawBawinVictoriato
southernNewSouthWalesandthewesternmarginofAustralianCapitalTerritory.These
communitiesarealsofoundinTasmania,andtypicallyoccurabovethetreelineinalpine,
subalpine,andmontaneenvironments.Thereisnostrictaltituderequirement,however,
sincelocalclimaticconditionscanenablethesecommunitiestoflourishatloweraltitudes
andbelowtheclimatictreeline.Alpinebogsandfensshelterendangeredplants,suchasthe
BogongEyebright(Euphrasiaeichleri),andaregenerallylessthan1hectareinsize
contributingtotheirprotectionundertheEnvironmentalProtectionandBiodiversity
ConservationActof1999.Forabroaderdescriptionofalpinevegetation,seeChapterXX.
Alpinebogsandfensarebothpeatlandecosystems.Peatisterrestrialsoilcomposedofat
least20%organicmatter,whichisatleast30cmdeep.Peatlandsoccurinareaswithhigher
waterinflowthanoutflow,orwherethereisalargesupplyofgroundwater.Waterlogged
soilproducesreduced,anaerobicconditionsthatinhibitactivityofmicrobialdecomposers,
allowingcarbon-richundecomposedplantremainstoaccumulate.Accumulationofplant
detritusintopeatcanproducesmalldams,whichfurthermodifyhydrologyinfavourof
continuingpeatformation.Dynamicgrowthofpeatlandscanproduceamosaicof
heterogeneoushabitatthatsupportsarangeofvegetationcommunities(Camill,1999).
Althoughalpinebogsandfensarebothcharacterisedbypresenceofpeatsoils,andoften
co-occurinthelandscape,theydifferinnutrientlevelsandthevegetationcommunitiesthey
support.Fensareprimarilyfedbysurfaceflowandgroundwater,whichisnutrientrich,and
supportsedgecommunitiesdominatedbyspeciessuchasCarexgaudichaudiana.Sphagnum
mossesaregenerallyabsentfromtheseareasastheyareoutcompetedbyplantsthatare
betterabletoexploithighnutrientenvironments.Bogs,incontrast,haveverylownutrient
levelsbecausetheymostlyrelyonrainwater(thoughstreamscanrunthrough“valley
bogs”).BogsoilsaregenerallymoreacidicandsupportsphagnummossessuchasSphagnum
18
cristatumandSphagnumnovozelandicumandsclerophyllousshrubsupto1mtallsuchas
Bossiaeafoliosa,Epacrisglacialis,andGrevilleaaustralis.
Alpinebogsandfensfaceanumberofthreatsrelatedtotheirrestrictedgeographicalextent
andsmallpatchsize.Therearemorethan11,000bogsandfensthroughouttheAustralian
AlpBioregion,thehighaltitudeareasofsouth-easternAustralia’sGreatDividingRange.
Theirsmallsizeandpatchydistributionmakethemdifficulttoprotectagainsttrampling
fromlivestockandferalanimals(e.g.horses,deer,pigs).Exoticungulates(e.g.cattle,sheep,
horses,pigs)tramplebogandfenvegetationandalsocreateincisionsinpeatsoilthatresult
inwetlanddrainage.
Presenceofwaterisvitalforthepersistenceofhydrophyticbogandfenvegetation,andso
threatsthatimpactwatersupplyorpeatstructuralintegrityendangertheselargelyendemic
communities(Wahrenetal.1999).Climatechangeispredictedtoincreaseoccurrenceand
severityofdroughtandfire,whichdamagepeat.Firescandestroycarbon-richpeat,
changingthephysicalstructureofbogandfensoilsandinhibitingtheirabilitytocaptureand
storewater.Modelspredictthatalpinebogsandfensaroundtheworldareamongthe
ecosystemsmostthreatenedbyclimatechange(Schuuretal.,2008).
Groundwaterdependentwetlandsofthesouthwest
Characteristicsoffreshwaterwetlandvegetationcommunitiesinsouth-westernAustralia
arelargelydeterminedbywetlandwatersource,sedimenttypeanddurationofinundation
(DEC2012).Thereisahighnumberofpermanentlyandseasonallyinundated,shallow(<3
m)wetlandsintheregionforwhichgroundwateristhedominantsourceofwater,either
fromlocalandregionalsuperficialgroundwaterorfromperchedgroundwaterheldbyan
impedingsedimentlayerthatisrechargeddirectlybyrainfall.
Despitehavingahot,dryMediterraneansummer,thesouthwestishometoflorathat
representstheworldcentrefordiversityinanumberofwetland-associatedplantfamilies
(e.g.Droseraceae,Restionaceae,Juncaginaceae,CentrolepidaceaeandHydatellaceae).The
vegetationcommunitiesincludearangeofendemicwetlandgenera(e.g.Reedia,
Cephalotus,Tribonanthes,Epiblema,Schoenolaena,Cosmelia,Euchilopsis,Acidonia,
Homalospermum,PericalymmaandTaxandria)andhighlevelsoflocalandregional
endemism.ThesouthernSwanCoastalPlainalonehasapproximately445wetland-
associatedplanttaxa,74%ofwhichareendemictoWesternAustraliaand3%endemicto
thesouthernSwanCoastalPlain(DEC2012).
19
ThedominantgrowthformsinSwanCoastalPlainwetlandsappeartoreflecttheseasonally
dryMediterraneanclimate.Thefloraisrichinshrubs,butherbsandsedgesmakeup77%of
taxa(Fig.4e).Although78%ofspeciesareperennial,22%oftheseregrowtheir
abovegroundbiomassfromundergroundstorageorganseachyear(DEC2012)–alikely
adaptationtoseasonaldroughtanddisturbancesuchasfire.
Seasonallywaterloggedwetlandsaretypicallymaintainedviaperchedgroundwaterand
havethegreatestdiversity(DEC2012).Thisfloristicdiversityreflectsspatialandtemporal
patternsinwaterlogging(e.g.duration),sedimentstratigraphy(e.g.distributionoforganic
fraction)andcompositionofimpedinglayer(e.g.ironstone,calcreteorgranite).These
systemsaredryinsummer,withtheplantdiversitynotbecomingapparentuntillatewinter
andspringwhenthesedgelandsandherblandsregrowfromtheirundergroundstorages.
Theytypicallysupportamosaicofvegetationunits,especiallywoodlands(dominatedby
EucalyptusrudisandMelaleucaspecies),shrublands(dominatedbyadiversesuiteofspecies
ofMyrtaceaee.g.Calothamnuslateralis,Melaleucateretifolia,M.viminea,Astarteaspecies,
Pericalymmaellipticum,Kunzeaspecies,Hypocalymmaangustifolium,andsome
Proteaceae),sedgelands,herblandsandrarelygrasslands.
Seasonallywaterloggedandperchedgroundwaterdependentwetlandswereonceextensive
inthesouthwest,particularlyontheSwanCoastalPlain,butduetolanddevelopmentand
hydrologicalchanges,manyarenowonlyrepresentedbyremnantportions(DEC2012).
GroundwaterlevelsontheSwanCoastalPlainhavebeendecliningsincethe1970sdueto
changesinclimate,landuseandgroundwaterextraction.Declininggroundwaterlevelshave
affectedvegetationingroundwater-dependentwetlandsinanumberofways,including:
reducedsurfacewaterlevelsandinsomecasesdryingandlossofwetlandhabitat;peat
fires;declininghealthanddeathofsomegroundwater-dependentvegetation;changesin
flowfromsprings/seeps;andacidificationofgroundwaterandwetlands(Sommerand
Froend2014).Withchanginghydrologicalconditions,manypermanent/semi-permanent
wetlandsaredevelopingvegetationcharacteristicsofseasonallywaterloggedwetlands,
whilstformerlywaterloggedareasarebeingencroachedbydrylandspecies.Longerperiods
ofexposed,drysedimentshavealsoleadtoincreaseddamagefromillegalvehicleaccess
anddisturbanceofsedimentsurfaces.Thewaterloggedfringesofmorepermanentwetlands
havealsobeenextensivelyreclaimedaswaterlevelsgraduallyfallandurbanisation
encroaches.
20
Artificialwetlands
Artificialwetlandsarewaterbodiesthatarewhollyorlargelyanthropogenicinorigin,in
contrasttonaturalwetlandsthathavebeenformedsolelybyhydrologicaland/or
geomorphicprocessesovertime.Theyaretypicallyusedforstockwatering(farmdams,
bore-fedwetlands),waterstorage(irrigationwaterstorages,weirpools,uplandreservoirs,
lowlandstorages),amenity(urbanlakesandponds,Fig.4f),watertreatment(wastewater
treatmentponds,pondsandmeadowsaspartofwater-sensitiveurbandesign)or
production(ricefields).Artificialwetlandsdifferfromnaturalwetlandsinbeingyounger,
andhavingdifferingcombinationsofsize,shapeandwaterregime:reservoirsandweirpools
areconsiderablydeeper;storagesandamenitylakesarepermanent;weirpoolsandamenity
lakeshavestablewaterlevels;ricefieldsprovideshallowclearwaterinspring-summerina
semi-aridregion.
Awetlandassemblagedevelops(orisplanted)thatisdominatedbynativespecies(Dugdale
etal.2009)butdistinctfromitsregionalequivalents(Badman1999).Riverinestoragesand
amenitylakesarenotableexceptionstonativedominance;theseareoftendominatedby
floatingorsubmergedmacrophytes,includinghighlyinvasiveexoticspecieslikeEgeria
densa,CabombacarolinianaandNymphaeamexicana(Fig.2d,Dugdaleetal.2009).
Characteristicsofartificialwetlandsthatmayconstrainvegetationassemblagesfrom
developingare:highturbidity,whichexcludessubmergedplants;waterdeeperthan1.5m
withsteepverticalbanks,whichprecludesthedevelopmentofalittoralzone;permanent
waterorextremefluctuationswhichprecludesuccessfulestablishmentandpersistence
(Casanovaetal.1997).
Hydrologicalconnectivityisvariable.Afewfarmdamsandallbore-fedwetlandsare
hydrologicallyisolated,andtheirplantassemblageshavedevelopedindependentlyof
hydrochory.Some,notablymeadowsinurbancontexts,areonlyintermittentlyconnected.
ThecontinuoushydrologicalconnectivityofriverinestoragessuchasLakeMulwalaonthe
RiverMurraymeansacontinualthreatofdownstreamdistributionofvegetativefragments
ofundesirablespecies.Althoughutilitarianinintent,artificialwetlandsmaydevelop
ecologicalvalueashabitatforfauna,suchaswaterbirds:anexampleistheRamsar-listed
WesternTreatmentPlantatWerribee,Victoria.
Summary
Theninecasestudiespresentedillustratecommonalityintheforcesthatstructurewetland
vegetationacrossAustralia,aswellastheprocessesthatthreatenthem(Fig.1).Theprimacy
21
ofhydrologyandwetlandwaterregimesfordeterminingthedistributionandcharacteristics
ofwetlandvegetationisparticularlyapparent.Itisthevariationineachofthesestructuring
forces,andinteractionsamongthem,thatgivetheplantcommunitiesofindividualwetlands
theirowncharacter.
Threats
Practicallyallwetlandsystems,withthenotableexceptionoftropicalfloodplainwetlands
andsomesprings,arethreatenedbychangesinwatersupplyandwaterregimes.Such
changesarecausedbytheextractionandregulationofsurfaceandgroundwater,with
modificationofsurfacewaterbeingparticularlypronouncedinsoutheasternAustraliaand
groundwaterextractionaffectingwetlandsincentralandwesternAustralia.Dependingon
thesysteminquestion,thechiefthreatmayinvolveanincreaseinwaterpersistence(i.e.for
wetlandsthatarenaturallyephemeralorintermittent)oradecrease(i.e.forwetlandsthat
arenaturallyalwayswet,likebogs,fensandsomesprings).Increasedwaterpersistence(e.g.
arounddamsandweirpools)canleadtotreedeathandshiftstowardsspeciesfavouredby
stablewaterlevels,e.g.Typhaspecies(Blanchetal.2000),whereasreductionsinflooding
canleadtowetlandlossorresultinnativemacrophytesbeingreplacedbywoodyspecies
(Bren1992)andexoticterrestrialherbs(Catfordetal.2014).Climatechangealsothreatens
wetlandhydrology,asillustratedinalpinebogsthreatenedbydecliningrainfallandrunoff,
andincoastalsystemsatriskofsaltwaterintrusionsfromrisingsealevels.Overall,climate
changehasthecapacitytoreducenativewetlandplantdiversity,promoteexoticinvasions,
acceleratewetlandfragmentationandhomogenisewetlandecosystemsatlocaland
landscapescales(Caponetal.2013).
ExoticspeciesarethreatsthroughoutAustralia,andarebothasymptom(e.g.inresponseto
flowregulationalongtheRiverMurray,seeCaseStudies)andacauseofchangesinnative
flora(e.g.exoticpasturesthatoutcompetenativevegetation,FenshamandFairfax2003).
Fifteenofthe32WeedsofNationalSignificanceinvaderiparianoraquaticsystemsandwere
intentionallyintroduced(seeChapterXXonInvasiveplants).Pondedpastureandother
exoticpasturescontinuetobeplanted,andnewvarietiesthatwilllikelyincreasetheir
invasionsuccesscontinuetobedeveloped(Driscolletal.2014).Exoticanimalsalsothreaten
nativeplantsdirectlythroughgrazing,tramplinganduprooting(e.g.ungulates,carp)and
indirectlythroughsoilcompactionorincreasedgullyerosion,forexample.Changesinthe
landuseofwetlands(e.g.livestockaccesstoalpineandMurray-DarlingBasinwetlands)and
theircatchmentsforagriculture,urbanisationandincreasinglymininghaveledto
22
sedimentation,pollutionandeutrophication,salinization,acidification,changestohydrology
andconnectivityamongwetlands.
Managementandpolicy
Policyrelatingtowetlandvegetation
Thefirstnationalpolicyonwetlandmanagementwasreleasedin1997(TheWetlandsPolicy
oftheCommonwealthGovernmentofAustralia).Whilstallstatesandterritorieshave
legislationtoprotecttheenvironmentandconservenaturalresources(e.g.environment
protection,landuseplanning,protectedareas,waterandvegetationmanagement),state-
levelpoliciesrarelyaddresswetlandsandwetlandvegetationdirectly.In2013,theNational
WetlandsPolicyforAustraliawasinitiatedandisdesignedtoimprovealignmentof
AustralianGovernment,state/territoryandcommunityactionandinvestment,andprovide
consistencyindecision-makingacrossgovernmentagencies(WetlandCareAustralia2013).
Whoisresponsibleforthemanagementofwetlandvegetation?
ThemanagementofwetlandsandassociatedvegetationinAustraliaisprimarilythe
responsibilityoflandownersandlandmanagers.Individualstatesorterritorieshavethe
legislativeandpolicyresponsibilityfornaturalresourcemanagement(Finlay-Jones1997).
TheAustralianGovernmentadministerstheRamsarConventiononWetlandsof
InternationalImportancebyprovidingnationalwetlandpolicy,leadershipanddirection.It
alsoimplementstheEnvironmentProtectionandBiodiversityConservationAct1999(EPBC
Act),anddevelopsprogramstoimprovethemanagementofwetlands.TheEPBCAct
specifiesthatanyactivitieswithinoroutsidedesignatedRamsarwetlandsthatarelikelyto
haveasignificantimpactontheecologicalcharacteroflistedwetland,includingthe
vegetation,mustbeapproved.Managersmayalsoneedapprovalfromtherelevantagencies
understatelegislationforactivitiespotentiallyimpactingRamsarlistedandnon-Ramsar
listedwetlands.Indigenousmanagementofwetlandvegetationcontinuesinmuchofthe
countryandhasbeenrevivedinsomeplacesasaresultofnativetitle.
Managementapproaches
Likeallplantcommunities,wetlandvegetationisshapedbythecompositionoftheregional
speciespool,localdispersal,environmentalconditionsandinteractionswithotherbiota(Fig.
1,CatfordandJansson2014).Alterationtoanyoneofthesefourelementsthroughe.g.
exoticspeciesintroduction,reducedconnectivityamongwetlandsandflowregulationcan
alterwetlandvegetation.Effectivemanagementrequiresacomprehensiveunderstandingof
23
thefactorsandprocessesthatinfluencewetlandvegetationsothatthechiefthreatsto
wetlandvegetationcanbeidentifiedandtargeted(Fig.1).
ThreatstowetlandvegetationalongtheRiverMurrayincludecattlegrazing,eutrophication,
drought,humanactivitiesaroundtownsandfarms,andflowregulation.Ofthese,flow
regulationwasfoundtobeprimarilyresponsibleforanobserveddeclineinnative
vegetation,andparticularlynativeamphibiousvegetation(Catfordetal.2014).Byaltering
historicalwaterregimes,andreducingfloodmagnitudeinparticular,flowregulationinhibits
nativeplantsthatarepoorlyadaptedtothemodifiedfloodingregimes.Withless
competitionfromnativeplants,exoticplantspecies(mostofwhichareterrestrial)have
increasedinabundance.Environmentalflowscanreducesomeofthesenegativeeffects,but
itisrarelypossibletoprovidethefullspectrumofneedsforwetlandplants,andalsoservice
otherwetlandneeds.Forexample,environmentalflowsarecommonlyusedtoextendthe
durationofnaturalfloodeventsbecauseflooddurationiscrucialforfishspawningand
waterbirdbreeding,butextendeddurationintosummermonthsfavourscompetitive
emergentmacrophytessuchasTyphaorJuncusingensandcanleadtoperverseoutcomes
(Box1).
Onceathreatisidentified,variedapproachescanbeusedtoameliorateit.Forexample,for
systemswithaninsufficientsupplyofpropagules,seedscanbesowndirectlyorhydrological
connectivitycanbere-establishedamongwetlandstofacilitatedispersal.Whenvarious
managementoptionsareavailableandthemosteffectiveoneunknown,modellingcanaid
decision-makingbypredictingthelikelyresponseofvegetationcommunitiestodifferent
managementactions.Basedonecologicalunderstandingandempiricaldata,astateand
transitionmodelhasbeendevelopedfortheRamsar-listedMacquarieMarshestomodel
effectsoffloodfrequency,distancetoriverandfirefrequencyonvegetationdynamics(Bino
etal.2015).
Modellingisavaluabletoolforanticipatingecologicalresponsestomanagementactions,
butcanalsobeusedtoanticipateeffectsofenvironmentalconditionsnotpreviously
experienced(Catfordetal.2013).Novelecosystemsthatarisefromglobalenvironmental
changeandexoticspeciesinvasionspresentnewchallengesforenvironmentalpolicyand
management.Incaseswheremaintenanceorrestorationofhistoricalvegetationis
unrealistic,wetlandmanagersmayinsteadfocusonthemaintenanceofkeyecosystem
servicesorfunctions(e.g.waterfiltering,carbonsequestration,floodattenuation).This
couldinvolvefacilitatingtheestablishmentofsalt-tolerantspeciesforwetlandsaffectedby
secondary(human-induced)salinization(Simetal.2006).
24
Conclusion
Wetlandsandwetlandvegetationareofcriticalecological,social,culturalandeconomic
value,exemplifiedbytheirlikelyroleasrefugiaandsteppingstonesfordispersalina
changingclimate(Caponetal.2013).OverhalfofAustralia’swetlandshavebeenlostinthe
last200years(Bennett1997).Thoseremainingareseverelydegradedyettheyarefacing
increasingthreatfromrisingwaterdemand,landusechange,mining,climatechange,
agriculturaldevelopmentinnewregions,risingsealevelsandassociatedsaltwaterintrusion,
andtheintroductionandspreadofinvasivespecies.Expansionofirrigatedagriculturein
northernAustraliawouldincreasepressureonfreshwaterecosystemsinthenorth(Douglas
etal.2011)andcontinuedextractionofgroundwaterwillexacerbatewetlanddegradationin
centralandwesternAustralia.Wetlandvegetationisresilientbyitsverynaturewithplant
physiologicalandlifehistoryadaptationstocopewithahighlyvariableenvironment.
However,theycanonlywithstandsomuch.Toincreaseprotectionofwetlandecosystems,
greaterinclusioninthenationalreservesystemisrequiredandincreasedpolicyinitiatives
thatprotectthemandthewateronwhichtheyrely.Thelossanddegradationofwetland
ecosystemsthroughouttheGreatArtesianandMurray-DarlingBasinsprovidesobering
lessonsforotherpartsofthecountry.
Acknowledgments
WethankDavidKeithforinvitingustowritethischapter,PatrickDriverfortheideaand
informationforBox1,andMargaretBrockandGregKeigheryforfeedbackonthechapter
plan,andMargaretBrockandananonymousreviewerforcommentsonachapterdraft.JAC
andSWacknowledgefinancialsupportfromtheARCCentreofExcellenceforEnvironmental
Decisions.
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Displayitems
Table1Hierarchicalclassificationschemeusedtocategorisewetlandspeciesbasedontheirresponsetowaterregime.ClassificationwasdevisedbyBrockandCasanova(1997)basedonfieldandgerminationtrials.
Box1Perverseoutcomesofenvironmentalwaterydelivery.
Figure1Keyabiotic,bioticandhumanfactorsthatshapethebiogeographyandecologyofwetlandvegetationinAustralia.Arrowsindicatemajorcausalrelationships(e.g.climateaffectshydrology;lithologyaffectgeomorphology;hydrology,geomorphologyandhydraulicscollectivelyaffectwaterqualityandhydrologicalconnectivity).Feedbacks(notshowntoavoidclutter)occuramongandwithintheabioticandbioticdrivers,betweenvegetationandabioticdrivers(e.g.vegetationcanmodifyhydraulics,waterquality,microclimates)andbetweenexternalfactors(e.g.bushfires,landusepractices)andtheabioticandbioticcomponentsofwetlands.Humansaffectwetlandvegetationdirectlyandindirectlybyalteringenvironmentalconditions,dispersalopportunitiesandbioticinteractions.
Figure2RangeofcommonAustralianwetlandplantspecieshighlightingthediversityofwetlandplantgrowthforms:a)Ludwigiapeploidessubsp.montevidensisandMyriophyllumspecies;b)outer,darkerbandofEleocharisacutaandinnerbandofPseudoraphisspinescensillustratecharacteristiczonesofwetlandvegetation;c)Typhaorientalis;d)exoticNymphaeamexicana,JerrabomberraWetlands,ACT;e)floatingAzollapinnatawithsubmergedexoticEgeriadensa,EustonLakes,NSW;f)emergentformofexoticSagittariaplatyphyllawithaninsetshowingitssubmergedform,whichisjuststartingtoboltintotheemergentform.Photocredits:JaneCatford(a,b,c,f:alltakeninRiverMurraywetlandsinVictoriaandNSW);JaneRoberts(d,e).
Figure3a)NumberofpublicationsinISIWebofScienceonwetlandvegetationgloballyandforthetencountrieswiththegreatestnumberofpublications[greybarsaretotalpublications–notethedisjointedy-axis;blackbarsarepublicationswithappliedangle;%indicatespercentageoftotalstudiesthathaveanappliedangle];yearoffirstpublicationpercountry,followedbyyearoffirstappliedpublicationinparentheses:global1900(1968),USA1900(1981),Canada1928(1983),China1991(1995),Germany1980(1991),England1973(1975),Australia1974(1990),Spain1985(1992),France1972(1990),Netherlands1973(1984),Sweden1972(1992);b)NumberofpublicationsoverfiveyearperiodsfocusingonwetlandvegetationinAustralia[greylineindicatestotalpublications(<16perfiveyearintervaluntil1991-1995period);blacklineindicatespublicationwithappliedangle(0before1990);numberof2015publicationsassumedtobethesameas2014].SearchtermsonWebofScience(15October2015):[TOPIC:((Wetland*ORBog*ORMarsh*ORSwamp*ORFen*ORMire*ORRiparian*ORLake*ORLittoral*ORSpring*)AND(VegetationORFloraORFloristic*ORPlant*ORMacrophyt*ORHydrophyt*));RESEARCHAREAS:(ENVIRONMENTALSCIENCESECOLOGYORPLANTSCIENCESORMARINEFRESHWATERBIOLOGYORWATERRESOURCESORPHYSICALGEOGRAPHYORBIODIVERSITYCONSERVATION);Timespan:Allyears.;Searchlanguage=Auto]plus[TOPIC:((manag*ORrestor*ORrehabilitat*ORappliedORpolicyORpolicies))]plus[Country:Australia].
31
Figure4:Examplesofwetlandecosystemtypes:a)tropicalcoastalfloodplain,NT;b)springwetlandincentralAustralia;c)floodplainwetlandoftheRiverMurray,Victoria;d)monocultureofexoticUrochloamutica(paragrass)inKakadu,NT;e)groundwaterdependentwetlandinsouthwestWA;andf)constructedstormwatertreatmentwetlandinCanberra,ACT.Photocredits:MichaelDouglas(a,d);JaneCatford(b,d,f);RayFroend(e).