Ecological consequences of Imperata cylindrica (cogongrass) invasion in Florida sandhill PDF
Preview Ecological consequences of Imperata cylindrica (cogongrass) invasion in Florida sandhill
ECOLOGICALCONSEQUENCESOFJMPERATACYLINDRICA(COGONGRASS) INVASIONINFLORIDASANDHILL By CAROLL.LIPPINCOTT ADISSERTATIONPRESENTEDTOTHEGRADUATESCHOOL OFTHEUNIVERSITYOFFLORIDAINPARTIALFULFILLMENT OFTHEREQUIREMENTSFORTHEDEGREEOF DOCTOROFPHILOSOPHY UNIVERSITYOFFLORIDA 1997 Dedicatedtothegophertortoisecrushedbymysand-skiddingtruck. ACKNOWLEDGMENTS Iamsincerelygratefultomyadvisor,JackPutz,foralwaysmakingtimetoprovide prudentandhelpfuladviceandinsightfulediting.Jack,withhisbroadknowledgeof ecologyandinfectiousenthusiasmforscience,encouragedmetoexpandmythinking aboutbiologicalinvasions.DoriaGordonwasareliablesourceofadviceandathorough reviewer.IthankBuzzHollingforhisunwaveringsupportandencouragementasI venturedintothetheoryofecosystemresilience.StimulatingconversationswithGeorge Tannerbolsteredmyconfidenceandmotivatedmetoworkevenhardertoward conservationandrestorationofnaturalareas.FromDonnShillingIlearnedtovalue contributionsfromtheagriculturaldisciplinestowardmanagementofinvasivespecies. IamgratefultoseveralmembersoftheUFAgronomyDepartment:JeffRayfor usefuldiscussionsofwaterlimitationexperiments,GradyMillerforuseofrootscanning equipment,KenBooteandJeanThomasforuseofaplanimeter,SandraMcDonaldfor sharingherdataoncogongrassbiology,andJimGaffheyforprovidinghisdataon rhizomecarbohydrates.IthankKathrynWilliamsandRussPierceoftheUFChemistry DepartmentforuseofabombcalorimeterandHenryGholzandKenClarkintheUF SchoolofForestResourcesandConservationforuseofalightceptometer. Friendsandfellowgraduatestudentsofferedtheirvaluabletimetohelpwithfield work:SethBigelow,MaryCarrington,ScotDuncan,MarkEdmiston,JillFisher,Jeff 111 Gerwing,AnkilaHiremath,DebbieKennard,BeckyOstertag,DeniseSauerbrey,andAnn Williams.StaffoftheWithlacoocheeStateForest,notablyJonBlanchardandAndrea Crisman,andofOcalaNationalForestwereenthusiasticcooperatorsinlocatingfieldplots andperformingprescribedburns.AtdecisivetimesIbenefitedfromthewiseand encouragingwordsofWalterJudd,JackFisher,BereeDarby,andBillStern.Ihavenever workedwithanyoneasconsistentlypleasantand dependableasPaulaRowe,theBotany Departmentsecretary. Iamgratefulforthesupportofmyfamily,particularlymymotherMargaret, brotherWoody,andsister-in-lawShirley.Iwouldnothaveattemptedandcompletedthis doctoralprogramwithoutthecheerleadingofdearfriends,especiallyStingerGuala,Kevin McNally,MarthaHoover,SusanJacobson,AnkilaHiremath,PeggyOlwell,andMark Edmiston. AGraduateResearchFellowshipfromtheNationalScienceFoundationallowed metofocuscompletelyonthisdissertationwork.Additionalfundingwasprovidedbythe UniversityofFloridaviaaCollegeofLiberalArtsandSciencesPre-doctoralFellowship,a GrinterFellowship,andtravelgrantsformtheGraduateStudentCouncilandtheCollege ofLiberalArtsandSciences. IV 1 TABLEOFCONTENTS page ACKNOWLEDGMENTS iii ABSTRACT viii CHAPTERS INTRODUCTION 1 BiologicalInvasionsandEcologicalResilience 1 GlobalGrassInvasions 6 CogongrassInvasionandSandhillResilience 9 FloridaSandhillEcosystems 12 CogongrassBiologyandEcology. 15 CogongrassInvasioninFloridaSandhill 17 ResearchHypotheses 19 COGONGRASSINVASIONDISPLACESSANDHILLPLANTSAND ANIMALS Introduction 20 CogongrassInvasion 21 DisplacementofSandhillVegetation 23 DisplacementofSandhillAnimals 24 Methods 28 CogongrassInvasion 29 DisplacementofSandhillVegetation 30 DisplacementofSandhillAnimals 3 Results. 32 CogongrassInvasion 32 DisplacementofSandhillVegetation. 36 DisplacementofSandhillAnimals 38 Discussion. 40 CogongrassInvasion. 40 DisplacementofSandhillVegetation. 43 DisplacementofSandhillAnimals. 44 page Conclusions 47 3 COGONGRASSINVASIONCHANGESSANDHILLFIREREGIME Introduction 48 FireinEcosystems 48 SandhillFireRegime 51 Methods. 53 Results. 55 Discussion 61 Conclusions 65 4 COGONGRASSINVASIONREDUCESSANDHILLSEEDLING RECRUITMENT Introduction. 66 SeedlingRecruitment. 66 SeedlingRecruitmentinSandhill 68 Methods. 70 Seed 72 Seedlings. 72 Results 74 Seed 74 Seedlings. 77 Discussion. 83 Conclusions. 88 5 COGONGRASSINVASIONLIMITSRESOURCESAVAILABLETO SANDHILLSEEDLINGS Introduction 89 ResourceAvailability. 90 InvasivePlantsandResourceAvailability 92 FloridaSandhillResources. 94 ResourceLimitationsinCogongrass. 95 Methods. 97 ResourceAvailability. 97 ResourceLimitations 100 SeedlingHerbivory. 103 Results. 103 ResourceAvailability. 103 ResourceLimitations. 110 SeedlingHerbivory. 118 VI page Discussion 118 ResourceAvailability. 118 ResourceLimitations 125 CogongrassAllelopathyReview. 126 Conclusions. 127 6 SUMMARYANDCONCLUSIONS CogongrassInvasionandSandhillResilience 129 CogongrassInvasionDisplacesSandhillPlantsandAnimals 130 CogongrassInvasionChangesSandhillFireRegime 132 CogongrassInvasionReducesSandhillSeedlingRecruitment. 132 CogongrassInvasionLimitsResourcesAvailable toSandhillSeedlings. 134 FunctionalEquivalenceandFloridaSandhillResilience. 135 SandhillManagementImplications 137 CogongrassInvasioninSoutheasternEcosystems. 140 GrassInvasionsinFloridaEcosystems. 141 FunctionalGroupsasPredictorsofEcosystemChange 142 LISTOFREFERENCES 145 BIOGRAPHICALSKETCH 165 vn AbstractofDissertationPresentedtotheGraduateSchool oftheUniversityofFloridainPartialFulfillmentofthe RequirementsfortheDegreeofDoctorofPhilosophy ECOLOGICALCONSEQUENCESOFIMPERATACYLINDRICA(COGONGRASS) INVASIONINFLORIDASANDHILL By CarolL.Lippincott December1997 Chairman:FrancisE.Putz MajorDepartment:Botany Ievaluatedthefunctionalequivalenceofanonindigenousinvader,Imperata cylindrica(cogongrass),andindigenousgrassesinFloridasandhill,asavannaecosystem.I compared33traitsofcogongrassandsandhillgrasseswithinkeyareasofsandhill ecosystemfunction.Ithenpredictedtheeffectofcogongrassinvasionontheecological resilienceandpersistenceofFloridasandhill. Rhizomatousspreadofcogongrasswasfastestinfrequently-burnedandclear-cut sandhill.Cogongrassdisplacedmostsandhillvegetationexceptlargetrees.Burrowing beetlesweredisplacedbycogongrassbutfrequencyofpocketgophermoundswasnot changed.Cogongrasswasalower-qualityforagethansandhillvegetation. Vlll Cogongrassfireswerehigher,hotter,morecontinuoushorizontally,andkilled morejuvenilelongleafpinesthansandhillfires.Fuelaccumulatedmorerapidlyin cogongrassthaninsandhill,sofirecouldignitemorefrequently. Cogongrassreducedrecruitmentofplantedseedsandseedlingsof7sandhill speciesrepresentingvariouslifeforms.Theonlysurvivorsfromplantedseedswereofa large-seededpalm.Incogongrass,clonalspeciesplantedasseedlingshadmoresurvivors andaN-fixingclonalshrubgrewbetterthanothertypesofseedlings.Fewerplantedpine seedlingssurvivedincogongrass,andsurvivorswereshorterthaninsandhill.Burning beforeplantingwasequallyimportanttoseedlingrecruitmentincogongrassandsandhill. Relativetosandhill,cogongrasslitterreducedlightmoreatgroundlevel. Cogongrass'higherleafarea,andgreaterrhizomeandrootmassandrootlengthdensity reducedsoilwatermorethaninsandhill.Soilnutrientavailabilitywasapparentlynot changedbycogongrass.Increasedgrowthofseedlingsinexclosureswasevidenceoflight andwaterlimitationsincogongrass.Seedlingsurvivaldependedstronglyonwater availability,whilegrowthdependedonbothwaterandnutrients. Tallrhizomatouscogongrassisnotfunctionally-equivalenttotheshort,caespitose grassesindigenoustosandhill.Cogongrassrepresentsanewfunctionalgroupthatcan exceedsandhillresiliencethroughchangesinvegetationstructure,soilprocesses,animal populations,fireregime,seedlingrecruitment,andresourceavailability.Cogongrasshas theabilitytoconvertFloridasandhilltotreelessspecies-poorgrassland.Comparisonsof functionalequivalencebetweeninvadersandkeyindigenousspeciesmayhaveutilityin predictingecosystemchangecausedbynonindigenousspecies. IX CHAPTER1 INTRODUCTION ThisdissertationexaminestheecologicalconsequencesofinvasionbyImperata cylindrica(cogongrass)inFloridasandhillecosystems.SpecificallyIaskifcogongrass,a nonindigenousspecies,cansignificantlyaltersandhillecosystemfunctioninwaysthat exceedresilienceofthesystem,resultinginashiftfrompineforesttograsslanddominated bycogongrass.InthischapterIbeginbydiscussingbiologicalinvasionsofnonindigenous speciesandtheiraffectsonecosystemstructureandfunction,emphasizinginvasiveplants. Ithenincorporatetheseideasintocurrentconceptsofecologicalresilienceasameansto predictandinterprettheeffectsofinvasivespeciesonecosystempersistence.Ithen reviewtheglobalroleofinvasivegrassesinalteringecosystemfunction.Finally,Ifocus onthedynamicsofcogongrassinvasioninFloridasandhillecosystemsandpresentthisas atestcasefordeterminingwhetheraninvasivespeciescanerodeecosystemresilienceto thepointofcausingashifttoanewtypeofecosystem. Biological InvasionsandEcologicalResilience Biologicalinvasionsofnonindigenousspeciesareanunder-emphasizedcomponent ofglobalenvironmentalchange,comparabletowidelyrecognizedphenomenasuchas land-usechangeandelevatedatmosphericcarbondioxide(Vitouseketal.1996,Huenneke 1997).Asagentsofglobalchange,invasivenonindigenousspeciesarereducingtheearth's
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