Tropical forest succession : integrating theory and application in forest restoration

144 Pages·2001·5 MB·English

by  Duncan, Robert Scot

TROPICALFORESTSUCCESSION: INTEGRATINGTHEORYAND
APPLICATIONINFORESTRESTORATION
By
ROBERTSCOTDUNCAN
ADISSERTATIONPRESENTEDTOTHEGRADUATESCHOOL
OFTHEUNIVERSITYOFFLORIDAINPARTIALFULFILLMENT
OFTHEREQUIREMENTSFORTHEDEGREEOF
DOCTOROFPHILOSOPHY
UNIVERSITYOFFLORIDA
2001
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wherevertheyare.
ACKNOWLEDGMENTS
Iextenddeepestgratitudetomyadvisor,ColinChapman. Hisvisionand
supporthavebeenfundamentaltothisproject. Ialsothankcommitteemembers
KaoruKitajima,CarmineLanciani,DougLevey,andFrancisPutzforgenerously
sharingwithmetheirtimeandknowledge. Thisprojectwouldnothavebeen
possiblewithoutthehardworkanddedicationoffieldassistantsFrancis
KaturamuAmooti,andespecially,SwaibuKatusabeAmooti. Iwishtothankthe
graduatestudentsoftheZoologyandBotanyDepartmentsatUniversityof
Floridafortheirintellectualsupportandfriendship. Finally,Ithankmywife,
GingerDuncan,forherunwaveringloveandencouragement. Fundingforthis
researchwasprovidedbytheFordFoundation,WildlifeConservationSociety,
NationalGeographicSociety,TheExplorer'sClub,LindberghFoundation,
UniversityofFlorida,andNationalScienceFoundation(NSFGraduate
FellowshipandgrantnumbersSBR-9617664,SBR-990899). Permissionto
conductthisresearchwasgivenbytheOfficeofthePresident,Uganda,the
NationalCouncilforScienceandTechnology,Uganda,theUgandaWildlife
Authority,andtheUgandanForestDepartment.
TABLEOFCONTENTS
page
ACKNOWLEDGMENTS
iii
ABSTRACT vii
CHAPTER
1 GENERALINTRODUCTION 1
2 INITIALRECRUITAVAILABILITYVERSUSANIMAL-MEDIATEDSEED
DISPERSALDURINGTROPICALFORESTSUCCESSION 6
Introduction 6
Methods 9
StudySite 9
SoilSeedBankinUnloggedPlantations 12
VegetationSurveys 14
BirdSurveys 17
MistnettingSurveysandSeedRainEstimates 18
MammalianDungSurveys 20
StatisticalAnalyses 22
Results 22
SoilSeedBankinUnloggedPlantations 22
VegetationSurveys 23
BirdSurveys 24
MistnettingSurveysandSeedRainEstimates 25
MammalianDungSurveys 25
Discussion 27
TheInfluenceofSeedDispersalonSuccession 27
SeedDispersalVersusInitialRecruitDensityinSuccessionalHabitats 30
TheManagementImplicationsofSuccessionalComplexity 33
3 MANAGEMENTIMPLICATIONSOFTREE-SHRUBINTERACTIONS
DURINGEARLYFORESTSUCCESSIONONDEGRADEDTROPICAL
LANDS 48
Introduction 48
Methods 50
IV
StudySite 50
TreeandShrubInteractions 51
Shrub-RemovalExperiment 54
Vegetation-RemovalExperiment 55
Statistics 56
Results 57
TreeandShrubInteractions 57
Shrub-RemovalExperiment 58
Vegetation-RemovalPlots 59
Discussion 61
TreeandShrubInteractions 61
Vegetation-andShrub-RemovalExperiments 63
PredictingInteractionsAmongandWithinPlantCommunities 65
4 EVALUATINGSTRATEGIESTORESTOREFORESTSONDEGRADED
LANDS:TROPICALFORESTSUCCESSIONINLOGGEDSOFTWOOD
PLANTATIONSINUGANDA 79
Introduction 79
Methods 82
StudySite 82
InfluenceofInitialRecruitAvailability 83
HarvestingEffectsonForestSuccession 85
Nativevegetationbeforeandaftertimberharvest 85
Stemdamagefromlogging 85
Damagefromfelling 86
Within-sitedisturbanceintensity 87
FacilitatingForestSuccession 88
Vegetationremovalexperiment 88
Seedlingplantingexperiment 89
Recruitmentbelowsnags 91
AlternativestoPlantations-FireExclusion 92
Results 93
InfluenceofInitialRecruitAvailability 93
HarvestingEffectsonForestSuccession 95
Nativevegetationbeforeandaftertimberharvest 95
Stemdamagefromlogging 96
Damagefromfelling 96
Within-sitedisturbanceintensity 97
FacilitatingForestSuccession 97
Vegetationremovalexperiment 97
Seedlingplantingexperiment 98
Recruitmentbelowsnags 99
AlternativestoPlantations-FireExclusion 99
Discussion 100
InfluenceofInitialRecruitAvailability 100
v
HarvestingEffectsonForestSuccession 102
FacilitatingForestSuccession 105
AlternativestoPlantations-FireExclusion 107
PlantationsasaRestorationTool 107
5 GENERALDISCUSSION 119
LISTOFREFERENCES 125
BIOGRAPHICALSKETCH 134
VI
AbstractofDissertationPresentedtotheGraduateSchool
oftheUniversityofFloridainPartialFulfillmentofthe
RequirementsfortheDegreeofDoctorofPhilosophy
TROPICALFORESTSUCCESSION: INTEGRATINGTHEORYAND
APPLICATIONINFORESTRESTORATION
By
RobertScotDuncan
May2001
Chairman: Dr.ColinA.Chapman
MajorDepartment: DepartmentofZoology
Duringthenextcenturymostremainingunprotectedtropicalforestswillbe
clearedforshort-termagricultureorpastureandabandoned. Forestshavethe
naturalcapacitytoregrowafterclearingviasuccession. However,forest
successionisoftensloworabsentondegradedlands,andourlimited
understandingofsuccessionhindersthedesignofsuccessfulrestoration
strategies. ToaddressthisproblemIstudiedtropicalforestsuccessioninKibale
NationalPark,Uganda,withinlargesectionsofforestconvertedtoagriculture
thenabandonedearlylastcentury. Theseareasbecamegrasslandsthat
persisteduntilmid-centurywhentimberplantationswereestablishedintheir
place. Unlikegrasslands,maturingplantationsfacilitatednativetreeandshrub
recruitmentintheirunderstories. Plantationharvestingbeganin1993,and
youngsuccessionalforestsgrowingintheirplacewerethefocusofmystudy.
First,Istudiedtheinterplaybetweenpost-disturbanceanimal-mediatedseed
vii
dispersalandseedlingrecruitment. Thisinterplaywascomplexanddependent
ontheinitialonsiteavailabilityofresourcesforsuccession. Birdseeddispersal
hadfarmoreimpactonplantrecruitmentthanmammalseeddispersal,though
fewseedlingsestablishedrelativetonumbersofseedsdispersed. Second,I
exploredtheinfluenceofplant-plantinteractions(competitionandfacilitation)on
forestsuccession. Correlativeanalysesfromvegetationsurveyssuggested
interactionsbetweengrowthforms(shrubsandtrees)andsizeclasses
(seedlingsandsaplings)wereoftenstrong. However,theseinteractionswere
complexandvariedamongsuccessions. Experimentalremovalofshrubsorall
non-treevegetationfailedtoenhancecommunity-widetreerecruitmentor
survival,thoughsomespeciesrespondedstrongly. Third,Iexploredrestoring
naturalforestsondegradedtropicallandsusingtimberplantations. Overall
forestregrowthwasdependentonavailabilityofnativestemsandpropagules
survivinglogging. Whileloggingkilledmanynativestems,itacceleratedforest
successionrelativetothatinunloggedplantations. Severalattemptstoenhance
forestsuccessioninloggedareasweremoderatelysuccessful,withsome
experimentssuggestingspecies-levelinterventionsmaybemoresuccessfulthan
community-wideinterventions. Finally,fire-exclusionappearsfasterthanusing
plantationstopromoteforestsuccessioningrasslands. Ineachofthesestudies
Iproposeguidelinesformanagingsuccessionsbasedonmyfindings.
viii
CHAPTER1
GENERALINTRODUCTION
Duringthenextcenturywewilllikelyseethelossofmostremaining
unprotectedtropicalforests. Theseforestsarecurrentlybeingclearedatarate
of127,300km2yr'1,loggedatarateof55,000km2yr'1,andburnedasquicklyas
30,000km2yr'1(FAO1999). Thisproblemiswidespread,withannualforestloss
at10.5%inAfrica,9.7%inLatinAmericaandtheCaribbean,and6.4%inAsia
andOceania(FAO1999). Restorationecologistsarealreadybeingaskedto
assistforestregrowth. Thismaybeoneofecology’sgreatestchallenges,forour
understandingofhowintacttropicalforestsfunctionisverylimited,andour
knowledgeofhowtorestoresuchsystemsisevenmorelimited(Chazdon1994).
Fortunately,forestshavethenaturalcapacitytogrowbackafter
disturbanceviatheprocessofsuccession(Brown&Lugo1990;Finegan1996;
Holl&Kappelle1999). Thisprocessisshapedbyinitialandrecurrent
disturbanceintensity,abioticandbioticresourceavailability,andchangesin
bioticinteractionsthroughtime(Uhl1982;Uhletal.1982;Finegan1984;Uhlet
al.1988;Finegan1992;Brown&Lugo1994). Aftersmall-scaleorminor
disturbances,secondaryforestreadilyestablishes,althoughhundredsofyears
maypassbeforeaforestresemblingtheoriginalreturns(Ewel1980;Finegan
1996). However,manyanthropogenicdisturbancesimpairtheabilityofforeststo
growback. Onsuchlands,forestsuccessionisoftenarrested,occursslowly,or
leadstoforestscompositionallyverydifferentfromtheoriginal(Borhidi1988;Uhl
1
2
etal.1988;Kuusipaloetal.1995;Chapman&Chapman1999). Currently,our
limitedunderstandingofforestsuccessionhindersourabilitytodesign
successfulrestorationstrategiesforsuchlands(Chazdon1994). Toaddressthis
problem,webeganstudyingtropicalforestsuccessioninwayswethinkare
relevanttodesigningsuccessfulrestorationstrategies. Thisapproach,an
integrationoftheoryandapplication,isonewethinkwillbeessentialfor
restorationecology’sfuturesuccess.
WestudiedforestsuccessioninKibaleNationalPark,Uganda,within
largesectionsofforestthatwereconvertedtoagricultureintheearly1900s.
Theseagriculturalareasweresoonabandonedduetoatsetseflyoutbreakand
thenbecamedominatedbyfire-maintainedgrassland(Osmaston1959). During
the1950sand1960s,whenKibalewasaforestreserve,manyofthese
grasslandswereconvertedtoexoticpine(PinuscaribeaeandP.patula)and
cypress(Cupressuslusitanica)plantations(Osmaston1959). Duringtheir
maturation,theseplantationsfacilitatednativetreeandshrubrecruitmentintheir
understories(Chapman&Chapman1996;Fimbel&Fimbel1996). Dueto
severaldecadesofpoliticalinstability,plantationswentunmanagedand
colonizingnativetreesandshrubswerenotcleared. Whenpoliticalstability
returnedandKibalebecameanationalparkin1993,officialsdecidedthat
plantationswouldbeloggedandnaturalforestallowedtogrowintheirplace.
SuccessionalforestsdevelopingonloggedplantationsatKibalewerethe
focusofourstudy. Nativestemrecruitmentinpineplantationswasgreaterthan
wasrecruitmentincypressplantations(Fimbel&Fimbel1996). Thus,