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Natural Areas Journal 30:�–19

Responses of Rare Plant Species to Fire in Florida’s Pyrogenic

Communities

Jodi L. Slapcinsky1,3

Doria R. Gordon1

Eric S. Menges2

1TheNatureConservancyandDepartmentofBiology

P.O.Box118526UniversityofFlorida,Gainesville,FL

32611

2ArchboldBiologicalStation

P.O.Box2057LakePlacid,Florida33862

3Correspondingauthor:jslapcinsky@tnc.org

� Natural Areas Journal Volume 30 (1), 2010

Natural Areas Journal 30:�–19

•

Responses of Rare Plant Species to Fire in Florida’s Pyrogenic

Communities

Jodi L. Slapcinsky1,3

Doria R. Gordon1

Eric S. Menges2

1TheNatureConservancyandDepartmentofBiology

P.O.Box118526UniversityofFlorida,Gainesville,FL

32611

2ArchboldBiologicalStation

P.O.Box2057LakePlacid,Florida33862

•

R E S E A R C H A R T I C L E

3Correspondingauthor:jslapcinsky@tnc.org

ABSTRACT:Lightning-andhuman-ignitedfireshaveshapedmanyofFlorida’snaturalcommunities.Plantpersistenceinthesehabitatsrequiresadaptationtosurvivehightemperatures,abilitytorespondtoabovegroundtissueloss,oravoidanceoftheseconditionsthroughsurvivalinunburnedpatchesorinthesoilseedbank.Limiteddistributionofmanyrarespecies in increasinglyfragmentedhabitatsanduncertaintyofwhetherrarespeciestolerate,require,orpersistthroughavoidanceoffirehampersfiremanagementwhenitispossibleandthreatenslong-termviabilityofplants.Wereviewupto14yearsofmonitoringdatafor18rareplantspeciesfrom14familiesoccurringonsandhill,scrub,pinerock-land,andmixeddeciduoushardwoodcommunitiesacrossFlorida.Foranumberofvariablesmeasured,includingdensity,frequency,flowering,andrecruitment,50%ofthespeciesshowedsignificantpositiveresponsestoburningand50%ofthespeciesshowedaneutralornoresponse.Noneofthespecieswereunabletorecoverpost-burn.Theseresultssuggestthatprescribedfireinthesepyrogenichabitatsneednotbedelayeduntilspecies-specificresponsestofireareunderstood.

Index terms:fire,Florida,Floridascrub,pinerocklands,pyrogenic,sandhill

INTRODUCTION

Recenthypothesessuggestthatfireplaysanimportantroleinshapingthecharacteristicsofmanyoftheworld’sbiomes(BondandKeeley2005).Fire-adaptedorpyrogenicecosystemshavebeenestimatedtocover40%oftheworld’slandsurface(Chapinetal2002),andit is thefireregime(fireintensity,severity,frequency,andseason)thathascreatedsomeofthemostbiodiversehabitats. Fire-adapted habitats includetropicalsystemsthatburninthedryseason,likesavannawoodlands,monsoonforestsandtropicalpineforests(Nasietal.2002),MediterraneanclimateregionsoftheworldthatincludehabitatsoftheMediterraneanbasin,Californiachaparral,SouthAfricanfynbosandAustralianheathlands(Cowl-ingetal.1996;BondandKeeley2005),andcircumpolarborealforests,taigaandtundra habitats with permafrost (Nasi etal.2002).

Among North American fire-maintainedecosystems are grasslands, prairies, andpineforeststhatrepresentover90%ofthesoutheastern United States (Frost 1995).Thesesystemsaresubstantiallyinfluencedbylightning-andhuman-ignitedfireandtropical storms (Brockway and Lewis1997).PeninsularFloridahasoneof thehighest incidencesof lightningstrikes intheworld(GoodmanandChristian1993).Lightningflashdensitiesaregreaterthan30flkm-2yr-1,secondonlytotheworld“hotspot” in the equatorial Congo Basin(Christianetal.2003).Historically,mostfireswerecausedbylightning,whichwasmostprevalentduringtheconvectivestormevents of the growing season (Huffman

2006).Pastfireregimeswereaugmentedby nativeAmerican-ignited fires (Brown2004) often set during times other thanthe lightning fire season (Snyder 1991).Today, prescribed fire for conservationand agricultural purposes now generallyreplacesthesenaturalandhistoricsourcesoffires(RobbinsandMyers1992).

As a consequence of fire’s consistentpresence on the Florida landscape, ap-proximately70%percentoftheterrestrialnaturalplantcommunitiesandnearly100%ofthepalustrinenaturalplantcommunitiesdescribed by the Florida Natural AreasInventory(1990)areconsideredfire-depen-dentorfire-adapted.Bothwide-rangingandgeographicallyrestrictedspeciesinthesecommunities have developed life historystrategiesinresponsetofire(MengesandKohfeldt1995).

Yearsoffire-suppressionandlossofhabitatdue to landdevelopment and conversion(Brockway andLewis1997)have led todeclining distributions of Florida’s rarespecies,especiallyinFloridascrub(Halletal.2002),pinerocklands(U.S.FishandWildlifeService1999),andsandhill(Noss1989;Frost1993).Landmanagersareoftenreluctanttousefireasamanagementtoolunless there are assurances that fire willnotthreatenimperiledspecies.Firereturnintervals,identifiedasthenumberofyearsbetween two successive fire events at aspecificsite,arecurrentlyincreasingevenwherefiremanagementdoesoccur(Hardin2002;Mulhollandetal.2003).In1926,theFloridaDepartmentofForestryandParksestimatedthatroughly5,260,921hectares,orapproximately75%ofthepinelandsin

Volume 30 (1), 2010 Natural Areas Journal �

Florida, burned annually (Baker 1926).From 1995 to 2003, the average annualnumberofhectaresthatburnedinFloridawasestimated tobe76,486,or less than1%ofthestate(FloridaDivisionofFor-estry2005).

GiventheimportanceoffiretorarespeciesinuplandFloridaecosystems,andthelikelynegativeimpactsoffiresuppression,moreinformationonfireresponsesofFlorida’srareplantsisessential.Here,weintegratepost-burndataonrarespeciesabundancesand vital rates (e.g., survivorship andreproduction),focusingondatacollectedby The Nature Conservancy (TNC) andArchboldBiologicalStation(ABS).Overthepast15years,bothorganizationshaveimplementedmonitoringandmanagementprogramsoftherareplantspeciesthatoccurontheir,andsomepubliclyowned,proper-ties.Theplantspeciesinbothmonitoringprogramsareglobally(rankedG1-G3)andlocally rare.NearlyeverynaturaluplandcommunitymaintainedbyfireinFloridaisrepresentedwithinthesepreservesandbothorganizationsmanagetheirpropertieswithfire(amongothermethods)atfrequenciesdependingonvegetationtype(RobbinsandMyers1992).Wesummarizetheresponsesof18rareplantstofire.

METHODS

Populationsof15ofthe18rareplantspe-cieshavebeenmonitoredannuallyon10preservespreviouslyorcurrentlyownedbyTNCinFlorida(Figure1).TheremainingthreespeciesweremonitoredonpropertyownedandmanagedbyABSormonitoredbyABSonpublicconservationareas.Allspeciesaremonitoredonhabitatsthatburnperiodicallyeithernaturallybylightning-causedfiresorbyprescribedfireathypoth-esizednaturalintervals(Table1).

Six of the rare species are found in oneof more than seven types of scrub habi-tats (e.g., scrubby flatwoods, white sandscrub, oak scrub; seeAbrahamson et al,1984,Menges1999,andSchmalzer2003for descriptions) on the preserves wherethey were monitored (Figure 1). For thepurposes of this paper, “Florida scrub”will be used for all Florida scrub-types.ThishabitatisfoundonABS(Highlands

County)andSaddleBlanketScrubPreserve(PolkCounty)locatedontheLakeWalesRidge (LWR). This relict shoreline anddunesystemischaracterizedbyrelativelyhigh elevation and excessively drainingsandysoils,anddatesbacktoatleastthePleistocene (White 1970; Myers 1990;Webb1990).Floridascrubismaintainedby recurrent disturbances including fire(Myers1990;GibsonandMenges1994;Menges1999) at intervals of every8-16years for scrubby flatwoods, every 5-12years for oak-hickory scrub, and every15-30yearsforrosemaryscrub(Menges2007). For our purposes, we define thefire return interval as a range from 5-30years(Table1).

Six species were monitored in sandhillat Tiger Creek Preserve (Polk County),CrookedLakeSandhillPreserve(VolusiaCounty),RockHillPreserve(WashingtonCounty),ApalachicolaBluffsandRavines

Preserve(LibertyCounty),andABS(Table1). InFlorida, longleafpine systemsoc-curmostly in thenorthandcentralpartsof the state, on gently rolling terrain ondeep,excessivelydrained,mostlyyellow,oligotrophic sands. These systems arecharacterized by frequent, low intensitylightning-causedfires thatoccurwithre-turnintervalsofonetofiveyears(Table1)(Christensen1981;MeansandGrow1985;Noss1989;Glitzensteinetal.1995).

Threeofthesixspeciesthatweremonitoredin scrubwerealsomonitored in sandhillhabitats(Table1).Bonamia grandiflora(A.Gray)Hallierf.wasmonitoredinsandhillatbothSaddleBlanketScrubPreserveandTiger Creek Preserve. Eriogonum longi-foliumNutt.var.gnaphalifoliumGandog.wasmonitoredinbothscrubandsandhillatArchboldBiologicalStation,andCon-radina brevifoliaShinnerswasmonitoredonbothhabitatsatSaddleBlanketScrub

Figure 1. Ten preserves, their associated habitat(s) and 18 species monitored in Florida.

� Natural Areas Journal Volume 30 (1), 2010

Spec

ies

Mon

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(yea

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keye

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land

2-15

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# pl

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221

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sis

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313

30 x

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ts1

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litze

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t al.

1995

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ges 2

007,

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t al.

1990

. The

bur

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07).

Tab

le 1

. Sp

ecie

s an

d va

riab

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used

in

this

stu

dy.

“Mon

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ed h

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at(s

)” i

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whi

ch t

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as m

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. Var

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), n

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# B

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the

num

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of s

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unit

s (#

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), t

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, an

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hat

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alyz

ed.

Volume 30 (1), 2010 Natural Areas Journal �

Preserve(Figure1).

FourofthemonitoredspeciesareendemictosouthFloridapinerockland,whichhasalimestonesubstratewithshallow,droughty,and sandy soils (Table1).Thehabitat isfiremaintainedwithanhistoricfrequencyofeithereverytwotothreeyears(basedonthetimeit takesforfuelstoaccumulate)orevery10to15years,anestimateofthetime it takes forherbaceousendemics tobe shaded by a closed canopy (Table 1)(Snyderetal.1990).TerrestrisPreserveisan8hapinerocklandhabitatinafreshwatermarshcommunityoncentralBigPineKey,MonroeCounty,Florida.

Finally, we use data from two rare spe-cies occurring in hardwood forests andin coastal habitats (Table 1). The MaysPondconservationeasementsite,JeffersonCounty, isadeciduous,mixedhardwoodforestinproximitytothenortheastshoreofLakeMiccosukeethatburnsinfrequently(G.Seamon,FireTrainingSpecialist,theNature Conservancy, pers. comm. 2007)andcontainstherareRibes echinellum (Co-ville)Rehder.TheNatureConservancy’sJohnH.PhippsPreserveisontheeastern-mostcoastalbarriershorelineinFranklinCounty where Liatris provincialis R.K.Godfrey occurs.This species was moni-toredonsanddunesandadjacentcoastalscrub habitat (Figure 1). The habitat isfurther described as evergreen oak-sandpinescrubbyGodfreyandWard(1979).Thesecoastalscrubhabitatsaresubjectedto frequent storm activity (flooding andwinds)andhavehypothesizedmodalhis-toricalburnfrequenciesofunder20years (Schmalzer2003).

Species and Data Collection Methods

All of the 18 species, except for Rhyn-chospora floridensis (Britton ex Small)H.Pfeiff,arestatelistedasendangeredinFlorida(Table1)andallbutfourspecies(Bigelowia nuttallii L.C.Anderson,Mar-shallia ramosa BeadleandF.E.Boynton, Ribes echinellum (Coville) Rehder, and Rhynchospora floridensis (Britton exSmall) H. Pfeiff are Florida endemics.Speciesweremonitoredfordifferenttraitswithvaryingpopulationandplotsizesand

weresubjectedtooneormoreprescribedburnsatvarioustimesduringmonitoring.MonitoringsitelocationsareinFigure1.

Bigelowia nuttallii L.C. Anderson, Nut-tall’sraylessgoldenrod,isanherbaceousperennial foundon the coastal plain andpiedmont of Georgia and Florida, theCumberland Plateau ofAlabama, and incentralandwesternLouisianaandeasternTexas.Thespeciesisfoundinfourlocalizedpatches in sandhill at TNC’s Rock HillPreserve(RHP).Weusedrestrictedrandomsamplinginsevensub-populationstoplacethree30-mx1-mbelttransectswithineachsub-population. We then counted repro-ductiveandnon-reproductiveplantseachSeptember annually from 1992 to 1995andthereafterbienniallyto2001.

Bonamia grandiflora(A.Gray)Hallierf.,Floridabonamia,isanendemictoFloridaandaperennialherbaceousvine.Wean-nually censused two sub-populations insandhill at TNC’s Tiger Creek Preserve(TCP)andtwosub-populationsatSaddleBlanket Scrub Preserve (SBSP) from1991-1997and taggedeachplant.Everyyear we re-located each individual andtaggednewindividualstoderivesurvivalandrecruitmentrates.

Chamaecrista lineata (Sw.) Greene var. keyensis (Pennell)H.S.IrwinandBarneby,BigPinepartridgepea, isanherbaceousperennialendemictoFlorida’spinerock-land habitat. We used restricted randomsampling to establish multiple 2-m widepermanentbelt transects ineachof threeburnunitsonTNC’sTerrestrisPreserveonBigPineKey.Startingin1993,wecountedindividuals annually along the2-mwidebelt transectsso thataveragedensityperm2couldbedetermined.

Chamaesyce deltoidea (Engelm. ExChapm.)Small subsp.serpyllum (Small)D.G. Burch, wedge spurge, is an her-baceous perennial endemic to Florida.We used restricted random sampling toestablish multiple 2-m wide permanentbelt transects ineachof threeburnunitsonTNC’sTerrestrisPreserveonBigPineKey. Starting in 1993, we recorded fre-quencyofthisspeciesincontinuous2-mx1-mplots.

Conradina brevifolia Shinners, short-leaved rosemary, is a shrub endemic toFlorida scrub. In 1999 at TNC’s SaddleBlanket Scrub Preserve, we estimateddensity annually in three permanent 15-m x 2-m plots randomly located withinthepopulationineachoffourburnunits.An additional five plots on the Preservewere added and sampled annually from2000-2003.

Conradina glabra Shinners,Apalachicolarosemary,amint,isanendangeredshrubendemictonorthFloridasandhill.Wesetup three permanent burn units at TNC’sApalachicolaBluffsandRavinesPreserveintowhichwetranslocatedpropagatedcut-tings in 1991 (Gordon1994).Beginningin 1992, we found and tagged naturallyestablishingseedlingsin45oftheexperi-mentallylocated3-mx3-mplotsineachburn unit annually. We stopped taggingnewrecruitsafter1995,butwecontinuedto census all taggedplants until 2002 todeterminesurvivalrates.

Crotalaria avonensis Delaney andWun-derlin, tortoise bells, is an herbaceousperennial,endemictoFloridascrub.From1992to2005,wesampledallplantswithinrandomlylocatedpermanent10-mx10-mor10-mx15-mplotsineachoffivesub-populationsatSBSP.Wemappedindividualplants annually to track recruitment andfloweringcondition.

Dicerandra frutescens Shinners, scrubbalm,isashrubendemictoFloridascrub.Wemarkedallindividualplantsat11sitesatABSandhavefollowedplantsurvival,growth,andrecruitmentsince1988,whichhasledtoarecentassessmentofpopulationviability(Mengesetal.2006).

Eriogonum longifoliumNutt.var.gnaphali-folium Gandog., scrub buckwheat, is anherbaceousperennialendemic toFloridascrub. From 1989 to the present, wemonitoredsixsub-populationsinfourburnunitsatABS,leadingtoanassessmentofpopulation viability (Satterthwaite et al.2002). Within each sub-population, weestablishedbetweenfourand14permanent10-m x 10-m plots, in which all scrubbuckwheat plants were tagged and cen-susedannually.Oneadditionalpopulation

� Natural Areas Journal Volume 30 (1), 2010

hasbeenmonitoredincircularpermanentquadrats (3m radius) at theLakeWalesNational Wildlife Refuge (Carter Creektract)since2001.

Eryngium cuneifolium Small, wedge-leavedbutton-snakeroot,isanherbaceousperennialendemictoHighlandsCountyinFloridascrub.Wehavecensused11sub-populationsandmarkedallindividualsatABS annually since 1988, leading to anassessmentofpopulationviability(MengesandQuintana-Ascencio2004).

Linum arenicola (Small) H.J.P. Winkler,or sand flax, is an herbaceous perennialendemictosouthernFloridapinerockland.We used restricted random sampling toestablish multiple 2-m wide permanentbelt transects ineachof threeburnunitsonTNC’sTerrestrisPreserveonBigPineKey. Starting in 1993, we counted indi-vidualsalongthe2-mwidebelttransectsannually so that average density per m2

couldbedetermined.

Liatris provincialis R.K. Godfrey, God-frey’sblazingstar,isanherbaceousperen-nial, endemic to the Florida panhandle.From1996-2002,wecensusedtwocoastalsandhillburnunitsatJohnS.PhippsPre-serveinthefallofeachyear(except1998)totrackpopulationsize.

Marshallia ramosa BeadleandF.E.Boyn-ton,pinelandBarbarabuttons,isaperennialherbknownfrom20-30sitesinsouthcen-tralGeorgiaandnorthwesternFlorida.WeannuallycensusedallMarshallia ramosaindividuals and the number of floweringindividualsineightsandhillburnunitsfrom1992-2002atRockHillPreserve.

Nolina brittoniana Nash, Britton’s bear-grass,isanherbaceousperennial,endemictoFloridathatoccursinscrubandsandhills(Mengesetal.2006).From1991to2001,wehaphazardlysetupfivepermanent10-mx10-mmonitoringplots inburnunitsatTigerCreekPreserveandtaggedplantsannually(except2000)totrackrecruitmentandflowering.

Prunus geniculata R.M. Harper, scrubplum, is a shrub endemic to sandhill onFlorida‘s LakeWales Ridge. From 1991

to 1996, we tagged all individual plantsannually to track population size at theTiger Creek and Crooked Lake SandhillPreserves.Wealsorecordedthepresenceofreproductivestructuresforeachplant.

Rhynchospora floridensis (Britton exSmall)H.Pfeiff,Floridawhite-top,isanherbaceous perennial found in about 49pinerocklandsitesinFlorida(NatureServe2006)andotherwiseknownonlyfromtheBahamas (Godfrey and Wooten 1981).We used restricted random sampling toestablish multiple 2-m wide permanentbelt transects ineachof threeburnunitsonTNC’sTerrestrisPreserveonBigPineKey. Starting in 1993, we recorded fre-quencyofthisspeciesincontinuous2-mx1-mplots.

Ribes echinellum (Coville)Rehder,Mic-cosukeegooseberry,isawoodysub-shrubknown from two mixed hardwood sitesin Jefferson County, Florida, and fromone site in McCormick County, SouthCarolina. We annually monitored plantdensity from 1992-2001 in eighteen 50-mx1-mandtwo30-mx1-mpermanentbelttransectslocatedthrougharestrictedrandomizationprocessattheMay’sPondsiteinnorthFlorida.

Warea carteriSmall,Carter’smustard,asandhillandFloridascrubendemicfoundon the Lake Wales Ridge, is an annual.Previous work on this species demon-stratedthatpopulationsarereleasedfromtheseedbankfollowingfire,anddeclineprecipitously thereafter (Menges andGordon 1996). We annually censusedthis species during peak flowering inTiger Creek Preserve sandhill. Startingin 1991, we recorded the total numberof plants per sub-population. Sites werecarefullysearchedeachyearandallnewsub-populationsweremapped.Atotalof66 sub-populationshavebeenmonitoredatTigerCreekPreserve.

Data Analysis

Atotalof24variablesfor18speciesweretested.Twelvevariablesweretestedwithrepeatedmeasuresanalysisofcovariance(RMANCOVA)and12weretestedwithanalysis of variance (ANOVA). Multiple

variablesweretestedforfivespecies(Table1).RMANCOVAwasusedtoexaminetherelationship between time since fire andabundanceorvitalrates(e.g.,survivorshipand reproduction) of 10 of the species(Figures2and3).Whereavailable,aco-variatewasusedtoexaminethevariationexplained by pre-burn (sometimes long-unburned,definedas>10yearssincefire)conditions.Covariatedatawasexpressedas density, plant numbers, frequency, orpercentflowering(dependingonthetrait(s)measured for each species).All assump-tionsassociatedwithRMANCOVAweretestedandweremet.Dataweretransformedas necessary to meet the assumption ofnormality.GraphsforvariablestestedwithRMANCOVAshowtheresponsevariableon the y-axis, with the covariate at zeroyearsinceburn(Figures2and3).

Wherewehadinsufficientpost-orpre-burndata to run RMANCOVA (12 variablesof eight species), we usedANOVA. Wetransformed the12 responsevariables toa percentage by calculating the percentchangefromoneyeartothenext,startingfrom zero year since burn. The percentchange for thevariable is againgraphedstartingwithoneyearsinceburnontheyaxis(Figures4and5).Usingthepercentchangeoftheresponsevariablefromoneyear to the next reduces the potentialeffects of pseudoreplication (Wiens andParker1995).

SignificancewasdeterminedattheP<0.05levelforallstatisticaltests.Themonitoringsite,population,orquadrat(ifapplicable)wereincludedasfixedeffectsforalltests.A positive response was identified byeither a significant initial increase in theresponsevariableafterfirethatmayormaynotbefollowedbyadeclineoraninitialdeclineafterfirefollowedbyalonger-termincrease. A neutral response to fire wasdetermined if response was independentoftimesincefire(P>0.05),andanega-tiveresponseoccurredwherepopulationsdeclinedsignificantlyafterprescribedfireandshowednorecovery.

Wehadnopre-firedataforthreespecies:Bonamia grandiflora,Eryngium cuneifo-lium, and Prunus geniculata (Table 1).Monitoring for these species started one

Volume 30 (1), 2010 Natural Areas Journal �

Figure 2. Species whose variables (A through F) were analyzed with repeated measures analysis of covariance (P < 0.05). The value separated from the line at 0 year since burn represents the covariate value: the pre-burn or long-unburned population condition. All graphs shown are ± 1 SE. Number above or below error bar denotes sample size. Where mean change obscures significant trends, population responses are shown separately. Significant p-values are italicized. Variable A = Bigelowia nuttallii density, B = B. nuttallii percent flowering, C = Chamaecrista lineata var. keyensis density, D = Chamaesyce deltoidea subsp. serpyllum frequency, E = Conradina brevifolia density, F = C. glabra density.

10 Natural Areas Journal Volume 30 (1), 2010

Figure 3. Species whose variables (A through F) were analyzed with repeated measures analysis of covariance (P < 0.05). The value separated from the line at 0 year since burn represents the covariate value: the pre-burn or long-unburned population condition. All graphs shown are ± 1 SE. Number above or below error bar denotes sample size. Significant p-values are italicized. Variable A = Crotalaria avonensis percent flowering, B = C. avonensis density, C = Dicerandra frutescens density, D = Marshallia ramosa number of flowering plants, E = Nolina brittoniana density, and F = Warea carteri number of plants.

Volume 30 (1), 2010 Natural Areas Journal 11

yearafterprescribedburn.Therefore,forthesethreespecies,apositiveresponsewasstatisticallysignificantatP<0.05wherethe population(s) showed an increasingtrendsincetheburn.

RESULTS

RM ANCOVA Results

Chamaecrista lineatavar.keyensisdensitysignificantlyincreasedafterfire,withsig-nificantsiteandcovariateeffects.Thesiteeffect (P = 0.0017) (Figure 2C) resultedfromincreaseddensityof thepopulationinunit2 fromthe third through thefifthyearafterburning,whileunit1showednochangeovertime.

Data were limited to the first two yearsafter burning for two scrub species thatexhibitedsignificantandpositiveresponsestofire.Crotalaria avonensisflowering(P= 0.0023) (Figure 3A) and Dicerandra frutescensdensity(P=0.0067)(Figure3C)increased the second year after burning.Wehadthreeyearsofpost-burndataforConradina glabra,whichshoweddensityincreasesinyearstwoandthreeafterfire(P = 0.0013) (Figure 2F).This responsevariedamongthesites(P=0.05)(Figure2F). Three years of post-burn data forWarea carterinumbers showedadramaticincrease one year post-burn followed bya sharp decline in the second year (P =0.0474) (Figure 3F). Species for whichwehadlongerpost-burnintervalsincludedConradina brevifolia,whichshoweddra-maticincreasesinplantdensitythesecondyearafterburningandcontinuedtoincreasethroughfiveyearsafterfire(P<0.0001)(Figure2E).

Traitsofthreespeciesshowedasignificantdependenceontimesincefire(P<0.05),but had non-significant overall models.These were frequency of Chamaesyce deltoidea subsp. serpyllum (P = 0.1068)(Figure2D),densityofBigelowia nuttallii(P=0.8683)(Figure2A),anddensityofCrotalaria avonensis (P=0.1223)(Figure3B).Neitheryearsinceburnnoranyothermodel variable significantly affected thepercentfloweringofBigelowia nuttallii (P=0.2066)(Figure2B),numberofflowering

plantsofMarshallia ramosa(P=0.2911)(Figure3D),ordensityofNolina brittoni-ana (P=0.3708)(Figure3E).

ANOVA Results

Threeoftheninespeciesshowedsignifi-cantpositivedependenceofpercentchangeinvital ratesor abundance traits onfire.Eryngium cuneifolium density increased(P=<0.0001)(Figure4E)graduallyuptosixyearspost-burnandremainedathighpopulationnumbersforaboutsixtonineyearspost-burn,beforegraduallydeclining.Eriogonum longifoliumvar.gnaphalifolium densityincreasedsignificantly(P<0.0001)(Figure4D)oneyearpost-burn,followedby a sharp decline thereafter. AlthoughsitefactorsweresignificantforbothtraitsmeasuredforRibes echinellum,percentre-productionincreasedthesecondyearafterburning(P=0.0096)(Figure5F);densityincreasedsteadilyforthreeyearsafterburnalthough no significant fire-dependencewasfound(P=0.2182)(Figure5E).

Sixofthespeciesshowednostatisticallysignificantresponsetoyearsincefire.Traitsfollowedforallthesespecieswerestableorshowedsomerecoveryafterprescribedburns.Numberofplants(P=0.4916)(Fig-ure4A),percentreproduction(P=0.1018)(Figure4B),andnumberofrecruits(P=0.0699) (Figure4C)ofBonamia grandi-florawereindependentoffiremanagement.Responses were also not significant fordensityofLiatris provincialis(P=0.6716)(Figure4F),percentfloweringofNolina brittoniana (P=0.3371) (Figure5B),ornumberofplantsofPrunus geniculata(P=0.6091) (Figure5C).Finally, twopinerockland species showed no statisticallysignificanttrends;neither Linum arenicoladensity (P = 0.0968) (Figure 5A) norRhynchospora floridensis frequency (P= 0.3790) (Figure 5D) changed over thedurationmonitored.

DISCUSSION

Across all species and life history traits,variablesfornineofthe18species(50%)showed statistically significant positiveresponses to fire, and variables for ninespecies (50%) showed neutral responses

to fire. Responses varied across species,traits, and sites (Figures 2, 3, 4 and 5).Nospeciesshowedasignificantlynegativeresponsetofire.

Plant Adaptations to Fire

This work contributes to the growingdocumentation of fire requirements forviability of species. Post-burn resprout-ing and obligate seeding in other fire-dependent communities have been welldocumented,includingtheMediterraneanBasin (Canadell et al. 1991; Lloret andLópez-Soria 1993; Pausas 1997; Quin-tana et al. 2004),Australia (Zammit andWestoby 1987; Benwell 1998), southernCalifornia (Keeley and Zedler 1978;Moreno and Oechel 1993), the southernAndes (Burns1993), southeasternBrazil(CirneandScarano2001),incircum-borealforests (Rowe 1983; Goto et al. 1996),andinSouthAfrica(HolmesandNewton2004).However,suchmechanismsoffireadaptationhavereceivedlessattentioninFlorida’spyrogenichabitats.

Recentworkhasdocumentedmechanismsthat contribute to species survival andviability in Florida scrub (Menges andKohfeldt1995;Carrington1999;Weekleyand Menges 2003; Menges 2007), sand-hill(MengesandDeyrup2001;Mulliganand Kirkman 2002), and pine rockland(Liuetal.2005;LiuandMenges2005).Adaptations that allow species to persistinhabitatsthatburnincludetheabilitytosurvive high temperatures and resproutaftertissueloss.Forexample,thepredomi-nantpinesofsandhillsandpinerocklands,Pinus palustris P. Miller (longleaf pine)and Pinus elliottii var. densa Little andDorman(Floridaslashpine),respectively,havemorphologicaladaptationsthatconferresistance to frequent, low intensityfires(MengesandDeyrup2001).Thegrowingmeristems of seedlings of both speciesareprotectedclosetothegroundwithinadense clusterofneedles.As adults, bothalsoshedlowerbranchesanddevelopthicklayersofbark.

Threespecieswedocumentwithsignificantresponsestoburninghavebeendemonstrat-edtoresproutaftertissuelossfromfireorotherdisturbance.Oneplantspeciesnative

12 Natural Areas Journal Volume 30 (1), 2010

Figure 4. Species whose variables (A through F) were analyzed with analysis of variance using percent change data (P < 0.05). All graphs shown are ± 1 SE. Number above or below error bar denotes sample size. Significant p-values are italicized. Variable A = Bonamia grandiflora number of plants, B = B. grandiflora percent reproduction, C = B. grandiflora number of recruits, D = Eriogonum longifolium var. gnaphalifolium density, E = Eryngium cuneifolium number of plants, and F = Liatris provincialis density.

Volume 30 (1), 2010 Natural Areas Journal 13

Figure 5. Species whose variables (A through E) were analyzed with analysis of variance using percent change data (P < 0.05). All graphs shown are ± 1 SE. Number above or below error bar denotes sample size. Significant p-values are italicized. Variable A = Linum arenicola density, B = Nolina brittoniana percent flowering, C = Prunus geniculata number of plants, D = Rhynchospora floridensis frequency, E = Ribes echinellum density, and F = R. echinellum percent reproduction.

1� Natural Areas Journal Volume 30 (1), 2010

tosandhills,Conradina glabra, respondstofrequentfirebyresproutingandrecruit-ingfromseedafterfireandisresilienttoa range of fire return intervals (Gordon1994; Menges 2007). Carrington (1999)reportedthatEriogonum longifoliumvar.gnaphalifolium resprouts and flowers inresponsetofireandhasstrongpost-burnseedlingestablishmentresponseswithin19monthspost-burn.Increasesinreproductiveoutputofthisspeciesresultfromincreasedfloweringfollowingfire(Satterthwaiteetal.2002).McConnellandMenges(2002)noted that seedling establishment of E. longifoliumvar.gnaphalifoliumincreasesinburnedareasduetolitterremovalasaresultofburning.Crotalaria avonensiscanresproutafterlowintensityfire(B.Pace-Aldana,MonitoringBiologist,TheNatureConservancy, pers. comm. 2008). ThisworkdemonstratessignificantincreasesinfloweringofC. avonensisthesecondyearafterburning.Morepost-burndatawouldbeidealfordocumentingfurthertrends.

Speciesseenheretohaveneutralresponsestofirehavebeendocumentedtoresproutinotherstudies.WeekleyandMenges(2003)describedBonamia grandifloraasastrongresprouterwithnosignificantdifferencesinrecruitmentpre-orpost-burn.HartnettandRichardson(1989)reportedincreasedreproductionandplantdensityofBonamia grandiflora in recently burned plots viaseedlingrecruitmentandresprouting.Wefoundno significant recruitmentofBon-amia grandiflora after burning, althoughourlowsamplesizemayhaveinfluencedthe result.Wealso foundnon-significantchange inbothplantdensityandflower-ingofNolina brittonianaandnumberofplants of Prunus geniculata with timesince burn.Weekley and Menges (2003)reported 98% survival of tagged Nolina brittoniana individuals and significantlyhigherpost-burnstemdensitiesofPrunus geniculata.Asseeninthisstudy,firedidnotresultinincreasedmortalityineitherspecies(WeekleyandMenges2003).

Otherspeciesinthesepyrogenichabitatsrespondsimilarlytofire(Table2),whichcan stimulate resprouting and flowering(Abrahamson1984a;Kirkmanetal.1998;Carrington1999;Yahretal.2000;Norman2003), especiallyaftercoolerfires(Spier

andSnyder1998),increasecover(ReinhartandMenges2004),andincreaserootandrhizome to shoot ratios (Hartnett 1987).Post-burnstimulationoffloweringinsomespeciesmaybedelayedforseveralyears(OstertagandMenges1994).

Otherspeciesarepost-burnobligateseed-ersthatarekilledbyfirebutrecruitfromseedbanks(Table2).Demographyofthesespecies can provide information aboutlikelynaturalfirereturnintervals(Menges2007). Longer-lived species that recoverfromseedbanksfollowingfireshouldbebetteradaptedtosystemswithlongerfireintervalsthanshouldrelativelyshort-livedperennials. Johnson (1982) hypothesizedthatfirereturnintervalsshorterthanabout10yearsmayeliminateCeratiola ericoides Michx.(Floridarosemary)fromscrubsites.Additionally, demographic transitions ofsome species are affected by time sincefire (Evans et al. 2008). Multiple matrixpopulationmodels,deterministicanalyses,andstochasticsimulationsofChamaecrista lineata var. keyensis demonstrated thatrecentlyburnedsites(1–2yearspost-burn)had the highest finite population growthrates in this species of all sites (Liu etal.2005).

Fire Management Implications

HabitatneedsofwildlifespeciesinFloridaalsosuggestthehistoricalfrequencyoffireforassociatedplantcommunities.Aphelo-coma coerulescens(Bosc,1795),orFloridaScrub Jay, often abandons habitat afterscrubvegetationexceeds threemeters inheight(WoolfendenandFitzpatrick1984;Schmalzer et al. 1994; Breininger et al.1999;Duncanetal.1999)orifsandpineinvadesthesite(WoolfendenandFitzpat-rick1984).Speciesfoundinsandhillandflatwoods require groundcover and openmidstories maintained within relativelyfrequentfire.ExamplesincludeGopherus polyphemus (Daudin, 1802), or GopherTortoise, which requires sufficient coverofherbaceousforagefoundinopenpine-lands(Breiningeretal.1994;Hermannetal.2002),andPicoides borealis (Vieillot,1809), the Red-cockaded Woodpecker,whichalsorequiresanopenmidstory(Ho-visandLabisky1985;Kellyetal.1994;Jamesetal.1997).Severalspeciesoccurin

habitatswithsignificantcoverofbaresoil,includingFloridaScrubJay(WoolfendenandFitzpatrick,1984),Sceloporus woodiStejneger,1918,orFloridaScrubLizard,andNeoseps reynoldsiStejneger,1910,orSandSkink(Greenbergetal.1994;Branchetal.1999;Gianopulos2001;Greenberg2002).

Evenwherefiremanagementremainsanactive practice, providing a variable ordiversefireregimemayhelpbenefitcon-servationofecosystemsinFlorida(Abra-hamson1984b;RobbinsandMyers1992;SpierandSnyder1998;Liuetal.2005).In the last century, prescribed burners,especiallythoseburningwithsilviculturalorrangelandgoals,concentratedonwinterburnstofacilitatefiremanagementandre-juvenatespringforage(RobbinsandMyers1992; Miller andWade 2003). However,morenaturalgrowingseasonburnsarees-sentialforcertainplantspecies.Severalofthosespeciesshowingneutralresponsestoprescribedfiremanagement in thisstudywereburnedmainlyinthewinterorearlyspring(Bigelowia nuttalliiwasburnedinFebruary,Marshallia ramosa wasburnedinFebruaryandMarch,and Nolina brit-toniana wasburnedfromOctoberthroughMarch).Thetimingofthesefiresmayhavebeeninsufficienttostimulatetheresponsesdescribedabovethatshouldhavefacilitatedpositiveresponsestofire.

Fire Surrogates

Today, prescribed fire for conservationand agricultural purposes now generallyreplacesthenaturalandhistoricsourcesoffire(RobbinsandMyers1992).ArecentanalysisbytheFloridaDivisionofForestryandtheFloridaParkServiceidentifiedasmuchas40%(104,836hectaresof262,090managedhectares)offire-dependanthabi-tatsmanagedbyFloridastateagenciestobefiresuppressed(Hardin2002).Difficultyoffiremanagementinanincreasinglydevel-opedlandscapeisresultinginsubstitutionofmechanical(mowing,chopping,disking)and herbicide approaches for vegetationmanagement.

These fire surrogates have been used topreparesitesforprescribedburnsorreplaceburningentirelywhenitisconsideredno

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longerfeasible.Clear-cuttingandsalvagelogging of Pinus clausa (Chapman exEngelmann)Sargent(sandpine)inscrub(Greenberg et al. 1996; Provencher etal. 2000), hardwood reduction usingherbicides and chain-saws in sandhills(Provencher et al. 2001), stand thinningin pine rocklands in southern Florida

(Maschinskietal.2005),andchoppingormowinginhabitatsfromflatwoodstodryprairietoscrub(Wattsetal.2006;Willigesetal.2006)haveallbeenused tomimicthe structural and fuel reduction impactsoffirewithsomemeasureofsuccessforsomespecies.However,theseapproachesappearnot tosubstituteforfireforsome

speciesconsideredkeystonetothesehabi-tats.Forexample,AristidastrictaMichx.(pineland threeawn or wiregrass) willflowerinresponsetovariousstresseslikedefoliation and soil disturbance (Parrott1967);however,itneedsasummerburntoproduceviableseed(Duever1989;Outcalt1994).Mechanicaltreatmentsthatarenot

Species Response to fire Habitat ReferenceAristida stricta Michx. Viable seed production Sandhill,

flatwoodsDuever 1989; Outcalt 1994; Mulligan and Kirkman 2002

Calamintha ashei (Weath.)Shinners

Increased seedling recruitment

Carrington 1999

Ceratiola ericoides Michx. Obligate post-burn seed bank

Florida scrub Johnson 1982

Chamaecrista lineata var. keyensi s

Obligate post-burn seed bank

Pine rockland Liu and Menges 2005

Conradina brevifolia Obligate post-burn seedbank Florida scrub B. Pace-Aldana pers. comm. 2008

Dicerandra frutescens Obligate post-burn seed bank

Florida scrub Quintana-Ascencio et al. 2003; Menges and Quintana-Ascencio 2004; Menges, unpublished data

Eryngium cuneifolium Obligate post-burn seed bank

Florida scrub Quintana-Ascencio et al. 2003; Menges and Quintana-Ascencio 2004; Menges, unpublished data

Garberia heterophylla (W. Bartram) Merr. and F. Harper

Resprout, stimulated flowering and recruitment

Florida scrub Carrington 1999

Hypericum cumulicola (Small) P. Adams

Obligate post-burn seed bank

Florida scrub Quintana-Ascencio et al. 2003

Lechea deckertii Small Increased seedling recruitment

Florida scrub Johnson and Abrahamson 1990

Lechea cernua Small Increased seedling recruitment

Florida scrub Johnson and Abrahamson 1990

Palafoxia feayi A. Gray Resprout, stimulated flowering

Florida scrub Ostertag and Menges 2004

Paronychia chartacea Fern Increased seedling recruitment

Florida scrub Johnson and Abrahamson 1990

Pinus clausa (Chapman ex Engelm.) Vasey ex Sarg.

Obligate post-burn seed bank, serotinous cones

Florida scrub Outcalt and Greenberg 1998

Polygala lewtonii Small Increased seedling recruitment

Sandhill U.S. Fish and Wildlife Service 1999; Weekley and Menges unpublished data

Warea carteri Obligate post-burn seed bank

Scrub, sandhill Menges and Gordon 1996

Table 2. Examples of plant species responses to fire in Florida’s pyrogenic habitats from the literature.

1� Natural Areas Journal Volume 30 (1), 2010

followedbyfirefailtoallowrecruitmentof endemic Florida scrub herbs (Rickeyet al. 2007), which is probably due topersistent litter that would otherwise beconsumedbyfire.Withoutunderstandingof the mechanisms behind responses ofspecies like the ones examined here, wecannotbeconfidentthatthesealternativeapproacheswillhavethedesiredeffectsonallcomponentsofthecommunity.

Implications for Future Research and Monitoring

Thedurationofthesemonitoringprojects,eventhosecontinuedforover10years,maybeinsufficienttofullyclarifypatternsofresponsetofire.Thelagtimeobservedforpositiveresponses,especiallyinthescrubspecieswhoseindividualsinitiallydieafterburning,representsthetimeneededforseedgerminationandseedlinggrowth.Longermonitoringandautoecologicalstudiesmayclarifypatternsforthosespeciesthathadinsignificantlypositiveresponsestofireinthis study.Alternatively, chronosequencestudies that monitor populations at mul-tiplesiteswitharangeoftimespost-burnmay be used to infer post-burn patterns(Menges2007).

While these results cannot be used toidentify life-history traits that are morecloselyassociatedwithsignificantpositiveresponse tofire (reproductive traitsweremeasuredforsixofthe18species),severallinesofevidencesuggestthattheabsenceoffireposesamorecriticalthreattoper-sistence of these rare species than doesits presence. Fire exclusion is predictedtocauselocalextinctionofFloridascrubplants (Menges and Quintana-Ascencio2004;Mengesetal.2006).Withincreasedtimesincefire,rareandcommonspeciesas-sociatedwithlongleafpine-wiregrasshabi-tatsmaydecline(Provencheretal.2001;Gray et al. 2003).Without fire, changesin community structure of sandhills willoccur(Mengesetal.1993);suchchangescan be reversed if fire is re-introduced,potentiallyfollowingfuelreductiontreat-ments (Provencher et al. 2001; Reinhartand Menges 2004). While, more studiesmeasuring multiple population variablesinadditiontoabundancemayhelpdefine

associationsofcertainvariablestofireandpossiblyprovidefuturedatasetsforamorecomplex meta-analysis, lack of data onspecificresponsesofindividualrarespeciesto fire in pyrogenic natural communitiesshouldnotprecludefiremanagement.

ACKNOWLEDGMENTS

Thisworkwouldnothavebeenpossiblewithoutthesupportofallofthefieldbi-ologiststhatmonitoredthespeciesonourpreserves.Weareverygratefulforthefieldsupport provided by staff ofThe NatureConservancy and Archbold BiologicalStation.WeespeciallythankC.Bergh,A.Higgins, B. Krieter, B. Pace-Aldana, D.Printiss,P.Quintana-Ascencio,G.Seamon,C. Weekley, and many others who havehelped to collect these long-term data.Wealsoappreciatecommentsfromthreereviewers that improved thismanuscript.SupportfromtheNationalScienceFoun-dation(DEB98-15370,DEB-0233899andDEB-0812717), the Florida Division ofPlant Industry, and the Florida ChapterofTheNatureConservancyaregratefullyacknowledged.

Jodi L. Slapcinsky is a Monitoring Ecolo-gist for the Florida Chapter of The Nature Conservancy. Her current research inter-ests include plant demography and the effects of fire on vegetation, and species and community monitoring and manage-ment in Florida natural areas.

Doria R. Gordon is Associate Director of Science for the Florida Chapter of The Na-ture Conservancy and Courtesy Professor of Biology at the University of Florida. Her research focus includes restoration of fire and species in longleaf pine ecosystems, identification and prediction of invasive non-native plant species, and ecology, conservation, and management of rare species and communities.

Eric Menges is a Senior Research Biologist at Archbold Biological Station. His main research and conservation interests include the biology of rare plants, population vi-ability, fire ecology and management, and restoration ecology. He has published over 110 papers on these topics.

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