Influence of the El Nin˜ O Southern Oscillation on Fire Regimes in the Florida Everglades

Ecology, 84(12), 2003, pp. 3124±3130 ᭧ 2003 by the Ecological Society of America

INFLUENCE OF THE EL NINÄ O SOUTHERN OSCILLATION ON FIRE REGIMES IN THE FLORIDA EVERGLADES

BRIAN BECKAGE,1,3 WILLIAM J. PLATT,1 MATTHEW G. SLOCUM,1,4 AND BOB PANKO2 1Department of Biological Sciences, Louisiana State University, Baton Rouge, Louisiana 70803 USA 2Everglades National Park, 40001 State Route 9336, Homestead, Florida 33034 USA

Abstract. Disturbances that are strongly linked to global climatic cycles may occur in a regular, predictable manner that affects composition and distribution of ecological communities. The El NinÄo Southern Oscillation (ENSO) in¯uences worldwide precipitation patterns and has occurred with regular periodicity over the last 130 000 years. We hypoth- esized that ENSO, through effects on local weather conditions, has in¯uenced frequency and extent of ®res within Everglades National Park (Florida, USA). Using data from 1948 to 1999, we found that the La NinÄa phase of ENSO was associated with decreased dry- season rainfall, lowered surface water levels, increased lightning strikes, more ®res, and larger areas burned. In contrast, the El NinÄo phase was associated with increased dry-season rainfall, raised surface water levels, decreased lightning strikes, fewer ®res, and smaller areas burned. Shifts between ENSO phases every few years have likely in¯uenced vegetation through periodic large-scale ®res, resulting in a prevalence of ®re-in¯uenced communities in the Everglades landscape. Key words: area burned; El NinÄo; ENSO; Everglades; ®re; Florida; global warming; La NinÄa; lightning; savannas; SOI; wet/dry season.

INTRODUCTION ciated with increased occurrence of ®res at subcontinental scales (Swetnam and Betancourt 1990, Brenner Fire is a pervasive natural disturbance in many land- 1991, Veblen and Kitzberger 2002). The precise mech- scapes (Bond and van Wilgen 1996). Fires depress anisms underlying ENSO±®re relationships may not be some plant populations, but enhance others (e.g., Glitz- apparent at subcontinental scales because many dif- enstein et al. 1995, Beckage and Stout 2000), in¯u- ferent landscapes occur in such broad regions but may Reports encing the composition and extent of communities be evident at local, landscape scales. (e.g., Johnson 1992, Higgins et al. 2000). A ®re regime We explored relationships between ENSO cycles, lo- that is predictable (i.e., with regular periods of in- cal weather patterns, and ®res within Everglades Na- creased ®re likelihood) can increase the potential for tional Park (USA) to address two questions: Are fre- evolutionary responses to ®re and strengthen effects quency and extent of ®res within the Park related to on plant populations and communities as subsequent ENSO cycles? Can we propose mechanisms whereby disturbances reinforce effects of prior ones (Mutch ENSO cycles in¯uence local ®re regimes? We ad- 1970, Platt 1999, Bond and Midgeley 2001). dressed these questions using time series data for global Predictable ®re regimes may result from global cli- ENSO cycles, long-term records for rainfall, surface matic cycles that produce conditions favoring large- water levels, and number of lightning strikes in the scale ®res (Johnson 1992, Veblen and Kitzberger Everglades region, and a 52-year record of ®res in Ev- 2002). One such climatic cycle is the El NinÄo Southern erglades National Park. Oscillation (ENSO). ENSO cycles, characterized by al- ternating periods of warm (El NinÄo phase) or cold (La METHODS NinÄa phase) sea surface temperatures in the central and Study area eastern Paci®c, have occurred with a periodicity be- 2 tween three and seven years for the last 130 000 years Everglades National Park is 3600 km (exclusive of (Tudhope et al. 2001). ENSO events affect global rain- marine areas), primarily Ͻ2 m above sea level with fall patterns (Allan et al. 1996) and have been asso- little relief (slope Ͻ3 cm/km). The major source of water is rainfall draining through a broad, slowly moving ``river of grass'' extending from Lake Okeechobee Manuscript received 2 April 2002; revised 3 April 2003; ac- cepted 22 April 2003; ®nal version received 9 June 2003. Cor- southwest to the Gulf of Mexico (Douglas 1947). Eco- responding Editor: K. D. Woods. logical communities are zoned by elevation relative to 3 Present address: Botany Department, Marsh Life Science this central drainage. Salt/brackish marshes and man- Building, University of Vermont, Burlington, Vermont 05405. groves (1920 km2 in area) occur along the coast at E-mail: [email protected] 4 Present address: Wetland Biogeochemistry and Coastal elevations Ͻ0.5 m. Short- and long-hydroperiod sub- Institute, Louisiana State University, Baton Rouge, Louisiana tropical savannas (1620 km2 in area) are located interior 70803 USA. to coastal regions, typically at elevations of 0.5±1 m, 3124 December 2003 ENSO CYCLES AND EVERGLADES FIRE REGIMES 3125 and pine savannas and subtropical hardwood forests (60 km2 in area) occur on limestone outcroppings at elevations of 1±4 m. Fires have been recorded in all Everglades habitats; coastal marshes, seasonal savannas, and pine savannas are maintained by ®re (W. B. Robertson, unpublished report). Most vegetation in these ecosystems resprouts or resists ®re damage, but less ®re-tolerant species, such as hardwoods, are strongly in¯uenced by ®re frequency and intensity. Annual cycles The Everglades are characterized by pronounced annual dry and wet seasons (Duever et al. 1994). The strongly seasonal hydrologic cycle de®nes the ``water year,'' beginning with the dry season that typically ex- tends from October to May (Fig. 1A). The wet season begins when rainfall increases in late May or early June, and the largest proportion of total annual rainfall occurs from June through September (Fig. 1A). Surface water levels are highest at wet season end in October and decline to their lowest levels by dry season end in May (Fig. 1B). Mean annual area burned each month peaks when surface water levels are lowest (Fig. 1C). About 80% of the total area that burns annually does so during the dry- to wet-season transition (April± June), and ®res during May account for almost half the total annual area burned. Reports ENSO indices We used two indices, NinÄo3 and Southern Oscillation Index (SOI), to characterize ENSO conditions. NinÄo3 is based on sea surface temperatures in the Paci®c FIG. 1. The annual hydrologic cycle in the Florida Ev- erglades and its relationship to area burned. (A) Proportion Ocean at latitude 5Њ Nto5Њ S and longitude 150Њ W of annual rainfall occurring each month. (B) Monthly devi- to 90Њ W. Monthly values of NinÄo3 anomalies from ation from annual mean water level in well P33 in Shark January 1950 through December 1999 were obtained Slough, Everglades National Park. Daily values of surface from the NOAA Climate Prediction Center (USA). SOI water level were partitioned into a seasonal component and trend using a moving average ®lter. The seasonal component is based on barometric pressure differences between is the deviation from the yearly average water level. Daily Tahiti and Darwin, Australia (Troup 1965). Monthly deviations were averaged across months within a year, and values from January 1900 to December 1999 were ob- monthly deviations were then averaged across years. (C) The tained from the Queensland Centre for Climate Appli- proportion of mean area burned each month. We used the cations (Australia). Positive SOI and negative NinÄo3 period from January 1948 to December 1999 for panels A and C. Panel B used surface water level data from October correspond to cold surface waters across the eastern 1952 to September 1980 because this was the longest period tropical Paci®c and La NinÄa conditions; negative SOI of record without missing values. and positive NinÄo3 correspond to warm waters and El NinÄo conditions. (Tucson, Arizona) for the period from January 1991 Data series (the beginning of record) through December 1999 for Rainfall records for Florida Division 5, encompass- the Everglades region (25Њ15Ј±25Њ45ЈN, 80Њ30Ј±81Њ6Ј ing the Everglades region, were obtained from the Na- W). Numbers of ®res and area burned were compiled tional Climatic Data Center (USA) from the beginning from Everglades National Park ®re records from the of the record in January 1895 through December 1999. beginning of the record in January 1948 through De- Everglades National Park provided records of daily sur- cember 1999. We included records for the area within face water levels from October 1952 through December the original Park boundaries and for the East Ever- 1999 for well P33, located in Shark River Slough glades region later acquired by the Park. Data for each (25Њ36Ј48.66Љ N, 80Њ42Ј09.28Љ W). We averaged the ®re included date of ignition and termination, ignition daily records for each month. Monthly counts of light- source, and size of area burned. We assigned each ®re ning strikes from the U.S. National Lightning Detection to a month and year based on date of ignition and Network were purchased from Global Atmospherics compiled monthly numbers of ®res and area burned. Reports SOI rainfall 5 Division water Surface ®res No. burned Area park re¯ect variability. they climatic as than ®res rather policies prescribed excluded We sourc- (human ignition es. unknown or incendiary prescribed), not lightning, but with caused, ®res included We 3126 oeaiepatterns examine analysis spectral to used We other. be- each described complement analyses, low, two The correlation. linear and ial in®atproiiisadascae con®- associated levels. statis- and dence report periodicities We signi®cant 1996). tically Lees non- to and multiple- robust (Mann also The is stationarity analysis 1996). spectral Lees of method and taper (Mann cli- systems in persistence mate temporal as- of background because noise and appropriate red was A analysis background. noise red spectral im- a sumes software multiple-taper The a Angeles. plements Los Uni- California, Group, of SSA-MTM Lees the versity and from Mann software We of and relationships. methods (1996) analysis infer spectral to the series used time sim- compared across We series. ilarities time each in peaks) (spectral a hnb oprdars iesre)adcorre- relationships and examine series) explicitly time to across analysis compared lation be then can ABLE oigaeae®tr hreigtelnt ftetm eis orltosand Correlations series. time the of length the shortening ®lter, average moving a Notes: tween Nin T eaaye hs aauigbt pcrlanalysis spectral both using data these analyzed We pcrlaayi dnie oiatfrequencies dominant identi®ed analysis Spectral r ae ntelnt ftesots iesre 4 years). (41 series time shortest the of length the on based are o n O) r-esnrifl,addysao ufc ae ee nteFoiaEverglades. Florida the in level water surface dry-season and rainfall, dry-season SOI), and Äo3 aibeNin Variable ieseries. time .Lna orltosbten®ergms(nulae und nulnme f®e) NOcce(dry-season cycle ENSO ®res), of number annual burned, area (annual regimes ®re between correlations Linear 2. eal fyal umre r ie nthe in given are summaries yearly of Details sn costm eis h eid(nyas and years) (in period The series. time across isons P ABLE rabre o rsNin ®res No. burned Area pcrlpeak. spectral Notes: nie (Nin indices 23(.1 14(.1 00(.5 23(0.01) 12.3 (0.05) 10.0 (0.01) 11.4 (0.01) 12.3 T auswr ae nteassumption the on based were values . (0.01) 1.0 (0.10) 3.4 (0.01) 5.0 .Seta ek orsodn oproiiisi rabre,nme f®e,ENSO ®res, of number burned, area in periodicities to corresponding peaks Spectral 1. aaanalysis Data within h ttsial in®atpaswti iesre r pcdt aiiaecompar- facilitate to spaced are series time within peaks signi®cant statistically The Ϫ Ϫ Ϫ o,SI,rifl,adsraewtrlvl nteFoiaEverglades. Florida the in levels water surface and rainfall, SOI), Äo3, .7( 0.87 ( 0.51 (0.039) 0.35 (0.001) 0.40 .5( 0.65 ahtm eis(patterns series time each . (0.01) 1.0 (0.05) 2.2 (0.01) 5.7 o SOI Äo3 Ͻ Ͻ Ͻ 0.001) 0.001) 0.001) RA EKG TAL. ET BECKAGE BRIAN . (0.01) 1.4 (0.01) 2.0 (0.01) 2.7 (0.01) 3.4 (0.01) 5.0 Ϫ Ϫ .6( 0.46 .2( 0.62 ( 0.53 .3(0.099) 0.23 o SOI Äo3 eidct (yr) Periodicity Methods Ͻ Ͻ Ͻ be- 0.001) 0.001) 0.001) httesetaaedsrbtdas distributed are spectra the that h iesre o ubro rsws®s erne using detrended ®rst was ®res of number for series time The . . (0.05) 2.1 (0.01) 2.4 (0.05) 2.8 (0.01) 3.6 (0.01) 4.9 (0.01) 6.1 pcr costm eist periodicities to series time appropriate across of the comparisons spectra our of limited We quantile distribution. 99th chi-square the beyond estimate ubro aesue nteetmto ftespectrum. a the of Therefore estimation the in used tapers of number vrMrhJn,tepro flws ufc water surface lowest of period aggregated the were to March±June, frequency over water sensitive strike Surface lightning 1994). is and al. levels and et (Duever severity conditions ENSO season largely dry period this determines Oc- during 1). over rainfall summarized (Fig. because were tober±April transition rainfall wet-season im- and the to indices re¯ect ENSO dry to the years sum- of water were portance to data respect Monthly variability with years. in marized across interested regimes were ®re we in as used were maries reo,where freedom, ahtm eist eieetmtsa rcsl as precisely as estimates (ln( transformed derive was burned to Area of possible. length series entire years. time the across using each calculated variability were in spectra interested The were we cause optn hi iercreain( correlation linear their computing from excluded thus and series analysis. the years) time spectral (9 of strike short skewness lightning relatively The was the series. of time because monthly analysis spectral to P eeaie eainhp ewe iesre by series time between relationships examined We au i aetee)aegvnfreach for given are parentheses) (in value Ϫ Ϫ iio 5 Divison .2( 0.72 (0.011) 0.45 ( 0.49 rainfall Ͻ Ͻ iiin5 Division P . (0.01) 1.0 (0.05) 1.1 (0.05) 2.0 (0.10) 3.3 (0.01) 5.7 0.001) 0.001) rainfall au f00 orsod oaspectral a to corresponds 0.01 of value ␯ sapoiaeyeult wc the twice to equal approximately is P aus(ottapd nparentheses) in (bootstrapped, values Ϫ Ϫ Water .6(0.002) 0.46 ( 0.50 ee o ®res No. level . (0.01) 1.0 (0.05) 2.9 Surface water level Ͻ clg,Vl 4 o 12 No. 84, Vol. Ecology, 0.001) ␹ 2 with ␳ .Ana sum- Annual ). .9(0.012) 0.39 ␯ x Ն ϩ ere of degrees erbe- year 1 ) prior 1)) December 2003 ENSO CYCLES AND EVERGLADES FIRE REGIMES 3127

RESULTS Spectral analyses of monthly time series identi®ed shared periodicities (spectral peaks) among area burned, Nino3, SOI, rainfall, and surface water level (Table 1). Area burned had four spectral peaks: 1.0, 3.4, 5.0, and 12.3 years. The 1.0- and 12.3-year cycles were similar to the 1- and 10±14 year cycles reported for south Florida by Gunderson and Snyder (1994). The 3.4- and 5.0-year spectral peaks matched periodicities in NinÄo3 precisely, and the 3.4-, 5.0-, and 12.3-year spectral peaks corresponded to periodicities in both SOI and rainfall. The 12.3-year cycle coincided precisely with a spectral peak in the surface water time series, suggesting a relationship between large areas burned and low surface water levels. The 1.0-year spectral peak re¯ects the in¯uence of the annual hydrologic cycle on ®re regime (Fig. 1). There were three signi®cant periodicities in number of monthly ®res at 1.0, 2.2, and 5.7 years (Table 1). The spectral peak at 5.7 years coincided exactly with a periodicity in rainfall and was similar to a 6.1-year signal in SOI. The 2.2-year periodicity corresponded with signals of similar period in the NinÄo3, SOI, and rainfall time series. The absence of the 2.2-year cycle in the area burned time series suggests that this periodicity involves years with smaller ®res. The spectral Reports peak at 1.0 years again re¯ects the annual hydrologic cycle. Annual variation in area burned and number of ®res was related to ENSO conditions; area burned and number of ®res were positively correlated with La NinÄa and FIG. 2. The relationship between Everglades' area burned, rainfall, surface water level, and NinÄo3. (A) Total dry-season (October±April) rainfall and mean NinÄo3 ENSO (El NinÄo Southern Oscillation) index during the dry season (October±April). (B) Surface water level above mean sea level (m.s.l.) at dry-season end (mean, April±June) with respect to total dry-season (October±April) rainfall. (C) Annual area burned and surface water level at dry-season end (mean, April±June). levels and largest areas burned. Area burned and numbers of ®res were summed from October to September (i.e., water years). The statistical signi®cance of linear correlations was established using a bootstrapping technique because the time series were autocorrelated (i.e., sequential observations were not independent). In the bootstrapping procedure, we created 2000 bootstrapped (surrogate) time series for one of the two time series (e.g., time series ts1). Each surrogate shared the same power spectrum and amplitude of the original time series (see Kaplan and Glass 1995). The linear correlation was calculated between the second time series (ts2) and each of the 2000 bootstrapped ts1's (i.e., FIG. 3. The relationship between number of lightning r ... r ), as well as with the observed time series strikes in the Everglades region of 25.25Њ N±25.75Њ N latitude 1 2000 and 80.5Њ W±81.1Њ W longitude during the dry±wet season (robs). The statistical signi®cance, i.e., two-tailed P val- transition (March±June) and dry-season ENSO (mean Octo- ue, of the relationship was computed by comparing robs ber±April SOI [Southern Oscillation Index]) from 1991 to to the distribution of r1 ...,r2000. 1999. Reports h r otewtsao a eae oteENSO the to related was season ( wet SOI Both the cycle. to dry the 2. Fig. in shown between are burned relationships The 2). (Nin (Table ENSO rainfall lev- and water surface els with correlated negatively were ®res Nin Nin La El 2). with correlated negatively 3128 n lt 03,eetn togi¯ec necolog- on in¯uence strong a exerting 2003), (Beckage predictable Platt landscape and Everglades produced the have in ®res should large-scale links al. et oc- Such (Tudhope years have 2001). of events thousands for ENSO regularly to as curred likely historically are occurred ®res and have conditions ENSO between links Nin El during Nin decreased La and during increased Everglades the in ®res nthe in ae ee tdysao n n oa r-esnrifl,ad()ana rabre n ufc ae ee tdry-season at level water surface and burned 2. area Fig. annual in (C) as and are rainfall, data dry-season and total and Units end end. dry-season at level water tie curddrn lNin El during Nin occurred La strikes lightning during increased occurred 3); strikes (Fig. frequency strike lighting ␳ϭϪ ( F ihnn tiefeunydrn h rniinfrom transition the during frequency strike Lightning uigteps afcnuy ubr n xetof extent and numbers half-century, past the During IG .Tredprue i i n i)fo h xetdrltosi ewe NOadae undta r examined are that burned area and ENSO between relationship expected the from iii) and ii, (i, departures Three 4. . Discussion 0.69; acniin,ae und n ubr of numbers and burned, area conditions, Äa o) anal ufc ae ee,adarea and level, water surface rainfall, Äo3), P h gr rsnstm eiso A oa r-esnrifl n enNin mean and rainfall dry-season total (A) of series time presents ®gure The . value ␳ϭ 0.81; D ϭ ISCUSSION .5)wr orltdwith correlated were 0.050) opae fES.Strong ENSO. of phases Äo P value oepisodes. Äo apae n reduced and phases Äa ocniin (Table conditions Äo ϭ .2)adNin and 0.027) RA EKG TAL. ET BECKAGE BRIAN aphases Äa Äo3 ufc.Ti ih euti ee ovciethun- convective land fewer the in of result warming might slow This may surface. transition the levels water during surface high wet and rainfall, to increased Nin clouds, dry El the during transition. ignition season of probability and, strikes the lightning thus, of frequency the ENSO in¯uences the cycle Second, 2002). Kitzberger Swetnam and and Veblen Baisan Nin 1990, (e.g., Nin ecosystems La El other after some during in years areas as several large than over rather ®res spread phases, that to so 2003), likely al. are et graminoid- (Slocum fuels pyrogenic, ®ne of dominated This period. continuity transition spatial the increases during water no of- contain drainages ten major and rainfall, Nin dry-season La decreased contrast, wet-season In to period. dry- the transition during water drainages higher major in in levels resulting Nin rainfall, con- El dry-season ENSO rainfall. increase First, dry-season ways. in¯uence two ditions in regimes ®re erglades or ecosystems. ®re other of in predictability drought increase similarly 1947). (Douglas may years ocean ENSO the 5000 from the emerged area over the since conditions evolutionary and ical epooeta NOeet aei¯ecdEv- in¯uenced have events ENSO that propose We opae htpouemore produce that phases Äo o NOidx B surface (B) index, ENSO Äo3 clg,Vl 4 o 12 No. 84, Vol. Ecology, apae produce phases Äa ophases Äo ophases Äo Äa December 2003 ENSO CYCLES AND EVERGLADES FIRE REGIMES 3129 Reports

PLATE 1. (Left) A thunderstorm over Taylor Slough in Everglades National Park. Lighting strikes from such storms provide a natural source of ignition for wild®res. (Right) The Ingraham Fire burning a tropical hardwood hammock. Fires are most likely to naturally enter hardwood hammocks in the dry-season to wet-season transition during severe droughts associated with La NinÄa conditions. The burning of litter and humus in hardwood hammocks during these extreme events begins the transformation of the hammock into an open pineland. derstorms and fewer lightning strikes, contributing to storms may result in high surface water levels during reduced numbers of ®res. In contrast, fewer clouds, the dry±wet season transition even during La NinÄa decreased rainfall, and low surface water levels during phases. For example, Hurricane Georges and tropical La NinÄa phases could cause rapid surface warming, storm Mitch both in¯uenced southern Florida weather resulting in more thunderstorms and lightning strikes in September and November 1998 respectively, pro- and increased likelihood of ignition of dry fuels over ducing increased rainfall and high water levels and re- large areas, contributing to larger numbers of ®res. We ducing area burned in 1999 despite La NinÄa conditions emphasize that increased numbers of lightning strikes (Fig. 4i). Second, years of few and small ®res during coincide with La NinÄa drought conditions, leading to La NinÄa conditions and low surface water levels have potentially extensive ®res. The 1989 Ingraham Fire, an followed years when large areas burned. These devi- example of such a La NinÄa-in¯uenced ®re, was ignited ations likely re¯ect the 2±3 years required for post®re by ®ve separate lightning strikes and burned 40 000 ha recovery of ®ne fuels (Gunderson and Snyder 1994). over 1.5 months (see Plate 1). Similar large, lightning For example, the 1962 peak in area burned (the largest initiated ®res probably occurred historically during ma- single ®re in park history) was followed by several jor La NinÄa phases when water levels were low years with small annual areas burned, despite low sur- throughout the Everglades and may be responsible for face water levels in 1963 and 1965 (Fig. 4ii). Third, the prevalence of ®re-adapted communities in the Ev- large ®res during La NinÄa episodes may have been erglades (W. B. Robertson, unpublished report). prevented because of anthropogenic ®rebreaks or sup- Deviations from the expected relationship between pression. For example, large ®res occurred in the north- ENSO and Everglades ®re regimes during the past 50 ern Everglades during a severe La NinÄa drought in years have involved three conditions. First, increased 1955±1956 (Loveless 1959) but would have had to rainfall near the end of the wet season from tropical cross US 41 to enter Everglades National Park. Only Reports uvr .J,J .Mee,L .Mee,adJ .Mc- M. J. and Meeder, C. L. Meeder, F. Hur- J. grass. J., of M. river Duever, Everglades: The 1947. S. M. Douglas, rne,J 91 otenOclainaoaisadtheir and anomalies plants. Oscillation and Southern Fire 1991. 1996. J. Wilgen. Brenner, van W. B. and J., W. Bond, resprouting of Ecology 2001. Midgley. J. J. and J., W. Bond, repeated of effects The 2000. Stout. J. I. and B., Beckage, wild®re severe Predicting 2003. Platt. J. W. and B., Beckage, a on history Fire 1990. Swetnam. W. T. and Nin H., El C. 1996. Baisan, Parker. E. D. and Lindesay, J. J., R. Allan, al. 2001). et al. et (Overpeck Holmgren gradients 1991, temperature species' in¯u- in along shifts warming through ranges global than other whereby ecosystems path ences indirect consti- may an regimes Rela- ®re tute ®res. and ENSO large-scale between severe, tionships more but frequent (Timmer- favoring less conditions se- warming creating possibly in 1999), global al. increase et with mann to frequency expected and are verity (Robertson events the frequency ENSO ®re in 1953). to ecosystems sensitive of are structure Everglades and relationship. composition ENSO±®re the The through Everglades the in Nin La severe during despite Park period the this inside burned subsequently area small a 3130 aintruhagnru rn rmteAde .Mellon W. Andrew the Foun- from Park grant Foundation. National generous the a by through Fellow- funded dation Research program a Ecological Program, Parks ship National the support Foun- Science and National ®nancial dation, the Tennessee, of acknowledges University the gratefully from Beckage manuscript. Brian the improved anonymous greatly two that comments and for Woods, reviewers Kerry Gross, Louis and function olm 94 h lmt fsuhFoiaadisrl in role its 225±248 and Pages Florida ecosystem. Everglades south the of shaping climate The 1994. Collum. USA. Florida, Miami, House, ricane eaint lrd idrs nentoa ora fWild- of Fire Journal land International wild®res. Florida to relation USA. York, New York, New Hall, and Chapman Ecology in Trends niche. Evolution persistence and the plants: woody in Vege- of of test Science Journal a tation hypothesis. sandhills: disturbance Florida intermediate in the richness species on burning and Ecology in Frontiers Environment Everglades. the Florida the in years Research Forest of Journal 1559±1569. 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