Fire Frequency Effects on Longleaf Pine (Pinus palustris P. Mi lIer) Vegetation in South Carolina and Northeast Florida, USA
RESEARCH ARTICLE ABSTRACT: Southeastern United States habitats dominated by longleaf pine (Pinus palustris P. Miller) have declined precipitously in area and extent. Conservation of diverse ground-layer vegetation in these endangered habitats depends on prescribed fire. While the need for prescribed fire is now· generally accepted, there is disagreement concerning the most appropriate fire regime. One of the more important variables is frequency of fire. Several hypothetical relationships between fire frequency and vascular plant richness and composition are suggested by the existing literature. Results of two long-term • prescribed fire studies support the hypothesis that burning as frequently as fuels permit is optimal for maintaining the largest number of native ground-layer plant species. However, frre frequency effects on species composition differed between the two studies. Increasing fire frequency in South Carolina Fire Frequency Ultisol flatwoods and wet savannas was associated with a distinct shift from woody to herbaceous dominated communities. Herbs, particularly bunchgrasses and perennial forbs, dominated annual- and Effects on Longleaf biennial-burn treatment plots, whereas triennial- and quadrennial-burn plots were shrub-dominated. In contrast, annual and biennial frres did not produce herbaceous dominated ground-layer vegetation in North Florida Spodosol flatwoods. Reduced dominance of saw palmetto and somewhat increased Pine (Pinus palustris importance of forbs and grasses, particularly rhizomatous grasses, distinguished the annually burned plots. However, biennial- and quadrennial-burn plots were similar in composition and did not differ P. Mi Iler) Vegetation signifrcantly in species richness at the largest spatial scale. in South Carolina Efectos de la Frecuencia del Fuego en la Vegetacion de Pi no de Hoja Larga (Pinus palustris P. Miller) en Carolina de Sur y el Noreste de Florida, USA and Northeast RESUMEN: Los habitats del Sur de USA, dominados por el pino de hoja larga (Pinus palustris P. Miller) han dec1inado drasticamente en area y extension. La conservacion de capas divers as de vegetacion en esos habitats amenazados dependen del fuego recetado. Mientras la necesidad del fuego recetado esta Florida, USA ahora generalmente aceptada, hay un desacuerdo acerca del regimen de fuego mas apropiado. Una de las variables mas importantes es la frecuencia del fuego. En la literatura existente se sugieren muchas relaciones hipoteticas entre la frecuencia del fuego y la riqueza de plantas vasculares y la composicion. Resultados de dos estudios de largo termino de fuego recetado, apoyan la hipotesis que la quema tan Jeff s. Glitzenstein1 frecuente como sea posible es el optimo para mantener el mayor numero de plantas de especies nativas. Donna R. Streng No obstante, el efecto de la frecuencia del fuego en la composicion de especies vario entre los dos estudios. El aumento de la frecuencia del fuego en los bosques de llanura Ultisol de Carolina del Sur Tall Timbers Research Station y en las savanas humedas estuvo asociado con un cambio distinto desde comunidades dominadas por l3093 Henry Beadel Drive lefiosas a herbliceas. Las hierbas, particularmente pastos asociadas ('bunchgrasses'), un 'forb' perenne, Tallahassee, FL 32312 USA domino las lotes tratados con fuego anual y bienal, mientras que los plots tratados con fuegos trienales y cuadrienales estuvieron dominados por arbustos. En contrate, los fuegos anuales y bien ales no Dale D. Wade produjeron una vegetacion dominada por herbaceas en los bosques llanos Spodosoles en el Norte de Florida. La disminucion de la dominancia de 'saw palmetto' y el aumento de la importancia de 'forbs' USDA Forest Service y pastos, particularmente los rizomatosos, distinguieron los plots anualmente quemados. No obstante, Southern Research Station los plots bienales y los cuadrienales fueron similares en composicion y no difirieron significativamente 320 Green Street en riqueza de especies a una gran escala espaciai. Athens, GA 30602 Index terms: fire frequency, fire regime, longleaf pine, Pinus palustris, prescribed burning •
INTRODUCTION way and Lewis 1997). Historically, recur ring low-intensity fires perpetuated Longleaf pine (Pinus palustris P. Miller) longleaf pine savannas. In the absence of dominated woodlands and savannas are fire the diverse longleaf ground-layer veg among the most species rich plant com etation, characterized by numerous grass munities in North America (Bridges and es, forbs, and low shrubs, is replaced by a Orzell 1989, Peet and Allard 1993). Un depauperate understory dominated by fortunately, these habitats are also highly hardwood trees and large shrubs (Hey endangered. Of an estimated 36 million ha ward 1939, Lemon 1949, Komarek 1974, lCorresponding author e-mail: of presettlement old-growth habitat, only Abrahamson and Hartnett 1990, Waldrop [email protected] about 3% remains in anything close to the et al. 1992, Brockway and Lewis 1997). original condition (Frost 1993). Fire ex Natural Areas Journal 23:22-37 clusion is the primary factor responsible The need for prescribed fire in manage for the loss of longleaf pine habitat (Brock- ment of longleaf pine dominated habitats
22 Natural Areas Journal Volume 23 (1),2003 is well established. However, numerous of fire frequencies that happened to be and vascular plant species richness be questions remain concerning the most ap encompassed by their own studies (Col tween burned and long-term unburned propriate burn regime and how that might lins et al. 1995, Beckage and Stout 2000). plots. However, differences among three vary among habitats and along environ~ fire frequency·treatments, that is, annual, mental gradients. One important question Several recent prescribed fire studies, in biennial, and triennial dormant-season concerns frequency of fire. Field observa cluding three in southeastern pinelands, burning, were relatively rilinor and, for the tions and some experimental data tend to have challenged the validity of both the most part, not statistically significant (P > suggest that very short fire return times, MFFH and IDH. Mehlman (1992), in a 0.05). An important point is that the fire that is, 1 to 3 y, are necessary to maintain long-term study of old field loblolly pine frequency treatments in this study were species richness of longleaf ground-layer (Pinus taeda L.) stands in north Florida carried out from 1942 to 1954 and that a vegetation (Lewis and Harshbarger 1976, (the Stoddard Fire Plots at Tall Timbers period of 24 y elapsed between the termi Komarek 1974, Walker and Peet 1983, Research Station), found that increases in nation of treatments and data collection in Peet et al. 1983, Waldrop et al. 1992; see fire frequency were associated with in 1980. During the interval all the plots went also Tester 1989, 1996 for similar results creased species richness but only up to unburned for 9 y and, when burning was obtained in midwestern oak savannas). some threshold level. Additional analysis resumed, the former annual, biennial, and These studies also documented strong ef of Mehlman's (1992) data suggested that triennial plots were all burned on a bienni fects of fire frequency on vegetation com fire return intervals of about six years al schedule. There may well have been position. Generally, annual or biennial would be sufficient to maintain maximal clear effects of the different frequency of burning resulted in ground-layer commu levels of species richness in the Stoddard burn treatments in 1954 that disappe"ared nities dominated by grasses, albeit often Plots and that more frequent burning would during the long interval prior to collection with small shrubs and some forbs in a have little additional effect (Beckage and of data. This study was further hampered sub dominant position. In contrast, less fre Stout 2000). We will henceforth refer to by low replication (n=2), making it even quent or periodic fires tended to favor the hypothesis that fire effects tend to pla more difficult to detect a treatment effect. shrubs and woody sprouts, with reduced teau or "saturate" as the Saturation Hy importance of grasses and forbs. pothesis (SH). Two recent studies in tallgrass prairie also challenged the MFFH and IDH. Collins et The studies cited above support what we In addition to reanalyzing Mehlman's al. (1995) demonstrated a negative corre will henceforth refer to as the "Most Fre (1992) data, Beckage and Stout (2000) lation between fire frequency and species quent Fire Hypothesis" (MFFH) oflongleaf presented results of their own study of richness. They suggested that too frequent pine ground-layer community manage frequency of burning in central Florida burning might enhance the competitive ment. This hypothesis suggests that burn sandhills. They were unable to detect a ness of dominant grasses at the expense of ing as frequently as fuels will allow is the statistically significant effect of fire histo forbs, thereby reducing rather than en best strategy for maintaining species rich ry on either species composition or spe hancing species richness. We will refer to ness and composition of the native longleaf cies richness in these sandhill plots. Beck this suggestion as the "Frequent Fire Spe ground layer. At present, the MFFH forms age and Stout (2000) acknowledged that cies Loss Hypothesis" (FFSLH). Engle et the scientific basis of most current fire this study, which was observational rather al. (2000) did not, however, find this effect management in longleaf pine stands. It is, than experimental, lacked replication and in "highly disturbed early successional however, at variance with results of sever statistical power, and therefore did not prairie communities" in Oklahoma. In their al recent publications as well as a popular constitute a strong test of the IDH or the experiment, differences in species compo hypothesis from plant community ecology MFFH. The authors concluded that at least sition and richness among treatment plots theory. The "Intermediate Disturbance three treatment replicates would be need were related to edaphic factors and time Hypothesis" (IDH; Connell 1978) postu ed to have at least a 50% probability of since the last burn rather than the fire fre lates that highest levels of species richness detecting a real fire frequency effect, quency treatments. in plant communities should occur at "in whereas six replicates w'ould be required termediate" disturbance frequencies that for a statistical power of 0.8., As Beckage One problem in comparing results of these allow persistence of both "early" and "late" and Stout (2000) pointed out, few fire ex various studies is scale. For example, successional species. Testing the IDH is periments, or observational studies, have Mehlman (1992) and Beckage and Stout difficult because of the difficulty of de fin ... anywhere close to this level ofreplication. . (2000) measured_species richness on .a ing an "intermediate" fire frequency. From relatively large scale, while Walker and the theoretical point of view, an intermedi Brockway and Lewis (1997), in an exper Peet (1983) and Brockway and Lewis ate fire return interval would be defined iment carried out in south Georgia longleaf (1997) made their observations on a much relative to the extremes of fire return times pine-Ilex glabra-Aristida beyrichiana smaller scale. Sampling over a range of naturally occurring in a particular habitat Trinius & Ruprecht-Sporobolus curtissii spatial scales might help to resolve some (Connell 1978). However, investigators flatwoods (nomenclature follows Kartesz inconsistencies. attempting to test the IDH have generally 1994 unless otherwise indicated), demon defined "intermediate" relative to the range strated major differences in composition We present results from two ongoing long-
Volume 23 (1),2003 Natural Areas Journal 23 term studies that constitute a strong test of tro1." One control and one triennial plot of the vegetation in our Tiger Corner study the MFFH and the various alternative hy were lost to salvage operations following plots (NatureServe Explorer 2001). These potheses. The two studies were carried out Hurricane Hugo in 1989. One plot assigned include (1) Pinus palustris-Arundinaria in longleaf pine-dominated flatwoods (wet an annual burn treatment was so wet that gigantea ssp. tecta-Liquidambar styraci savannas were admixed at one of the loca it rarely burned; it was consequently ex jlua-Andropogon glomeratus-Sarracenia tions), albeit in different geographic loca cluded from the study. Numbers of treat minor Woodland (G1 global ranking), (2) tions and with very different species com ment ftres applied during the study period Pinus palustris-Clethra alnifolia-Gaylus positions. Both studies were experiments ranged from 44 for the annual plots to 11 sacia jrondosa-Quercus pumila-Schiza with random treatment assignment and for the quadrennials. Biennial plots burned chyrium scoparium Woodland (G 1 global adequate replication (n=4 in one study, 22 times and triennials were burned 14 ranking), and (3) Pinus palustris~P. sero n=6 in the other) to detect any meaningful times. Fires were generally administered tina-!lex glabra-Lyonia lucida Woodland effects. The range of ftre frequency treat in late winter, usually in February or early (G3-G4 global ranking). Maintaining these ments in these experiments (1- to 4-y ftre March. Wade et a1. (1993) documented globally rare associations could be consid return intervals) was not sufficient to elu post-Hugo ftre behavior in the plots. ered a management priority despite their cidate the full relationship between ftre local abundance. frequency and species richness. However, The vegetation in the Tiger Corner plots it probably was sufficient to allow us to can be classifted according to Peet and In the Tiger Corner study plots, longleaf test for a "saturation" effect of the sort Allard (1993) as Atlantic Longleaf Flat pine is the dominant canopy tree in only found in Mehlman's (1992) data or a neg woods with inclusions of Atlantic Mesic one of the four blocks (mean canopy cover ative effect of very frequent ftre as found Longleaf Woodland, Atlantic Longleaf approximately 18%, vegetation sampling by Collins et a1. (1995). Our sampling and Savanna, and Longleaf Seepage Bog (see methods are discussed below). In the other analytical techniques also allowed for a Peet and Allard 1993 for lists of species blocks loblolly pine was the canopy dom test of scale effects on species richness. associated with each of these community inant prior to Hurricane Hugo (in fact, that types). Dominant Atlantic Longleaf Flat was one reason for blocking), but the hur woods species cited by Peet and Allard ricane decimated loblolly pine throughout METHODS (1993) include Pinus palustris, P. elliottii, much of FMNF (Sheffield and Thompson P. serotina, Ilex glabra, Serenoa repens, 1992), including at Tiger Corner. Present Tiger Corner Study Quercus pumila, !lex coriacea, Cyrilla ly, loblolly pine still dominates the canopy Francis Marion National Forest (FMNF) racemif/ora, Myrica cerifera, Gaylussacia in a single block, though mean canopy is located in the Atlantic Coastal Plain, just jrondosa, Lyonia mariana, Pteridium aq cover is less than 10%. In one block loblolly northeast of Charleston, South Carolina. uilinum, and Aristida stricta, "although and longleaf pines now co-dominate, each In addition to the Tiger Corner Study, to be not all the species occur throughout the with less than 5% mean cover, and in the discussed herein, FMNF was the site of range." In central South Carolina where remaining block canopy dominance is split another long-term fire study, the well our plots are located, Pinus elliottii is rare equivalently between longleaf, loblolly, known Santee Fire Study located at the except in maritime vegetation and Aristida and pond pines, all with less than 5% can Santee Experiment Station near Cordes strictaibeyrichiana and Serenoa repens are opy cover. Despite these differences in ville (Waldrop et a1. 1992 and earlier pub absent. Instead, Pinus taeda, Aristida vir pine species dominance, now much re lications cited therein). The Santee Study, gata, Clethra alnifolia, Schizachyrium sco duced due to Hurricane Hugo, similar which spanned the 43-y period between parium, Andropogon virginicus var. decip mixtures of ground-layer communities 1946 and 1989, was discontinued follow iens, Andropogon glomeratus, Vaccinium occur in each of the blocks. This is indicat ing Hurricane Hugo, a category 4 storm tenellum, Lyonia lucida, Lyonia ligustri ed by the fact that Redundancy Analysis that came ashore in September 1989 and na, and Arundinaria tecta (Walt.) Muh1. (RDA) ordination (this analytical technique caused substantial canopy damage through are characteristic, dominant, or subdomi will be discussed in detail below) failed to out much of the national forest. nant, flatwoods plants (Komarek 1974; detect any statistically signiftcant differ Porcher 1995; E. Kjellmark, P. McMillan, ences in species composition related to The Tiger Corner study site is located ap R.K. Peet, lS. Glitzenstein, D.R. Streng, blocking (F = 1.06, P = 0.46, Monte-Carlo proximately 4 kIn southeast of Jamestown, unpub1. data). The combination of the lack n = 99). The conclusion seems to be that South Carolina, and 15 kIn northeast of of wiregrass and the admixture of bog and current differences in pine species domi the old Santee Fire Study plots. The exper cane-break type shrubs within flatwoods nance among blocks are most likely relat iment, ongoing since 1958, originally con is apparently unique to the outer Coastal ed to logging history and perhaps ftre his sisted of 20 0.8-ha plots arranged into four Plain of central South Carolina. The Na tory during the early phases of post-logging blocks of ftve plots each. Five experimen ture Conservancy (TNC) recognizes three stand regeneration and do not indicate sig tal treatments were randomly assigned to globally rare South Carolina variants (i.e., niftcant environmental differences. In all plots within blocks. The treatments includ associations in TNC terminology) of At probability, longleaf pine was historically ed ftre frequencies ranging from annual to lantic Longleaf Flatwoods that are com the dominant canopy tree on all the sites quadrennial as well as an unburned "con- mon in FMNF and comprise the majority (Frost 1993). We therefore feeljustifted in
24 Natural Areas Journal Volume 23 (1),2003 classifying the plots as longleaf woodlands but one were sampled during the first grow score of 0.5. For these "residual" species whether or not longleaf pine is presently ing season after burning and the other plot only, cover was estimated across the entire the dominant canopy tree. was sampled early in the following grow 20-m x 50-m plot. ing season. Triennial plots were not sam Soils in the Tiger Corner plots are Ultisols, pled since they were not due to burn again A list of all the vascular plant species en primarily of the Lynchburg series (fine until late winter 2002 (they will be sam countered in the Tiger Corner NCVS study loamy, siliceous, thermic Aeric Paleaquult; pled during the 2002-growing season). plots is provided in Appendix A, available see Binkley et al. 1992). Ultisols are soils Controls also have not yet been sampled online at
Volume 23 (1),2003 Natural Areas Journal 25 ties in the north Florida-south Georgia tion data were analyzed using redundancy Figure 5.13 in Ter Braak 1995). This line region (FNAI-FDNR 1990; Streng et al. analysis (RDA) , available through the is the fIrst principal component, or fIrst 1993; Brockway and Lewis 1997; E. Kjell CANOCO software package (Ter Braak "PCA axis" in ordination terminology. The mark, P. McMillan, and R.K. Peet, unpubl. 1987-1992). RDA is closely related to fIrst axis site scores are determined by data). PCA, a commonly used multivariate tech extending a perpendicular from each point nique (Ter Braak 1995). Like PCA, RDA to the line. The two-dimensional variabil Soils in the Osceola study plots are Spodo assumes linear relationships between spe ity among sites has now been reduced to a sols, primarily Leon sands (sandy siliceous cies abundances and environmental gradi single dimension, albeit with some loss of thermic Aeric Haplaquod; see McKee ents. Unlike PCA and other indirect ordi information. If instead of two species we 1982). Spodosols are sandy soils distin nation techniques, the ordination axes in have many species, the concept is thesame guished by a "spodic horizon", that is, "a RDA and other types of direct ordinations although impossible to visualize graphi subsurface zone in which organic matter are "constrained" (this term will be ex cally. A single ordination axis will gener in combination with aluminum and/or iron plained below) to be linear functions of ally be inadequate to describe the varia has accumulated due to downward leach the independent variable(s). When com tion in a multidimensional system and it ing." Spodosols lack the clayey subsoil bined with the Monte-Carlo randomiza will consequently be necessary to extract that is characteristic of Ultisols and conse tion test included with CANOCO, RDA ~dditional axes. The second and higher quently have somewhat poorer moisture permits a direct statistical test of the effect axes are located analogously to the fIrst, and nutrient retention during dry periods. of the independent variables on species except that they are oriented in the direc "Aquods are spodosols that are wet for composition. RDA is particularly useful tion of the highest amount of residual vari extended periods in most years" (Brown et for analyses of experimental data because ance that is orthogonal to (i.e., not corre al. 1990). Perhaps due to the difference in experimental treatments typically produce lated with) the axes already derived. soil orders, soil nutrient responses to fIre unidirectional response patterns that meet appeared to differ between the two study the required assumptions of linearity. It is A PCA ordination axis, like any indirect areas. McKee (1982) reported generally therefore recommended for analysis of ordination axis, is a purely mathematical higher soil nutrient concentrations in vegetation experiments with large num entity that must be interpreted with refer burned as compared to unburned plots at a bers of species (Ter Braak 1987-1992, ence to external data. For those of us who variety of Coastal Plain locations, includ 1995). MANOVA, the multivariate exten like to think in terms of real environmental ing our ONF study plots. sion of ANOVA that would generally be effects, it is convenient to think of an indi used for such analyses, is useless when the rect ordination axis as an underlying, but We did not collect biomass data from ONF. number of dependent variables (species in unknown, environmental gradient that in However, NCVS data were collected us an ordination analysis) exceeds the num fluences species composition in some im ing the same methods as in the Tiger Cor ber of experimental units. Thus RDA can portant way (Ter Braak 1995). Once the ner Study. Once again, all bum treatment be viewed as a replacement for MANOVA ordination is completed one is still, howev plots were sampled in the growing season when the limitations of the latter are ex er, left with the task of determining which, following bums the previous winter. Con ceeded (Ter Braak 1987-1992). if any, actual environmental gradients are trols were not sampled. A vascular plant represented by a particular ordination axis. species list for the ONF experiment is pro Since readers may be unfamiliar with PCA RDA is an extension of PC A that attempts to vided in Appendix B, available online at and RDA we will attempt a brief summary circumvent this problem. It does so by in
26 Natural Areas Journal Volume 23 (1),2003 dent variable was fire frequency, that is, ed to site scores and essentially indicate 1969: 325). Single degree of freedom poly time between fires, so we were certain that the contribution of each species to the nomial contrasts were used to test for lin the first ordination axis extracted by RDA placement of the ordination axis. Thus ear and second order trends, thereby eval would be related to this variable. Since the species with high scores on a particular uating the hypotheses discussed in the second and higher axes were not con axis are those that are strongly positively introduction. A significant increasing lin strained by any independent variables, correlated with that axis. Treatment means, ear trend coupled with a nonsignificant these axes were the same as would be referred to as centroids, can be displayed second-order term would be consistent with derived through PCA with the qualifica in ordination space by averaging· across the MFFH but not with any other hypoth tion that they must be orthogonal to the sites receiving the same experimental treat esis. In contrast, a significant quadratic first constrained axis. At this point there ments. contrast coupled with an insignificant lin still remained the issue of statistical sig ear contrast would be consistent with the nificance. As noted above, this is solved in When interpreting ordinations, one ordi IDH. Support for the FFSLH would come CANOCO through a Monte-Carlo random narily graphs the site and species scores from a negative linear contrast. A com ization procedure. The observed eigenval- onto the coordinate space defined by the plete lack of significance (i.e., no signifi . ue, a measure of the amount of explained major axes (Ter Braak 1995). Because of cant contrasts) might indicate the absence variance for the first (i.e., constrained) axis the large numbers of species at our two of any meaningful effect of frequency of was compared to eigenvalues obtained by sites (Tiger Corner n = 278, Osceola n = burn on species richness. However, such ordinating artificially generated data 110), displaying ordination results of indi an outcome might also be consistent with wherein species and associated abundance vidual species was confusing and uninfor "saturation" at a longer fire return interval data were randomly assigned to experi mative. Consequently, we divided species than the range encompassed by our stud mental treatments. If eigenvalues from 5 into 32 groups (see figure legends for Fig ies. A final possibility, "saturation" at very or fewer in 100 random permutations ex ures 1 and 4 and the appendices
Volume 23 (1),2003 Natural Areas Journal 27 dina ria tecta, switchcane) a dominant spe frequency of burn treatments. Quadrenni frequency gradient was in the relative dom cies of wet flatwoods and swamp ecotones al-burn plots were located toward the top inance of woody and herbaceous plants in the outer South Carolina Coastal Plain of this axis and annual-burn plots were at (Figure IE). Woody species were clus (Komarek 1974), was a good indicator for the bottom. Biennial-burn plots occupied tered toward the low fire end of the gradi the wet end of the moisture axis (right side an intermediate position between the other ent while herbaceous species predominat of Figure lC). Group GM (non-Poaceae two treatments, but tended to be more close ed at the high end. This trend was evident graminoids, particularly wet savanna Car ly associated with the annual-burns than in the biomass data as well (Figure 2B). ex and Rhynchospora) was another good the quadrennial-burns (Figure lA, note the Ordination trends may sometimes reflect wet end indicator. locations of treatment centroids). Accord relative rather than absolute changes for ing to the CANOCO Monte-Carlo test, the certain groups, but that was not the case The first RDA cover axis (y-axis in Figure frequency of burn effect was marginally for Tiger Corner. Absolute cover and bio 1), constrained to be a function of fire significant (F = 1.96, P = 0.06, n = 99 mass of woody plants declined substan frequency, was the second most important permutations). tially with increases in fire frequency while in terms of percent of explained cover herbaceous species showed the opposite variance (17.7%). This axis clearly sepa The most obvious change in vegetation trend (Figures 2A, 3). Within the woody rated the Tiger Corner plots according to composition across the Tiger Corner fire and herbaceous categories, most dominant
TIGER CORNER EXPERIMENT
A COVER DATA C LO ~~E 2- 4B FIRE 0.8- PV TG 4A
SF + • ANNUAl. 1- • BIENNIAl. BS 0.4 - 40 QUADRENNIAL + lS
4C wv 2C ~ TS 2. U) WF WG 0- FE H~ 0- CT ~ BG • (3 FA IF AF 0:: GM 20 2A SB AG 10 pfSF SG -1- RG OR SR 1A RF IF • -0.4 - 1C CG
I I HI I I I I FIRE -2 -1 0 -0.8 -0.4 0 0.4 0.8
MESIC RDAAXIS2 RDAAXIS 2 B LO MESIC WET FIRE 0.8- W F G W
W F W
0.4 - W ::JW'lw F Figure 1. Results of the RDA ordination of the Tiger Corner cover data. (A) Plot scores. (B) Species scores classified according to three major life forms: Woody [W], Grass [G] and Forb [F]. (C) Species scores averaged
U) 0- into "functional groups"; abbreviations and number of species per group are as follows: AF = Annual Forb, 14; AG = Annual Grass, 2; BF ~ = Biennial Forb, 3; BG = Bunch Grass, 20; BS = Biennial Shrub, 2; CG (30:: -0.4 - = Climax Grass, 8; CT = Coniferous Tree, 4; FA = Fabaceae, 30; FE = Fern,S; GM = Graminoid Monocot, excluding Poaceae, 20; HV = Herbaceous Vine, 8; IF = Insectivorous Forb, 4; LF = Leafy Forb, 64; LS = Large Shrub, 15; OR = Orchidaceae, 9; PF = Prostrate Forb, 7; PV -0.8- = Parasitic Vine, 1; RF = Rosette Forb, 37; RG = Rhizomatous Grass, GRASS 6; SB = Small Bunchgrass, 19; SF = "Shrubby" Forb, 1; SG = Shrubby w:x:JJV HI Grass, 1; SR = Small Rosette, 14; SS = Small Shrub, 11; TG =Shade FIRE -1.2 I I I I I I Tolerant Grass, 1; TS = Hardwood Tree-Sprout, 16; WF = Weedy Forb, -1.2 -0.8 -0.4 0 0.4 0.8 1.2 13; WG = Weedy Grass, 14; WV = Woody Vine, 7. Species included in each group are listed in Appendix A
28 Natural Areas Journal Volume 23 (1),2003 species showed similar, and statistically woody plants and herbs, grass and forb almost the same location in the ordination significant, trends (Figure 3). species were distributed similarly with scatterplot. respect to fIre frequency (Figure 1B). In In contrast to the different responses of fact, the centroids of these groups were in Centroid plots of fIner groupings were a bit more interesting (Figure 1C). As would be expected, most of the woody plant groups occurred near the low fIre frequen cy end of the fue axis (upper half of Figure 1C). Rubus spp. (group BS, biennial shrub) TIGER CORNER EXPERIMENT responded as typical for woody plants. In A contrast, Arundinaria tecta (SG, shrubby . WOODY PLANTS grass) did not. This species occurred close 750 GRASSES AND FORBS 1100 to the high fIre end of the fIre frequency .....: F=3.61 df=3,10 axis (bottom right of Figure 1C), suggest 0 p<.05 900 ing considerable tolerance for even very 0~ LO 550 frequent fues. This result is consistent with Q') + 700 the observation that Arundinaria is, and NE- was even in presettlement times, an impor ~ 500 350 tant dominant of wetter fIre-maintained -9 pinelands in the Carolinas (Lawson 1709, (f) (f) 300 Hughes 1966, Komarek 1974). Another <{ interesting observation was the tendency ~ 150 0 100 for small shrubs (group SS), such as Gay CO lussacia spp., Hypericum crux-andreae, -100 -50 --1.______---1.._ H. galioides, Quercus pwnila, Vaccinium 1 YR 2YR 3YR 4 YR 1 YR 2 YR 3 YR 4 YR tenellum, to occur closer than the other woody plant groups (TS, LS, WV) to the FIRE RETURN INTERVAL high fIre frequency end of the gradient. This fInding is consistent with plant com B BIOMASS CCA (P < .02) munity surveys (Peet and Allard 1993) 2.00 and results of other fIre studies (e.g., Abra hamson 1984, Waldrop et al. 1992, Streng et al. 1993) in demonstrating that these PLANT TYPE SHRUB + SPROUT small, mostly rhizomatous shrubs can be Grass Forb 1.00 important components of frequently burned pinelands.
Most herbaceous groups were closely as sociated with the high end of the fIre fre quency gradient (Figure 1C). Group CG was particularly favored by very frequent fue. This group included "climax" or ma trix grasses Schizachyrium scoparium, <> Ctenium aromaticum, Muhlenbergia ex pansa (Poir.) Trin., Andropogon gerardii, Sorghastrum nutans, Andropogon virgin i -2.00 cus var. decipiens, and Panicum virga tum. -These grasses are collectively characteris- - Figure 2. Effects of fire frequency on biomass composition in the Tiger Corner Study plots. (A) Absolute tic of pristine soils in the outer Coastal differences in woody and herbaceous biomass. ANOV As include a block and treatment effect. Error degrees of freedom were reduced by two to account for two missing observations (Sokal and Rohlf 1969: Plain region of central South Carolina (Peet 338): the annual plot that was too wet to burn and a triennial plot excluded due to salvage damage (see and Allard 1993; Porcher 1995; P. Mc text). (B) CCA ordination scatterplot. Each symbol represents a single species. First axis is constrained Millan, IS. Glitzenstein, D.R. Streng, and to be a function of fire frequency. Moisture effects are reduced in this ordination because elevation, R.K. Peet, unpubl. data). Other groups ap presumed to be a surrogate for hydrology, was explicitly controlled for when collecting the data (see pearing to be exceptionally favored by, or text). CCA ordination is similar to RDA ordination discussed in the text but assumes unimodal rather than linear species responses to treatments. Similar results for the two types of ordinations and input dependent on, frequent fIre included ro data (i.e. biomass and cover) provide confidence that the fire treatment effect is indeed meaningful. sette forbs (group RF), small rosettes
Volume 23 (1), 2003 Natural Areas Journal 29 (group SR; e.g., Lachnocaulon anceps, Rhynchospora chapmanii), insectivorous TIGER CORNER EXPERIMENT forbs (group IF, including Sarracenia spp., Drosera spp., Pinguicula lutea), and Or COVER DATA chidaceae (group OR). 25 All herbaceous groups were not associat CJ) 20 0::: ed with frequent burning, however. One ill > PERENNIAL FORB curious example was the parasitic forb 0 15 () Cuscuta compacta (PV = parasitic vine in u.. 10 the RDA ordination scatterplot). This ge 0 nus lacks roots as mature plants and de 2 rives nutrition through haustorial connec ::J 5 CJ) tions with host plants. According to 0 Godfrey and Wooten (1981), c. compacta has been shown to parasitize a fairly large 0 1 2 3 4 5 number of host plants, many of which are 20 common hardwood trees and shrubs of PERENNIAL GRASS flatwoods and swamp ecotones (e.g., Mag CJ) 16 nolia virginiana, Cyrilla racemiflora, 0::: Clethra alnifolia, Rubus spp., Myrica spp.). ill > 12 We have observed it to be particularly 0 abundant on sprouts 1-2 y after fire. Ap () u.. 8 parently it was favored in the quadrennial 0 bum plots by the greater density and vigor 2 4 of hardwood sprouting. ::J CJ) 0 Another herb associated with lower fire frequencies was the shade-tolerant grass 0 1 2 3 4 5 40 Chasmanthium laxum (TG). This grass is found in a wide range of habitats from CJ) WOODY pine savannas and flatwoods through var 0::: 30 w ious types of closed woodlands and even > hardwood bottomlands (Godfrey and 0 () 20 Wooten 1979, Weakley 1999). Compared LL to most other Poaceae it appeared to toler 0 ate and perhaps even prefer longer fire 2 10 ::J return intervals. On the drier end of the CJ) moisture gradient, the same could perhaps 0 be said for (SF) Baptisia tinctoria. Based on its position in ordination space, this 0 1 234 5 robust forb appeared to be more tolerant FIRE RETURN INTERVAL (YRS) of less frequent fire than most other le gumes. Ferns (group FE, including Pte rid Figure 3. Effects fire frequency on individual and cumulative species cover scores in the Tiger Corner study plots. All species occurring in at least ten plots were included. Cover scores and associated cover ium aquilinum, Osmunda spp., and Wood ranges are as follows: 1 = trace, 2 = 0-1 %,3 = 1-2%,4 = 2-5%, 5 = 5-10%, 6 = 10-25%,7 = 25-50%, wardia spp.), another shade-tolerant 8 = 50-75%, 9 = 75-95%, 10 = 95-100%. Note that the sum of cover scores for a particular plant herbaceous group (Grime et al. 1988), also category is not equivalent to plot cover for that category (e.g., sum of cover scores for woody plants is appeared to tolerate a somewhat reduced not equivalent to woody plant cover). Nevertheless, the sum of scores does represent an alternative frequency of fire. unbiased indicator of the importance of a particular group in a plot. Species abbreviations: Woody: SA = Sorbus arbutifolia (L.) Heynh., RA = Rubus m"gutus, RC= Rhus copallillum, MC = Myrica cerifera, MH = Myrica heterophylla, MV = Magllolia virgillialla, IG = Ilex glabra, HC = Hypericum crux-andreae, GF Last, and perhaps most unexpectedly, the = Gaylussacia frolldosa, CA = Clethra alllifolia, AR = AceI' rubrum; Grasses: SS = Schizachyrium groups WG (weedy perennial grasses) and scoparium, SG = Saccharum giganteum, CA = Ctelliulll aromaticulll, DS = Dichallthelium strigosulll, DT WF (weedy forbs) were also associated, at = Dichalithelilllll dichotomum tellue, A/Ulropogon virgillicus decipiens; var. AV = var. Forbs: PG = least to a greater extent than most other Pityopsis graminifolia, HA = Helianthus allgustifolills, EP = Eupatorium pilOSIllIl, EL = Eupatorium leucolepis, CP = CmphepllOrus palliculatlls, CL = Coreopsis lillifolia, EN = Bigelowia lIudata, AD = Aster herb groups, with the low end of the fire dumosus, RA = Rhexia alifallus. P-values from ANOVA tests are listed next to the species codes. frequency axis. We hypothesize that these
30 Natural Areas Journal Volume 23 (1),2003 ruderal species may benefit from tempo cies composition between quadrennial and munity may be able to tolerate longer in rary windows of reduced competition in more frequently burned plots (Figure lA). tervals between fires without loss of spe the less frequently burned plots. Such This may reflect the fact that most of the cies. Plant community differences related "wiildows" may open briefly when shrubs larger shrubs (e.g., Lyonia lucida, Ilex gla to frre history did appear to be more dis are temporarily damaged following higher bra, Clethra alnifolia, Myrica cerifera) tinct in the wetter Tiger Corner plots. An intensity fires resulting from excessive fuel were more prevalent toward the wetter end nually and biennially burned plots on the accumulations and less weedy herbs have of the moisture gradient. With even minor "wet" end of the soil moisture gradient been reduced or eliminated during several reductions in burn frequency-for exam encompass some of the finest wet savan fire-free years. ple, from biennial to quadrennial burn nas in the FMNF while the less frequently ing-these wet flatwoods shrubs increase burned triennial and quadrennial plots on A final interesting pattern in the Tiger greatly in cover (Figure 3) and biomass similarly moist soils are shrub-dominated Corner ordination data concerned a possi (Figure 2), in the process competitively flatwoods. ble interaction between soil moisture and excluding grasses and forbs. Toward the fire frequency. Moving from wet to dry drkr end of the moisture gradient, where Osceola Experiment across the moisture axis, there was some large shrubs are less important due to suggestion of increasing similarity in spe- edaphic restrictions, the ground-layer com~ The dominant mode of variation in the
OSCEOLA EXPERIMENT
COVER DATA
A LO 2- LO FIRE 'A FIRE O.S- ANNUAL C BIENNIAL 45 • 2F • QUADRENNIAL SP 1- 40 + + 2C 4F 4B 4C 2E 2B 0.4 - • TS ..-- 0- ..-- en 20 en ! LS WG WJ ~ ~ 0- SS CT C§ lA 10 C§ 0:: -1- 2A BG AF PF 0:: SB RF LF GM BSFA lB lCe CG HV SR lE -0.4 - WF -2- RG IF
HI -3 HI FIRE I I I I FIRE -O.S I I I I I -2 -1 0 1 2 -0.4 -0.2 0 0.2 0.4 0.6 MOIST RDAAXIS2 SUBXERIC MOIST RDAAXIS2 SUBXERIC I LO O.S- B FIRE - W W Vi G F 0.4 - fW W F G W Figure 4. RDA results from the Osceola study site. (A) Plot W
Volume 23 (1),2003 Natural Areas Journal 31 Osceola cover data (RDA axis 2, 1st un constrained axis, 30.9% explained vari OSCEOLA EXPERIMENT ance, x -axis in Figure 4) was again related to soil moisture rather than fire frequency. 10 Again, groups FA (Fabaceae), HV (herba CI) PERENNIAL FORB 0:::: 8 ceous vine), and PF (prostrate forb) were ill good indicators for the dry end of the > 0 6 moisture gradient (right side of Figure 4), U while SR (small rosettte) and GM (non u.. 4 Poaceae graminoid monocot) helped to 0 identify the wetter end. Group LS (large ~ ::J 2 shrub), including moist flatwoods domi CI) nants flex glabra and Lyonia fruticosa, as 0 well as shrub bog species !lex coriacea and !lex myrtifolia, also occurred close to 0 1 2 3 4 5 the wet end of the Osceola moisture gradi ent. In addition to the group means, the 30 identities of individual species found at CI) the opposite ends of the gradient suggest PERENNIAL GRASS 0:::w ed moisture differences as the explana > 20 tion. The six species with the lowest RDA 0 second axis scores included moist/mesic 0 LL flatwoods indicators !lex glabra, Rhyncho 0 10 spora plumosa, Aristida spiciformis, and ~ Andropogon glaucopsis Elliott (Godfrey ::J CI) and Wooten 1979, 1981; FNAI-FDNR 0 1990; Peet and Allard 1993; Streng et al. 1993). At the other extreme, the six spe 0 1 2 3 4 5 cies with the highest scores on this axis included dry flatwoods/sandhill species 40 WOODY Quercus minima, Cnidoscolus stimulosus, CI) Elephantopus elatus, Aster walteri, Seric 0:::w 30 ocarpus tortifolius (Michx.) Nees, and > Tephrosia hispidula (FNAI-FDNR 1990, 0 U 20 Peet and Allard 1993, Streng et al. 1993). LL 0 The RDA ordination identified frequency ~ 10 ::J of burn as the second most important in CI) fluence on vegetation composition in the 0 Osceola study plots. Axis 1 (y-axis in Fig ure 4), constrained to be a function of fire 0 1 2 3 4 5 frequency, accounted for 21.8% of the FIRE RETURN INTERVAL (YEARS) species variance and was statistically sig nificant (Monte-Carlo F = 3.07, P = 0.02). As at Tiger Corner, quadrennial-burn and Figure 5. Effects of frequency of fire on individual and cumulative species cover scores in the Osceola annual-burn plots were at opposite ends of study plots. All species occurring in at least 16 plots were included. Cover scores and associated cover the fire frequency axis. Biennial-burn plots ranges are as follows: 1 = trace, 2 = 0-1 %, 3 = 1-2%,4 = 2-5%, 5 = 5-10%, 6 = 10-25%,7 = 25-50%, again occupied an intermediate position, 8 = 50-75%, 9 = 75-95%,10 = 95-100%. See note in the legend for Figure 3 concerning interpretation of sum of cover score measurements. Species abbreviations: Woody: AA Asimilla allgustifolia, GD but here, unlike the Tiger Corner ordina = = Gaylussacia dumosa, GT =Gaylussacia tomelltosa (Gray) Pursh ex Small, IG = Ilex glabra, LF = Lyollia tion, they were more closely associated fruticosa, SR = Serelloa repellS, VM = Vaccillium myrsillites, QM = Quercus millima; Grasses: AG = with, and tended to overlap, the quadren Alldropogoll glaucopsis Elliott, AV = Alldropogoll virgillicus var. decipiells, AB = Aristida beyrichialla nial-burn plots (Figure 4A). Trinius & Ruprecht, AS = Aristida spicijormis, DC = Dichallthelium chamaelollche (=Palliculll chamaelollche Trin.), DL = Dichalltheliulll portoricellse (Desv. ex Ham.) B. F. Hansen & Wunderlin, PA = PalliculIl allceps var. rhizolllatulIl (A. S. Hitchc. & Chase) Fern., SS =Schizachyrium stolollije/'lllll, SC Distributions of species groups across the = Sporobolus curtissii; Forbs: EM = Eupatoriulll lIlohrii, PG = Pityopsis gralllillijolia, PP = Pterocauloll Osceola fire frequency axis were perhaps Pycllostachyulll (Michx.) Ell., XC =Xyris carolillialla. P-values from ANOV A tests are listed next to the deceptively similar to Tiger Corner. Woody species codes.
32 Natural Areas Journal Volume 23 (1),2003 plants and herbs were again clustered in that sexual reproduction and hence popu sistent with its occunence in frequently opposite halves of the ordination graph, lation growth of this important grass may burned flatwoods or mesic savannas woody plants associated with less frequent have been limited by the lack of growing (Weakley 1999). fire, herbs the reverse (Figure 4B). How season fIres (see Streng et al. 1993). ever, an examination of absolute cover Asclepias pedicellata (stalked milkweed), values revealed an important difference As expected from mean cover scores (Fig another globally rare plant (Nature Con between the two sites. At Tiger Corner, ure 5), Serenoa repens (group SP) was servancy G-Rank = 3) occuned in all an changes in fIre freq\J.ency were associated closely associated with the low fIre end of nual and quadrennial NCVS sample plots with absolute changes in cover and biom the Osceola burn frequency axis. Other at the Osceola study site. However, the ass of both woody and herbaceous spe woody plant groups were also associated species was present in only three of six cies. At Osceola, in contrast, total woody with this end of the fIre gradient, though to biennial burn plots. Given the sparse dis cover and mean cover values for dominant a lesser extent than Serenoa. Small shrubs tribution of this plant (overall mean cover woody species were relatively unaffected (group SS, e.g., Quercus minima, Q. pumi < 1%), lower occurrence rates in the bien by frequency of fIre (Figure 5). The one la, Vaccinium myrsinites, V. stamineum, nial-burn treatment plots are probably of exception was Serenoa repens, which had Hypericum microsepalum, Gaylussacia little consequence. However, its occunence significantly lower cover scores in the spp.) once again appeared to be more tol in all of the quadrennial plots suggests that annually burned plots. Overall, however, erant of closely spaced fires than did other it may be more tolerant of longer interval differences in relative abundance of woody groups of woody plants, but the difference fires than many forb species (Appendix B and herbaceous species suggested by the between LS and SS was narrower than at
Volume 23 (1),2003 Natural Areas Journal 33 We tentatively conclude, therefore, that TIGER CORNER EXPERIMENT decreases in longleaf ground-layer species A 160 richness with less frequent burning are more evident at smaller spatial scales. A critical issue is therefore whether this buff SCALE P-VALUE ering capacity, as we might refer to it, at a large scale is likely to be a stable feature of 120 1000.0. Cf) these habitats or represents instead an W ephemeral condition. We suspect that it is U W ephemeral and is due to patchiness in the a.. .11 Cf) rate at which large woody species become LL 80 established and displace other ground-layer 0 plants. Thus, we hypothesize that reduc a:::: w tions in species richness related to reduc III tions in fire frequency appear fIrst at small ~ :::> .07 scales and are then translated to increas Z 40 10.0 ingly larger scales, leading ultimately to community scale and even landscape scale .02 1.0 declines in biodiversity. An alternative hypothesis is that patches of habitat suit .10 -. • able for herbs and small shrubs may be .01 • ... 0 consistently generated at longer fIre return 0 1 2 3 4 5 intervals, though these patches may make up a smaller proportion of the total area FIRE RETURN INTERVAL (YRS) then would be the case with more frequent burning. Repeated sampling over time in the same plots will be necessary to dis criminate between these two hypotheses. OSCEOLA EXPERIMENT B 60 DISCUSSION AND CONCLUSIONS SCALE P-VALUE Our results overall strongly supported the • MFFH and will perhaps serve to further 1000.0 emphasize to ecologically oriented land Cf) managers the need for short interval burns W in southern pinelands. This conclusion is U 40 • W 0.29 consistent with the fIndings of the Santee a.. • Cf) Study (Waldrop et al. 1992) which, to LL 100.0 gether with our own results, would appear 0 • to constitute the best available information a:::: w on this topic. Annual and biennial burns III also produced the fInest quality, most spe ~ 20 cies-rich wet savanna communities in the :::> 10.0 Z • renowned Green Swamp area of North Carolina (Walker and Peet 1983) and in 1.0 0.03 numerous sites sampled by Taggart (1990). Our ONF results suggest that long-term 0.1 - • 0.01 annual burning, particularly during resto 0.01 0.00 ration, may be necessary in systems dom 0 inated by highly fire-tolerant shrubs such 0 1 2 3 4 5 as Serenoa repens. FIRE RETURN INTERVAL (YRS) Before concluding, however, we would like to advance a few caveats and sugges Figure 6. Species richness curves for the (A) Tiger Corner and (B) Osceola studies. P-values of single degree of freedom linear contrasts are shown to the right of each fitted line. Each point represents an tions for future research. Perhaps the most average of all data collected at the scale in square meters indicated to the left of the line. important caveat is that before prescribing
34 Natural Areas Journal Volume 23 (1),2003 any particular fIre regime, managers need ductions in fIre frequency the scrub oaks (Wade et al. 1993). Brewer (2002) exper to consider the conservation priorities at get larger but, being more widely spaced, imentally demonstrated increased rates of their own site. For example, if one is man they may not be as effective as flatwoods Ilex glabra seedling appearance in small aging a rare shrub (e.g., Elli()ttia racim1O shrubs in competitivelyexduding herbs. artifIcially generated soil disturbances, and sa, Stachydeoma graveolens, Fothergilla Based on our own fIeld experience, and the same phenomenon presumably occurs garden ii, Lindera melissifolia), quadren results from the dry end Tiger Corner and in natural disturbances. Thus hUlTicanes nial burning in late winter may be a per Osceola plots, we tend to agree with Beck and reductions in fIre frequency may in fectly appropriate management strategy. age and Stout (2000) that sandhills may be teract to promote establishment and growth The same may apply to rare shrub-domi less sensitive to variations in fIre return of shrubs in wet savanna habitats. Increas nated communities. For example, two lo intervals than are flatwoods. ing competition from shrubs might then cally abundant but globally rare FMNF lead to substantial reductions in abundance flatwoods communities (Pinus palustris In addition to drier longleaf pine sites, and diversity of wet savanna herbs, such Clethra alnifolia-Gaylussacia frondosa some studies have suggested that wet sa as we observed at Tiger Corner. Quercus pumila-Schizachyrium scopari vanna sites and the species therein may um Woodland Association and Pinus also be less sensitive than flatwoods to One conclusion from the above discussion palustris-P. serotina-Ilex glabra-Lyonia longer fire return intervals (Streng and is that cross-habitat comparisons of fIre lucida Woodland Association) in the Tiger Harcombe 1982, Brewer 1999). The data frequency treatments would appear to be a Corner plots may be threatened over the from this study, however, do not support profitable area for future research (see also long term by long-term annual and bienni this hypothesis. Most groups of wet savan Liu et al. 1997). Even within flatwoods al fIres. If maintaining these shrub-domi na indicator species, such as small rosette communities, comparisons across geogra nated associations is considered to be an forbs and sedges, Orchidaceae, and insec phy and soil formations may be of interest. important management priority, it might tivorous plants, were amongst the most Comparisons of Tiger Corner and Osceola be helpful to set aside certain sections of sensitive to reductions in fIre frequency. data, along with results of other studies, FMNF for slightly longer interval burns. Brewer (1999) criticized previous studies strongly suggest that Spodosol Flatwoods as not providing truly conclusive evidence and Ultisol Flatwoods respond differently A second important caveat is that we need of the need for annual or biennial fIres for to the same fIre frequency treatments. Fire to recognize that most fIre frequency ex maintenance of Sarracenia popUlations. frequencies (i.e.,' annual, biennial burns) periments in longleaf pine communities, Our results, involving long-term random that produced herbaceous dominated com including our own, have been carried out ly applied burn treatments and observa munities in Ultisol flatwoods (Santee in flatwoods. Flatwoods, by defInition, are tions standardized for time-since-burn ef Study, Tiger Corner Study, Brockway communities with a strong shrub compo fects, appear to avoid most of Brewer's Lewis Study) had little effect on shrub nent or, at least, environmental conditions (1999) criticisms. Perhaps our disagree cover in Spodosol flatwoods (Osceola conducive to shrub invasion (Abrahamson ment can be resolved when we consider Study). Biennial burning, regardless of and Hartnett 1990). Reducing fIre frequen that Brewer's (1998, 2002) own studies burn season, has also not reduced biomass cy, even slightly, stimulates sprouting and indicate that dominant flatwoods shrubs of dominant flatwoods shrubs in the long vegetative proliferation of shrubs, reduc such as Ilex glabra can invade pine savan term St. Marks season-of-burn study (J.S. ing space available for herbaceous plants na habitats under certain circumstances. Glitzenstein, D.R. Streng, unpubl. data). and decreasing species richness (Waldrop Furthermore, Brewer (2002) acknowledged Flatwoods plots in the St. Marks Study are , et al. 1992, Brockway and Lewis 1997). It that reduced fIre frequency is one of sev also located on Spodosols. It would ap is therefore .not surprising that data col eral factors that may facilitate invasion of pear that, on the whole, shrubs on Spodo lected in flatwoods are consistent with the flatwoods shrubs into bogs and wet savan sols are more tolerant of closely spaced MFFH. nas. It therefore seems reasonable to hy fIres (see also Taggart 1990). This hypoth pothesize that lower fIre frequencies main esis is consistent with other observations In contrast to the various studies of flat tained over several decades, as in our study, that woody plants on coarser textured soils woods, Beckage and Stout (2000) is the might gradually lead to conversion of wet are generally more resistant to stress. For only fire frequency study that we know of grass-dominated savannas into wet shrub example, as climate becomes limiting in that focused on drier longleaf pine habi dominated flatwoods. This is a likely sce Oklahoma and central Texas, eastern trees tats. Despite the limitations of that study,· nario in oUl~ Tiger. Corner study plots. since and shrubs become restricted. almost. en". straightforwardly acknowledged by the most of the wet savanna patches occur tirely to sandy soils (Costello 1969). authors themselves, the results are inter along ecotones or in small inclusions within esting. In contrast to flatwoods, sandhill the flatwoods. HUl:ricanes such as Hugo Given that we accept the MFFH, a related longleaf pine forests typically lack an un might accelerate the conversion of savan issue concerns fIre season. Prior to the derstory of dense shrubs, although an un nas to flatwoods by increasing the area arrival of humans in North America it is derstory-midcanopy layer of "scrub" oaks and rate of natural soil disturbances in probable that most fIres in southeastern (e.g., Quercus laevis, Q. incana) is present cluding tip up mounds and high intensity longleaf pine woodlands, ignited by light either as sprouts or small trees. With re- fIres associated with fuel accumulations ning associated with thunderstorms, oc-
Volume 23 (1),2003 Natural Areas Journal 35 curred during the growing season (May manuscript. Lastly, we are indebted to Caldwell. 1992. Soil chemistry in a loblol September; Komarek 1968). Thus, the Steve Brewer, Bill Platt, Brian Beckage ly/longleaf pine forest with interval burn growing season is the "natural" fIre season and other conference participants for a ing. Ecological Applications 2:157-164. to which, presumably, most native plants series of particularly stimulating e-mail Brewer, lS. 1998. Patterns of plant species have adapted. It is also true that humans exchanges. Financial assistance was pro richness in a wet slash-pine (Pinus elliottii) savanna. Journal of the Torrey Botanical have been burning during the fall and win vided by the US Forest Service, Southern Society 125:216-224. ter for hundreds, if not thousands of years, Research Station, Grant # 29-634. Brewer, I.S. 1999. Short-term effects of fire and that these human-started fires covered and competition on growth and plasticity of large areas of the landscape (Lawson 1709, Jeff Glitzenstein is a Research Associate at the yellow pitcher plant, Sarracenia alata Elliott 1816-1824). Plants not also adapt Tall Timbers Research Station. His inter (Sarraceniaceae). American Journal of Bot ed to this anthropogenic fIre season would ests include effects of environmental gra any 86:1264-127l. long since have been selected out of exist dients and natural and managed distur Brewer, J.S. 2002. Disturbances increase seed ence. It is not within the scope of this bance regimes on plant communities and ling emergence of an invasive native shrub paper to take sides in the issue of growing in pitcher plant bogs. Natural Areas Journal populations. Recent research he has con versus dormant-season fIre (see Streng et 22:4-10. ducted with his Wife, Donna Streng, in al. 1993). We merely note, as has been Bridges, E.L., and S.L. Orzell. 1989. Longleaf volves experiments with prescribed burn noted previously by others (Waldrop et al. pine communities of the West Gulf Coastal ing, rare plant population establishment, 1992, Brockway and Lewis 1997), that Plain. Natural Areas Journal 9:246-263. and other restoration techniques in longleaf frequent dormant-season fIres can be used Brockway, D.G., and C.E.Lewis. 1997. Long pine savannas. to maintain species-rich and apparently term effects of dormant-season prescribed fire on plant community diversity, structure high quality longleaf pine ground-layer in Donna Streng, a Research Associate at and productivity in a longleaf pine-wire a variety of habitat types. Of this there is Tall Timbers Research Station, is particu grass ecosystem. Forest Ecology and Man no doubt. It may be desirable to switch larly interested in the conservation ofplant agement 96:167-183. from dormant-season burning to growing biodiversity in fire-maintained communi Brown, RB., E.L. Stone, and V.W. Carlisle. season burning while maintaining an equal ties of the southeastern United States. Her 1990. Soils. Pp. 35-69 in RL. Myers and ly high fIre frequency (e.g., growing-sea other interests include rare and common J.l Ewel, eds., Ecosystems of Florida. Uni son burns may have more effectively versity of Central Florida Press, Orlando. plant demography as well as floristics of promoted establishment of wiregrass and 765 pp. southeastern Coastal Plain plant commu Collins, S.L., S.M. Glenn, and D.J. Gibson. other dominant bunchgrasses in our Os nities. ceola plots). However, managers should 1995. Experimental analysis of intermedi be aware that reducing fIre frequency or ate disturbance and initial floristic compo Dale Wade is a Research Forester with the sition: decoupling cause and effect. Ecolo area burned in order to burn at a more USDA Forest Service, Southern Research gy 76:486-492. "natural" season is likely to be a risky Station. His interests include fire behavior Connell, lH. 1978. Diversity in tropical rain strategy. and vegetation dynamics in southern pine forests and coral reefs. Science 199: 1302- stands, with particular emphasis on link 1310. ACKNOWLEDGMENTS ages between these two sets of variables. Costello, D.F. 1969. The Prairie World. Crow He maintains long-term studies of pre ell Co., New York. 242 pp. The long-term studies described herein scribed burning in several southeastern Elliott, S. 1816-1824. A Sketch of the Botany would have been impossible without the ecosystems. of South Carolina and Georgia. Vols. 1 and sustained help and cooperation of the Fran 2. Reprint 1971, Hafner Publishing, New cis Marion National Forest and the Osceo York. 606 pp. and 743 pp. la National Forest. We are deeply grateful LITERATURE CITED Engle, D. M., M. W. Palmer, l S. Crockett, R. to numerous individuals in both national Abrahamson, W.G. 1984. Species responses to L. Mitchell, and R Stevens. 2000. Influ forests. Ted Ash, David Combs, and An fire on the Florida Lake Wales Ridge. ence of late season fIre on early succession drew Hulin deserve special recognition for American Journal of Botany 71:35-42. al vegetation of an Oklahoma prairie. Jour nal of Vegetation Science 11:135-144. long-term help with data collection and Abrahamson, W.G., and D.C. Hartnett. 1990. plot maintenance. Jimmy Rickards, Susan Flatwoods and dry prairies. 1990. Pp. 103- FNAI-FDNR (Florida Natural Areas Inventory Carr, and members of South Carolina Na 149 in RL. Myers and IJ. Ewel, eds., Ec and Florida Department of Natural Resourc tive Plant Society, especially John Brubak osystems of Florida. University of Central es). 1990. Guide to the Natural Communi Florida Press, Orlando. ties of Florida. Available online
36 Natural Areas Journal Volume 23 (1),2003 States: Monocotyledons. University of Mehlman, D.W. 1992. Effects of fire on plant Taggart, lB. 1990. Inventory, classification, Georgia Press, Athens. 712 pp. community composition of North Florida and preservation of Coastal Plain savannas Godfrey, RK., andJ.W. Wooten. 1981. Aquatic second growth pineland. Bulletin of the in the Carolinas. Ph.D. diss., University of and Wetland- Plants of Southeastern United Torrey Botanical Club 119:376-383. North Carolina, Chapel Hill. 229pp. States: Dicotyledons. University of Geor NatureServe Explorer: an online encyclopedia Ter Braak, C,J.F. 1987-1992. CANOCO: a gia Press, Athens. 933 pp. of life [web application]. 2001. Version 1.6. fortran program for canonical community Grime, J.P, J.G. Hodgson and R Hunt. 1988. NatureServe, Arlington, Va., USA
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