Effects of Fire Regime and Habitat on Tree Dynamics in North Florida Longleaf Pine Savannas

Abstract

Frequent, low intensity fire was an important component of the natural disturbance regime of presettlement savannas and woodlands in the southeastern USA dominated by longleaf pine (Pinus palustris), and prescribed burning is now a critical part of the management of these endangered habitats. Fire season, fire frequency, and fire intensity are three potentially important, though still little understood, components of both natural and managed fire regimes. In this long—term (8—yr) study, we experimentally (through the use of prescribed burning) tested for effects of fire season (eight different times throughout the year) and fire frequency (annual vs. biennial burning), on population dynamics (recruitment, growth, mortality, change in density, and change in basal area [the total basal area of all stems in a plot]) and species composition of trees in two quite different types of longleaf—pine—dominated habitats (north Florida sandhills and flatwoods). Limited fire temperature and intensity data were also collected during one year to examine the relationship between fire behavior (temperature and intensity) and tree mortality. Contrary to prior hypotheses, our results showed few systematic or predictable effects of season or frequency of burning on dynamics of longleaf pine. Instead, variability in the population dynamics of this species appeared to be related largely to variation in fire behavior, regardless of the season of burning. Consistent with prior hypotheses, we found that deciduous oak species (Quercus laevis, Q. margaretta, and Q. incana) were least vulnerable to dormant—season burning and most vulnerable to burning early in the growing season. This was shown particularly by seasonal trends in the effect of burning on oak mortality (both topkill and complete kill) and, to a lesser extent, on oak recruitment. Oak densities and basal areas also declined in the spring—burned plots, resulting in a shift away from oaks and towards increased dominance by longleaf pine. Detrimental effects of spring burning on oaks were partly explained by fire behavior, but there appeared also to be an important residual effect of burning season, particularly on complete kill. Though longleaf pine population dynamics did not differ markedly as a result of burning season and frequency, we did find important differences in pine dynamics between the two habitats (i.e., sandhills and flatwoods). In general, populations of longleaf pines in the sandhills appeared to be density regulated, while flatwoods pine populations were declining regardless of the level of intraspecific competition. This suggests that long—term persistence of longleaf pine, and perhaps other fire—adapted species in frequently burned longleaf—pine—dominated communities, may be determined by complex interactions between habitat factors and fire regimes.

Effects of Prescribed Burning on Game Species in the Southeastern United States. A Literature Review

“…In contrast, Glitzenstein, Streng, and Platt (1990) reported that longleaf pine mortahty, growth, and recruitment each did not differ significantly between plots burned in the growing season (April-August) and plots bmned in the dor-ERDC/CERLTR-03-13 15 mant season (October-February). Glitzenstein, Platt, and Streng (1995) gave supporting evidence that season of bum does not influence longleaf pine populations. Brockway and Lewis (1997) reported the lengthiest study of the effects of fire on longleaf pine.…”

“…Brose and Van Lear (1998) foimd that the density of oaks was positively influenced by both spring and winter bums, but growth rates were greater following winter bums. Glitzenstein, Streng, and Platt (1990) and GUtzenstein, Platt, and Streng (1995) foimd, however, that oak mortality was significantly greater after spring hvams (April, May) than bxmis in any other season. Oak recruitment was not affected by the season or frequency of burning, but growth was affected (GUtzenstein, Streng, and Platt 1990).…”

“…Fires in spring and early siunmer tend to bum completely, which kiUs hardwood stems and significantly diminishes woody cover (Ferguson 1957;Ferguson 1961;Brender and Copper 1968;Boyer 1990;GHtzenstein, Platt, and Streng 1995). Ambient factors in spring and summer often create pyre that is drier and will bum more intensely (Chen and (Jerber 1990), causing the greater mortaUty (GHtzenstein, Platt, and Streng 1995). Burning during winter, the dormant season, reduces cover until new growth occurs in spring (Robbins and Myers 1992), and may expose birds to increased predation (MueUer, Atkinson, and DeVos 1989).…”

Dendrochronological Field Methods for Fire History in Pine Ecosystems of the Southeastern Coastal Plain

“…An increase in woody species (shrubs and trees) also occurs in when fires are less frequent (Glitzenstein et al 2003). Dormant season fires also favor the increase of woody species (Glitzenstein et al 1995, Drewa et al 2002, Drewa et al 2006. The recent history of less frequent and more dormant season fires likely has resulted in increased woody cover in upland habitats such as dry prairie, pine flatwoods and sandhill.…”

“…Our fire history focused on two important aspects of past fire regimes: fire frequency and intra-annual (or seasonal) timing of fire. Frequency is a very important aspect of fire regimes and differences in fire intervals over time may result in important differences in the structure and composition of biotic communities (Glitzenstein et al 1995(Glitzenstein et al , 2003. Likewise, the intra-annual timing of fire has important influences and many…”