Fire Effects in Florida Scrub

In Florida scrub, most areas affected by fire are burned with an intense fire that moves through the shrub canopy, not merely along the ground. The shrubs are top-killed, although most readily resprout. As a result, the most obvious effect of fire is reducing shrub heights (Schmalzer 2003). This reduction in shrub height is considered key for habitat of the Florida scrub jay (Woolfenden and Fitzpatrick 1996, Breininger et al. 1995). Low intensity patches may fail to kill small shrubs, creating spatial heterogeneity that may be key to some species that lack seed banks and are killed by fire. Patches of tall oaks are also potential nest sites for the Florida scrub jay (Woolfenden and Fitzpatrick 1996).

Fires increase the size of gaps as shrub canopies are temporarily reduced (Schmalzer 2003). Intense patches may also completely kill small areas of oaks and palmettos, creating new gaps (Menges, personal observation). Individual species have a range of life history strategies with respect to fire (e.g. Menges and Kohfeldt 1995, Menges and Hawkes 1998, Ostertag and Menges 1994, Weekley and Menges 2003), and these are part of the effects of fire. For example, fires kill Florida rosemary so that rosemary-dominated areas may be very open for years postfire. The spatial and age structure of rosemary stands reflects its disturbance history (Gibson and Menges 1994).

Fire may kill some animals, although most are able to flee or take cover. Gopher tortoise holes are thought to provide temporary shelter for many species. Fire behavior and lighting patterns probably affect animal survival, with unburned patches promoting survival and ring fires causing higher mortality. As with plants, various animal species are benefited by the postfire environment to various degrees. Gopher tortoises benefit postfire from the increased herbaceous growth. Florida scrub jays recolonize large burned areas once acorns are produced (about 1-4 years; Abrahamson and Layne 2002a) and continue to utilize patchily burned areas immediately after fire. Effects of Florida scrub fires on soil and water have not been studied. Fire destroys the alga-dominated biological soil crust, but its recovery is fairly rapid (Hawkes 2004).

Short- and Long-term Post-fire Recovery Patterns

Florida scrub recovers from fire within a few years, depending on what feature of recovery is considered. Shrub regrowth is rapid; as palmettos increase leaf production rates and actually carry more leaves in recently burned stands than in long-unburned stands (Abrahamson 1995). Cover, diversity, and general species composition return to preburn levels within 1-5 years (Abrahamson 1984a, Abrahamson and Abrahamson 1996, Greenberg 2003, Schmalzer 2003) but height increases are gradual and may take many years (Schmalzer 2003, Greenberg 2003) However, long-unburned scrub that is finally burned may not show the characteristic increase in herbs (e.g., Weekley and Menges 2003) that are seen in periodically burned stands (Abrahamson and Abrahamson 1996). Soil crusts recover various functions in months or a few years (Hawkes 2004). Florida scrub jays return to burned scrub once acorns are produced on oaks, varying from 1-4 years depending on the oak species (Abrahamson and Layne 2002a). Ground lichen recovery is slower. These organisms are not visible for about 4 years or so, and continue to increase their cover with time-since-fire (Johnson and Abrahamson 1990, Menges and Kohfeldt 1995, Yahr 2000).

Longer–term changes in vegetation structure and composition are slow and variable in direction in space and time (Givens et al. 1984, Menges et al. 1993). This is probably due to the high survival and competitive ability of the clonal shrubs that dominate long-unburned scrub. For example, palmettos have high survival even in droughts (Abrahamson and Abrahamson 2002). Oak genets probably have extremely high survival. However, ramet turnover varies among oak species. Those with more rapid ramet turnover (e.g., Q. inopina; Johnson and Abrahamson 2002) are likely to decline in long-unburned scrub as taller oaks overtop them (Menges et al. 1993).

Florida scrub influences the fire dynamics of associated ecosystems by acting as a fire barrier during the first decade or so postfire, when flatwoods, sandhills, and seasonal marshes that have more continuous fuels are likely to burn. Conversely, seasonal marshes and other grassy areas (e.g., cutthroat dominated areas; Yahr et al. 2000) probably increase the fire frequencies of associated scrub patches. Scrub patches isolated by permanent water are likely to have had a lower fire return interval than those embedded in flammable vegetation.