Effects of differences in prescribed fire regimes on patchiness and intensity of fires in subtropical savannas of Everglades National Park, Florida

We investigated effects of fire frequency, seasonal timing, and plant community on patchiness and intensity of prescribed fires in subtropical savannas in the Long Pine Key region of Everglades National Park, Florida (U.S.A.). We measured patchiness and intensity in different plant communities along elevation gradients in "fire blocks." These blocks were prescribed burned at varying times during the lightning season and at different frequencies between 1995 and 2000. Fire frequency, seasonal timing, and plant community all influenced the patchiness and intensity of prescribed fires. Fires were less patchy and more intense, probably because of drier conditions and pyrogenic fuels, in higher elevation plant communities (e.g., high pine savannas) than in lower elevation communities (e.g., long-hydroperiod prairies). In all plant communities fires became increasingly patchy and less intense as the wet season progressed and moisture accumulated in fuels. Frequent prescribed fire resulted in increased patchiness but a wider range of intensities; higher intensities appeared to result from regrowth of more flammable vegetation. Our study suggests that frequent early lightning season prescribed fires produce a wider range of post-fire conditions than less frequent late lightning season prescribed fires. Our study also suggests that natural early lightning season fires readily carried through pine savannas and short-hydroperiod prairies, but lower elevation long-hydroperiod prairies functioned as firebreaks. Natural fires probably crossed these firebreaks only during drier years, potentially producing large landscape-level fires. Knowledge of how patchily and intensely fires burn across a savanna landscape should be useful for developing landscape-level fire management.