A history of lightning- and human-caused fire in South Florida has resulted in fire-dependent ecosystems over most of the area. Much of the remaining natural area is public land subject to wildland fire, with the National Park Service (NPS) managing over 4,000 km² of Federal land in Everglades National Park and Big Cypress National Preserve. Other U.S. Department of the Interior units with fire-maintained vegetation include the National Key Deer Refuge, Florida Panther National Wildlife Refuge, and Loxahatchee National Wildlife Refuge. Fire management, both wildfire suppression and prescribed fire, is a major natural-resource management activity throughout the area. The oldest prescribed fire program in the NPS began in Everglades National Park in 1958 and, today, the majority of prescribed fire conducted by the NPS is in South Florida. Big Cypress National Preserve has developed the largest management-ignited prescribed fire program in the NPS, often burning more than 15,000 ha (35,000 acres) in a year.

Fire plays an important role in controlling the distribution and composition of plant communities in South Florida. Some 65 vascular plant taxa are endemic to southern Florida; more than half are herbs and low shrubs restricted to pine forests. These species are quickly shaded out in the absence of fire. Lightning is assumed to have been an important source of fire ignitions throughout the evolution of the South Florida landscape, although humans have been influencing the fire regime for thousands of years. However, in the last several decades increased human intervention in the form of hydrologic alterations, creation of artificial firebreaks (such as roads and canals), fire suppression, and intentional and accidental ignitions has severely disrupted the natural fire regime. In fact, next to hydrological modifications, alteration of the fire regime is one of the most pervasive impacts of humans on the South Florida ecosystem.

The main objective of this study is to establish the baseline conditions and begin the experimental treatments for a long-term study of season and frequency of burning in South Florida pinelands. The long-term study will document the ecological effects of a wide range of potential fire-management strategies (Snyder 1991). The research will provide detailed data on vegetation responses to different burning regimes that will be considered along with wildlife, public safety, and other management concerns in refining prescribed burning programs on Interior lands in South Florida. Specific objectives for the initial phase include: (1) describing the vascular plant communities of all treatment units to document initial conditions, (2) conducting all the initial experimental burning treatments, and (3) documenting the short-term effects (< 1 year) of season of burning and fire intensity on selected vegetation parameters.

The experimental study has been set up in eastern Big Cypress National Preserve, where the only extensive unlogged stands of South Florida slash pine (Pinus elliottii var. densa) remain. The pinelands exist as a mosaic of small, slightly elevated "islands" within a matrix of cypress domes and dwarf cypress prairies. The substrate is a shallow layer of sand over limestone bedrock, making these pinelands transitional between the true rockland pine forests of the Miami Rock Ridge and the widespread pine flatwoods to the north. The study site of 2,573 ha surrounds the Raccoon Point oil field and is divided into 18 experimental burn units each containing at least 50 ha of pine forest. Each burn unit contains three 1.0 ha tree plots in which all trees with diameter at breast height (dbh) >5.0 cm are tagged and mapped. Smaller 0.1 ha vegetation plots are located in the center of each tree plot and at two additional locations to sample herbaceous and shrubby vegetation. There are a total of 54 tree plots and 90 vegetation plots. The tree plots (containing a total of 16,370 trees) show the Raccoon Point pinelands to have average stand densities (trees/ha) of 227 pines, 53 cabbage palms, and 24 cypress.

The experimental design consists of burning at three seasons (spring, summer, winter) and two frequencies (every 3 years and every 6 years) for a total of six treatment combinations. Each treatment is replicated three times, with one replicate being burned per year for 3 years. The project is a cooperative effort of the USGS and the NPS and all the experimental prescribed burns are conducted by the Big Cypress National Preserve Fire Management Division. Beginning in June (spring) 1996, two units have been burned at each season, representing both short and long frequency treatments. By spring 1999 all 18 of the initial experimental prescribed burns will have been completed and the second cycle of burns of the 3-year treatments will begin.

Over the next 3 years, while the short-frequency burn treatment units are being burned for the second time, vegetation plots will be resampled to detect effects of season of burning. In addition, short-term responses to season of burning, such as the survival and establishment of pine seedlings and the flowering and fruiting of selected herbaceous species (for example, pineland clustervine (Spier and Snyder, 1998)) will be documented.

A significant part of the funding for this research was provided from the U.S. Department of the Interior, South Florida Ecosystem Restoration Program "Critical Ecosystems Studies Initiative" (administered through the National Park Service) and from the U.S. Geological Survey, Florida Caribbean Science Center.

REFERENCES

Snyder, J.R., 1991, Fire regimes in subtropical south Florida: Tall Timbers Fire Ecology Conference Proceedings, v. 17, p. 303-319.

Spier, L.P., and Snyder, J.R., 1998, Effects of wet- and dry-season fires on Jacquemontia curtisii, a South Florida pine forest endemic: Natural Areas Journal, v. 18, no. 4, p. 350-357.

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