Fire Ecology and Management in the Everglades

The Everglades is a large mosaic of primarily herbaceous freshwater wetlands located in south Florida. The broad, flat expanse called the river of grass, is a mosaic of plant communities situated on shallow, nutrient poor organic soils overlying limestone bedrock. Large expanses of sawgrass marsh, wetter freshwater marshes, tree islands embedded in the river of grass, and drier fresh and brackish water prairies with marl soils characterize vegetation. Rainfall is the main source of water with most rainfall occurring in wet season, May to October. Water naturally traversed wetlands from north to south in shallow slow moving sheetflow with water levels fluctuating with rainfall. Hydrology, particularly water depth, is one of the main determinants of plant community development. Fauna of the Everglades is similar to that in the rest of peninsular Florida except diversity is generally lower. The Everglades is home to a number of rare animal species including wading birds, the snail kite, Cape Sabal Seaside Sparrow, and the Florida Panther. Within the last century, the extent of the historical Everglades has been reduced by nearly half due to human demands and due to human modification of the processes driving ecosystem function (hydrologic, fire and nutrient regimes). The introduction of invasive exotic species has also become a large ecological concern.

Fire is an instrumental shaping force in the ecology of the Everglades. Under the natural fire regime fires were started by lightning during the wet season, with the most acreage burning in the transition from the dry to the wet season. It is thought that Native Americans who inhabited the region also used fire to modify the environment. The frequency with which fires occurred is not well understood, but it is thought that sawgrass marsh and certain types of marl prairie burned frequently. Long hydroperiod marshes likely acted as firebreaks except under drought conditions. Tree islands and tropical hammocks burned the least frequently. Surface fires were common and relatively frequent, while more severe, larger fires involving ground fuels were associated with drought and occurred less frequently, perhaps once a decade. Ground fires change soil elevations and thus are instrumental in causing changes in plant communities.

The natural fire regime of the Everglades has been altered by humans in several ways. Human ignitions of fires tend to be distributed throughout the dry season with the largest acreage burning in the late dry season, somewhat earlier and under drier conditions than the natural fire regime. The acreage burned by humans is not trivial being twice that burned by lightning. Large-scale changes to hydrologic patterns has also affected the natural fire regime, with some areas being wetter than historically thus burning less frequently. Other areas are drier than historically and likely experience more frequent ground fires. The introduction of invasive exotic plants has also affected the natural fire regime.

Under a regime of frequent surface fires, most plant communities of the Everglades regrow and undergo little change. Fire acts in Everglades marshes much like it does elsewhere, pruning back invading woody vegetation. Sawgrass, the dominant species of Everglades vegetation, is well adapted to fires. It is extremely flammable, and is able to recover from fire rapidly. Severe ground fires, however, cause more pronounced changes. Consumption of organic matter by fires leads to changes in soil elevation, soil chemistry, and soil physical properties. Changes in soil elevation drive changes in plant communities by altering the hydrologic regime. Changes in soil elevation coupled with liberation of phosphorus may have caused increases in cattail dominance in some locations.

Animals in the Everglades are well adapted to fires under the natural fire regime. Direct mortality from fires has been noted for some animals. However, fires create foraging opportunities and modify habitats for animals. Post-fire regrowth is attractive to some animals such as deer. Habitat alterations such as creating deeper water habitats may benefit some animals such as aquatic fauna and wading birds that feed on aquatic fauna.

Prescribed fire in the Everglades has been used for fire hazard reduction in sawgrass (i.e., fuel management) to help control dry season fires, to protect resources like hammocks, to clear vistas, to maintain plant communities, to manage habitat for game and endangered animals, and as a tool to control exotic plants. Prescribed fires have historically been set throughout the year with the largest acreage burned in the dry season. Numerous issues such as managing fires on organic soils, burning amongst exotic vegetation, burning under altered hydrologic regimes, pose challenges to prescribed fire managers.