The role of fire in sustaining populations of Cape Sable seaside sparrows within the southern Everglades

Lockwood, Julie; Logan, Joshua; Curnutt, John; Bass, Oron

Between 1948 and 1992 the wetland areas of Everglades National Park experienced 752 fires for an average of 17 fires per year (Gunderson and Snyder 1994). The plants and animals ofthis region are adapted to these frequent burns (Robertson 1953, Egler 1952). Fire is a necessary component of the Everglades. It maintains a habitat mosaic and prevents hardwood shrubs from invading the characteristically open Everglades marshes (Taylor 1983). The Cape Sable seaside sparrow (Ammodramus miratimus mirabilis), an endangered subspecies endemic to the southern Everglades, relies on a specific type of Everglades marsh (Werner 1975). The sparrow places its nest near the ground, imbedded in the base of grarninoid plants such as muhly grass (Mnhlenbergiafillipes), black-top sedge (Schoenus nigra), and sawgrass (Cladiumjamicense) (Lockwood et al. 1997, Werner 1975). This vegetation association is restricted to seasonally dry marshes imbedded in marl, inorganic soils (Gunderson 1994). As it has proved difficult to delineate the extent of these marl prairies, the role of fire in their maintenance is largely unknown. However, sparrow biologists have long believed that fire was critical for maintaining suitable breeding habitat (Werner 1975, Taylor 1983, Kushlan and Bass 1983, Curnutt et al. 1998). We first review this work, making explicit the proposed mechanistic links between fire, sparrow occupancy, vegetation, and soil depth. We then test aspects of this mechanism by combining two long-term data sets, one on sparrow density and the other on the spatial extent of fire within the southern Everglades.