FLORIDA

Habitats
Florida's mild climate and abundant water supply support natural communities of exceptional diversity, yet Florida's ecosystems must also adapt to difficult environmental conditions. Many communities cling insecurely to foundations of hard limestone or sand. In addition, the flat topography makes habitats vulnerable to seemingly small changes in water levels and other climatic factors, which can rapidly unbalance an area's ecology. Against this subtle and shifting background, it is difficult to define Florida's habitats exactly or to generalize as to their distribution. Reefs, tropical hardwood hammocks, mangrove forests, and large marsh systems tend to prevail in the south; lakes, ponds, swamps, prairies, and temperate hardwood forests are more dominant inland, in northern or central Florida; and pinelands, although most prevalent in northern and central regions, can be found nearly everywhere.

Effects of Fire
Although it is seldom directly observed, fire is a primary factor in shaping Florida's ecosystems, especially dry, well-drained habitats. Dry prairies regularly experience wildfires in a natural state; indeed, fire is instrumental in suppressing the growth of woody plants that would otherwise transform these areas into woodlands. Wet prairies, by comparison, host a specialized set of herbaceous (nonwoody) plant species that can withstand both occasional fires and periodic flooding. Some pinelands, such as the Sand Pine scrub in the panhandle, require periodic fires to trigger the release of their seeds. Habitats such as northern hardwood forests and southern hardwood hammocks are not fire-resistant and can thrive only in locations that offer relative safety from burning.

Effects of Wind
Wind has two primary effects on Florida's habitats. First, it carries salt mist and airborne sand particles ashore, which spray and scour coastal habitats. Only communities that can withstand this physical and chemical abuse--mangroves, maritime forests, and dunes stabilized by vegetation--can survive. Second, violent tropical storms destroy most habitats in their path, and any natural community positioned to experience storm damage must be able to regenerate efficiently afterward. Mangroves and maritime forests recover quickly, but hardwood hammocks destroyed by Hurricane Andrew in 1992 will take years to regenerate fully, and habitat managers must struggle in the interim to prevent alien plants such as Melaleucas and Brazilian Peppers from overgrowing these areas.

Effects of Water
The level and salinity of a region's water supply are important in determining the biological communities that can exist there. Naturally, maritime environments, including reefs, salt marshes, and mangrove swamps, require a constant supply of salt water. Freshwater habitats such as wet prairies, marshes, and swamps lack tolerance for salt water and can be killed or damaged by overwashes (such as the "storm surge" caused by hurricanes) or by the infiltration of salt water into underground aquifers. With the diversion of fresh water from the Everglades during the 20th century to support the ever-growing human population, salt-tolerant mangrove forests have extended progressively farther inland.

Effects of Earth
Though much of Florida's geology is based on forms of a single rock, limestone, the relationship between ecosystems and the geological substrate is nonetheless variable and complex. Sandy habitats-- dunes, maritime forests, and pinewoods--are widespread, occurring inland as well as along the shore. Such habitats drain rapidly and are susceptible both to dehydration and to the loss of minerals and nutrients through leaching. Stony habitats, in which limestone exists near the surface with little accumulated organic material, include the hardwood hammocks and rimrock pinelands of southern Florida. Tree growth can be limited in these areas because nutrients are in short supply and it is difficult for trees to establish secure root systems. If the rock is particularly porous, lack of water may further limit plant life. Habitats that develop over clay substrates or very fine sand, such as the Everglades, pine flatwoods, and some northerly hardwood forests, retain water, providing favorable conditions for moisture-loving plant communities. Cypress swamps, salt marshes, and mangrove swamps have poorly oxygenated soils dominated by fine silt and "muck" that pose special challenges to plant growth.

PHOTO: Claudine Laabs