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South Florida rocklands

Extreme southern Florida is characterized by thin, droughty soils situated on outcroppings of limestone. Pinelands and tropical hardwood hammocks cover virtually all of these outcrops and are considered as rockland ecosystems. The best examples of the pine rocklands, an ecosystem that once covered about 1,500 km2, are located at the southern tip of Florida above an extrusion of limestone known as the Miami Rock Ridge and along the lower Florida Keys. Pine rocklands are fire-maintained pine forests (dominated by slash pine, Pinus elliottii) with a mixture of tropical and temperate understory plants (Snyder et al. 1994). The associated hardwood hammocks contains a rare intrusion of tropical hardwoods more typical of the Bahamas and Greater Antilles than the adjacent southeastern conifer forests. We chose to put this ecoregion in the Tropical Moist Forest MHT rather than in the Subtropical and Tropical Coniferous Forest MHT, in deference to the extraordinary richness of its tropical hardwood flora.

  • Scientific Code
    (NT0164)
  • Ecoregion Category
    Neotropical
  • Size
    800 square miles
  • Status
    Critical/Endangered
  • Habitats

Description
Biological Distinctiveness
The South Florida Rocklands support the only true tropical forest on the U.S. mainland. Tropical epiphytic orchids, bromeliads, and ferns festoon the trees of the hardwood hammocks and are restricted to southern Florida. At least 137 species of trees and shrubs occur here, 18 species of vine and scandent shrubs, and seven species of palms (Snyder et al. 1994). Some experts argue that while the tree flora is similar to a Bahamian forest flora, the South Florida hardwood hammock species have been isolated long enough to be considered as distinct populations from the rest of the Caribbean forest species. Thirty-seven species of herbs are endemic to the pine rocklands, among the more than 250 species of herbaceous plants recorded. Unlike the flora, which maintains a strong Caribbean influence, the fauna is largely derived from southeastern temperate habitats.

Fire is essential for maintenance of rockland pine forest and determines the relative dominance of pine forest versus hammock, the latter being less likely to burn.

Conservation Status

Habitat Loss
The South Florida Rocklands were never widespread and are now virtually gone as a result of population growth and land clearing in the Miami area and the Keys. Only two percent of the original habitat is thought to remain, making the pine rocklands one of the most endangered of ecoregions (Noss and Peters 1995). Besides Long Pine Key in Everglades National Park, conversion of pine rocklands communities on the Miami Rock Ridge has left perhaps 2percent intact within the other major block of this ecoregion. Hardwood hammocks are under much greater threat of development in the Keys, where they are mostly privately owned. Other reasons for habitat loss include conversion to agriculture through the use of rock plows to break up the limestone for planting, fire suppression, and introduction of exotic species such as Brazilian pepper (Schinus). The increase in water table from agricultural irrigation, beetle epizootics, and the effects of Hurricane Andrew damaged part of the remaining stands (A. Mack, pers. comm.).

Remaining Blocks of Intact Habitat
The largest blocks of habitat occur in

•Long Pine Key in Everglades National Park
•Big Pine Key in the Key Deer National Wildlife Refuge
Snyder et al. (1994) review the conservation status of the pine rocklands in detail. Only three remnant fragments are larger than 50 hectares. The remaining hammocks on the Rock Ridge are not in danger of being cleared as they are owned by Dade County.

Degree of Fragmentation
Only small remnants are left and the increased number of small fragments surrounded by other forms of land use, particularly urban areas, restricts fire management. Much of the remaining areas are surrounded by water or cities, making restoration of corridors highly unlikely.

Degree of Protection
What little remains is represented by the existing reserves listed above. These habitats and the species they support are not secure because of fire suppression, edge effects, and high mortality of fauna from road networks and heavy vehicle traffic.

Types and Severity of Threat
Most of the privately owned lands containing rocklands have been converted and little remains to be put under conservation management. Continued fire suppression and invasion of exotic species could drastically degrade these remaining blocks over the next two decades. Exotic plants pose a serious threat to the integrity of the rocklands.

Suite of Priority Activities to Enhance Biodiversity Conservation
A number of important areas on private land have been proposed for purchase under habitat conservation programs. These efforts should be given top priority.

Snyder et al. (1990) concludes that while it is essential to put under protection the remaining sites of pine rocklands, just as important will be increased active management, particularly for controlled burning to maintain the integrity of these habitat patches and reduce the spread of invading species.

Conservation Partners

•Conservation and Recreation Lands Program (CARL) of the state of Florida
•The Nature Conservancy
•The Nature Conservancy of Florida
•Florida Natural Areas Inventory

Relationship to other classification schemes
This ecoregion is not delineated by Bailey or Omernik. Boundaries were taken from Küchler (1964).

Prepared by: E. Dinerstein, A. Weakley, R. Noss, K. Wolfe

 

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