Habitat fragmentation and conservation strategies for a rare forest habitat in the Florida Keys archipelago

Habitat loss and fragmentation are principal causes for population declines and the loss of biodiversity across the globe. In the United States, tropical hardwood hammock is a threatened forest ecosystem that occurs only in extreme south Florida, primarily on the Florida Keys archipelago. This rare forest type is characterized by high plant diversity that is strongly influenced by tropical, mast-producing trees and shrubs of West Indian origin. Tropical hardwood hammocks in the Florida Keys provide important habitat for resident and migratory birds, particularly Neotropical species that rely on suitable stopover habitat during migration. The Florida Keys are under intense development pressure, particularly in higher elevation sites where tropical hardwood hammock occurs. With exception of a survey completed during 1991 in the Upper Keys, information regarding habitat loss and current coverage, conservation status, and how best to conserve remaining patches of this rare forest habitat are lacking. We used a Geographic Information Systems approach to assess the extent of loss and fragmentation of tropical hardwood hammock in the upper Keys during 1991-2004, quantify area and number of hammock patches under private ownership and in conservation status throughout the Florida Keys as of 2004, and evaluate strategies to most effectively conserve large blocks of remaining tropical hardwood hammock. Total remaining hammock habitat throughout the Keys encompassed 3,712 ha and hammock habitat declined by 31% in the upper Keys during 1991-2004. Hammock habitat in the upper Keys encompassed 1,962 ha among 124 habitat patches (median = 1.5 ha, range = 0.1-205.7 ha), of which 1,066 ha (54%) were under conservation status. Hammock habitat in the lower Keys encompassed 1,750 ha among 102 patches (median = 4.4 ha, range = 0.3-96.3 ha), of which 1,283 ha (73%) were protected under conservation status. Approximately 37% of total remaining hammock habitat remained unprotected. However, our analyses revealed that many unprotected areas >20 ha were contiguous with protected hammocks. Safeguarding 22 partially protected patches >20 ha (17% of remaining patches) would protect an additional 750 ha of hammock habitat, which represents 55% of all remaining unprotected hammock habitat in the Keys, and would increase the mean patch size of these larger forest patches from 55 to 89 ha. Consequently, strategically focusing conservation efforts on remaining forest patches of tropical hardwood hammock >20 ha in size and contiguous to existing protected areas represents the most effective use of conservation dollars and would provide greater ecological benefits than conservation of small patches of highly fragmented habitat.