Tree islands, forested islands in an herbaceous freshwater wetland landscape, are a major landscape feature in the Florida Everglades. The vegetation communities on the heads of 31 tree islands, including eight islands with recreational camp structures, were assessed throughout Water Conservation Area 3 to determine their composition, structure, and distribution across the landscape. The islands were a sample of the most elevated islands in the local landscape. Measures of forest canopy (> 3 m) and sub-canopy (1–3 m) structure and composition, including cover, species richness, number of exotics, and total canopy basal area were ordinated onto six hydrologic variables estimated from the South Florida Water Management Model (v5.5) simulation from 1984 to 1997, and history of recent fire. Ordination allowed identification of four island groups: Group A, higher islands, most with camp structures, low or no canopy structure, high level of fire history, driest hydrology, and largest number of exotic species in canopy; Group B, variable canopy development including many plots without canopy cover, some fire history, and exotics in sub-canopy; Group C, highest islands with well developed canopy structure and no canopy exotics; and Group D, low elevation islands, wettest hydrology, no exotics, and deep peat soils. Cluster analysis of the vegetation cover data was used to identify sub-canopy and canopy communities of the island groups. Our results indicated that the forest canopy of elevated tree islands is similar throughout the central Everglades and that differences in tree island forest composition and structure were the result of local differences in island topography, hydrology, direct human disturbance, and past fire history. Canopy composition and structure were strongly correlated with extreme wet or dry hydrologic events rather than mean or median annual water levels. Fern species were also found to be a ubiquitous component of the sub-canopy. The results of this study identify potentially successful species and provide some basic guidelines for restoring the forest head communities of degraded tree islands.
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Vol. 28 • No. 2