PARENT SESSION
Oral Session # 15: Wetland Ecology I: The Everglades and Southern Wetlands.
Presiding: J Chick
Tuesday, August 5. 8:00 AM to 11:30 AM, SITCC Meeting Room 101.

Vegetation structure and composition along hydrologic gradients in Everglades Tree Islands.

Sah, Jay¹, Ross, Michael¹, Reed, David¹, Ruiz, Pablo¹, Jones, David¹, ¹ Florida International University, Miami, FL

ABSTRACT- Tree islands, an integral component of the landscape in the Shark River Slough of the Everglades, have continuously been affected by management-oriented changes in water flow pattern. Our study determined the variation in plant community structure within Shark Slough tree islands, and examined its associations with recent hydrologic conditions. Three tree islands, Black Hammock, Gumbo Limbo, and Satinleaf, were selected for this study. Forests on each island were classified into hardwood hammock, bayhead, and bayhead swamp. Hydrologic gradients in the islands were calculated from elevation data collected at 5-10 m intervals along four transects, one along the long axis of the islands, and three others perpendicular to it. Vegetation was sampled along the transects as well as within three permanent plots of 25 x 25 m, 20 x 20 m, and 15 x 15 m established in the hardwood hammock, bayhead, and bayhead swamp, respectively. Tree, sapling, shrub and herb strata were sampled separately in a nested design. The surface elevation decreased from hardwood hammock through bayhead to bayhead swamp, suggesting deeper water and longer hydroperiod in reverse order of the above. On each tree island, the three forest types differed significantly in species composition. Plant species diversity was highest in the wetter types. Species hydrologic niches calculated for each island using abundance-weighted averaging techniques indicated strong correlations in species′ behavior among the three islands. Canopy height exhibited a strong positive association with surface elevation, but understory cover showed an opposite trend. Litterfall data suggested that the pattern of decreasing canopy height was also associated with a gradient of decreasing site productivity, presumably as a result of hydrologically related factors. Differences in vegetation structure and productivity on tree islands in relation to hydrology may help in establishing monitoring criteria for the assessment of Everglades restoration efforts.

Key words: Shark River Slough, Hydrology, Everglades, Tree islands