TREE ISLAND PALEOECOLOGY AND THEIR RESPONSE TO HYDROLOGIC CHANGE, ARTHUR R. MARSHALL LOXAHATCHEE NATIONAL WILDLIFE REFUGE, FLORIDA

The Loxahatchee National Wildlife Refuge (NWR) is located in the northern Everglades and includes the oldest organic peat deposits found in the subtropical wetland. Plant communities within the refuge include deep-water sloughs, sawgrass marshes, wet prairies, and tree islands. Tree islands are particularly important communities in the Everglades ecosystem because they serve as refugia for plants unable to survive in the longer hydroperiod and deeper water marshes and sloughs that make up the bulk of the Everglades wetland.

Water management practices of the past 100 years have affected the distribution of tree islands throughout the Everglades ecosystem. Impacts include drowning and disappearance of tree islands subjected to excessively long hydroperiod and water depth and expansion of tree-island size after water supply was diverted from sheet flow through canal systems. We use biostratigraphical (pollen) and chronostratigraphic analyses of sediment cores, collected on tree islands and adjacent marshes, to evaluate the response of tree island communities to 20th century compartmentalization and water-management practices. Using palynological analysis, we also document the timing and patterns of tree-island formation and development, and evaluate trends in regional climate change.

Results from analysis of sediment cores collected from Loxahatchee strand islands provide an archive of development of strand island development in response to natural variation, as well as modern changes, in hydrology. Significant changes in species composition during the past 50 years are correlated with altered water-management practices. Integration with these results from other studies in the Everglades provide insights into the tolerance of tree-island species for hydrologic change and the ability of these communities to recover under different restoration strategies.