Project: Evolution of Everglades Tree Islands

Web Site: http://flaecohist.er.usgs.gov

Location: Central Everglades; Broward and Miami-Dade Counties

Principal Investigators: Debra A. Willard, dwillard@usgs.gov, 703.648.5320; William H. Orem, borem@usgs.gov, 703.648.6273

Project Personnel: Harry Lerch, tlerch@usgs.gov 703.648.6278; Charles Holmes, cholmes@usgs.gov, 727.803.8747x3056

Other Supporting Organizations: South Florida Water Management District, Everglades National Park, Loxahatchee National Wildlife Refuge, and Florida Fish and Wildlife Conservation Commission

Associated Projects: South Florida Ecosystem History: Terrestrial and fresh-water ecosystems

Overview & Status: This project aims to: determine the age of Everglades tree islands; determine the geologic and hydrologic controls on tree-island formation, development and sustainability; establish vegetational trends in tree-island development; determine the role of tree islands in the geochemical budget of nutrients; and investigate the use of sediment phosphorus as a tracer of historic bird populations in the Everglades. To date, cores have been collected on sixteen tree islands: two in Loxahatchee NWR, one in WCA 2A, eleven in WCA 3A, and two in WCA 3B. During the summer of 2000, two tree islands in Everglades National Park will be sampled, as will additional sites in WCA 2A. Palynological and geochemical analyses are complete on two islands in WCA 3B, and preliminary palynological analyses have been completed on an island in WCA 3A and a degraded tree island in WCA 2A. These analyses indicate that tree islands have existed in the Everglades for at least 3,000 years and that development into modern tree islands took 1,000 to 2,000 years. Preliminary results from a "drowned" tree island also indicated unprecedented vegetational changes during the last century, highlighting the impact of altered hydrology on these long-term features of the Everglades landscape.

Needs & Products: The environmental parameters necessary for formation and maintenance of Everglades tree islands are being established. Products will include evidence on the timing of tree-island formation and patterns of tree-island development at sites across the Everglades. These data will provide critical data on the tolerance of tree islands to hydrologic change. Comparison of the time needed for both tree-island development and degradation will help establish management strategies to ensure the survival of the remaining tree islands and to provide guidance on parameters needed to restore or create tree islands.

Application to Everglades Restoration: The sensitivity of tree islands to hydrologic changes makes them key indicators of the health of the Everglades ecosystem.