U.S. Geological Survey Fact Sheet 2004-3095
September 2004 - Online Version 1.0
Islands of the Florida Everglades—
Long-Term Stability and Response to Hydrologic Change
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Tree islands are important centers of biodiversity in the Florida Everglades; they have two to three times the plant and animal diversity of the surrounding wetlands. This high diversity is due primarily to their higher elevation relative to the adjacent wetlands. In the natural Everglades system, water levels fluctuated seasonally with rainfall, and tree islands were the only sites that escaped flooding during the wet season. These seasonally dry sites provided refugia and nesting sites for animals and allowed tree and shrub communities to flourish.
Major changes to the natural Everglades hydrology occurred after severe flooding from hurricanes in 1947 and 1948. As a result of those storms, millions of acres of land were under water for several months. Shortly thereafter, the Central and Southern Florida (C&SF) Project for Flood Control was implemented to protect urban areas from flooding. Beginning in 1952, the C&SF Project constructed three Water Conservation Areas (WCAs) that hold surface water to augment water supply in the east and to maintain water discharge to Everglades National Park in the south. Construction of the Water Conservation Areas resulted in hydrologic fragmentation of the greater Everglades ecosystem and disrupted seasonal freshwater flow through the system. Consequently, wading bird populations were reduced, and it is estimated that half the tree islands were lost or degraded.
In an effort to increase water supplies to restore the Everglades to a more natural state while still meeting other regional water needs, Congress authorized the Comprehensive Everglades Restoration Plan (CERP) in 2000. Research is underway to ensure that restoration targets reflect the natural predrainage hydrology and ecology.