Thomas J. Smith III¹, Gordon H. Anderson¹, Ginger Tiling² and Greg A. Ward^3
1USGS, Florida Integrated Science Center, St. Petersburg, FL, USA
²ETI Inc. c/o USGS, Florida Integrated Science Center, St. Petersburg, FL, USA
³CSC Inc. c/o USGS, Florida Integrated Science Center, St. Petersburg, FL, USA

A “myth of the mangroves” is that they are adapted to relatively frequent disturbance by hurricanes. The first real examination of hurricane impacts on mangrove ecosystems followed the passage of Hurricane Donna over southwest Florida in 1960. Researchers at that time realized that the Labor Day Hurricane in 1935 also had severe impacts on the forest. Thus was born the idea that mangroves were adapted to a 25 yr hurricane return time (1960 – 1935 = 25!). Following Hurricane Andrew in 1992, an intensive effort was launched to sample the hydrology, vegetation and sediment dynamics in the mangroves forests of southwest Everglades National Park. Historical nautical charts, reports from biological expeditions, and air photos have allowed a reconstruction of past vegetation, dating to 1853 for parts of Cape Sable and from the early 1920s for most of the southwest coast. Permanent vegetation plots, hydrology stations and sediment elevation tables with marker horizons have been used for almost 10 years to study change in detail. The passage of Hurricane Wilma (October 2005) has afforded the chance to study continued, cumulative impacts of disturbance. Examination of historic charts and photos indicated that the Labor Day hurricane caused catastrophic change at a number of locations, especially on Cape Sable. Mangrove forests were converted to intertidal mudflats. Interior brackish and low salinity wetlands were converted to open water. The air photos also indicated that portions of the area that were recovering from the Labor Day storm were set back by Donna. Hurricane Andrew caused catastrophic damage, but only in a small portion of the southwest coast. Data from permanent plots indicated that recovery of the forest was well underway when Hurricane Wilma hit. Hurricane Wilma caused less intensive damage than Andrew, but the moderate to severe damage from Wilma was far more extensive, stretching from Cape Romano to Cape Sable, over 100 miles. Sampling of surface elevation tables indicated that intertidal mudflats, created by the Labor Day storm, are continuing to erode. Wilma removed some 30mm of sediment from these flats, equal to the previous seven years of loss. Wilma deposited from 20-60mm of sediment within parts of the coastal mangroves.

Repeated impacts from hurricanes are occurring at a time of rising sea-level and the addition of freshwater by the Everglades restoration (CERP). Understanding cumulative impacts from storms, sea-level and CERP will be necessary for effective management of the southwest coastal Everglades.

Contact Information: Thomas J. Smith III, U.S. Geological Survey, Florida Integrated Science Center, 600 Fourth Street, South, St. Petersburg, FL 33701, Phone: 727-803-8747, Fax: 727-803-2030, Email: Tom_J_Smith@usgs.gov

(This abstract is from the 2006 Greater Everglades Ecosystem Restoration Conference.)

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