Tree Islands of the Everglades

Chapter 4.
Paleoecological Insights on Fixed Tree Island Development in the Florida Everglades: I. Environmental Controls

Debra A. Willard¹, Charles W. Holmes², Michael S. Korvela³, Daniel Mason^4,5, James B. Murray¹, William H. Orem⁶, and D. Timothy Towles⁷
email: dwillard@usgs.gov
¹U.S. Geological Survey, MS 926A, 12201 Sunrise Valley Drive, Reston, VA 20192 USA,
²U.S. Geological Survey Center for Coastal and Marine Geology, 600 4th Street South, St. Petersburg, FL 33701 USA,
³South Florida Water Management District, Watershed Research and Planning Division, Everglades Research Department, 3301 Gun Club Road, West Palm Beach, FL 33406 USA,
⁴Florida Center for Environmental Studies, Florida Atlantic University, Palm Beach Gardens, FL USA,
⁵present address: Indiana Dunes National Lakeshore, Porter, IN USA,
⁶U.S. Geological Survey, MS 956, 12201 Sunrise Valley Drive, Reston, VA 20192 USA,
⁷Everglades Protection and Restoration Program, Florida Fish and Wildlife Conservation Commission, 255 154th Avenue, Vero Beach, FL 32963 USA.

From Tree Islands of the Everglades edited by Fred H. Sklar (South Florida Water Management District) and Arnold G. van der Valk (Iowa Lakeside Laboratory)

Abstract

Palynological and geochemical analyses of sediment cores collected on two tree islands in the Florida Everglades indicate long-term hydrologic and chemical differences between tree islands and surrounding marshes and sloughs. Gumbo Limbo and Nuthouse tree islands are elongate, teardrop-shaped islands in Water Conservation Area 3B. Prior to tree island formation at both sites, pollen records indicate that sites on modern tree island heads were covered with sawgrass marshes with abundant weedy annuals. Such vegetation is characteristic of moderate water depths and hydroperiods with frequent droughts or disturbances. Contemporaneously deposited sediments on tree island tails indicate progressively deeper water conditions with increasing distance from the head; wetlands surrounding tree islands were covered by sloughs with deep water and long hydroperiods. Tree island formation occurred at about 1200 BC on Gumbo Limbo Island, with mature tree island vegetation established by about 800 AD. On Nuthouse Island, tree island formation occurred around 300 AD, shifting to mature tree island vegetation around 1400 AD. Thus, tree island formation began on these islands between 3.2 Ka and 1.7 Ka. Maturation of tree islands took between 1,000 and 2,000 years, and vegetation on these tree islands has been relatively stable for the last 600 - 1,200 years. Phosphorus levels on tree island heads have been extremely high (approximately six times greater than baseline levels in marshes) throughout the history of the sites, and phosphorus content in tree island tails began increasing when tree island formation occurred. Elevated phosphorus content may reflect the long-term presence of wading birds at these sites and provide a proxy for reconstructing the historic distribution of wading bird populations.

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