Tree Islands of the Everglades

Chapter 3.
Bayhead Tree Islands on Deep Peats of the Northeastern Everglades

Peter A. Stone¹, Patrick J. Gleason², and Gail L. Chmura³
email: stonepa@gw.state.sc.us
¹South Carolina Department of Health and Environmental Control, Bureau of Water, Columbia, SC 29201,
²Camp Dresser & McKee, Inc., 1601 Belvedere Rd., West Palm Beach, FL 33406,
³McGill University, Department of Geography, Montreal, Quebec, Canada.

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

The northeastern Everglades contain a vast (originally ca. 800 km²), dense cluster of red bay and dahoon holly tree islands on deep peats (>1.5 m). Unlike most other parts of the Everglades, the specific locations and origins of these tree islands appear unrelated to local mounds or depressions on the buried limestone bedrock or sand substrates, and instead solely reflect peatland accretionary and successional processes. A very broad shallow peat swale has maintained deeper-water marsh vegetation with abundant waterlilys and much less sawgrass in this region when compared to adjacent Everglades terrain to the west. Protection from fire and promotion of floating peat-island formation are some apparent ecological linkages between tree islands and waterlily marshes.

Tree islands in this major regional cluster are mainly of two types. Thousands of small tree islands (ca. 15-30 m wide) are populated with red bay (Persea borbonia), are round or irregular in map view and are located on distinct, relatively high, peat mounds (ca. 0.75-1 m). Intermingled among these small tree islands are more than a hundred very large tree islands (ca. 1-2 kms long) that are typically dominated by dahoon holly (Ilex cassine), distinctly elongated in map view, and are only moderately elevated above the surrounding marshes. The two types are of dissimilar origins and possibly different ages. Both types have forest peat only as the top layer, with marsh peats below, demonstrating that they were produced by peatland biogeomorphic processes and that they are not relict features. Large elongated tree islands have no prominently raised and vegetationally distinct "head" on their northern upstream tips, and the raised small tree islands have no distinct downstream "tails," features typical of bedrock (or sand-mound) focused tree islands found widely elsewhere in the Everglades. In the northeastern Everglades, it appears that most small tree islands were initiated on floating peat islands or their successional geomorphic descendants and most, if not all, large tree islands succeeded on large sawgrass strands (themselves of uncertain origin and shaping).

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