Tree Islands of the Arthur R. Marshall Loxahatchee National Wildlife Refuge

Abstract

The Arthur R. Marshall Loxahatchee National Wildlife Refuge (Loxahatchee) is a remnant of the northern Everglades wetlands. Tree islands are a prominent feature of the landscape. Despite their prominence in the landscape, few studies specifically on the ecological importance of tree islands have been conducted. This chapter reviews and summarizes what studies have been done in Loxahatchee that provide information on tree islands. The studies reviewed fall in to four basic categories: 1) Characterization and distribution, 2) Vegetation composition, 3) Tree island change and 4) Faunal use. The data on tree island origin in Loxahatchee suggest two possible routes of formation for tree islands: development from floating batteries or peat mats, or formation along the ridges in the ridge and slough landscape. Most of the tree islands in Loxahatchee are small, round or elliptical, and slightly elevated islands that may have formed via the former mechanism. Tree islands are not distributed uniformly throughout Loxahatchee, with more small islands in the north and west. Natural processes such as fire and hydrology have, and continue to play a role in tree island structure and distribution. Tree islands in areas of longer hydroperiod and deeper water depths have decreased in size, probably as a result of flooding, while tree islands in drier areas have increased in size and developed less distinctive shapes (no longer round or elliptical). There is evidence that fire occurred on islands. One study showed how fire can structure the islands by burning the vegetation along the outside and leaving the interior vegetation intact. Seventy plant species and 86 vertebrate species have been observed on or associated with tree islands. The studies reviewed in this chapter span a period of 50+ years and provide a recent historical basis for evaluating tree island change. These past studies provide us with a starting point for development and testing of hypothesis on the ecological importance of tree islands in Loxahatchee and the rest of the Everglades.