Restoring Tree Islands in the Everglades: Experimental Studies of Tree Seedling Survival and Growth Arnold G. van der Valk, 1,2 Paul Wetzel, 3 Eric Cline, 1,4 and Fred H. Sklar 5 Abstract In May 2004, 400 tree seedlings of seven different species found on tree islands in the Florida Everglades were planted at different elevations along five transects on eight newly constructed tree islands, four with and four without limestone cores. Seedlings suffered between 40 and 85% mortality during the first 120 days, the period with the lowest water levels. Ilex cassine L., Salix caroliniana Michx., Chrysobalanus icaco L., and Annona glabra had the highest number of surviving seedlings, whereas Mag- nolia virginiana L., Myrica cerifera L., and Acer rubrum L. had the fewest. During the remainder of the study, water levels were mostly higher and sometimes covered the entire islands for months at a time. After 220 days, nearly all seedlings of M. virginiana and My. cerifera had died. At the end of the study, seedlings of I. cassine and A. glabra had the highest survivorship rates. Seedling bio- mass of C. icaco and I. cassine was greatest at the highest elevations, whereas seedlings of A. glabra had similar bio- mass at all elevations. Seedling survivorship was not statis- tically different between islands with and without limestone cores; however, when seedlings of all species were combined, island core type was significantly different for aboveground biomass, seedling height, and canopy width. Because of the higher survivorship under both low and high water conditions, A. glabra, I. cassine, and S. caroliniana are the most suitable species for establishing tree species on restored tree islands in the Everglades. Key words: Everglades, flooding tolerance, peatland, res- toration, revegetation, wetland. Introduction Tree islands (Fig. 1) are an important component of the Everglades and many other wetlands around the world (Wetzel 2002b). They form due to internal redistribution processes within wetlands that result in small increases in local elevations that become colonized by tree species (Wetzel et al. 2005). In the Everglades, the vegetation of tree islands, which are only slightly higher in elevation than surrounding sloughs, wet prairies, and Sawgrass (Cla- dium jamaicense Crantz) flats, contains a number of ter- restrial tree, shrub, and herbaceous species that are found nowhere else in this wetland (Davis 1943; Loveless 1959; Armentano et al. 2002; Heisler et al. 2002). Tree islands are also essential habitat for many animal species. In the Everglades, White-tailed deer (Odocoileus virginianus), American alligators (Alligator mississipiensis), small mammals, reptiles, and many bird species use tree islands for nesting, foraging, and resting (Meshaka et al. 2002). For example, more songbird species are found on tree islands than any other habitat in the central Everglades (Gawlik & Rocque 1998). Many different tree species dominate the vegetation on tree islands in the Everglades (Armentano et al. 2002; Heisler et al. 2002; Mason & van der Valk 2002; Wetzel 2002a), and field studies have shown that their distribution on a given island and among islands seems to some extent to be a function of elevation, that is, how long an area where individuals of a tree species are growing is flooded annually (Armentano et al. 2002; Heisler et al. 2002; Wetzel 2002a; Ross & Jones 2004). Low islands have tree species that are mostly found at the lower elevations of high islands, and high islands have species that are typically restricted only to the higher parts of these islands and that are rarely found on low islands. Unfortunately, little data on the flooding tolerances of the tree species, especially their seedlings, are available (Conner et al. 2002). It is not known whether the distribution of tree species along ele- vation gradients is due largely or in part to recruitment patterns, plant–plant interactions, plant–animal interac- tions, or some combination of them. In the central Everglades, in which water slowly flows from north to south, tree islands are typically tear shaped and consist of two parts, the head and the tail. The head, 1 Department of Ecology, Evolution and Organismal Biology, Iowa State Uni- versity, Ames, IA 50011, U.S.A. 2 Address correspondence to A. G. van der Valk, email valk@iastate.edu 3 Department of Biological Sciences, Smith College, Northampton, MA 01063, U.S.A. 4 Present address: Southeast Environmental Research Center, Florida Inter- national University, Miami, FL 33199, U.S.A. 5 South Florida Water Management District, West Palm Beach, FL 33406, U.S.A. Ó 2007 Society for Ecological Restoration International doi: 10.1111/j.1526-100X.2007.00311.x JUNE 2008 Restoration Ecology Vol. 16, No. 2, pp. 281–289 281