slightly elevated oolitic outcrops 

 that vary in area from several 

 square meters to well over a hect- 

 are. The oolite is present as a 

 table-like formation that is much 

 like an island, being surrounded by 

 less elevated pinnacle rock and 

 associated muhly prairie vegetation. 

 This community type designation is a 

 more advanced successional stage, 

 and is typically more extensive spa- 

 tially than transitional prairies. 



Wax myrtle ( Myrica cerifera ) 

 and saltbush ( Baccharis halimifolia ) 

 are the dominant species, and they 

 usually account for more than 50% of 

 the aerial cover of the community. 

 The remaining fraction of the cover 

 is composed of a large number of 

 broad-leaved trees, shrubs, herbs, 

 and an occassional slash pine ( Pinus 

 elliottii ) . The floristic composi- 



tion of this remaining fraction 

 varies greatly from site to site, 

 but several tree species are usually 

 present. These include: myrsine 

 ( AAyrsine quianensis ), Florida trema 

 ( Trema micrantha ) , poisonwood ( Meto- 

 pium toxiferum ), blolly ( Pisonia 

 discolor ) , strangler fig ( Ficus 

 aurea ) , willow bustic ( Dipholis 

 salicifolia ) , dahoon holly ( Ilex 

 cassine ) , and indigo berry ( Randia 

 aculeata ) ♦ Willow thickets are very 

 widespread in the East Everglades 

 agricultural area and appear to be 

 increasing in size and abundance. 

 Willow thicket vegetation is gener- 

 ally restricted to marshlands, but 

 are occassionally present in season- 

 al muhly prairies and in close asso- 

 ciation with various broad-leaved 

 tree islands that are located in 

 either marshes or prairies. Willow 

 thickets occupy deep soils of muck, 

 peats, or peaty marls and reach the 

 most vigorous development in areas 

 with a hydroperiod of more than 5 

 months. This vegetation type often 

 forms the margins of seasonal ponds, 

 alligator holes, and other depres- 

 sions in the Everglades. 



Structurally, willow thickets 

 are somewhat dome-shaped when pres- 

 ent singly in the open marsh, but 

 many willow thickets are circular, 

 roughly rectilinear, or trapezoidal 

 in outline when associated with 

 other arboreal vegetation, or when 

 senescence, fire damage, or exten- 

 sive flooding has occurred. Salix 

 caroliniana is the dominant species 

 with regard to cover, density, and 

 above-ground biomass, and this com- 

 munity is essentially a monoculture. 

 The height of the willow is usually 

 between 1.8 and 4 m (6 to 13 ft) 

 above the soil surface. Very often, 

 some of the larger trunks of Salix 

 are oriented parallel to the sub- 

 strate and extend several meters 

 under water. These individuals give 

 rise to many vertical coppices 

 (stems) that later take root and 

 become new individual trees. 



Willow thickets are ecological- 

 ly important because they serve as 

 feeding, nesting, and roosting habi- 

 tat for many of the herons, egrets, 

 and other wading birds. Gallinules 

 feed heavily on willow catkins. 

 Additionally, they provide a general 

 habitat for the alligator and most 

 of the aquatic vertebrate fauna in 

 the Everglades marsh ecosystem. 



Coco plum ( Chrysobalanus icaco ) 

 form thickets that are prominent 

 tree island features along the east- 

 ern margins of the Shark River 

 Slough and are especially well-deve- 

 loped in the Taylor Slough region of 

 the East Everglades. As a rule, 

 these islands are less than 0.5 

 hectares (1.2 acres) in extent and 

 inhabit peat soils that overlie 

 slightly elevated patches of oolitic 

 rock. This community rarely devel- 

 ops on deep peats without a slight 

 rock elevation present. The soil 

 surface is often submerged for 2 

 months in the peak of the wet season 

 and has an effective hydroperiod of 

 1 or 5 months. These communities 



115 



