The Ecology of Hydric Hammocks - USGS National Wetlands ...

first, Shep's Island (Table 51, adjacentto Upper Myakka Lake, consists ofcabbage palm and live oak and has I lr;-tle shrub and ground Vegetation. Thesecond hammock, located about 20 km tothe east in Deer Prairie Slough, containsa number of hardwoods absentfrom Shep's Island, as well as copiousshrubs and herbs. The hydric hanlmockin Deer Prairie Slough occupies aslightly elevated area that is completelysurrounded b~ mi xed hardwoodswamp. We suggest that this contrastin hammock vegetation i s due to d ii i F-ference in fire frequency and intensity.Presumably fires that sweep thevast marshes of the Myakka region alsoburn Shep's Island but are damped bythe swamp in Deer Prairie Slough andonly rarely reach the hammock there.It also is possible that the hydrologicalconditions of the two hammocksdiffer enough to account for some ofthe differences in species composi -tion. The swamp may modulate theflooding regime of the Deer PrairieSiough ild111111u~k i u ~ h t h ~ th: dcr:t'c::of flooding is less than in the Shep'sIsland hammock and drydowns are not assevere.The plant composition of the Tosohatcheehydric hammock (upper St.Johns River) varies greatly on a localscale (Figure 36). Portions of thehammock jmmedi ately adjaceqt to freshwatermarsh (Figure 36c, d) are theleast diverse. Fire scars are pervasive,signal 1 i ng more frequent burnsin these sites than in hammock portionsnext to a mixed hardwood swamp(Figure 36b) and a creek (Figure 36a).The low basal area of forest (d) andits short stature (the average heightof the canopy is 12 m, in contrast to17 m in site (b)) probably are due to80 - cabbage'760-40I-Iswdmpoak 01QnUt Floridasouthernred- sweet--cedar gum redw r-7 r 1 ?kor~ 25 I I 1 ] mulberrycabbagered -ZE!%sugar- I/ / 1 livewaxmyrtleFigure 36. Species comf30sition Of nearby Portions of a hydric-hammock stand in the northernpart of Tosohatchee State preserves Orange Total basal area is listed for each site.