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

grass. Sal t-tolerant shrubs such as1r.a frotescens (marsh elder), Lycrrtmcarol inianum (Chri stmasberry), andBaccharis angust if07 ia, B.g70merulifolia, and B. ha7imifolia(saltbushes) are abundant at the forestedge in some locations. Vines arerare at the edge, and both vines andshrubs are scarce in the forest interioruntil at least 1 km inland. Theground cover is very sparse. Thiscoastal part of Gulf Hammock is quitesimil ar to the hydric hammocks borderingthe marshes along the St. Johnsand Myakka Rivers.With increasing distance from thesalt marsh, cabbage palm, live oak,and southern red-cedar decl ine andhardwoods increase in dominance. Beginningat about 2 km inland, GulfHammock is divisible into three mainvegetation types. Swamps of bald cypress,red maple, swamp tupelo, andgreen ash occur in low areas and alongthe poorly defined creek drainages.Forests that might be considered eithermesic or hydric hammock occupysl ightly elevated ridges. The overstorycontains swamp chestnut, Shumard,live, laurel, and water oaks,plus sweetgum, southern magnol i a, sugarberry,winged elm, Florida elm,Florida maple, lob101 ly pine, southernred-cedar, pignut hickory, persimmon,red mulberry, and basswood. The understoryand ground cover also are diverse.The third type of vegetation,the majority of Gulf Hammock, is betweenthese two "extremes" in speciescomposition and is clearly hydric hammock.This major hydric hammock (Figure19) consists mainly of swamp laureloak and sweetgum in combination withlive oak, water oak, loblolly pine,Florida elm, basswood, persimmon, redmaple, sweetbay, sugarberry, and cabbagepalm. The average height of thedominant canopy trees is about 30 m,with scattered lob1 01 ly pines emerging3-6 m above the canopy. The scatteredlive oaks are by far the largesttrees, averaging about twice the trunkdiameter and crown spread of the othercanopy tree species. The ground atthe bases of these big live oaks oftenis raised by the root system to form amound. This microtoaoara~hv is particularlywell suited for the estab-1 ishment of magnolias, and, in conjunctionwith the spreading crown ofthe live oak, for the growth of severalspecies of vines (bullace andsummer grape, pepper vine, rattanvine, and climbing buckthorn). A subcanopydominated by hornbeam, wax-myrtle,swamp dogwood, and various treesap1 ings often is we1 1 developed. Theground layer commonly is a dense mixtureof grasses, sedges, and ferns,but in wet areas the cover is mostlyleaf 1 itter with only a scattering ofherbaceous pl ants.Patches of hydric hammock dominatedby loblolly pine are found within GulfHammock. Some of these are naturaland others are the result of human activity.Some of the higher ridgeswere cleared for farmjng 1 ong ago, apparentlyby German immigrants, andthen abandoned. Now stands of largeloblolly pines, locally known as"German Islands", cover the oldfields. A modern activity with similarresults is the clearcutting of extensiveareas of Gulf Hammock foll owedby the planting of loblolly pine.Gulf Hammock and its surroundingsare very flat, with one exception.Old sand dunes .covered with sand pinescrub vegetation are found on thenorth side, just inland from CedarKey. A mixture of swamp and hydrichammock occurs adjacent to the dunes,but both of these types are somewhatdifferent in composition than elsewherein Gulf Hammock, presumably dueto the continuous supply of waterseeping out of the dunes and to thethicker layer of organic muck. Swamptupelo, the dominant tree or codominantwith green ash, is much moreabundant than in other swamps of theregion. The hydric hammock also isdifferent in its abundance of needlepalm, which is quite scarce elsewherein Gulf Hammock. This part of GulfHammock is most similar to the hydrichammocks at Wekiva Springs, MormonBranch Botanical Area in the Ocala NationalForest, and Tiger Creek.