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

RIVER HYDRICSWAMP HAMMOCK SCRUBBY FLATWOODS BAYWEAD SCRUBBY FLATWOODSwater taMI_ surface of soilFigure 8. Sequence of plant communities from the lower St. Johns River to upland scrubbyflatwoods. In the higher flatwoods, water percolates to the hardpan and moves laterally until itemerges in the bayhead at the base of the slope. Ground water also seeps into the hydric hammock(from Laessle 1942).STREAM HYDRIC HAMMOCK MESlC HAMM--- APPROX MEAN WATER TABLEFigure 9. Generalized profile of a spring-fed stream and adjoining hydric hammock. The wavy linesindicate the annual fluctuation in river level. A high water table beneath the hydric hammock ismaintained by the spring run (adapted from Wharton et al. 1977).A1 ong the spring runs, hammock vegetationoccurs where the water table usuallyis below the surface and wherespring seepage is supplemented byrainfall and runoff from the uplands.These examples suggest that, whileconsiderable variation exists amonghydric hammocks, they differ from bothbottomland hardwood forests and bay-heads in their mixture of watersources. Bottom1 and hardwood forestsreceive most of their water from riverflow, and bayheads are characterizedby ground-water seepage..Within a hydric hammock, hydrologicalinputs vary with season.Rainfall is distributed very unevenly