The hydrology of cypress wetlands in Florida pine flatwoods

The poorly drained pine flatwoods of the Lower Coastal Plain of the Souther n United States, including Florida, contain many pond cypress (Taxodium asc endens) wetlands, which cover about one-third of the area. Management of th e resource includes pine silviculture and cypress harvesting for lumber, pl ywood, paper, and mulch. Concern about the ecological impacts and hydrologi c effects prompted a cooperative study of cypress wetlands integrating seve ral disciplines. This paper reports results of clear-cut harvesting on the wetland hydrology. Three wetlands of about 0.5 ha were selected and instrum ented to measure the climatic and hydrologic variables before and after tre atments from January 1993 to January 1997. Silvicultural treatments were we tland-only clear-cut harvesting, wetland plus surrounding upland clear-cut harvesting, and an undisturbed control. The absence of observable soil surf ace runoff thigh infiltration rate) and slow ground-water movement in the u pland pine flatwoods suggested that normally the precipitation and evapotra nspiration balanced each other and that the wetlands generated most of the runoff from the landscape mosaic as a whole. However, the results showed th at open-water evaporation after wetland harvesting exceeded evapotranspirat ion of the control, explaining in part a decrease in outflow after wetland- only harvesting. increased runoff from the pine upland, generated by reduce d evapotranspiration and expanded saturated areas after clear-cut harvestin g, apparently was buffered to some extent by increased evaporation from the embedded clear-cut cypress wetland. The average open-water area was about fifty percent larger than the wetland area as defined by the vegetation. Ho wever, excess wetland water balance data suggested the presence of a rain-c atchment area that was 2-3 times larger than the vegetative wetland area be cause of semi-saturated soil in the low slopes. Therefore, the actual catch ment area of a cypress wetland in the pine flatwoods may be variable in tim e, space, and silviculture depending on the topography, the extent of open water, and saturated soil. The application of this information in water man agement is for better control of first-year runoff from the pine-cypress la ndscape as a whole. Furthermore, silvicultural Best Management Practices fo r cypress wetland water management need to consider a variable source area for surface-water pollution that is larger than the wetland area as defined by the vegetation.