Ground-water-table rise after forest harvesting on cypress-pine flatwoods in Florida

Forest removal represents one of the large-scale ecosystem disturbances tha t concern water quality degradation, species composition change, and wildli fe habitat alteration along the Florida coast. We conducted a five-year stu dy with the objective to address effects of two forest management scenarios on the water regimes of cypress-pine flatwoods ecosystems in the lower coa stal plain. Three experimental blocks (16-21 ha) were used in this study, w ith one representing control (C), one wetlands-harvest-only (W), and one we tlands + uplands harvest (ALL). Within the center of each block, a represen tative cypress wetland and its surrounding pine upland were extensively ins trumented to quantify the changes of each hydrologic variable induced by tr ee removal. Water levels in cypress wetlands in both treatment areas were s ignificantly elevated about 32-41 cm on average, and outflow doubled in the five-month dry period immediately following the tree harvesting. The groun d-water table in the upland was also raised by about 29 cm on average due t o ALL, but it was not affected significantly during the entire post-treatme nt period by W. During wet periods, the: treatment effects for both wetland s and uplands were not significant. Causes for spatial and temporal variabi lity of hydrologic responses to forest harvesting are speculated to be 1) t otal evapotranspiration does not change significantly in flatwoods after tr ee removal during wet seasons; 2) specific yield of the flatwoods soils is variable in time and space; and 3) lateral water movement from uplands to w etlands. From this study, we conclude that harvesting both uplands and wetl ands causes greater response than harvesting wetlands only. The impacts las ted for more than two years but were most pronounced only in the dry period s. Temporal and spatial variations of each hydrologic component should be c onsidered in evaluating the hydrologic impact of forest management on the f latwoods landscape.