| The Okefenokee Swamp is one of the largest freshwater wetlands in the world. Currently protected and managed as a national wilderness area and national wildlife refuge, the swamp has a history of human-caused manipulation and modification. The swamp landscape is dynamic; vegetation compositions and distributions continually change as the hydrologic environments change. These dynamics are driven by natural processes such as peat accumulation and wildfire, as well as the artificial manipulations of the recent past.; The Suwannee River sill was constructed following extensive wildfires during 1954–1955, with the intent of protecting the swamp and surrounding uplands from effects of wildfires. During subsequent years, concern was raised that the dam might be adversely affecting the swamp, ecology by extending periods of inundation, increasing water depths, and subsequently affecting swamp vegetation. Delineating the effects of the Suwannee River sill on the swamp hydrologic environment and vegetation distributions, in the process of exploring relationships among driving functions and landscape responses, was a purpose of this dissertation research.; Data collected at various spatial and temporal scales were examined to identify the sill's effects. A water level recorder network was spatially linked with a global positioning system survey, and the resultant topographic surface and hydrologic data were included in a grid-cell based hydrology model to track water movement throughout the swamp. Model simulations illustrated swamp water level fluctuations before and after the sill was in place, and predicted recent hydrologic history in the sill's absence, as well as sensitivities of swamp hydrology to altered evapotranspiration rates. Model simulations also predicted that the sill was affecting about 18% of the swamp area with increased inundation depths and durations, and vegetation change attributed to the sill was limited to this area.; Vegetation dynamics were also assessed at several scales, with remote sensing techniques, species-hydroperiod descriptions, and seed bank analysis and hydrologic manipulation. Current vegetation distributions are artifacts of historic logging and recent lack of fire, and also show sensitivity to local hydrologic environments. Inundation depth and hydroperiod create hydropatterns that influence species distributions. The swamp landscape is an expression of local dynamics, coupled with landscape-level processes such as fire, drought, and extensive historic logging occurring at multiple temporal scales. |
