Karst wetlands of The Barrens: Geomorphic control of wetland hydrology and plant distribution on the highland rim of Tennessee

Karst wetlands are widely distributed throughout the southeastern United States and support a wide variety of distinct plants and animals far from their normal ranges. Previous studies conclude that the ecological distinctiveness of these wetlands reflects their geomorphic and hydrologic characteristics. However, few studies provide detailed information on these characteristics or their interaction with biota. This investigation documents the geomorphology, water regimes, and tree distribution patterns of several karst wetlands in The Barrens of central Tennessee. Methods used in the study include: cartographic analysis of bedrock geology, topography and wetland distribution; field examination of landforms and hydrologic processes; monitoring of water levels in seasonally flooded karst depressions and nearby wells; and tree-species identification and tree-diameter measurements along transects through depressions and interconnecting channels.; The geomorphology of The Barrens reflects the variable lithologies of the underlying, gently dipping limestones. Factors that produce low relief and poor drainage include thick, impermeable residuum, high primary porosity, high concentrations of non-carbonate minerals, and limited carbonate-aquifer thickness. Three landform types closely associated with wetlands are karst pans, compound sinks, and intermittent drainageways. Karst pans are distinguished from compound sinks by relatively shallow depth and absence of visible internal drains. Intermittent channels include broad, poorly defined swales and more distinct channels with bank heights typically less than 1 meter. Both types of drainageway typically carry flow during the late fall and winter.; Compound sinks rise and recede abruptly, have maximum flooding depths exceeding 2.5 meters, and are closely connected to the ground-water system. Pans flood and recede more gradually, have maximum flooding depths less than 1.5 meter, and are perched above the water table. Transects through compound sinks and pans have fewer trees but more basal area per unit area of land surface than transects through channels. Sampled pond interiors are dominated by a single obligate or facultative-wet tree species. Transects across broad swales have a large degree of vertical zonation, with facultative species preferentially colonizing the swale bottoms. Transects across well-defined channels show little vertical zonation among species.