Ecotone characterization between upland longleaf pine/wiregrass stands and seasonally-ponded isolated wetlands

We examined the physical and ecological characteristics of ecotones between longleaf pine/ wiregrass upland and seasonally-ponded isolated wetlands dominated by herbaceous species in a fire-maintained, karst landscape of southwestern Georgia. The purpose of this study was to 1) examine patterns of plant species richness across the upland/wetland transitional zone relative to elevation and moisture gradients; 2) identify discontinuities (boundaries) of soil morphological characteristics, soil moisture, soil nutrient availability, and vegetation and their spatial relationships in the ecotone; and 3) examine the degree of coincidence of ecological thresholds with that of jurisdictional wetland/upland boundaries. Transects from upland to wetland were established relative to hydric soil boundaries for measurements of vegetation abundance, biomass, volumetric soil moisture, oxidation reduction potential, relative elevation, soil textural analysis by horizon, and available nitrogen and phosphorous. We used a moving windows analysis and multivariate analyses to examine ecological discontinuities in the ecotone. Ground-cover species richness was high along all transects with a peak in species richness in the non-hydric ecotonal zone. Abrupt changes in vegetation and environmental variables (soil moisture, soil depth to argillic horizon, and soil texture) were generally located below the hydric soil boundary and are likely related to frequent fire regimes. Discrepancies occurred in the determination of hydrophytic vegetation depending on methodology. These results have implications for the conservation of regional diversity, for depressional wetland restoration, and for regulatory decisions.