ECOTONE DYNAMICS AND BOUNDARY DETERMINATION IN THE GREAT DISMAL SWAMP

Data on hydrogeology, soils, and vegetation collected on four transect s across the 48-km wetland-to-upland transition zone of the Great Dism al Swamp of Virginia/ North Carolina, USA, were used to analyze change s along the moisture/elevation gradient, to characterize the wetland-u pland ecotone, and to select tentative wetland-upland boundaries based on these three parameters. Transition zone vegetation was dominated b y three facultative hydrophytes: Acer rubrum, Liquidambar styraciflua, and Nyssa sylvatica. On the basis of ordination performed on consecut ive 25-m transect increments, each transect was divided into three zon es: wetland, ecotone, and upland. The water table was within the root zone (0-30 cm below the ground surface) an average of 25-100% of the g rowing season at all well sites in wetland, <25-100% for most well sit es in the ecotone, and <25-50% for well sites in upland. Soils were hy dric in the wetland and ecotone, and histosols were found only in the wetland zone. Soils were generally nonhydric in the upland zone. Wetla nd boundaries determined on the basis of each parameter differed; they were within 38 m horizontal distance and 1.1 m vertical distance on t he transects where all three boundaries could be determined. These bou ndaries were relatively close considering the length of the transects, the coarse resolution of the soils and hydrology data, and certain as sumptions made during the analysis. On one of the remaining transects, the hydrology and soils boundaries differed by > 100 m horizontal dis tance and 0.4 m vertical distance. Only a vegetation boundary was esta blished on the fourth transect.