Data on hydrogeology, soils, and vegetation collected on four transects across the 48-km wetland-to-upland transition zone of the Great Dismal Swamp of Virginia/ North Carol_ina, USA, were used to analyze changes along the moisture/elevation gradient, to charactenze the wetland-upland ecotone, and to select tentative wetland-upland boundaries based on these three parameters. Transition zone vegetation was dominated by three facultative hydrophytes: Acer rubrum, Liquidambar styraciflua, and Nyssa sylvatica. On the basis of ordination performed on consecutive 25-m transect increments, each transect was divided into three zones: wetland, ecotone, and upland. The water table was within the root zone (0-30 em below the ground surface) an average of 25-100% of the growing season at all well sites in wetland, <25-100% for most well sites in the ecotone, and <25-50% for well sites in upland. Soils were hydric in the wetland and ecotone, and histosols were found only in the wetland zone. Soils were generally nonhydric in the upland zone. Wetland boundaries determined on the basis of each parameter differed; they were within 38 m horizontal distance and 1.1 m vertical distance on the transects where all three boundaries could be determined. These boundaries were relatively close considering the length of the transects, the coarse resolution of the soils and hydrology data, and certain assumptions made during the analysis. On one of the remaining transects, the hydrology and soils boundaries differed by >100m horizontal distance and 0.4 m vertical distance. Only a vegetation boundary was established on the fourth transect.

A weighted average method was used to analyze transition zone vegetation in the Great Dismal Swamp to determine if a more uniform determination of wetland boundaries can be made nationwide. The method was applied to vegetation data collected on four transects and three vertical layers across the wetland‐to‐upland transition zone of the swamp. Ecological index values based on water tolerance were either taken from the literature or derived from local species tolerances. Wetland index values were calculated for 25‐m increments using species cover and rankings based on the ecological indices. Wetland index values were used to designate increments as either wetland, transitional, or upland, and to examine the usefulness of a provisional wetland‐upland break‐point. Most increments were designated wetland or transitional when all species were used. Removal of three or five ubiquitous species either gave a wider range of wetland index values with a more variable designation of increments or caused designation of increments to be similar for all layers. The use of locally‐derived rankings showed the sensitivity of the weighted averages method to ecological indices of species with large importance values. The weighted average method did not provide for an objective placement of an absolute wetland boundary, but did serve to focus attention on the transitional boundary zone where supplementary information is necessary to select a wetland‐upland breakpoint.

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Both color infrared aerial photography and Landsat data are being used to provide information to meet present and future management goals for the Great Dismal Swamp National Wildlife Refuge. High and low altitude color infrared photographs are being used to study the hydrology and map the present vegetation of the swamp. A variety of significant ecologic units have been identified using these photographs. The completed maps will be used to evaluate analyses of landsat digital data. Once the present data base is compiled, it is hoped that routine analysis of Landsat data can be used for updating or to indicate areas where low altitude coverage or ground checking is desirable. The data base will also aid in identifying and evaluating trends that may provide guidelines for wetland management.