Michael Simpson, MS
Department of Environmental Studies
A comparison of two quantitative delineation techniques used for the delineation of bordering vegetative wetlands in Massachusetts was performed in a forested wetland in Marion, Massachusetts. Both quantitative techniques have been accepted as valid and conforming to the requirements of the Massachusetts Wetland Regulations by administrative law judges. One technique was relative dominance of wetland species by layers (RDL), which averages the percent cover of wetland plants for each vegetative layer. Using the RDL paradigm, plants are considered upland plants or wetland plants. The other method analyzed was the Wetlands Site Index (WSI). The WSI analysis establishes a wetness index based on the United States Fish and Wildlife Service plant list and the abundance of each plant. A group of wetland delineation experts also individually determined the edge of the wetland in their usual manner for delineating Bordering Vegetated Wetlands (BVW) in Massachusetts. Some of the experts used soils in their determination of the BVW edge while others used solely vegetation. Those experts who used vegetation alone had a quartile deviation (QD) of ten feet or less, 55% more often than the experts who used soils and vegetation. The BVW edge established by RDL was closer to the mean BVW edge derived from the experts analysis, and had a higher correlation to the mean BVW edge of the experts, than the BVC edge established by the WSI. For red maple, Acer rubrum, forested swamps the WSI must be modified to be an effective BVW delineation tool.