Examining Wetland Frequency Discrepancies Produced by Data Collected at Wetland Boundaries and across the Landscape: Using Tsuga canadensis (L.) Carr. (Eastern Hemlock) as a Case Study

Abstract : This study examined two types of data for determining a species wetland frequency and rating during rating-change-request challenges to the National Wetland Plant List (NWPL). Tsuga canadensis (L.) Carr., a species with a problematic wetland rating, was used as a case study. Boundary data were collected on wetland boundaries during delineations by Corps regulators and private consultants, and Landscape data were collected across the landscape during vegetation research projects by the Cold Region Research and Engineering Laboratory team. This investigation compared the wetland frequencies and ratings produced by Boundary data and Landscape data across a large and a moderately large study area. In both study areas, the Boundary data produced a higher wetland frequency (36 40 ) and a wetter wetland rating (Facultative FAC) than the Landscape data (15 18 , Facultative Upland FACU). These results demonstrate why wetland delineation data should not be used for determining wetland frequency and ratings during challenges to the NWPL because (1) they do not represent a species entire distribution across the landscape; (2) only dominant species are recorded on delineation data forms; (3) large, adjacent boundary plots are statistically likely to produce a FAC rating; and (4) delineation data are difficult to access from both regulatory agencies and public sector environmental consulting firms.