Wetlands Research Program. Evaluation of Methods for Sampling Vegetation and Delineating Wetlands Transition Zones in Southern Louisiana, January 1979-May 1981

摘要

Nine study sites in the Mississippi Delta region of Southern Louisiana, representing both freshwater and brackish marshes and freshwater swamps, were studied in order to develop techniques for wetland delineation. In Phase I, numerous methods were evaluated for sampling trees, shrub, and herbaceous layers in three sites dominated by each of the different strata. Phase II consisted of field verification of the selected methods in terms of adequate sample size, efficiency, accuracy, and ability to delineate transition zones at six additional wetland sites. Testing of the recommended methods resulted in a recommended sampling strategy based on a series of transects at each site composed of contiguous quadrats to determine density. The line-intercept modification was recommended for determining cover. Although most stands in the region were found to be similar in type and composition, variability among sites and patterns of zonation was great enough that criteria based on structure could not be established to delineate zones of transition. Several vegetative criteria, including total abundance patterns, species density, species composition trends, indicator species groups, and continuum indices were evaluated as delineation criteria. On the basis of the results at the Phase II study sites, continuum index ranges were proposed to delineate wetland, transition, and upland zones in Louisiana. These ranges were found to allow consistent interpretations among results from three vegetation strata.