AUTHORS: Carol A. Johnston*, South Dakota State University; Nancy E. McIntyre, Texas Tech University
ABSTRACT: Agricultural expansion is a documented source of wetland area loss in the Dakota Prairie Pothole Region (DPPR), which could potentially affect the distribution of wetlands in the landscape and their accessibility to fauna with limited mobility. Using an existing map of DPPR wetland losses derived from the 2001 USGS National Land Cover Dataset and the 2011 USDA Cropland Data Layer, we analyzed the number, size, and connectivity among prairie pothole wetlands, comparing sampled quadrangles having a priori-defined high and low wetland loss rates. Connectivity was assessed using a suite of graph theoretic metrics. We expected that wetland density (i.e., the number of wetland patches per unit land area) would decrease with wetland areal loss and that the network’s coalescence distance would increase as wetlands became more sparse and separated from each other, which would be reflected in changes in metrics that quantify degree of linkages among wetlands and overall network connectedness. We found that average area per wetland decreased in quadrangles with high areal losses of wetlands (12 to 38% loss of wetland area between 2001 and 2011), but that wetland density and wetland connectivity did not change significantly in high or low loss quadrangles. Areal losses rarely resulted in total wetland elimination, instead subdividing and “nibbling away” at the edges of wetlands. This spatial pattern of wetland loss may reduce the impacts to organisms that must traverse the landscape from patch to patch, but may be more difficult to detect because it is so diffuse.
