To calculate the effect of beaver activity on species richness of the riparian zone at the landscape scale, one must first estimate the species richness of a landscape without beaver-modified habitats, and then of an equally sized area with beaver-modified habitats. The difference between the species richness of the landscape with a mix of beaver-modified and forest plots and the landscape composed of only forest plots provides an estimate of the contribution of beaver-modified areas to the total species richness of the riparian zone. Estimates of species richness of forest plots were calculated using all forest plots in the data set, and estimates for the beavermodified plots were calculated using all meadow and alder plots in the data set. Estimates for total riparian zone richness were drawn from a data set constructed using data from all three habitat types. We used estimates of the relative abundance of each habitat type in the landscape, as generated from aerial photograph analysis (see below), to determine the relative abundance of beaver-modified habitat and forested habitat in the constructed data set. All estimates of species richness were rarefied to correct for differences in sample pool size and represent the mean richness of 50 runs of the Coleman rarefaction estimate for 120 plots (Colwell 1997).