As a result of this high degree of dissimilarity between the engineered and unengineered habitat types, species richness (S) estimated by randomly sampling plots of all three habitat types was 1.33 times higher than richness estimated when drawing only from forest or beaver-modified plots (mean ± 1 SE:S=79.7±2.9 for all plots, S=59.9±0.3 for forest plots, and S=67.3±2.4 for beaver-modified plots) (Fig. 3). Beaver-modified habitat occupied 26.7% of the riparian zone of the HWF on a per unit length basis, with as many as 4.3 sites km–1 stream length in some drainages. In all, 151.5 ha of the HWF were classified as being either beaver meadow or alder habitat associated with beaver disturbance in 1997. An additional 45.4 ha were classified as active ponds that are likely to eventually develop into either meadows or alder habitat. Altogether, beaver had modified 3.21% of the study area in the 1997 aerial photographs. Of the 54 regulatory wetlands on the HWF that were reliably associated with known wetlands, 83.3% were associated with beaver activity. These beaver associated wetlands accounted for 92.2% of the 333.3 ha of reliable regulatory wetlands.