Castor canadensis (Beaver) impoundment associated with geomorphology of southeastern streams

We used a geographic information system (GIS) and logistic regression to investigate relationships between geomorphology and Castor canadensis (North American beaver) impoundment of lower-order, blackwater streams of a southeastern landscape. Using GIS, we divided streams into 632 500-m reaches and measured a set of geomorphic variables for each reach. Beavers were most likely to impound stream reaches crossed by roads with a gradient of ≈ 0.6 to 1.2% and watershed sizes of ≈ 2500 ha; reaches with watershed sizes < ≈ 500 ha or > 5000 ha were almost completely avoided. Gradient and road crossings contributed little to discrimination among impounded and unimpounded reaches, suggesting these variables had relatively small influences on beaver impoundment when compared to stream size. Our results indicate that GIS and geomorphic variables can be used to model the impoundment of streams over larger areas (e.g., the proportion of third-order watersheds impounded), but are less accurate at predicting the impoundment of individual reaches. However, the temporal dynamics of impoundment creation and abandonment will need to be incorporated into region-specific models before they can be used in ecosystem integrity assessment.