Predicting Potential Beaver Dam Sites on Lake Superior's North Shore

Abstract

Beavers (Castor canadensis) play a substantial role in coastal Lake Superior ecosystems, as the creation of beaver dams and ponds results in riparian habitat that can be vastly different from habitats before beaver activity (Naiman et al. 1988, Rosell et al. 2005). Beaver dams can influence water temperatures, flow regimes, channel morphology, and sediment dynamics (Gurnell 1998, Pollock et al. 2003, Westbrook et al. 2006, Burchsted et al. 2010, Bouwes et al. 2016). Understanding where beavers are likely to build dams and ponds has many practical implications for resource managers and citizens. Current climate models have predicted an increase in the prevalence of extreme precipitation events that may cause an increase in erosion and flooding events in the North Shore (Herb et al. 2016). Beaver dams have been shown to mitigate the downstream effects of high-precipitation events by reducing stream energy and increasing water retention time (Law et al. 2016, Puttock et al. 2017, Karran et al. 2017); their presence in the North Shore may be an important natural mechanism for minimizing impacts from natural hazards. But they also may have an adverse effect on fisheries, particularly steelhead (Oncorhynchus mykiss) and brook trout (Salvelinus fontinalis) (Johnson-Bice et al. 2018), leading to controversy within coastal communities and complex management decisions. The goal of this study was to create a model that predicts potential beaver dam locations based on existing habitat characteristics, stream gradient, and stream power and flow estimates. Building from an existing data set that includes spatial information of beaver-created wetlands within five North Shore watersheds, we also conducted a rapid assessment of water and sediment storage contained within beaver ponds across the North Shore. The key deliverables of this project are: ● An interactive online map showing historic and potential beaver dam locations ● Estimates of water and sediment storage in North Shore beaver wetlands ● A downloadable spatial database of existing and predicted beaver dam locations, with FGDC-compliant metadata ● This report describing methods, results, and interpretations These products will be important for resource managers that make land-use decisions based on current and future hydrologic and sediment pathways in Lake Superior tributaries.