Beavers are recognized for their ability to restore floodplain hydrology and biological function, yet finding suitable places for their reintroduction remains a conservation challenge. The goal of this study was to identify places in the Snohomish River basin of Washington state suitable for beaver reintroduction.
Because of their abilities to modify streams and floodplains, beavers have the potential to play a critical role in shaping how riparian and stream ecosystems respond to climate change. The Pacific Northwest of the United States is experiencing increases in annual air temperature and decreases in snow pack and summer precipitation, resulting in lower base flows, particularly in streams that rely on late season snowmelt. Climate shifts have altered stream-temperature regimes to the detriment of cold-water fishes, including Pacific salmon. Recent increases in winter precipitation and storm magnitude have increased the potential for stream scour, channel incision, and floodplain disconnection, thereby promoting the drying of adjacent riparian areas [Dittbrenner 2018: 2].
By damming streams, beavers create pond and wetland complexes that increase spatial heterogeneity and geomorphic complexity, species and habitat diversity, and therefore ecosystem resilience to climate-induced environmental change. Beaver impoundments slow stream velocity allowing sediment suspended in the water column to settle, aggrading incised stream systems, and reconnecting streams with their floodplains. The increase in surface water promotes groundwater recharge, storage, and supplementation during base flows. The increased geomorphic complexity also promotes higher thermal variability and coldwater refugia in deeper waters and in areas of downstream upwelling [Dittbrenner 2018: 2].
To qualify as a suitable site for beaver reintroduction, a site needs to be intrinsically suitable beaver habitat and clear of competing human interests.
Of 5,019 stream km assessed in this study, just 33% had moderate or high intrinsic potential for beaver habitat. “Of the riparian areas around streams with high intrinsic potential for beaver, 38% are on public lands and 17% are on large tracts of privately-owned timber land” [Dittbrenner 2018: 1], while the rest was on human-dominated landscapes (agricultural, industrial, residential, etc.). Thus, the areas available for beaver reintroduction are limited. Even so, the authors argue that beavers can play a critical role in adapting to climate change, and they propose that watersheds dominated by public ownership, “provide ample opportunities to test how beavers can be reintroduced into landscapes where they are absent or at low population levels” [Dittbrenner 2018: 11].
Dittbrenner, Benjamin J., Michael M. Pollock, Jason W. Schilling, et al., 2018, Modeling intrinsic potential for beaver (Castor canadensis) habitat to inform restoration and climate change adaptation, Plos One, https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0192538.