Using beaver to reconnect floodplains and restore riparian habitat in an incised stream

摘要

We report results from a long-term restoration and monitoring program to help recover riparian and stream habitat in the John Day basin in eastern Oregon. We use a novel restoration technique, working with beaver (Castor canadensis), to restore an incised, degraded high desert stream that has a small native steelhead {Oncorhynchus mykiss) population. We hypothesize that beaver build dams that, if they remain intact, will substantially alter the hydrology, geomorphology and sediment transport within the riparian corridor. Our restoration strategy is to provide beaver with low-cost instream structure so they can build stable dams, and also to create structures that mimic certain aspects of beaver dams in sites where vegetative or geomorphic conditions are not currently ideal for beaver colonization. The long term goal is to convert a linear, entrenched, simplified stream into a sinuous, structurally complex stream that is reconnected to its floodplain, resulting in a substantial expansion of riparian vegetation and improved instream habitat. We treated four reaches and compared them to four controls where no restoration occurred. Observations to date suggest that beaver dams: 1) increase floodplain connectivity, 2) raise water tables 3) increase the extent of riparian vegetation, 4) increased pool frequency and depth, 5) increase stream sinuosity and sediment sorting and 6) lower stream temperatures. Although we only have one year of post treatment data, initial results suggest that in treated reaches, the physical characteristics of the riparian corridor are generally moving towards our desired goals relative to untreated control reaches.