Associate Professor Utah State University, Utah, United States
Abstract: Processed-based stream restoration with beaver-mimicry and beaver relocation is an increasingly popular strategy to improve ecosystem functions, processes and resiliency across North America and Europe. We wished to better understand the impacts of beaver-mediated restoration to a rapidly urbanizing stream system near Park City, UT, USA by assessing the impacts of two beaver dam analog (BDA) projects relative to control reaches and a natural beaver dam complex. Our goals where to understand how BDAs impact stream ecosystems relative to control reaches and compare BDAs natural beaver complexes. We investigated the effects of BDA treatments to the fish community, sediment budgets, water depths, water temperature, and riparian productivity using a variety of survey techniques. We monitored our sites 6 sites (2 BDA, 1 beaver complex, and 3 control reaches) for 1 year prior to BDA installation and 2 years after installation wherever possible.
Low flows were common throughout our 2019-2021 study period, with only 2019 having mean annual flows above 0.75 cubic meters / second. The fish communities were different between site types, with brown trout (Salmo trutta) being more abundant in beaver dams than BDA or control reaches. Meanwhile, Utah sucker (Catostomus ardens) adults were most abundant in control reaches. Mean growth rates of brown trout were 0.3 g/day in natural beaver dams but less than 0.25 g/day in both BDA and control reaches. Control sites had a mean wetted area of 562m2 and a mean depth of 0.19m, while BDA sites had a mean wetted area of 943m2 with mean depths of 0.37m. The natural beaver sites had a wetted area if 1429m2 and a depth of 0.46. We found no significant differences between our control and BDA reaches with respect to sediment budgets (p-value = .42), which can be likely attributed to the low flows experienced during our study period. Installation of the BDAs had limited impacts on the water temperatures across the sites, with similar patterns of warming across sites during the before and after periods. Growing season primary productivity averaged 0.2 NDVI higher at BDA locations relative to their controls after installation, with the most notable gains occurring during late summer and early fall. Overall, BDAs appeared to be emulating some of the ecosystem functions and processes without fully capturing the suite of ecosystem modulations that natural beaver dams provide.
