RIVERS AND BEAVER-RELATED RESTORATION IN COLORADO

Scamardo, Julianne

ABSTRACT: Interest in beaver-related restoration, such as reintroduction and dam analogs, for repairing incised and degraded streams is apparent across the American West. North American beaver (Castor canadensis) were historically abundant across their ecological range, and headwater streams across the U.S. likely held many beaver dams in the channel and on the floodplains. Beaver dams can effectively trap sediment, water, and solutes, and a thriving beaver meadow can have implications for biodiversity and carbon storage. After historical declines in populations throughout the 19th and 20th century, enthusiasm for reintroduction and dam analogs has grown for naturally restoring degraded streams that once housed beaver. To guide enthusiasm in the State of Colorado, understanding (i) where reintroductions are viable and (ii) how beaver dam analogs change stream morphology and hydrology is critical. This study tackles those two objectives by modeling potential dam densities in 63 watersheds across Colorado as well as monitoring beaver dam analog restoration projects in two watersheds in the Colorado Front Range. While density models may not be accurate at small scales, regional patterns in dam density across Colorado suggest that many streams can still support beaver populations despite larger decreases from historic dam densities. Reintroductions could spur vegetation growth and create side channels through overbank flow, which would increase the capacity of a given stream to support beavers. On streams where densities are low or have been reduced to no beaver capacity, beaver dam analogs could be installed to aggrade channels and create ponds. Unlike natural beaver dams, the beaver dam analogs monitored here did not create a groundwater response within the first year of restoration, which could be a limitation to restoration projects hoping to increase riparian vegetation. However, this study only covers the first year post-restoration and long-term restoration outcomes could differ from the short-term. In the future, smaller scale watershed modeling and site visits to watersheds or streams with high modeled dam densities are necessary to determine precise stream reaches that are prime for reintroductions. Additionally, post-restoration studies that extend over a longer time frame and include more watersheds are needed to fully understand the magnitude of change post-beaver-related restoration.