A wet meadow restoration project along Sylvies River, Oregon. Photo courtesy of Caroline Nash.
Findings help managers set realistic expectations for stream restoration in the Western United States, and are being utilized in new legislation to promote stream restoration in eastern Oregon.
Stream and watershed restoration is a multi-billion dollar enterprise globally, and a major focus of federal land managers and specialists throughout the Western United States. Many of these efforts target upland valley floors where streams have deeply incised their channels, turning previously wet meadows into dry, flat terraces. Common strategies to restore wet meadows typically involve raising channel beds back to their former levels by various means, including constructing artificial beaver dams. An oft-cited benefit for this type of restoration is that by raising channel beds, late-summer streamflow will increase. An interdisciplinary team of scientists assessed beaver-related restoration projects in western rangelands through both field studies, hydrogeological modeling, and using remote sensing along with climate data. They looked at how these restoration practices affect hydrology, plant biodiversity, fish communities, and socioeconomic dynamics in the region.
They found that restoring incised channels by raising their beds did not increase streamflow. In fact, diminished summer streamflows can be expected owing to increased evapotranspiration by riparian and meadow vegetation. Overall, water storage increases in restored systems because of higher water tables, but this did not notably increase discharges to streams. The raised water tables do contribute directly to increased availability of water for vegetation, however, with many concurrent habitat and temperature benefits to streams.
After evaluating 97 restoration projects, they found that beaver-related restoration has outpaced research on its efficacy and best practices. Additional research is necessary to inform clear guidelines for best practice.