Oral Presentation Society for Freshwater Science 2026 Annual Meeting

Multiyear stream and riparian responses to beaver dam analogs in a headwater tributary (136048)

Hannah Halvorson 1 , Lisa Eby 1 , Andrew Lahr 2
  1. University of Montana, Missoula, MONTANA, United States
  2. Northern Rocky Mountain Science Center, US Geological Survey, Missoula, Montana, United States of America

Beaver are ecosystem engineers with well-established influences on the geomorphology and hydrology of streams, as well as riparian vegetation. Beaver-related restoration has become a common approach with techniques such as beaver dam analogs (BDAs) commonly used to aid in the recovery of stream ecosystems. These restoration projects are being frequently implemented, yet the practice has outpaced the sciencea. A need for monitoring across a range of stream conditions and broader temporal scales has been identifiedb, as few published studies evaluating their impact >3 years exist. We conducted a Before, After, Control, Impact study on a restoration project in Teepee Creek, a second-order stream near Lolo in Western Montana. We collected data on instream habitat, stream discharge, water temperature, and riparian vegetation in the summers of 2019 (pre-restoration) and 2025 which was 6 years post-project implementation. This project was periodically maintained over the study period. Six years after the BDA project, we observed evidence of erosion and depositional processes that promote an inset floodplain. Specifically, we quantified decreased bank stability compared to the control reach and a doubling of undercut banks in the restored reach while undercut banks decreased in the control reach. The restored reach showed more heterogeneity in instream habitat characteristics, with an increase in islands, bars, and wood in the stream. Large woody debris and wood aggregates increased 5 times more in the restored reach compared to the control reach. In addition, we observed a 4% increase in woody vegetation and 15% increase in sedges in the restored reach, while the riparian vegetation composition remained relatively similar across this time period. Additionally, the BDA reach supported greater water retention later into the year compared to the upstream control, and temperatures showed no significant warming or cooling as water flows through the restored reach. Overall, beaver dam analogs supported more surface water and longer residence times, increased presence of woody shrubs and sedges in the riparian, and greater heterogeneity in instream habitat. This case study demonstrates the progression of a restoration project over 6 years, highlighting that many of the expected changes associated with low-tech, beaver-based restoration are occurring.

  1. A- Pilliod, D. S., Rohde, A. T., Charnley, S., Davee, R. R., Dunham, J. B., Gosnell, H., ... & Nash, C. (2018). Survey of beaver-related restoration practices in rangeland streams of the western USA. Environmental management, 61(1), 58-68.
  2. B- Nash, C. S., Grant, G. E., Charnley, S., Dunham, J. B., Gosnell, H., Hausner, M. B., ... & Taylor, J. D. (2021). Great expectations: Deconstructing the process pathways underlying beaver-related restoration. BioScience, 71(3), 249-267.