Climate change and fire suppression have altered historic fire regimes creating conditions for larger, high severity fires. Intense burns denude the landscape of vegetation, alter hydrology, cause mass erosion events, and impair riparian function. Burn severity varies based on topography and increases with distance from water sources like lakes, streams, and wetlands as higher energy levels are required to desiccate and eventually combust available fuels. Beaver (Castor canadensis) have an uncanny ability to dam streams, repair channel incision, divert water onto the floodplains and create wetland environments. The objective of this study was to assess whether beaver impoundments increase landscape resistance to wildfire by increasing riparian soil and vegetation moisture levels. We hypothesize that riparian areas impounded by beaver will have increased soil and fuel moisture throughout the fire season compared to riparian zones without beaver. To assess potential ignition and fire behavior, we collected soil and fuel moisture samples throughout the fire season, above, within and below 10 beaver impounded streams and 10 non-impounded reference reaches within the Methow Watershed, WA, USA. Soil moisture differences among transects and beaver/non-impounded sites were compared using a repeated measures analysis and general additive modeling. GIS analysis of post fire burn severity maps and infrared drone imagery examining plant water stress (NDVI) were included to support in situ soil and fuel moisture measurements.
Results/Conclusions
We found that beaver impounded sites contained higher average soil and dead fuel moisture levels than non-impounded sites throughout the fire season. We also found that beaver impounded areas maintained wetter soils at greater distances from the water source within the respective site. Unexpectedly, beaver dam presence was not associated with increased live fuel moisture content. We attribute this result to capabilities of riparian vegetation to access groundwater at great depths, regardless of beaver presence. These results suggest that beaver impounded riparia may have a higher capacity to withstand low to moderate burn events compared to non-impounded riparian zones. Beaver restoration could provide land managers with a low-cost method to increase riparian burn resistance on a watershed scale and help buffer the effects of a changing climate.