Beaver Library

Climate change will diminish the quality and connectivity of stream and riparian habitats and threaten native stream-associated species across western North America. Ecological restoration that mitigates these impacts and supports processes that confer adaptability is urgently needed. The ecosystem engineering capabilities of beaver (Castor canadensis) are increasingly applied (through beaver reintroductions and beaver mimicry) in ecological restoration to reestablish ecosystem processes. However, there are no systematic syntheses on the impacts of beaver-related restoration (BRR) at the regional scale that incorporate both beaver and beaver mimicry or highlight key climatic and ecological contexts where BRR may be most impactful. We conducted a comprehensive literature review focused on BRR’s influence on habitat and biodiversity attributes that confer climate resilience in western North America. Using 161 sources, we assigned confidence scores for specific outcomes and identified climatic and hydrogeomorphic contexts where BRR may be most impactful at building climate resiliency. There is substantial evidence that BRR increases climate resiliency of stream and riparian ecosystems by reducing summer water temperatures, increasing water storage, and enhancing floodplain connectivity. BRR can ameliorate negative impacts of high-flow events, create fire-resistant habitat patches, and foster heterogeneous habitat mosaics that enhance watershed-level biodiversity of aquatic and riparian ecosystems. However, these benefits are only likely to accrue under certain climatic and hydrogeomorphic conditions, and we highlight the deficit of peer-reviewed literature at the spatial and temporal scope necessary to bridge our understanding of the expected potential and the realized benefits of BRR.

This report reviews published research and unpublished case study information on the effects ofrestoring incised and degraded headwater streams in western states with low-tech processbased restoration methods (LTPBR). LTPBR is a subset of process-based restoration (PBR) that seeks to re-establish natural stream processes by reconnecting incised streams with their floodplains and adjacent wetlands so that more frequent inundation of the floodplain occurs. Projects involve the use of simple, temporary, hand-built wood and rock structures that mimic
natural beaver structures, acting as speed bumps that capture sediments to aggrade the stream. LTPBR approaches are substantially less expensive than form-based stream restoration approaches that employ heavy equipment.i This approach is appealing in part because low project costs enable implementation at a scale that can respond to the extent of floodplain alteration, which is estimated at 45% of headwaters streams in Colorado. ii Negative effects of disconnected floodplains include lower groundwater tables, lower summer base flows,
warmer water temperatures, and substantial loss of riparian habitat.