The Nature Conservancy (TNC), with funding from the National Fish and Wildlife Foundation, lead a study to assess the potential to incorporate beaver and beaver-dam analogs into habitat restoration in the Sierra Nevada. This includes models of beaver dam capacity and human-beaver conflict potential for stream reaches in the Sierra Nevada using the Beaver Restoration Assessment Tool (BRAT).
StoryMap
Project Area & Regions
Project Goals
The backbone to BRAT is a capacity model developed to assess the upper limits of riverscapes to support beaver dam-building activities. It outputs an estimated density of dams (i.e. dams per length of stream) and a rough count of an upper limit (i.e. capacity) of how many dams the conditions in and surrounding a reach could support.
The objective of using BRAT in this project was to help meadow and stream restoration practitioners identify the most appropriate locations for beaver-assisted restoration projects.
Further information can be found on the BRAT website in the TNC BRAT folder.
The objective of using BRAT in this project was to help meadow and stream restoration practitioners identify the most appropriate locations for beaver-assisted restoration projects.
Further information can be found on the BRAT website in the TNC BRAT folder.
Findings
The beaver dam capacity model was run for existing conditions and estimates existing capacity at 715,548 dams, or roughly 6 dams/km.
The same model driven with estimates of historic vegetation types estimated the capacity at 1,398,540 dams, or roughly 11 dams/km.
This reflects the existing capacity at a 49% loss compared to the historic capacity.
Nearly all of the capacity loss from historic conditions can be explained in terms of riparian vegetation loss, vegetation conversion and degradation associated with high intensity land use including:
- conversion of valley bottoms to urban and agricultural land uses,
- overgrazing in riparian and upland areas, and
- conifer encroachment of wet meadow areas.
Despite the losses in beaver dam capacity, California’s waterways are still capable of supporting and sustaining a substantial amount of beaver dam-building activity (715,548 dams).
The same model driven with estimates of historic vegetation types estimated the capacity at 1,398,540 dams, or roughly 11 dams/km.
This reflects the existing capacity at a 49% loss compared to the historic capacity.
Nearly all of the capacity loss from historic conditions can be explained in terms of riparian vegetation loss, vegetation conversion and degradation associated with high intensity land use including:
- conversion of valley bottoms to urban and agricultural land uses,
- overgrazing in riparian and upland areas, and
- conifer encroachment of wet meadow areas.
Despite the losses in beaver dam capacity, California’s waterways are still capable of supporting and sustaining a substantial amount of beaver dam-building activity (715,548 dams).
Existing Capacity (Truckee Watershed)
Customizations for this project
TNC staff extended the BRAT model to include strategy outputs/maps that were used to identify opportunities for conserving existing beaver populations, areas suitable for promoting the growth of dam building beaver populations, and identifying areas that would require restoration prior to promoting beaver.
TNC staff and project partners also provided detailed review of preliminary BRAT data and we incorporated their suggested changes into the model. This resulted in improvements to the risk, limiting factors, and restoration and conservation outputs.
TNC staff and project partners also provided detailed review of preliminary BRAT data and we incorporated their suggested changes into the model. This resulted in improvements to the risk, limiting factors, and restoration and conservation outputs.
TNC BRAT Deliverable Data Products include:
This project consisted of implementing BRAT across the entire project area. This included calibration, validation and refinement of the BRAT models based on feedback from TNC and project partners.
Deliverable data products include:
- Developed and ran BRAT on the perennial portion of the 1:24K NHD network (60,484 miles) segmented at 300m including:
- Existing (based on 2014 LANDFIRE data, the most current data available) beaver dam capacity estimates (dams /km)
- Historic beaver dam capacity estimates(based on LANDFIRE BPS data (dams /km)
- Potential for human beaver conflict (probability)
- Refine conflict model. This resulted in a model that assesses risk and opportunity for using beaver in conservation and restoration.
- Calibration and validation of BRAT performance using a web-map based inventory of existing beaver dams and field based data collection of dam locations, and
- Interpretive report with management recommendations and a draft manuscript for peer-reviewed publication. The manuscript will be developed and co-authored in collaboration with TNC and partners on the results of the BRAT model and their implications for beaver-based restoration in the Sierra Nevada, Cascades, and Klamath Mountains of California.
Deliverable data products include:
- KMZ of each of four primary BRAT outputs (existing capacity, historic capacity, risk, limiting factors, and conservation and restoration opportunities)
- Shapefiles and layer packages of each of four primary outputs (existing capacity, historic capacity, risk, limiting factors, and conservation and restoration opportunities)
- Posting of existing and historic beaver dam capacity output layers to public website
- Full interpretive report with management recommendations
- Priority watershed-wide virtual inventory of existing beaver dams as KMZ
- Atlas of BRAT outputs
- Draft manuscript
