The Role of Beaver in Southwest Montana


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An overview of the role of beaver in stream condition in SW Montana

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  • The Role of Beaver in Southwest Montana

    1. 1. The Role of Beaver in Managing Sediment and Water in Southwest Montana W ATERSHED C ONSULTING , LLC
    2. 2. Historical Background <ul><li>Study in Colorado (Ives 1948) concluded many valleys previously thought to have been formed from glacial activity were actually formed by beaver (some by Pleistocene spp). </li></ul><ul><li>Geographic extent of beaver used to be much greater </li></ul><ul><ul><li>were common throughout North America and Europe </li></ul></ul><ul><ul><li>were in many areas now uninhabitable for beaver </li></ul></ul><ul><li>From 1810’s through 1830’s thousands of beaver trapped out of watersheds in the upper Missouri (and other times in less concentrated efforts). </li></ul>
    3. 3. <ul><li>Population estimates for Pre-Columbian times range from 60-400 million, or 10-60 beaver per stream mile; recent population estimate at 6-12 million animals (5-10% of previous population). </li></ul><ul><li>Another estimate (Mills 1913) of up to 200 beaver per square mile (pre-trapping). </li></ul><ul><li>When in the Three Forks area Lewis and Clark noted the streams “stretched away in a succession of beaver ponds as far as the eye could reach.” </li></ul>More History…
    4. 4. Signs of past activity
    5. 5. <ul><li>Food sources </li></ul><ul><li>Aspen is primary food- abundance of aspen the most significant factor of population density in many Rocky Mountain systems (Hubert and Olson) </li></ul><ul><li>Other foods: willow, cottonwood, alder, red-osier dogwood, aquatic plants, grasses, sedges, rushes. </li></ul><ul><li>Other requirements </li></ul><ul><li>Construction material- anything seems to do </li></ul><ul><li>Permanent, relatively constant flow of water (0.5 cfs min.) </li></ul><ul><li>Flat floodplain preferred- valley width over 150 ft optimal </li></ul><ul><li>Low gradient stream (<3% preferred but up to 15% used) </li></ul><ul><li>Adequate nearby habitat (cyclic nature of colonies) </li></ul>Habitat Requirements
    6. 6. Beneficial Influences of Beaver Activity <ul><li>Water Storage: Beaver moderate high stream flows and preserve summer flows by slowing drainage and keeping water in floodplain </li></ul><ul><li>Reduce channel erosion by preventing scour from flood waters and increasing wet floodplain vegetation </li></ul><ul><li>“ Flooding down the stream’s channel above the beaver pond, came a roaring avalanche of water…with a rubbish-filled front that was five or six feet high. …A half a dozen ponds immediately below sufficed so to check the speed of this water and so greatly to reduce its volume that as it poured over the last dam… it was no longer a flood.” (Mills 1913) </li></ul>
    7. 7. Upstream… … to Downstream. Beaver complex filtering water (Middle Fork Ruby River)
    8. 8. Beaver ponds trap sediment Beaver pond on Basin Creek trapping sediment from natural sediment source and grazing-related inputs. Ruined beaver pond on Indian Creek had trapped about 3 feet of sediment over a wide area.
    9. 9. <ul><li>More Benefits of Beaver </li></ul><ul><li>Raise water table/groundwater recharge in floodplain </li></ul><ul><li>Increase riparian vegetation </li></ul><ul><li>Trap sediment/filter water </li></ul><ul><li>Build meadows </li></ul><ul><li>Increase wildlife browse </li></ul><ul><li>Increase habitat for waterfowl and other birds </li></ul><ul><li>Retain nutrients </li></ul><ul><li>Diversify aquatic habitat </li></ul><ul><li>Increase fish biomass </li></ul><ul><li>Provide habitat for other furbearers </li></ul>
    10. 10. Potential Detrimental Effects of Beaver <ul><li>Cut down trees valued for aesthetics or shade </li></ul><ul><li>Plug culverts and flood roads </li></ul><ul><li>Dam irrigation ditches </li></ul><ul><li>Flood areas used for pasture or cropland </li></ul><ul><li>Can cause local temperature warming and increase bacteria </li></ul><ul><li>Some dams act as fish barriers </li></ul><ul><li>Beaver carry and spread Giardia- but may be species-specific </li></ul><ul><li>Abandoned dams sometimes break through and lead to downcutting- usually a case where habitat is reduced </li></ul>
    11. 11. <ul><li>Many detrimental effects are due to reduced habitat and colony size, as well as interface with human activities </li></ul><ul><ul><li>Beaver pond complexes are generally smaller than in past (due to fewer building sites, smaller workforce) and are less stable in flooding. </li></ul></ul><ul><ul><li>Riparian area cover is much lower than historic levels. Beaver have fewer places to build and less food – more likely to overuse resources. </li></ul></ul>
    12. 12. Current Local Research and Efforts <ul><li>University studies- influence of beaver on ground water, wildlife populations </li></ul><ul><li>Beaver live trapping and relocation initiated by USFS on experimental basis </li></ul><ul><li>Reintroduction of beaver to headwaters areas considered a potential restoration tool in several southwest MT watersheds </li></ul><ul><li>Recent preliminary modeling- AGWA </li></ul>
    13. 13. Summary of AGWA modeling results related to beaver <ul><li>Simulated the effects of sediment storage provided by beaver pond complexes. </li></ul><ul><li>Warm Springs Creek: Placement of one small pond complex had a larger impact in sediment yield reduction ( 3% ) in the watershed than either of the other two modeled scenarios (riparian enhancement or road removal). </li></ul><ul><li>Alder Gulch: Less reduction ( <1% ) in sediment yield </li></ul><ul><li>Results from modeling just one in-channel pond complex suggest sediment reduction due to beaver pond complexes could be substantial over an entire watershed. </li></ul>
    14. 14. Why increase beaver populations in headwaters? <ul><li>Beaver dramatically increase riparian vegetation and water retention in floodplains. </li></ul><ul><li>One possible way to meet water quality targets </li></ul><ul><li>Beaver can be relocated from areas where they’re causing problems to quality habitat sites away from use conflict. </li></ul>
    15. 15. How do we do it? Some recommendations: <ul><ul><li>Develop standard criteria for reintroduction sites: habitat requirements and socioeconomic considerations </li></ul></ul><ul><ul><li>Document baseline conditions and changes after beaver establishment, including flow patterns, riparian/floodplain vegetation communities, sediment transport, and fish and wildlife populations/habitat use. </li></ul></ul><ul><ul><li>Develop long-term management plan for beaver and their habitat </li></ul></ul>
    16. 16. Considerations for Reintroduction <ul><li>Both USFS and BLM recognize the ecological benefit of increasing beaver populations in headwaters. </li></ul><ul><li>Many new sites in southwest Montana could support beaver. </li></ul><ul><li>Reintroduction to the wrong sites could result in detrimental effects - economic and ecologic. </li></ul><ul><li>Establishing large populations in headwaters areas needs to incorporate a long-term plan to manage populations , including initial protection in those areas (headwaters protection areas) and a focus on increasing aspen and willow. </li></ul>
    17. 17. More considerations… Fish habitat and beaver habitat are both much reduced - not much room for natural cycle of beaver ponds or cyclic local impacts on fish populations. Newly-formed meadows and silted-in dams are very susceptible to severe erosion due to trampling, and prone to incisement. Grazing management must be part of any plan for beaver reintroduction. Increasing riparian vegetation in areas where it is lacking should be part of a long-term strategy for beaver reintroduction and watershed restoration.
    18. 18. Your turn.