Livestock grazing limits beaver restoration in northern New Mexico

The North American beaver (Castor canadensis) builds dams that pond water on streams, which provide crucial ecologicalservices to aquatic and riparian ecosystems and enhance biodiversity. Consequently, there is increasing interest in restoringbeavers to locations where they historically occurred, particularly in the arid western United States. However, despiteoften intensive efforts to reintroduce beavers into areas where they were severely reduced in numbers or eliminated dueto overharvesting in the eighteenth and nineteenth centuries, beavers remain sparse or missing from many stream reaches.Reasons for this failure have not been well studied. Our goal was to evaluate certain biotic factors that may limit the occurrenceof dam-building beavers in northern New Mexico, including competitors and availability of summer and winter forage. Wecompared these factors at primary active dams and at control sites located in stream reaches that were physically suitable fordam-building beavers but where none occurred. Beaver dams mostly occurred at sites that were not grazed or where therewas some alternative grazing management, but were mostly absent at sites within Forest Service cattle allotments. Resultsindicated that cattle grazing inuenced the relation between vegetation variables and beaver presence. The availability ofwillows (Salix spp.) was the most important plant variable for the presence of beaver dams. We conclude that grazing by cattleas currently practiced on Forest Service allotments disrupts the beaver-willow mutualism, rendering stream reaches unsuitablefor dam-building beavers. We recommend that beaver restoration will require changes to current livestock managementpractices