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    Author(s): Todd M. WillsonEric D. Forsman
    Date: 2013
    Source: In: Anderson, P.D.; Ronnenberg, K.L., eds. Gen. Tech. Rep. PNW-GTR-880. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest Research Station: 79–90.
    Publication Series: General Technical Report (GTR)
    Station: Pacific Northwest Research Station
    PDF: View PDF  (238.79 KB)


    Th inning has been promoted as a method for accelerating the development of late-seral habitat and improving the overall health and function of young forests in the Pacifi c Northwest. Population studies have shown early and positive responses to thinning by some small forest-floor mammals (primarily mice, terrestrial voles, and shrews). However, thinning reduces the abundance of some tree-dwelling rodents, especially Northern Flying Squirrels (Glaucomys sabrinus) and Red Tree Voles (Arborimus longicaudus), that are important prey species for Northern Spotted Owls (Strix occidentalis caurina). Recent studies suggest that reductions in Northern Flying Squirrel abundance following thinning may be driven by increased susceptibility to predation created by removal of critical above-ground cover. Predation, lack of canopy connectivity, and reduction in suitable nest substrates may all contribute to reduced Red Tree Vole abundance following thinning. The longterm benefi ts of some thinning treatments may be positive for both flying squirrels and Red Tree Voles, but may not be realized for several decades or more, as the development of a midstory layer of trees may be critical to the success of thinning in promoting habitat for these species. Additional research into the ecology of the two woodrat species (Neotoma fuscipes and N. cinerea) found in the Pacific Northwest is needed to provide a more complete understanding of the effects of forest management activities on spotted owls and their prey. It may be possible to design thinning prescriptions that lessen the short-term negative eff ects on arboreal rodents. Long-term goals should focus on creating more structurally and biologically complex forests across the landscape at scales and patterns compatible with the ecologies of spotted owl prey and other organisms. Joint research-management eff orts to test new silvicultural prescriptions, expand current predictive models of high-quality prey habitat, and develop management strategies that consider the temporal effects of management on owl prey at the stand, landscape, and regional levels, could advance our understanding of owl prey ecology and help ensure that healthy populations of spotted owls and their prey persist on the landscape over the long term.

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    Wilson, Todd M.; Forsman, Eric D. 2013. Thinning effects on spotted owl prey and other forest-dwelling small mammals. In: Anderson, P.D.; Ronnenberg, K.L., eds. Gen. Tech. Rep. PNW-GTR-880. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest Research Station: 79–90.


    Thinning, variable-density thinning, Northern Spotted Owl, Northern Flying Squirrel, Red Tree Vole, Northwest Forest Plan, old-growth forest.

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