Abstract:

"To predict fisher distribution across the region, we created a multiple logistic regression model using data from 682 previously surveyed locations and a vegetation layer created from satellite imagery.

"Fisher distribution was strongly associated with landscapes with high levels of tree canopy closure. Regional gradients such as annual precipitation were also significant. At the plot level, the diameter of hardwoods was greater at sites with fisher detections. A comparison of regional fisher distribution with land-management categories suggests that increased emphasis on the protection of biologically productive, low- to mid-elevation forests is important to ensuring the long-term viability of fisher populations.

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"The 67,000-km 2 area we analyzed includes the Klamath region of northwestern California and Southwestern Oregon and adjacent portions of the northern California coast." (1346)

"Data used to develop the habitat model came primarily from surveys conducted between 1991 and 1995 by land management agency or tribal personnel to determine the presence of fishers at sites where management activities (e.g., timber harvest, recreational development) were planned." (1346)

"GIS data available for analysis included information on roads, hydrology, elevation, and land-management category (U.S. Forest Service, unpublished data), as well as vegetation (California Timberland Task Force [TTF] 1993; W. Cohen, unpublished data) and precipitation (Daly et al. 1994)." (1346)

"In our construction of a model of fisher distribution, the best predictors proved to be landscape- and regional-scale variables, rather than the fine-scale variables often used in wildlife-habitat models. If, as our study suggests, habitat selection by fishers is dominated by factors operating at the home-range scale and above, regional-scale conservation planning for the fisher may be possible without fine-scale data on vegetation or prey abundance." (1352)

"Two factors may explain the importance of large hardwoods for fishers. Cavities in large hardwoods are frequently used as resting and denning sites (W. Zielinski, unpublished data), and these trees produce mast, which may stimulate higher prey densities (Powell & Zielinski 1994). Information on the distribution of these resources may be important in the management of habitat quality and connectivity at the within-home-range scale to complement landscape-level planning." (1353)

"Among the vegetation variables, the tree canopy closure [Moving Average] has the highest significance and the clearest biological interpretation. Landscapes with higher levels of overhead cover may provide increased protection from predation, lower the energy costs of traveling between foraging sites, and provide more favorable microclimate and increased abundance or vulnerability of preferred prey species (Buskirk & Powell 1994; Powell & Zielinski 1994)." (1353)

"Our study further documents the discontinuous distribution of fishers in the Pacific coastal states. If the metapopulation concept is applicable here, as has been proposed (Heinemeyer & Jones 1994), the isolation of fisher populations in the western. United States from one another and from the more continuous populations in northern Canada and the eastern United States may be of concern." (1357)

"Current land-use strategies that incorporate short timber harvest rotations may isolate remnant areas of fisher habitat. Regional or landscape-level thresholds of habitat value, area, or connectivity may exist below which population viability is compromised due to an imbalance between immigration and emigration (Lande 1987; Noon & McKelvey 1996). Maintaining viable and well-distributed fisher populations may require increased levels of canopy closure and retention of large hardwoods on managed lands, especially in areas that appear from habitat analyses to be plausible regional habitat linkages. Conservation planning for nonfederal lands-for example, through development of habitat conservation plans-should prioritize surveys to validate the .areas of potential habitat identified in regional-scale analyses." (1357)

"Because little low-elevation forest is contained within existing protected areas, conservation of forest carnivores such as the fisher may depend on multi-ownership cooperative management at the regional scale (Mladenoff et al. 1995)." (1357)