Landscape permeability for grizzly bear movements in Washington and southwestern British Columbia

Abstract

Providing opportunities for grizzly bears (Ursus arctos) to move between blocks of habitat is important for the long-term conservation of grizzly bear populations. While the particulars of grizzly bear habitat selection during long-distance movements are poorly understood, some landscape characteristics such as road density and land cover type are correlated with grizzly bear habitat use at various scales. We compiled digital maps of roads, human population density, land cover class, and topography to evaluate the resistance of the year 2001 landscape to grizzly bear movement in Washington State and adjacent portions of Idaho and British Columbia (BC). We developed habitat association and dispersal habitat suitability models based on published literature and used geographic information system (GIS) weighted-distance and least-cost analysis techniques to evaluate landscape permeability for grizzly bear movement. Our analysis identified 5 blocks of potential grizzly bear habitat in Washington and adjacent areas, including the Columbia–Selkirk Mountains, the North Cascades, the Central Cascades, the South Cascades, and the Coast Range. We evaluated landscape permeability between these habitat blocks and highlighted potential linkage areas. Our models indicated the Stevens Pass fracture zone between the North and Central Cascades blocks was the most permeable, followed (in order of relative permeability) by the Fraser–Coquihalla fracture zone between the North Cascades and the Coast Range, the Okanogan–Kettle fracture zone between the North Cascades and the Columbia Mountains, and the Snoqualmie Pass fracture zone between the Central and South Cascades. This evaluation provides a consistent measure of the expected potential for grizzly movement across a broad landscape that can be used to target areas for finer-scale evaluation and help identify landscape management priorities at a regional scale.