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Open Access Publications from the University of California

Modeling highway impacts related to grizzly bear core, living, and connectivity habitat in Idaho, Montana, and Wyoming using a two-scale approach

  • Author(s): Craighead, Lance
  • Olenicki, Tom
  • et al.

To address highway impacts on grizzly bear movements and population persistence (and by inference other wildlife species) a two-tiered modeling approach was used. At a coarse scale, highway segments were ranked in importance based upon their relative effects on grizzly bear core and connectivity habitat. At a fine scale, influences were examined by including highway features such as jersey barriers and bridges in the modeling process. Grizzly bears are widely considered an “umbrella” or “focal” species whose protection and persistence will benefit a broad assemblage of plant and animal species; in general, maintaining grizzly bears will maintain biodiversity and the health and function of natural ecosystems. Highways have negative impacts on grizzly bears, biodiversity, and natural ecosystems that can be mitigated to some degree by reducing the fragmentation effects of the highway. To address fragmentation effectively, highway segments need to be prioritized based upon their relative impact on grizzly bear habitat and movement. Highway mitigation efforts and habitat conservation efforts can then be guided to address the areas of greatest impact. Factors found to affect grizzly bear movement and habitat quality are road density, building density, land cover type, habitat heterogeneity, and amount of forest-grassland edge habitat. Within a geographic information system (GIS), habitat quality was modeled and used to define core areas (large enough area for a small population to survive), living habitat (large enough for an individual to survive), and connectivity habitat (connections between core habitat). Highway impacts on grizzly bear habitat and movement were estimated at the coarse scale by estimating the total length of highway intersecting: (1) suitable grizzly living habitat, (2) core grizzly habitat, and (3) connectivity habitat. Highways were weighted to reflect their overall impact, and lengths of highway segments were estimated to reflect the relative impact of each highway on grizzly bear habitat. Highway impacts on grizzly bear habitat and movement at the fine scale incorporated data on building locations, road sinuosity, slope, and global positioning system (GPS) locations of highway features such as jersey and/or texas barriers, and presence of guardrails. These features tend to affect animal and/or motorist behavior during attempts at highway crossings. At the fine scale, areas of secure habitat were delineated based upon contiguous areas of high quality habitat encompassing 10 km2 or larger. A pilot modeling project was completed for the Bozeman Pass, Montana, area that should be applicable to other highway segments within potential grizzly bear habitat of Montana, Idaho, and Wyoming. Our approach offers the ability to identify important areas at a coarse scale and then use fine-scale efforts to identify specific road segments of concern. Fine scale modeling should be done at all high-impact sites to help determine optimal locations where animals may attempt to cross highways. Additionally, other species may be modeled to examine locally important wildlife.

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