UBC Theses and Dissertations
Grizzly bear (Ursus arctos) responses to forest harvesting : a review of underlying mechanisms and an empirical case study Colton, Christopher
Active forest management for timber production, through the harvesting of forest stands using cut blocks, frequently overlaps grizzly bear (Ursus arctos) habitat on multi-use landscapes in North America. Thus, it is critical to understand how forest harvest management can effectively support grizzly bear conservation efforts. While many localized studies have investigated relationships between forest harvest and grizzly bear habitat use, a synthesis of our current understanding of these complex interactions is warranted. This thesis reviewed publications that empirically assessed grizzly bear use of recently harvested forest stands (<40 years since harvest) and found all studies reported grizzly bear use of forest cut blocks. Several studies reported grizzly bear selection of forest cut blocks, however with substantial variation in selection across seasons and local environment (ecoregions). Seven underlying factors were identified that influence grizzly bear responses to forest harvest: natural forest openings, cut block design, silvicultural techniques, age since harvest, grizzly bear food availability, human activity, and grizzly bear sex and age. This synthesis suggests that grizzly bears may frequently use forestry cut blocks when vegetative forage is present, especially if human activity is minimal and natural forest openings are limited. To further explore how age since harvest affects grizzly bear behaviour, I undertook an empirical case study using a camera trap survey of grizzly bears in southwest BC. Results from a linear regression model suggested relatively lower use of areas with recently harvested cut blocks (β = -0.0096, p = 0.040), while other cut block age classes had little effect on grizzly bear habitat use. This highlights the importance of minimizing forest harvest nearby important habitat features such as alpine/sub-alpine meadows and whitebark pine stands in the study area. While knowledge gaps remain in understudied ecoregions of grizzly bear range, key forest management actions such as controlling motorized human access, avoiding forest harvest nearby critical habitat and implementing riparian buffer zones are well supported. Future research should incorporate more information on grizzly bear demography (i.e. density and survival) and forestry operations (i.e. silviculture, cut block design, and human activity) to better understand the underlying mechanisms influencing grizzly bear-forestry relationships.
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