Cecily M. Costello, Lori L. Roberts, Sarah N. Sells

Forest disturbance can reinstate early successional vegetation, often providing abundant grizzly bear foods. However, uncertainty remains in factors influencing how grizzly bears respond to forest disturbance. We used GPS collar data from 91 individual grizzly bears between 2000 and 2022 to evaluate how disturbance from timber harvest and fire influenced habitat selection by grizzly bears in the Northern Continental Divide Ecosystem of northwest Montana, USA. We hypothesized that grizzly bears select disturbance because it can provide important foods. We further hypothesized that selection would be influenced by season, and the type, severity, and availability of disturbance patches because of their impact on forage availability and vegetation regeneration. We fit step selection functions using conditional Poisson mixed models to test our hypotheses, accounting for additional factors known to influence grizzly bear habitat selection in this ecosystem. Grizzly bears generally selected fire disturbance, especially in spring. Only grizzly bears without access to recent fire disturbance selected regenerative timber harvest in summer. Regardless of population level results, grizzly bears showed highly variable individual responses in selection for both timber harvest and burns across our study. Our results support the hypothesis that grizzly bears show stronger selection for natural disturbance sources and that selection of harvested forests is influenced by availability of recent natural disturbance. Moreover, this study represents the most comprehensive broad-scale evaluation of forest disturbance effects on grizzly bear habitat on the southern extent of their range in North America, with important management implications.