Vulnerable caribou and moose populations display contrasting responses to mountain pine beetle outbreaks and management.

Rising global temperatures and changing landscape conditions have led to widespread mountain pine beetle (MPB) outbreaks in western North America. Extensive management has been implemented in response, via forest harvesting and prescribed burning. However, the impacts of MPB and MPB-management on ungulate populations, particularly caribou and moose, remain poorly studied. Given the differing specialisations of these species (caribou are habitat specialists, moose are generalists), their responses to these disturbances may vary. This could, in turn, lead to unintended, indirect effects (e.g., disturbance-mediated apparent competition, whereby increased moose presence results in increased predator presence, with resultant caribou declines). Unravelling these responses is crucial for informing MPB management and ensuring that applied actions do not exacerbate adverse effects. We assessed the effects of early-stage MPB-infestation, harvest, and fire, on habitat selection by caribou (boreal and central mountain designatable units) and moose in west-central Alberta. We built resource selection functions and functional response models using GPS collar data collected 3-5 years after MPB infestation and found that responses varied between species. Caribou had complex seasonal responses to MPB, generally avoiding areas with more MPB disturbance in winter but using them in summer. Caribou typically avoided harvested and burned areas, though this was dependent on the overall degree of disturbance within their ranges. In contrast, moose had positive responses to both MPB and burned areas year-round. These findings suggest that MPB may negatively impact long-term winter habitat availability for threatened caribou populations, but may have positive impacts on moose habitat. However, moose use of MPB-impacted areas could further affect caribou by contributing to disturbance-mediated apparent competition. Synthesis and applications: The negative impacts of forest harvest and burning on caribou suggests that less intensive actions are required for MPB management within caribou ranges. While moose selectively used harvested and burned areas, it is possible that they may have adverse responses to cumulative disturbance over time. As caribou and moose responded to MPB soon after infestation, ongoing monitoring is required to detect MPB early and facilitate proactive management, though further study is needed to determine the most effective actions.