Year of Award

2021

Document Type

Dissertation

Degree Type

Doctor of Philosophy (PhD)

Degree Name

Fish and Wildlife Biology

Department or School/College

W.A. Franke College of Forestry and Conservation

Committee Chair

Mark Hebblewhite

Commitee Members

Jedediah M. Brodie, Erick Greene, John Kimball, Joshua Millspaugh

Keywords

boreal forest, caribou, fire, habitat, human disturbance, resource selection

Abstract

In North America’s boreal forest, wildfire has long been the dominant form of natural disturbance. However, the human footprint in the region is steadily growing. Large-scale forest harvest and energy development have fragmented late-successional forests, leading to habitat loss for species such as caribou (Rangifer tarandus) that rely on these ecological communities. Caribou have experienced widespread population declines and local extirpation throughout the western boreal forest in recent decades. I first analyzed caribou resource selection responses to fires in >685 female caribou across 15 populations that span a wide gradient of fire frequency but are exposed to relatively little human disturbance. Caribou generally avoided burned areas, but season, burn severity and time since fire affected the magnitude of avoidance. Consistent avoidance of burns in winter and avoidance of high severity burns across the range of burn availability suggested that future increases in fire frequency and severity will lead to habitat loss for caribou. Disturbance-caused habitat loss (whether direct or indirect) does not necessarily translate to negative demographic effects. My second set of analyses linked disturbances to caribou behavior and demography throughout western Canada by relating resource selection responses to vital rates. I found a strong negative relationship between human disturbance footprint and calf recruitment. I also found evidence of adaptive resource selection, where increased road avoidance in summer predicted higher recruitment. Increased road avoidance by caribou in winter decreased mortality hazard in adult females, but disturbance and behavior were less predictive of adult female survival than of recruitment. Many of the most imperiled caribou populations live in mountainous areas in British Columbia, where extensive forestry and energy development have facilitated increased predation on caribou. Southern mountain caribou are listed as Threatened under Canada’s federal Species at Risk Act (SARA), yet critical habitat identified under the law provides incomplete protection for southern mountain caribou. My spatial analysis showed that nearly 1,000 square kilometers of critical habitat were logged in the five years following its legal identification under SARA. Halting or reversing caribou population declines requires innovative, multi-pronged policy efforts combining short-term efforts to reduce predation with long-term habitat restoration.

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