How fires are changing caribou habitat

Caribou generally avoid burned areas, but some questions remain. As fires become more common in caribou habitat, we want to know more about the potential impacts.

An international team of caribou researchers, including from the National Park Service, investigated the impacts of wildfire severity using a dataset of over 650 collared caribou from 15 different populations from Alaska and northwest Canada. While decades-long avoidance of previously burned areas in winter by caribou is relatively well known and studied, there have been some lingering questions.

These questions include:

Why do some caribou use burned areas?
What are the impacts of burn severity (intensity) on caribou avoidance?
Do caribou avoid these burned areas during summer as well as winter?

Using this large caribou dataset, along with new satellite-based data on burn severity and lichen abundance, the team set out to answer these questions.

Caribou preferred food is lichens, especially in the winter. Caribou avoid burned areas, especially those areas severely burned where lichens are gone.

Similar to previous studies, the team documented caribou avoiding burned areas in winter across the vast study area for about 30 years. Lichen abundance was lower where burn severity was greater. Caribou that did wander in burned areas tended to use patches that experienced lower burn severity and had greater lichen abundance. Despite how quickly some vascular vegetation (i.e., grasses but not lichens) can recover after a fire and provide high-quality forage for some herbivores, caribou also avoided burned areas in the summer, though not as strongly as during winter.

This studied showed how collaborations, which can increase sample size and scope, and newer, more precise data on burns and vegetation can advance our understanding of animal ecology. This research also has important implications regarding climate change impacts on caribou habitat, as wildfires are predicted to increases in both number and severity as the North warms.

Increasing fire frequency and severity will increase habitat loss for a boreal forest indicator species

Abstract

Climate change will lead to more frequent and more severe fires in some areas of boreal forests, affecting the distribution and availability of late-successional forest communities. These forest communities help to protect globally significant carbon reserves beneath permafrost layers and provide habitat for many animal species, including forest-dwelling caribou. Many caribou populations are declining, yet the mechanisms by which changing fire regimes could affect caribou declines are poorly understood. We analyzed resource selection of 686 GPS-collared female caribou from three ecotypes and 15 populations in a ~600,000 km² region of northwest Canada and eastern Alaska. These populations span a wide gradient of fire frequency but experience low levels of human-caused habitat disturbance. We used a mixed-effects modeling framework to characterize caribou resource selection in response to burns at different seasons and spatiotemporal scales, and to test for functional responses in resource selection to burn availability. We also tested mechanisms driving observed selection patterns using burn severity and lichen cover data. Caribou avoided burns more strongly during winter relative to summer and at larger spatiotemporal scales relative to smaller scales. During the winter, caribou consistently avoided burns at both spatiotemporal scales as burn availability increased, indicating little evidence of a functional response. However, they decreased their avoidance of burns during summer as burn availability increased. Burn availability explained more variation in caribou selection for burns than ecotype. Within burns, caribou strongly avoided severely burned areas in winter, and this avoidance lasted nearly 30 years after a fire. Caribou within burns also selected higher cover of terrestrial lichen (an important caribou food source). We found a negative relationship between burn severity and lichen cover, confirming that caribou avoidance of burns was consistent with lower lichen abundance. Consistent winter avoidance of burns and severely burned areas suggests that caribou will experience increasing winter habitat loss as fire frequency and severity increase. Our results highlight the potential for climate-induced alteration of natural disturbance regimes to affect boreal biodiversity through habitat loss. We suggest that management strategies prioritizing protection of core winter range habitat with lower burn probabilities would provide important climate-change refugia for caribou.

Palm, E. C., M. J. Suitor, K. Joly, J. D. Herriges, A. P. Kelly, D. Hervieux, K. L. M. Russell, T. W. Bentzen, N. C. Larter, and M. Hebblewhite. 2022. Increasing fire frequency and severity will increase habitat loss for a boreal forest indicator species. Ecological Applications e2549.