Moose, caribou, and fire: have we got it right yet?

Abstract

Natural disturbance plays a key role in shaping community dynamics. Within Canadian boreal forests, the dominant form of natural disturbance is fire, and its effects are thought to influence the dynamics between moose (Alces alces (Linnaeus, 1758)) and the boreal ecotype of woodland caribou (Rangifer tarandus caribou (Gmelin, 1788)). Boreal caribou are considered “threatened” and population declines are attributed, at least in part, to disturbance-mediated apparent competition (DMAC) with moose. Here, we tested a primary prediction of the DMAC hypothesis: that moose respond positively to burns within and adjacent to the caribou range. We assessed moose selection for ≤25-year-old burns (when selection is predicted to be strongest) at multiple spatial scales and evaluated whether moose density was correlated with the extent of ≤40-year-old burns (a time frame predicted to negatively affect caribou). Against expectation, moose showed avoidance and low use of ≤25-year-old burns at all scales, regardless of burn age, season, and type of land cover burned. These findings mirrored the demographic response, as we found no correlation between ≤40-year-old burns and moose density. By contradicting the prevailing hypothesis linking fires to caribou population declines, our results highlight the need to understand regional variation in disturbance impacts on caribou populations.