Predator–prey co‐occurrence in harvest blocks: Implications for caribou and forestry

Abstract

Forest harvesting alters habitat, impacts wildlife, and disrupts ecosystem function. Across the boreal forest of Canada, forest harvesting affects ungulate prey species and their predators, with cascading impacts on other species, including threatened woodland caribou. We used camera and vegetation data and occupancy modeling to investigate what characteristics in and around forestry harvest blocks influenced the occupancy and co‐occurrence of primary prey (elk, moose, mule deer, white‐tailed deer) and predators (black bear, cougar, grizzly bear, wolf) in harvest blocks. Occupancy was linked to forage, the surrounding habitat and anthropogenic disturbance, and silviculture practices. Black and grizzly bear occupancy was influenced by the presence of deer, and bear–deer co‐occurrence was influenced by site‐specific silviculture practices and surrounding anthropogenic disturbance. In the context of caribou recovery, our results indicate that forestry within caribou ranges could consider site‐specific silviculture practices and landscape‐level planning to reduce use of harvest blocks by primary prey. Future caribou recovery efforts may also consider the roles of deer and bears in caribou predation risk. Our study provides the first insights into the impacts of forestry and silviculture on boreal forest predator–prey co‐occurrence and provides practical management applications to mitigate the impacts of anthropogenic activities on the boreal forest ecosystem into the future.

Ungulate occurrence in forest harvest blocks is influenced by forage availability, surrounding habitat and silviculture practices

“…Caribou are exposed to increased predation risk in areas where they overlap with ungulates and shared predators (Latham et al, 2011; Mumma et al, 2018; Whittington et al, 2011), specifically during the summer (Seip, 1992; Serrouya et al, 2011; Wittmer et al, 2005) and fall migration periods (Blagdon & Johnson, 2021). Recent research in our study area found an increased probability of bear occupancy in harvest blocks that were occupied by deer, suggesting that harvest blocks may directly influence predator–prey dynamics (McKay & Finnegan, 2022). The seasonal differences in occurrence we observed in this study could indicate seasonal differences in the spatial overlap of ungulates, caribou, and predators in areas with harvest blocks, with an associated increased caribou predation risk during the summer.…”

Whose line is it anyway? Moose (Alces alces) response to linear features

“…During winter, as previously mentioned, pipelines likely offer less shelter, cover, and forage available above the snowpack than seismic lines, which is likely driving winter moose selection for pipelines only when other linear features are not available to them. At the fine scale, we found that moose were indifferent to pipelines regardless of the surrounding habitat or underlying soil wetness but that there were differences among individuals, and therefore, like seismic lines and harvest blocks, moose use of pipelines is most likely linked to finer scale characteristics like vegetation composition, lateral cover, and the presence of game trails (McKay & Finnegan, 2023; Tattersall et al, 2023).…”

“…During summer, the width of pipelines combined with ongoing vegetation management may result in pipelines having similar thermal cover, but less forage availability than harvest blocks and wildfires, making pipelines less attractive to moose when harvest blocks and wildfires are available. Moose use of harvest blocks and pipelines during summer is linked to the availability of shrubs and lateral cover (McKay & Finnegan, 2023; Tattersall et al, 2023); pipelines are periodically cleared to maintain line‐of‐sight (Alberta Energy Regulator, 2016; MacDonald et al, 2020), while with the exception of mechanical or chemical stand tending a few years after planting, harvest blocks are left to regenerate. Therefore, harvest blocks and areas that are naturally regenerating after wildfires are likely more attractive sources of shrub and sapling moose forage than maintained pipelines with graminoids and clover less preferred by moose (MacDonald et al, 2020; McKay & Finnegan, 2023; Tattersall et al, 2023).…”

“…Moose use of harvest blocks and pipelines during summer is linked to the availability of shrubs and lateral cover (McKay & Finnegan, 2023; Tattersall et al, 2023); pipelines are periodically cleared to maintain line‐of‐sight (Alberta Energy Regulator, 2016; MacDonald et al, 2020), while with the exception of mechanical or chemical stand tending a few years after planting, harvest blocks are left to regenerate. Therefore, harvest blocks and areas that are naturally regenerating after wildfires are likely more attractive sources of shrub and sapling moose forage than maintained pipelines with graminoids and clover less preferred by moose (MacDonald et al, 2020; McKay & Finnegan, 2023; Tattersall et al, 2023). During winter, as previously mentioned, pipelines likely offer less shelter, cover, and forage available above the snowpack than seismic lines, which is likely driving winter moose selection for pipelines only when other linear features are not available to them.…”

“…A parallel study in the same area which used field data (tracks and signs and vegetation cover) found that moose use of seismic lines was linked to the availability of specific forage species and the availability of game trails (Tattersall et al, 2023). It was curious that we found no links between the percent conifer surrounding seismic lines and moose response because moose generally select areas with higher availability of broadleaf trees (Courtois et al, 1998;Gagné et al, 2016;McKay & Finnegan, 2022). It is possible that the scale we measured percent conifer surrounding seismic lines (30 m) was too fine to capture moose response to stand-level tree species.…”