Effect of Forest Understorey Stand Density on Woodland Caribou Habitat Use

Steve Wilson
Thomas Nudds
Philip Green
Andrew de Vries
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Woodland caribou (Rangifer tarandus caribou) are considered to preferentially use older forests that provide abundant terrestrial lichen forage and refuge from predators. However, structural characteristics vary widely, differing in terms of forage availability but also, perhaps, in the ability of caribou to move freely through forests to access the available forage or to escape predation. We examined the effect of forest understorey stand density, defined as standing and downed biomass, on caribou habitat selection. Because this density is correlated with other features that could also drive habitat selection, we conducted a multivariate analysis of stand conditions in two geographically and biophysically distinct regions to identify the independent effects of various habitat drivers.

We fitted a sample of telemetry locations collected from GPS-collared caribou, along with an equal number of random locations, to Bayesian network models to predict the probability of habitat use (i.e., selection if >50%) based on a set of remotely sensed habitat inputs. Caribou in the Bistcho range (northwestern Alberta) selected non-forest/sparsely forested areas while caribou in the Trout Lake region (northwestern Ontario) used primarily forested habitats. Despite these differences, caribou appeared to pursue the same functional strategies with respect to understorey stand density in both regions, preferring forest stands that allowed greater ease of movement. We suggest that, rather than responding to coarse-scale policy interventions based simply on stand age or stand type, habitat management may require different treatments in different parts of the species’ range to address what are nevertheless common pathways to decline.