The mountain caribou is a threatened ecotype of the woodland caribou restricted to east-central and southeast British Columbia as well as adjacent portions of Washington and Idaho. In winter these animals forage almost exclusively on arboreal hair lichens, especially Bryoria. Here we examine the vertical and horizontal occurrence of hair lichens within the canopy of a mid-successional, mid-elevational forest dominated by Engelmann spruce and subalpine fir. Our study yielded five key findings: 1) all hair lichen species potentially important to caribou are present 60 yr after stand initiation; 2) low-biomass sorediate species (mostly B. fuscescens) predominate in the lower and middle canopies; 3) high-biomass non-sorediate species (mostly B. fremontii and B. pseudofuscescens) are most abundant in the upper canopy; 4) hair lichen biomass is higher in open stands than in closed stands; and 5) hair lichen loadings are low when compared with earlier reports from old-growth stands. The last finding apparently reflects—in the upper canopy—a lack of defoliated branches and—in the middle and lower canopies—humid, poorly ventilated conditions. We suggest that a judicial use of stand thinning could considerably augment the production of non-sorediate Bryoria species in defoliated portions of the middle canopy. Within the lower canopy, however, thinning is unlikely to increase Bryoria loadings, except as a result of inoculation from the middle canopy.