Stand openness predicts hair lichen (Bryoria) abundance in the lower canopy, with implications for the conservation of Canada’s critically imperiled Deep-Snow Mountain Caribou (Rangifer tarandus caribou)

Abstract

Tree-dwelling hair lichens in the genus Bryoria provide crucial late-winter forage for Deep-Snow Mountain Caribou (DSC), an imperiled ungulate endemic to south-central British Columbia, Canada. Because DSC survival requires continuous access to heavy hair lichen loadings, conservation efforts can benefit from an improved understanding of the factors that contribute to such loadings. Here we quantify the relation of Bryoria abundance to stand spacing by testing an “Angle-To-Canopy-Skyline” (ATCS) protocol as a measure of stand openness and a proxy for ventilation. Fieldwork conducted in 60-year-old conifer forests on a 250-m conical volcano within the range of DSC yielded three principal findings: (1) Bryoria abundance strongly increases with increasing stand openness; (2) Pinus contorta supports much heavier Bryoria loadings than other local host trees; and (3) ATCS is a powerful predictor of arboreal hair lichen abundance in general across a wide range of environmental settings, but does not predict the abundance of foliose lichens. We suggest that canopy openness, at least within the range of DSC, complements stand age as a key factor in the development of heavy Bryoria loadings, consistent with the hypothesis that Bryoria benefits from rapid drying after rain. The possibility that anomalously high Bryoria abundance on Pinus may hold promise for accelerated DSC habitat restoration following clearcut logging is explored but rejected.