Scale-dependent microhabitat selection by threatened mountain caribou (Rangifer tarandus caribou) in cedar–hemlock forests during winter

Abstract

Mountain caribou, an endangered ecotype of woodland caribou ( Rangifer tarandus caribou Gmelin, 1788), live in late-successional coniferous forests where they depend largely on arboreal lichens as winter forage. While radio-telemetry has been used to understand caribou habitat selection patterns at broad scales among and within populations, here we use snow-trailing in old cedar–hemlock forests between 1992 and 2003 to study three finer scales of habitat selection: (1) forest stands used for foraging from available forest stands (among-stand selection), (2) foraging paths within selected stands relative to random paths within those same stands (within-stand selection), and (3) feeding items along foraging paths. Relative to stands that were available on the landscape, caribou selected stands with more windthrown trees and standing snags. Within stands, caribou selected paths that had more live trees, snags with branches and bark, and trees with larger diameters. All of these habitat attributes facilitate access to arboreal lichen. Of the potential forage items encountered along foraging paths, caribou preferred to feed on windthrown trees, lichen litterfall and falsebox ( Paxistima myrsinites (Pursh.) Raf.). Our results go beyond telemetry studies by revealing that not all old forests are of equal value to mountain caribou. Prioritization among old stands will help refine conservation measures, as will silvicultural systems that incorporate key habitat attributes to maintain winter habitat in low-elevation cedar–hemlock ecosystems.