Arboreal Squirrel Abundance in Response to a Gradient of Mountain Pine Beetle Attack in Sub-boreal Forests

Abstract

To assist in evaluating habitat retention options, the abundance of northern flying squirrels (Glaucomys sabrinus) and North American red squirrels (Tamiasciurus hudsonicus) wer examined in 2005 and again in 2010 across a gradient of mountain pine beetle (Dendroctonus ponderosae) attack intensity in sub-boreal forests of west-central British Columbia. Among 30, 16-ha live-trapping grids, estimated mean abundance of both species increased non-linearly with remaining basal area of live overstorey (live trees ≥ 7.5 cm diameter at 1.3 m height). A weak (most likely positive but possibly negative) additional response of flying squirrels to dead overstorey (on average 1 m2/ha dead ≈ +0.11 m2/ha live basal area) was evident. The basal area of live spruce-fir (Picea spp., Abies spp.) overstorey, understorey tree density, and tree diameter covariates did not have substantive additional effects on estimated squirrel abundance. Whereas survey year affected overall abundance, it did not change the relationship with habitat attributes. The results suggest that dead lodgepole pine (Pinus contorta) has low habitat value for arboreal squirrels and thus is of lower impact on squirrels if salvage-harvested; however, retention or re-growth of sufficient live overstorey is necessary to maintain or recover squirrel abundance. The basal area oflive overstorey appears a simple yet useful management metric for prioritizing habitatvalue, at least as indicated by relative abundance for squirrels in beetle-affected forests.