Arboreal Squirrel Response to Silvicultural Treatments for Dwarf Mistletoe Control in Northeastern Oregon

Abstract

Abstract Various silvicultural treatments are commonly used to sanitize stands by removing trees infected with dwarf mistletoe (Arceuthobium spp.), yet witches' brooms in trees infected with dwarf mistletoe often provide structures used by many wildlife species. We compared relative abundance, habitat use, and area of use of red squirrels (Tamiasciurus hudsonicus) and northern flying squirrels (Glaucomys sabrinus) before and after two different treatments designed to remove a range of dwarf mistletoe-caused witches' brooms in northeastern Oregon in 1998–2002. Dwarf mistletoe sanitation treatments included: (1) an island treatment, with retention of up to 0.5 ha groups of trees containing witches' brooms in evenly distributed uncut islands, and all harvest activity confined to thinning from below outside these islands to eliminate trees containing witches' brooms; and (2) a total removal treatment, which consisted of removing all trees that contained a witches' broom estimated to be >25 cm in diameter. Before treatment, over half of the red squirrels and northern flying squirrels in the treatment area occupied summer rest sites in witches' brooms on large Douglas-fir (Pseudotsuga menziesii). Live trapping indicated a pretreatment abundance of 1.0 per 100 trap/nights for red squirrels and 0.4 per 100 trap/nights for northern flying squirrels, and a posttreatment abundance of 2.1 per 100 trap/nights for red squirrels and 0.2 per 100 trap/nights for northern flying squirrels. Type of rest site and amount of red squirrel reuse did not change after the island treatment, although the number of red squirrels located in rest sites increased with the island treatment. Most of the red squirrel locations occurred within the islands. Area of use by red squirrels did not change with island treatment. Type of rest site used by red squirrels and northern flying squirrels shifted after the total removal treatment from mostly witches' brooms to predominantly tree cavities. Area of use by red squirrels increased from 1.8 to 7.6 ha after the total removal treatment. Results suggest that retention of trees containing witches' brooms in small groups or islands offers an opportunity to retain rest site habitat, although northern flying abundance declined with both treatments. West. J. Appl. For. 19(2): 133–141.