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

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.

Wildlife Use of Douglas-Fir Dwarf Mistletoe Witches' Brooms in the Southwest

“…Our study and several others (Vahle 1978, Patton and Vahle 1986, Parks et al 1999, Tinnin and Forbes 1999, Bull et al 2004 indicated that small mammals, particularly red squirrels, frequently use brooms for nesting sites and that the characteristics and locations of the brooms used were similar. The small mammal nests we found occurred more often in Type II brooms, but Type I and III brooms were also commonly used.…”

“…Most red squirrel nests we found in brooms were also located within 3 m of the main bole and between 4.5 m and 10 m above the ground. Tinnin and Forbes (1999) and Bull et al (2004) reported similar nest heights for the red squirrel nests they found in brooms. We also found that large brooms with some type of platform were more frequently used by small mammals for nesting sites than were small brooms.…”

“…WILDLIFE AND DWARF MISTLETOE BROOMS 453 northern flying squirrels (Glaucomys sabrinus). Red squirrels and northern flying squirrels also commonly use brooms as nesting sites in northeastern Oregon (Bull et al 2004).…”

“…We were able to easily classify all of the brooms we examined. The type of broom is important because most use by red squirrels reported by other investigators has been in Type II or III brooms (Parks et al 1999, Tinnin and Forbes 1999, Bull et al 2004.…”

Nest Site Selection by Western Gray Squirrels at Their Northern Range Terminus

“…Retention of patches that include a mix of conifer species or conifer and deciduous trees and moderate to high basal area could promote nesting opportunities, connectivity for arboreal travel, as well as abundance and diversity of hypogeous fungi (Dodd et al 2003;Lehmkuhl et al 2004Lehmkuhl et al , 2006b. We recommend experimental studies to explore the effect of patch retention on western gray squirrels, including assessment of optimal patch size and efficacy of the treatment for retaining mistletoe structure for wildlife use while protecting the surrounding stand from mistletoe spread and wildfire (Bull et al 2004). To enhance nesting opportunities for western gray squirrels, we recommend retaining trees .20 cm diameter at breast height (min.…”