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Biodiversity within dry forests of the interior of British Columbia : the role of aspen and stand structure Oaten, Dustin Kyle

Abstract

The dry interior forests of British Columbia are composed of contiguous coniferous forests dominated by Douglas-fir (Pseudotsuga menziesii), with a small portion consisting of trembling aspen (Populus tremuloides). These aspen trees are of particular interest as there is evidence that they may support a relatively abundant and diverse faunal community. However, this potential has not been extensively explored within these forests. Two bioindicator taxa, small mammals and cavity-nesting birds, were investigated within aspen stands near Kamloops, British Columbia, Canada during 2005 and 2006, and were compared to neighbouring Douglas-fir and mixedwood stands. Seven thousand ninety seven captures of 12 small mammal species were made during 15,761 trap nights, with 48% of captures within aspen stands. Seven species were numerically dominant within these stands including the deer mice (Peromyscus maniculatus), southern red-backed vole (Clethrionomys gapperi), long-tailed vole (Microtus longicaudus), montane vole (Microtus montanus), meadow vole (Microtus pennsylvanicus), and the northwestern chipmunk (Tamias amoenus). Eight stand level attribute variables were highly correlated with total small mammal abundance: percent aspen, total plant cover, number of grass species, snag density (stems/ha), CWD volume (m³/ha), plant richness, and shrub and herb cover. Fourteen cavity-nesting bird species were detected 1541 times during 288 point count surveys, with 48% of detections within aspen stands. Four species dominated the counts: three weak secondary cavity excavators and a single primary cavity excavator. The total abundance of cavity-nesting bird species was correlated with total volume of CWD (m³/ha), snag volume (m³/ha), snag density (stems/ha), downed CWD volume (m³/ha) and percent aspen. Overall, the pure stands of aspen supported the largest numbers and diversity of small mammals and birds; these results highlight the importance of aspen stands as they may serve as biodiversity 'hotspots' within dry interior British Columbia forests. Forest managers should incorporate the maintenance of these stands into their long-term management plans.

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