Shelly A. Johnson, Carol L. Chambers
Western North American Naturalist 77 (3), 355-368, (16 October 2017) https://doi.org/10.3398/064.077.0308
Ponderosa pine (Pinus ponderosa) forests in the southwestern United States, used by 16 species of bats, are managed with thinning and prescribed fire to restore tree densities and fire regimes to conditions that existed prior to Euro-American settlement. Using 2 approaches (roosting and foraging) to categorize forest habitat for bats, we evaluated how restoration treatments may affect habitat use. We hypothesized that more foraging activity would occur in thinned stands because more species are adapted to open forest, but that more roosts would occur in unthinned stands where snags were unaffected by mechanical treatments and prescribed fire. During the summers of 2006 and 2007, we used acoustic detectors to record call rates of bats as a measure of activity level and compared activity levels among stands that had undergone 3 thinning treatments (light, moderate, and heavy, with 245, 172, or 142 trees per hectare postthinning, respectively) and an unthinned stand as a control (1201 trees per hectare). With radiotelemetry, we located roosts used by reproductive females of 2 common species of forest-associated bats (long-eared myotis, Myotis evotis, and Arizona myotis, Myotis occultus) during summer 2007. We measured roost characteristics at 3 spatial scales (roost, microplot, and surrounding landscape) to contrast between roosts used by Myotis species and randomly selected comparison snags, microplots, and study area landscape. Among thinned and unthinned stands we did not detect a difference in activity levels for all bats (P = 0.2), nor a difference in call rates for Myotis spp. (P = 0.1). However, there was lower activity (P = 0.01) for non-Myotis bats in unthinned compared to thinned stands. This is probably because most non-Myotis species are better adapted to foraging in open forests. Of 24 roosts for long-eared myotis and Arizona myotis, only 31% and 25%, respectively, occurred in thinned stands. Bats selected large-diameter (>68 cm diameter at breast height) ponderosa pine snags with exfoliating bark. Roosts for Arizona myotis were in areas with elements of old-growth structure, whereas roosts for long-eared myotis occurred in areas similar to stratified, midsuccessional, even-aged forest. Managing for large-diameter ponderosa pine snags and a variety of tree densities and age classes will provide roosting and foraging habitat for bats. We found no distinct “best” treatment to recommend overall, likely because of species differences, with some bats better adapted to opencanopy and some to closed-canopy forest. Maintaining diverse habitat will support a diverse bat assemblage.