Relationship of bat occupancy and activity to post-fire structural conditions on the Cumberland Plateau
Wildfires are predicted to increase in occurrence, size, and severity due to changing climates, and prescribed fire has become a widely accepted management tool for the propagation of native species and the control of combustible fuels. Thus, understanding the dynamics of wildlife response, such as bat presence and activity, to the structural changes generated by fire is of increasing importance. The direct risks of burning such as harm from heat and gas, along with roosting response after burning, has been investigated, but little is known regarding the impact of post-fire landscape conditions on bat activity. Past studies suggest reduction in vegetation from burning may increase access and foraging efficiency for bats. Our objective was to investigate bat activity in relation to burn history and vegetation structure in the Big South Fork National River and Recreation Area, in Kentucky and Tennessee. We compared use of forest sites with varying burn histories (frequency, severity, and time since burn) to adjacent unburned forest sites. We used AnabatII detectors to acoustically monitor activity levels for ≥ 2 nights during the 2014 maternity season across 22 paired treatment and control areas. All trees and snags >1.4 m tall and >10 cm diameter at breast height (DBH) in a 0.1 ha circular plot around each detector were identified and measured. Echolocation files were filtered and separated into high (≥36 kHz) and low (≤35 kHz) phonic groups using a combination of AnalookW software and manual examination.
We recorded 4079 bat passes at 66 sites. The mean number of total bat passes and the mean number of high and low frequency calls were greater in burned sites than unburned sites, and these differences were statistically significant (p < 0.003). As stem density was significantly lower (p < 0.0001) in burn sites compared to controls, and bat activity was significantly higher (p < 0.0004) in stands with lower stem densities, differences in activity between burns and controls appear related to differences in stem densities. Additional analyses among burned sites suggest that interactions between stand type and burn parameters (fire frequency, severity, and burn year) affect stem density. Although ongoing analyses of the structural effects of burning and the influence of meteorological factors will provide further insight, fire’s subsequent effect on forest structure appear to have increased the suitability of forested sites for bats in our study area.