Bat activity in relation to fire and fire surrogate treatments in southern pine stands

Abstract

Forest managers often use thinning and prescribed burning to reduce the risk of wildfire and insect outbreaks. Because thinning and burning alter the structure of forest stands and may affect insect prey abundance, they may change the suitability of stands for bats. Our objective was to test the effects of thinning and burning on bat foraging and commuting activity in pine stands in the Clemson Experimental Forest in the Piedmont of South Carolina. We also tested whether vertical use of stands varied with treatment and whether activity of three common species varied among treatments. Twelve stands in the Clemson Experimental Forest dominated by loblolly ( Pinus taeda) and shortleaf ( P. echinata) pine and at least 14 ha in size were selected and three replicates of four treatments were installed. The treatments were: (1) prescribed burning (Burn), (2) thinning to 18 m 2/ha (Thin), (3) thinning to 18 m 2/ha followed by prescribed burning (Thin&Burn) and (4) no treatment (Control). Bat activity was sampled with AnabatII bat detectors May–August 2001 and 2002. Big brown bats ( Eptesicus fuscus), eastern red bats ( Lasiurus borealis), and eastern pipistrelles ( Perimyotis subflavus) were the most frequently recorded species and activity was significantly greater in 2001 than in 2002. In 2001, overall activity was significantly greater in the Thin stands than in the Control stands; activity in the Burn and Thin&Burn stands was intermediate. Activity was also greater in treated stands than in the Control stands in 2002, but the difference was not statistically significant ( P = 0.08). In both years we recorded significantly more calls at 9 m than at 0.5 m above ground but the treatments did not affect vertical use of the stands. Activity of big brown bats and red bats was significantly higher in Thin stands than in Control or Burn stands, whereas activity of pipistrelles did not vary among treatments. Our results suggest that treatments that reduce clutter, particularly thinning, increase the suitability of pine stands for bats’ foraging and commuting activity in the Piedmont region. Thus, use of these practices may help to preserve the biodiversity of managed pine forests in the South.