Bat activity in thinned, unthinned, and old-growth forests in western Oregon

Many aspects of the influences of forest management activities on bats (Chi roptera) in the Pacific Northwest are poorly known. We compared thinned and unthinned forest stands of the same age and old-growth forest stands to de termine potential differences in structure and amount of use by bats. We hy pothesized that activity levels of bats would differ in stands differing in structure as a result of management history and that activity of bats woul d be similar in stands of similar structure. We used automated ultrasonic d etectors (Anabat II) to record calls of bats in 50-100-year-old thinned and unthinned stands, and in old-growth (greater than or equal to 200 vr old) stands in the Oregon Coast Range during the summers of 1994 and 1995. Our m edian index of bat activity was higher in old-growth than in unthinned stan ds and higher in thinned than in unthinned stands. We were not able to dete ct a significant difference between the index of median bat activity for ol d-growth and thinned stands. More than 90% of identifiable passes were iden tified as calls from Myotis species. The 3 stand types we examined differed in certain structural characteristics such as density and size of trees, a nd amount of overstory and understory cover. We concluded that the structur al changes caused by thinning may benefit bats by creating habitat structur e in young stands that bats are able to use more effectively.