Graduate Thesis Or Dissertation
 

Activity of bats in thinned, unthinned, and old-growth forests in the Oregon Coast Range

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  • Ten species of bats occur in the Oregon Coast Range and are hypothesized to be associated with late-successional forests. The development of characteristics of late-successional forests in young forest stands can be accelerated through silvicultural practices such as thinning I examined the effects of thinning on the use of forests by bats in the Oregon Coast Range. I used automated ultrasonic detectors to record bat calls in 50- to 100-year-old thinned and =thinned stands as well as in old-growth (2200-year-old) stands in 11 sites in the Oregon Coast Range during the summers of 1994 and 1995. I compared bat activity levels among the 3 stand types. In addition, I classified bat calls into 1 of 5 species groups: Eptes/Las, Myev/vo, Myyu/ca, MythCory, and Mysp. I measured selected vegetation and environmental variables in conjunction with bat activity. I also compared bat activity on roads with activity in the stand interior at 1 site. Bat activity was higher in old growth than in young stands, and higher in thinned than in =thinned stands in 1995 and over both seasons combined. I did not detect a difference in bat activity among stand types in 1994, until I removed 1 site from the analysis. The Mysp and MythCory species groups exhibited differences among stand types. Bat activity along roads was higher than activity within stands. Tree density, tree diameter, tree height, shrub cover, and shrub height varied significantly between old-growth and young stands. Tree density, tree diameter, shrub cover, canopy cover, and crown height varied significantly between thinned and unthinned stands. Bat activity, overall or by species group, was significantly related to structural variables, including mean snag diameter, mean distance from the detector to snags, and percent shrub cover. My results suggest that bats are sensitive to stand structure and that silvicultural practices, such as thinning, which promote development of structural characteristics found in old-growth stands, would benefit bat populations. Further study is needed to clarify the habitat preferences of separate bat species and to specify habitat elements required by bat species.
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