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Title: Responses of the woodland salamander Ensatina eschscholtzii to commercial thinning by helicopter in late-seral Douglas-fir forest in northwest California

Author: Welsh, Hartwell Jr.; Waters, Jeff; Hodgson, Garth; Weller, Ted; Zabel, Cynthia;

Date: 2015

Source: Forest Ecology and Management

Publication Series: Scientific Journal (JRNL)

Description: We examined responses of the woodland salamander Ensatina (Ensatina eschscholtzii) to commercial thinning by helicopter in late-seral Douglas-fir forest in northwestern California, USA, using a before-after control-impact (BACI) design. We employed passive pitfall traps on eight (four each treatment and control) 100 trap grids over eight years (1996–2003), three years pre- and five years post-treatment. We conducted 3–11 weekly site visits within each of 10 trap periods depending upon weather over two spring and eight fall periods for a total of 50 visits to test for differences in surface counts and body condition. We standardized data to captures/1000 trap nights. Surface counts over the eight years were highly variable with less surface activity in spring compared to fall. Although the BACI design allows for initial differences among pre-treatment grids there were none. However, in the three years post-treatment (1999–2001) mean counts on treatment grids were significantly lower than on control grids. By 2002 and 2003, post-treatment counts on control and treatment grids both declined substantially, such that despite 47% more salamanders on control grids, variability was sufficient to preclude statistical significance. Recapture rates averaged 23.3% for three years pre-treatment, but increased to 51.4% for the five years post-treatment. Pre-treatment population estimates increased on control grids post-treatment, however, surface density estimates declined. On treatment grids both population and density estimates declined following treatment. Body condition analyses indicated no significant differences between controls and treatments for either sex prior to or post-treatment. The three years of significant differences in surface counts between controls and treatments post-treatment, followed by no differences in the last two years of the study, combined with no differences in BCIs, lead us to conclude that the surface activity of Ensatina on treatments grids was only temporarily impacted by the thinning. Declining population estimates on treatment grids also indicated at least a temporary reduction in those populations. We unexpectedly found declines in counts and density estimates on both sets of grids over the eight years, suggesting a wider effect may be causing reductions in the surface activity of these salamanders, and possibly in their populations.

Keywords: Helicopter thinning, Woodland salamander, Ensatina eschscholtzii, Old-growth Douglas-fir forest, Pseudotsuga menziesii, Northwest California

Publication Notes:

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  • This article was written and prepared by U.S. Government employees on official time, and is therefore in the public domain.



Welsh, Jr. H.H.; Waters, J.R.; Hodgson, G.R.; Weller, T.J.; Zabel, C.J. 2015. Responses of the woodland salamander Ensatina eschscholtzii to commercial thinning by helicopter in late-seral Douglas-fir forest in northwest California. Forest Ecology and Management. 335: 156–165.


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