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The response of terrestrial salamanders to forest harvesting in southwestern British Columbia Maxcy, Katherine Alexandra

Abstract

Forest harvesting reduces the abundance of terrestrial salamanders although the mechanism of the response is unknown. Maintaining riparian buffers around headwater streams has been suggested as one strategy to protect amphibians from the effects of forest harvesting. To understand better the proximate response of terrestrial salamanders to forest harvesting and to determine the efficacy of 30 m riparian buffers in mitigating these effects, I sampled amphibians with increasing distance from streams before and after harvesting. The three treatments were each replicated twice: control, 30 m buffer and clearcut. The relative abundance of aquatic-breeding salamanders (Ambystoma gracile and Taricha granulosa) changed little one year post-harvest in the buffer and clearcut treatments indicating harvesting did not immediately impact their numbers. The response of the terrestrial salamanders to forest harvesting was more variable. The relative abundance of Ensatina eschscholtzii decreased on the buffer and clearcut sites while the relative abundance of Plethodon vehiculum increased after harvesting. I suggest the changes in relative abundance by the terrestrial-breeding salamanders are due to changes in movement patterns which alter their capture rates rather than an actual increase or decrease in relative abundance for either salamander. Movement patterns provided ambiguous results for all four salamanders as to whether they were showing compensatory behaviour in response to harvesting. The movement distances and rates of the four species did not appear to be related to habitat type. The growth rates of Ambystoma gracile, Ensatina eschscholtzii, and Plethodon vehiculum recaptured in clearcuts were lower than those individuals recaptured in forested habitat, indicating there was some cost associated with being in clearcut habitat. Thirty-meter riparian buffers appear to be effective in mitigating the effects of forest harvesting for three of the four salamanders captured. The proportion of captures within 30 m increased in the buffer after harvesting for Ambystoma gracile, Taricha granulosa, and Plethodon vehiculum. Buffer strips may be even more critical to juvenile survival since over 80% of juvenile Ambystoma gracile were captured within 30 m of the stream in the buffer treatment and only 40% in the control and clearcut treatments respectively. Additionally, the proportion of aquatic-breeding salamanders moving parallel to the stream increased postharvest in the buffer treatments indicating the riparian buffer may be used as a corridor for movement during their breeding migrations. Overall, all species were present on treated sites after harvesting indicating direct mortality from the physical process of logging itself was limited. Shifts in distribution and increased parallel movement for the aquatic-breeding salamanders in the buffer treatments indicate these buffers are acting as corridors for movement.

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