Low thermal tolerances of stream amphibians in the Pacific Northwest: Implications for riparian and forest management

Temperature has a profound effect on survival and ecology of amphibians. In the Pacific Northwest, timber harvest is known to increase peak stream temperatures to 24◦C or higher, which has potential to negatively impact cold-water stream amphibians. I determined the Critical Thermal Maxima (CTmax) for two salamanders that are endemic to the Pacific Northwest. Rhyacotriton variegatus larvae acclimated at 10◦C had mean CTmax of 26.7 ± 0.7 SD◦C and adults acclimated at 11◦C had mean CTmax of 27.9 ± 1.1◦C. These were among the lowest known values for any amphibian. Values were significantly higher for larval Dicamptodon tenebrosus acclimated at 14◦C (x̄ = 29.1± 0.2◦C). Although the smallest R. variegatus had some of the lowest values, size of larvae and adults did not influence CTmax in this species. Current forest practices retain riparian buffers along larger fish-bearing streams; however, such buffers along smaller headwaters and non-fish bearing streams may provide favorable habitat conditions for coldwater-associated species in the Pacific Northwest. The current study lends further evidence to the need for protection of Northwest stream amphibians from environmental perturbations. Forest guidelines that include riparian buffer zones and configurations of upland stands should be developed, while monitoring amphibian responses to determine their success.