Distribution and habitat relationships of amphibians on the Potlatch Corporation operating area in northern Idaho

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The general objective of this study was to investigate the distribution and habitat relationships of amphibians in the Potlatch Corporation operating area (PCOA) in northern Idaho. Such information is required for developing effective adaptive management plans for the forest ecosystem. The specific objectives of the study included 1) developing a surveying protocol for amphibians in the PCOA, 2) determining how amphibians are distributed across the landscape, 3) determining how the occurrence of amphibians is related to various habitat variables, and 4) providing recommendations on factors that may influence persistence of amphibians on the PCOA. The authors conducted surveys of amphibians at 199 wetland sites from 1994–1996. Both systematic and stratified-random sampling schemes were used to select sites (119 and 80 sites, respectively). The authors primarily used timed visual encounter and area-constrained surveys to sample for amphibians. Habitat data were gathered and analyzed at three spatial scales: landscape, macrohabitat, and microhabitat. Statistical analyses included contingency table analyses and T-tests of the relationship between the habitat variables and the occurrence of amphibians. Six of the ten amphibian species potentially occurring in the PCOA were found; the Coeur d’Alene salamander required a different surveying procedure and was to be described in a separate report. Long-toed salamanders, tailed frogs, Pacific treefrogs, and Columbia spotted frogs were found widely distributed over the PCOA. Idaho giant salamanders and western toads were found to have spotty distributions. Spotted frogs and long-toed salamanders were abundant; tailed frogs and Pacific treefrogs were common; and Idaho giant salamanders and western toads were uncommon. Sample sizes for the common and abundant species were large enough to permit statistical analyses of habitat relationships. Long-toed salamanders, western toads, Pacific treefrogs, and Columbia spotted frogs were positively associated with ponds, silt-mud substrates, and warmer water temperatures. Long-toed salamanders, western toads, and Columbia spotted frogs were also positively associated with distance to forest. Idaho giant salamanders and tailed frogs were positively associated with crown closure, streams, rocky substrates, and cooler water, and they were negatively associated with fine sediments. Results are generally consistent with studies of these species elsewhere. The authors are especially concerned about two species. Idaho giant salamanders warrant special consideration because of their spotty distribution, relatively small populations, positive association with relatively mature forest conditions, and large fraction of overall range occurring within the PCOA. Western toads warrant special consideration because of their spotty distribution and declines elsewhere in their range. However, western toads appear to be more abundant on the western edge of the PCOA. The authors believe that the Idaho giant salamander and tailed frogs would benefit most from a Habitat Conservation Plan that increased protection for streams and riparian areas. The authors make several recommendations regarding future surveys and monitoring. [Comments by an unnamed reviewer appear on 4 numbered pages between the title page and introductory pages of this report.]

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ELECTRONIC FILE - Zoology