Habitat classification and characteristics of small mammal and amphibian communities in beaver-pond habitats of the Oregon Coast Range

Graduation date: 1992Presentation date: 1992-02-19During 1988-1989, stream habitat variables were compared between beaver-dam sites and unoccupied-stream sites to identify variables that may have been important for beaver (Castor canadensis) in selecting dam sites in the streams of the Drift Creek basin, Lincoln County, Oregon. Increasing valley floor width and grass/sedge cover and decreasing stream width, stream gradient, red\ud alder (Alnus rubra) cover, and shrub cover had positive effects on selection of dam sites. A discriminant function model correctly classified 83% of beaver-dam sites and 88% of unoccupied-stream sites with\ud chance-corrected classification rate of 69% (Kappa statistic). Applicability of the U.S. Fish and Wildlife Service Habitat Suitability Index (HSI) model for beaver was\ud tested in the basin. HSI-model scores were highly influenced by the water life requisite and differed between darn sites and unoccupied sites. Scores for the food life requisite did not differ between dam sites and unoccupied sites; food may not be a factor influencing selection of dam sites. The water fluctuation variable was subjective and was not sensitive enough to\ud differentiate darn sites from unoccupied sites. Three geomorphic characteristics (stream width, gradient, and valley floor width) were used in developing a new Habitat\ud Suitability Index (HSI) model for the basin. The HSI model scores produced by the new model were different between darn sites and unoccupied sites. Capture frequencies of small mammal and amphibian species were compared between beaver-occupied reaches and\ud unoccupied reaches in 5 streams in the Oregon Coast range during the fall of 1989. Species richness, species diversity, and equitability of small mammal and amphibian\ud communities did not differ between occupied and unoccupied reaches. The capture frequency of Microtus spp. was consistently higher at occupied reaches than at unoccupied\ud reaches. None of small mammal and amphibian species had consistently higher or lower capture frequencies at occupied reaches than at unoccupied reaches in each of 5 streams. Inconsistent abundance of small mammal and\ud amphibian species may reflect diverse habitat conditions among occupied reaches