Forest managers in the Pacific Northwest are faced with new challenges of providing for all wildlife in managed forests. Our objective was to elucidate the factors governing the composition and biomass of forest floor mammal communities that are amenable to management. We sampled small mammal communities in forests of various management histories on the Olympic Peninsula and contrasted our results with those of other large studies in the Pacific Northwest. Forest floor mammal communities in forests >35 yr old in the Western Hemlock Zone of Washington and Oregon are composed of 5‐8 characteristic species. These include Sorex trowbridgii (numerically the most dominant); one species each of Clethrionomys, the Sorex vagrans complex, and Peromyscus; and Neurotrichus gibbsii. Species composition changes from south to north, and the communities on the Olympic Peninsula contain two or three additional species compared to communities to the south. Communities in naturally regenerated and clearcutting regenerated (managed) young forests are similar in composition to those in old growth, old growth, however, supports 1.5 times more individuals and biomass than managed forest. Community diversity seems related to the south‐north moisture‐temperature gradient that is reflected in increased diversity of canopy conifers, development of forest floor litter layers, accumulation of coarse woody debris, and abundance of herbs, deciduous shrubs, and shade‐tolerant seedlings (as opposed to understories dominated by evergreen shrubs). Previous work found few habitat variables that were good predictors of species abundance in natural young and old‐growth stands. Naturally regenerated young stands had higher levels of coarse woody debris than old growth. Managed stands had much lower abundance of coarse woody debris and tall shrubs than old growth. Understory vegetation (herbs and shrubs) and coarse woody debris accounted for a major part of the variation in abundance of six of eight species in managed stands, but only two species in old growth. Management of Western Hemlock Zone forest for conservation of biodiversity and restoration of old‐growth conditions should concentrate on providing multispecies canopies, coarse woody debris, and well‐developed understories.
The differences between Phenacomys and Arborimus are evaluated. Elevation of the subgenus Arborimus to full generic rank is proposed.The heather vole and the red tree vole each are rare in museum collections and difficult to obtain in the field. Thus, information regarding these genera has been slow in accumulating. Merriam (1889) described the genus Phenacomys, designating Phenacomys intermedius as the type species. Subsequently, Hall and Kelson (1959) listed nine subspecies from Canada and the northwestern United States. True (1890) described Phenacomys longicaudus, the red tree vole, from Marshfield, Coos Co., Oregon. This species (including P. silvicola) is known to occur from the Columbia River in Oregon southward to Sonoma County, California. It is generally found at lower elevations in associations of Douglas-fir (Pseudotsuga menziesi), grand fir (Abies grandi-A. concolor complex), Sitka spruce (Picea sitchensis), and western hemlock (Tsuga heterophylla ). Merriam (1901) described a terrestrial species, Phenacomys albipes, which is similar in several respects to P. longicaudus, and occurs in the same general region.Taylor (1915) erected a new subgenus, Arborimus, for the tree voles, and Howell (1926) reviewed the genus Phenacomys. Only Taylor and Howell have dicussed the relationships in detail. Much information has been obtained since then.My investigation of the natural history and systematic relationships of the red tree vole began in 1955, and, from 1965 on, was continued in association with Chris Maser and Donald Roberts. Additional microtine genera and species were examined in the field and laboratory, and breeding colonies of several microtine genera have been maintained in order to obtain comparative data.From these studies, it has become apparent that the heather vole and the red tree vole are well differentiated from each other. I first proposed the elevation of Arborimus to generic rank at the annual meeting of the American Society of Mammalogists in 1966. Subsequently I have reappraised and refined my proposal. MATERIALS AND METHODSThe red tree vole was studied throughout its geographic range in order to evaluate any variation in habits. Large series of museum specimens were obtained, including material for special examination, such as skeletons, hyoid bones, bacula, and preserved soft tissues; and I examined most of the specimens in North American museums. A colony of tree voles was maintained for several years. Blood proteins and karyotypes were studied, and reproductive biology and behavioral characteristics observed and correlated with field studies. Live heather voles were also kept for comparative purposes.
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