Arboreal rodents are important elements of regional biodiversity. They play a critical role in energy flow in Oregon Coast Range forests and are important in dispersal of the spores of mycorrhizal fungi. In addition, arboreal rodents are primary prey species of many predators, including the northern spotted owl. Hence, the response of arboreal rodents to management of young stands is an important area of investigation.
Previous research indicates that arboreal rodents may be particularly sensitive to changes in forest structure, but their response to forest management has not been fully elucidated. Although some studies suggest that arboreal rodents are closely associated with late-seral-stage forests, little empirical research is available on this question, and almost no data are available from Oregon Coast Range forests. The lack of information is particularly acute for questions concerning use of young forest stands by flying squirrels and concerning our ability to create suitable habitat for arboreal rodents silviculturally--through commercial thinning, for example. In addition, information on habitat relationships of another species of arboreal rodent, the red tree vole, is very poor, and much of it is scattered in obscure sources.
A better understanding of the habitat relationships of arboreal rodents will help forest resource managers make more-informed decisions. In this study we examined the biology of arboreal rodents in the Oregon Coast Range in order to improve our understanding of how various silvicultural and management activities influence arboreal rodent populations in managed forests.
The study has three primary objectives: 1) to determine the relationship between forest structure and habitat utilization by arboreal rodents, 2) to synthesize existing information concerning patterns of habitat utilization, natural history, and biology of the red tree vole, and 3) to determine the value and feasibility of additional field research on arboreal rodents in young and managed forests in the Oregon Coast Range.
For the field component of the project, we are looking at fire-regenerated stands of over 120 years old and Douglas-fir plantations 10-15 years old, 20-25 years old, and 30-35 years old. Three study stands have been selected in each of these four age classes. Mammals in the stands were trapped with Tomahawk live traps. All chipmunks and flying squirrels captured were marked and released.
Two 6-week trapping sessions were conducted during the fall of 1992 and the spring of 1993. Field assessment of the vegetative characteristics of the sites was also completed. Substantial population data were collected for chipmunks and flying squirrels. Densities of chipmunks were among the highest reported from any previous study. Results of the trapping were presented in the COPE Report 6(2):4-6 and in the 1993 Annual Report.
Analyses of vegetation data for the stands were conducted during the past year. Chipmunk populations were closely associated with percent cover of salal in the understory. The data suggest that management activities that open up the overstory, such as commercial thinning, may enhance the habitat for this species in the Coast Range.
The literature review on red tree voles was completed. Sixty-eight pertinent references were identified and reviewed. A manuscript outlining all aspects of the biology of the species has been prepared and submitted for publication.
This research demonstrated that flying squirrels in some young forest stands can attain densities similar to those found in mature stands in the Oregon Coast Range. In part as a result of our findings from this study, we have joined in a collaborative effort with Robert Anthony of the Oregon Cooperative Wildlife Research Unit to examine the influence of commercial thinning on arboreal rodent populations. Please see the next report in this volume, titled Influence of Silvicultural Operations on Stand Structure and Wildlife Abundance and Diversity in Managed Coast Range Forests.
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