A New Elevation Record for the Red Tree Vole in Oregon: Implications for National Forest Management

Article excerpt

ABSTRACT.-We document the capture of a red tree vole (Arborimus longicaudus) at a new location and higher elevation than previously recorded for the species. This finding shows that the red tree vole occurs outside the current survey and management areas designated for its protection in Oregon federal forests.

INTRODUCTION

The red tree vole (Arormus longicaudus) is an arboreal arvicoline rodent restricted to the conif erous forests of western Oregon (Johnson and George, 1991; Maser, 1998); its reclassification into the genus Arborimus from Phenacomys remains under dispute (see Murray, 1995). Red tree voles are not readily captured; consequently, it is difficult to ascertain their abundance, behavior or habitat relationships (Corn and Bury, 1986, 1988; Gillesberg and Carey, 1991). In some locations red tree voles are major prey of the northern spotted owl (Strix occidentalis caurina; Forsman et al., 1984), a federally listed threatened species (USDI, 1990). Partly because of the importance of the red tree vole as spotted owl prey and largely because of its association with late successional and old growth forests, this vole has been designated a species to be protected through survey and management strategies in federal forests throughout its known range (USDA Forest Service and USDI Bureau of Land Management, 1994).

We present details of a red tree vole captured in the Cascade Mountains of southern Oregon, outside the range identified by verified museum specimens (Verts and Carraway, 1998) or the distribution implied from field summaries (Hayes, 1996), but within its proposed potential range (Csuti et al., 1997). The animal was caught during the USDA Forest Service Demonstration of Ecosystem Management Options (DEMO) project, an investigation of the effects of green tree retention harvest on forest ecosystems (Halpern and Raphael, 1999).

METHODS

The study area is on the Diamond Lake District of the Umpqua National Forest, Douglas County, Oregon (43 deg 12'N, 122 deg 18'W), approximately 12-km w of the northwest corner of Diamond Lake and directly north of Dog Prairie Creek. The area is within 20 km of the Cascade crest, on a SW aspect at 1600-m elevation. Slopes range from 40-60%. Overstory vegetation is dominated by Douglas-fir (Pseudotsuga menziesii) with lesser amounts of white fir (Abies concolor) and incense cedar (Calocedrus decurrens). In the stands sampled, canopy closure was complete and little ground vegetation or down wood was present. Stand ages were approximately 165 y, but trees were thinned to a basal area of 68 m^sup 2^/ha in 1986. Trees had a mean dbh of 60 cm.

Six trapping grids were established in an area approximating 220 ha, each consisting of 63 (9 x 7) trap stations with 40 m between stations. Small mammals were captured in pitfall traps (15-cm diam, 72-cm long), with one trap per station. In accordance with field methods approved by the American Society of Mammalogists (1987), water was placed in pitfalls to a depth of 10 cm. Pitfalls were checked weekly for 28 consecutive days during October and November 1995 and 1996. Specimens were frozen after collection. In the laboratory species identifications were confirmed and reproductive organs were measured to determine reproductive status. Positive identification of the red tree vole was made using dental and tail attributes described by Maser and Storm (1970).

RESULTS

During 21,168 trap nights across the six trapping grids, a single red tree vole was captured on 18 October 1995. The vole was a 24-g nonscrotal male with a total length of 159 mm and a tail length of 68 mm. Testes were abdominal and measured 3 X 2 mm. Maximum length of the seminal vesicles was 2 mm. Epididymal development was consistent with a nonreproductive state. The specimen is in the Mammal Collection, University of Alaska Museum, Fairbanks (catalog number UAM 47122). Frozen tissues (heart, liver, kidneys and spleen) are preserved and catalogued separately (AF# 23744). …