Small-Mammal Relationships with Down Wood and Antelope Bitterbrush in Ponderosa Pine Forests of Central Oregon

Abstract

Abstract The influence of down wood on fire behavior in ponderosa pine (Pinus ponderosa) forests in central Oregon is much understood. However, little is known about down-wood affiliations with wildlife in this area. Antelope bitterbrush (Purshia tridentata) contributes to wildfires, nitrogen fixation, and the food web, yet its influence on small-mammal populations remains poorly defined. In this study, population density, survival, and reproductive status of yellow-pine chipmunks (Tamias amoenus), golden-mantled ground squirrels (Spermophilus lateralis), and deer mice (Peromyscus maniculatus) are estimated under three down-wood and shrub-cover conditions in ponderosa pine/antelope bitterbrush forests of Oregon. The odds for golden-mantled ground squirrel survival are 4.2 times greater on units with high (x¯ = 117.8 m3/ha) versus low down-wood volume (x¯ = 15.8 m3/ha), and each 35.1-m3/ha increase in down wood coincides with a 10% increase in ground squirrel density. Yellow-pine chipmunk densities are 57% higher on units with high (x¯ = 31.2%) versus low total shrub cover (x¯ = 9.2%), and 4.4 and 2.3% increases in total shrub and live bitterbrush cover, respectively, coincide with 10% increases in chipmunk density. Deer mouse populations are little affected by down-wood volume or shrub cover. Study results suggest that management activities influencing down wood or bitterbrush will likely affect the composition of small-mammal communities through population changes in one or more small-mammal species. FOR. SCI. 50(5):711–728.