Small Mammal Survival and Downed Wood at Multiple Scales in Managed Forests

Abstract

Conservation of small mammals requires knowledge of ecologically meaningful spatial scales (e.g., individuals or populations) at which species respond to habitat heterogeneity. Between July and October of 1998, we sampled small mammals, understory vegetation, and downed wood (DW) at multiple scales (trap sites, 1-hectare forest patches, and stands) in 2 Douglas-fir (Pseudotsuga menziesii) forests in western Oregon. Our objectives were to determineifDWorunderstoryvegetationvariedamongorwithinforestpatchesoramongforeststandsandwhether variation in survival of small mammals coincided with the scale in which these varied. Understory vegetation explained most of the variation within patches, but did not vary among patches or stands. Survival of the 2 most abundant species, the deer mouse (Peromyscus maniculatus) and creeping vole (Microtus oregoni), also varied within patches by differing among individual home ranges, and was most related to DW volume (cubic meters per 0.01hectare)andherbandgasscover(%).Survivalofdeermicewasexplainedbya2nd-degreepolynomialfunction of DW within individual home ranges, and peaked at 2.0 m 3 per 0.01 ha. Survival of creeping voles was dependent on a negative loge function of DW within home ranges, and was highest in home ranges lacking DW. Our results demonstrate that these species may not be generalists, as previously suspected, but rather specialists tied to specific amounts of particular habitat components within home ranges. We recommend that future studies of relationships betweensmallmammalsandhabitatsconsidermultiplespatialscalesthatareecologicallymeaningfulforthespecies of interest (e.g., home ranges), and examine demographic parameters including survival.