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Effective conservation and management of small mammals require knowledge of the population dynamics of co-occurring species. We estimated the abundances, autocorrelations, and spatiotemporal associations of 4 small-mammal species from 2011–2016 using live-trapping mark-recapture methods on 9 sites across elevation and canopy openness gradients of a late-successional forest in the H. J. Andrews Experimental Forest, on the west slope of the Oregon Cascades. We also quantified species-specific spatial variation in adult sex ratios and body mass. We used Huggins closed capture models to estimate site- and year-specific abundances of 4 target species: Humboldt’s flying squirrels (Glaucomys oregonensis), Townsend’s chipmunks (Neotamias townsendii), western red-backed voles (Myodes californicus), and deer mice (Peromyscus maniculatus). We estimated the temporal autocorrelations among site- and species-specific abundance estimates and used generalized linear mixed effects models to investigate the effects of 7 spatiotemporal covariates on species-specific mean abundance estimates. Species-specific adult sex ratios, juvenile to adult ratios, and adult body masses were not widely variable among study sites. Abundance estimates varied by as much as 4-fold among years and 6-fold among sites. Humboldt’s flying squirrel abundance was temporally autocorrelated at intervals of 1 and 5 years, Townsend’s chipmunk abundance was temporally autocorrelated at intervals of 1–4 years, and western red-backed vole abundance was temporally autocorrelated at 1, 4, and 5 years. Mean fall abundance estimates were associated with elevation and climate and in some cases, canopy openness and berry-producing shrubs, but the direction of the association differed among species for some covariates. Our findings could provide additional management tools for small-mammal abundance objectives, and highlight the importance of careful covariate selection in studies using indices of small-mammal abundance.

We studied the effects of 6 green-tree retention levels and patterns on the diets of northern flying squirrels (Glaucomys sabrinus), Townsend's chipmunks (Tamias townsendii), Siskiyou chipmunks (T. siskiyou), western red-backed voles (Myodes californicus), and southern red-backed voles (Myodes gapperi) using fecal pellet analysis. These rodents are truffle spore dispersers and prey for forest predators such as the northern spotted owl (Strix occidentalis caurina). Pretreatment diets showed differences in truffle and plant consumption among genera. Tree harvesting, especially in the 15% aggregated retention pattern, reduced frequency of Rhizopogon spores in the diet of voles, which may reflect a reduced ability of these animals to forage for Rhizopogon truffles, a decreased access to these truffles, or a reduction in Rhizopogon truffle abundance or frequency. Habitat island effects and edge effects provide conceptual frameworks for the reduction in consumption of Rhizopogon truffles by voles in green-tree aggregates. Overall, small mammal consumption of truffles showed little change in response to the treatments. Animals may be compensating for a locally declining food source by altering their foraging behavior. The long-term effect of this postulated behavioral compensation on small mammal energetics and population dynamics is unknown. Forest managers may reduce the impact of tree harvesting on these key forest ecosystem components by including green-tree aggregates within a dispersed retention matrix.

Forests in the Sierra Nevada, similar to those across the continent, have been substantially altered by logging, fire exclusion, and other human activities. Current forest management emphasizes maintenance or restoration of resiliency in the face of contemporary disturbance factors that include wildfire, climate change, continued urbanization, and invasive species. We evaluated responses of small mammals to forest management by monitoring a series of 12 replicate trapping grids in compositionally homogeneous forest over 8 years, and implemented 2 levels of canopy thinning. Livetrapping efforts (119,712 trap-nights) yielded 15,613 captures of 2,305 individuals of 13 species, and although forest structure was significantly influenced by canopy treatments, small mammal numbers and assemblage composition were not. To better understand this we assessed habitat associations of small mammals at 599 census points on 75 transects established in a stratified random manner throughout Plumas National Forest. We analyzed these data with 2 complementary forms of constrained ordination (canonical correspondence and canonical correlation) that extract major gradients in 1 data set (e.g., distribution of small mammal captures) and explain these in terms of measured variables from a 2nd data set (e.g., habitat and environmental measurements). Over 3 years and 57,504 trap-nights of effort we captured 1,367 individuals of 11 species. Both forms of ordination exposed significant associations between small mammals and underlying habitat metrics, but they explained remarkably little variation in these data, suggesting that small mammals are responding only modestly to habitat variation as expressed by the available environmental variables measured at each plot. We followed this with stepwise multiple Poisson regression to build models of habitat associations of these species. We applied model-averaging and employed Akaike's information criterion corrected for small sample size (AICc) to evaluate candidate models. Reflecting ordination results, competitive models (e.g., those with Akaike differences [ΔAICc] < 2.0) cumulatively explained little variation (12–36%) and regression coefficients were very low. Hence, both ordination and Poisson multiple regression suggest that the limited response by small mammals to canopy thinning primarily reflects the generalist habits of the common species in this forest. We propose that anthropogenic influences have led to structural homogenization of these forests, even across > 800 m of elevation, such that habitat specialists (e.g., old-forest–dependent species such as Myodes [Clethrionomys] californicus and Glaucomys sabrinus) have become less common due to the lack of suitable habitat. Further efforts should target nonforested habitats (meadows and riparian corridors), but results presented here suggest that managers should strive to increase heterogeneity at large spatial scales and especially to promote the development of mature forest structure.