The Effects of Forest Management on Small Mammal Community Dynamics in Southwestern Ponderosa Pine Ecosystems

In the southwestern United States, ponderosa pine (Pinus ponderosa) forests have been decreasing in biological diversity for the past century. Today's forests are characterized by dense stands of small-diameter trees that are susceptible to stand-replacing crown fires. There is now an emphasis on ecological restoration in the Southwest, whereby forests are thinned to reduce fuel content so that the natural fire regime can be reintroduced. However, given the multiple impacts humans have had on the landscape over the past 100 years, it is unclear whether thinning and burning treatments will restore all aspects of ecosystem health. Given this uncertainty, managers and stakeholders want information on the impacts of treatments on multiple ecosystem components, including wildlife. I used meta-analysis to compare effects of restoration treatments on wildlife species in southwestern conifer forests. Thinning and burning treatments had positive effects on most small mammals and passerine bird species reported in 25 studies suitable for meta-analysis; overstory removal and wildfire resulted in an overall negative response. I recommend that managers implement thinning and burning treatments, but that future research efforts focus on long-term responses of species at larger spatial scales and target species for which there is a paucity of data. iii No comprehensive analysis of the small mammal community in response to restoration treatments at large scales has been conducted in ponderosa pine forests. Small mammals are important in forest ecosystems in serving as prey, recycling nutrients, dispersing fungal spores and seeds, and aerating soils. During 2006-2009, I trapped eight species of small mammals at 294 sites in northern Arizona, and used occupancy modeling to determine wildlife responses to habitat. The most important habitat variables in predicting small mammal community occupancy were pine basal area, treatment intensity (percent of trees removed and time since treatment), the number and length of time slash piles are left on the ground, rock cover, and snags >40cm diameter. The average occupancy of all species was positively related to thinning treatment and slash. No one treatment benefitted all species, but rather an arrangement of dense and open stands across the landscape with heterogeneity in fine-scale features is likely the best management approach for restoring and maintaining a diverse small mammal community. Similarly, community composition differed in each of 6 years following treatment, but total density remained constant. Total species densities were significantly lower in stands with dense conditions than in stands with more open structural conditions similar to those of presettlement times, which had similar small mammal densities as the thinning treatments. In addition, tassel-eared squirrels (Sciurus aberti), golden-mantled ground squirrels (Spermophilus lateralis), and gray-collared chipmunks (Tamias cinereicollis) appeared to play a functionally redundant role in dispersing ectomycorrhizal fungi across different stand structures. These results iv suggest that restoration treatments can maintain ecosystem stability in terms of small mammal community structure and function. Finally, I found that the rapid assessment, occupancy and density modeling approach was highly effective in evaluating the response of the small mammal community to treatment and other habitat attributes. Particularly in the arid Southwest, most small mammal population studies end up primarily tracking precipitation patterns, but I showed a lack of a year effect by all species. Although this study was a big effort, it obtained more reliable, repeatable results for a greater number of species than many equally-intensive small mammal studies with similar objectives, which relied on mark-recapture methods and density estimation. I suggest this design be utilized in other studies that grapple with high variability and large spatial and temporal scales in assessing general impacts of treatments or habitat change on wildlife species