Mammals in Mechanically Thinned and Non-Thinned Mixed-Coniferous Forest in the Sacramento Mountains, New Mexico (Report‪)‬

Coniferous forests in the American Southwest have experienced changes in structure, composition, and processes due to human activities over the past century (Dahms and Geils, 1997; Huggard and Gomez, 2001). The major structural change has been an increased density of younger trees, which has resulted in significant economic losses through factors such as reduced productivity of marketable timber and increased susceptibility to, and occurrence of, large, high-intensity crown fire (Kaufmann et al., 1998; Agee and Skinner, 2005). Mechanical-thinning treatments are common silvicultural techniques used to enhance production of board feet in these coniferous forests. More recently, these techniques also have been evaluated for reducing fuel loads, and thereby, fire severity (Cram et al., 2006; Mason et al., 2007). In response to economic losses associated with recent forest fires, United States policy during the 2000s has been directed at widespread fuel reduction, especially through mechanical thinning (Agee and Skinner, 2005). However, in the American Southwest there is little information regarding ecological effects of mechanical thinning in coniferous forests, and this is especially true for wildlife in mixed-coniferous forests, which are those widespread montane forests typically dominated by Douglas fir (Pseudotsuga menziesii) or white fir (Abies concolor, Dick-Peddie, 1993). Rather, most previous studies in the Southwest focused on effects of thinning in ponderosa pine (Pinus ponderosa) forests, particularly with regards to ecosystem-restoration treatments (e.g., Chambers and Germaine, 2003; Waltz and Covington, 2004). Knowledge about potential ecological effects of thinning southwestern mixed-coniferous forests is hampered not only by a lack of specific studies on effects of thinning, but also by a paucity of basic natural-history information on most kinds of wildlife inhabiting these ecosystems. This lack of knowledge is particularly acute for mammals in the southern Sacramento-Manzano Mountain Section of the Arizona-New Mexico Mountains Province (see W. H. McNab and P. Avers, http://www.fs.fed.us/land/pubs/ ecoregions/, for ecological subregions; but see Ward, 2001). The dominant physiographic feature of this region is the Sacramento Mountains, which is a large mountain range in Lincoln and Otero counties in south-central New Mexico. The Sacramento Mountains reach high elevations (3,693 m) and elevations above ca. 2,500 m form an extensive area of nearly continuous mixed-coniferous forest (Kaufmann et al., 1998). Desert and grassland ecosystems of the surrounding valleys result in isolation of the mountaintop-forest fauna, which has produced a distinctive mammal community composed of both endemic species and a unique assemblage of more widely distributed species (Frey, 2004; Frey et al., 2007). Thus, given both the paucity of information on mammals in thinned, mixed-coniferous forests and the unique mammal fauna of the Sacramento Mountains, the overall goal of this research was to present a case study that assessed differences in terrestrial-mammal communities in mechanically thinned and non-thinned stands of mixed-coniferous forest in this region. Specifically, we evaluated differences in richness, relative abundance, and survival of small mammals and activity of large mammals in three commonly applied mechanical-thinning treatments (commercial harvest, lop-pile thinned, and lop-scatter thinned) and in two non-thinned stands that differed in age (i.e., 20-30 and 60100 years post commercial harvest).