MAMMALS IN MECHANICALLY THINNED AND NON-THINNED MIXED-CONIFEROUS FOREST IN THE SACRAMENTO MOUNTAINS, NEW MEXICO

Mechanical thinning is an important silviculture technique for timber production and reducing woody fuels in coniferous forest, but little is known about its effect on wildlife in mixed- coniferous forests in the American Southwest. During 2005-2006 we examined diversity, abundance and survival of terrestrial mammals in thinned and non-thinned mixed-coniferous forest in the Sacramento Mountains, Lincoln National Forest, in southern New Mexico. The three thinning treatments included two non-commercial thins with different slash treatments (i.e., lop-pile, lop-scatter) and a commercial harvest using selective logging. There were two non-thinned treatments that differed in age of stand (i.e., 20-30 years and 60-100 years post harvest). In general, thinned treatments had higher richness and abundance of mammals in comparison with the older non-thinned stand, but did not differ in richness and abundance from the younger non-thinned stand. Abundance of the North American deermouse (Peromyscus maniculatus) and red squirrel (Tamiasciurus hudsonicus) did not differ among treatments. However, survival of P. maniculatus varied more in the non-thinned stands. Abundances of the gray-footed chipmunk (Tamias canipes) and long-tailed vole (Microtus longicaudus) were significantly lower in the older non-thinned stand than in all thinned treatments. Most large mammals were documented in thinned treatments. These results suggest that thinning older stands of mixed- coniferous forest that are overly dense compared with historical conditions benefit the mammal community through increases in diversity and abundance. In comparing the three mechanical-thinning treatments evaluated, none provided a clear cost or advantage to mammals. However, additional controlled experiments are needed to further corroborate these results. RESUMEN—El clareo mecanico de arboles en bosques es una tecnica importante en la silvicultura para la produccion de madera y para la reduccion de combustible lenoso en bosques de cono ´feras. Sin embargo, se sabe poco acerca de su efecto sobre la fauna silvestre de bosques de cono ´feros mixtos en el suroeste de los Estados Unidos. Durante 2005-2006 examinamos la diversidad, abundancia y sobrevivencia de los mamo ´feros terrestres en bosques de cono ´feras mixtos, clareados y no clareados, en las Sacramento Mountains, Lincoln National Forest, en el sur de Nuevo Mexico. Se compararon 3 tratamientos de clareo: desbrozar-apilar, desbrozar-dispersar y corte selectivo comercial. Los bosques no clareados difirieron en sus edades (20-30 anos y 60-100 anos posteriores a la ultima cosecha). En general, los rodales clareados tuvieron una mayor riqueza y abundancia de mamo ´feros en comparacion con el rodal no clareado mas viejo, pero no difirieron en la riqueza y la abundancia con respecto al rodal no clareado mas joven. La abundancia del raton de campo (Peromyscus maniculatus) y la ardilla roja (Tamiasciurus hudsonicus )n o difirioentre tratamientos. Sin embargo, la sobrevivencia de P. maniculatus variom as en los rodales no clareados. La abundancia de la ardilla de pata gris (Tamias canipes) y del raton de cola larga (Microtus longicaudus) fue significativamente mas baja en el rodal no aclareado mas viejo que en todos los rodales clareados. La mayoro ´a de los mamo ´feros grandes se encontroen sitios clareados. Los resultados sugieren que el clareo de bosques de cono ´feras mas viejos que son mas densos comparados con condiciones historicas beneficia la comunidad de mamo ´feros, incrementando su abundancia y diversidad. Al parecer, ninguno de los tres tratamientos de clareo fue mejor o peor para mamo ´feros; sin embargo, es necesario llevar a cabo experimentos controlados que permitan corroborar estos resultados.