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Short-term effects of group-selection timber harvest on landbirds in montane hardwood-conifer habitat in the central Sierra Nevada

Garrison, Barrett A., Triggs, Matthew L., Wachs, Robin L.
Journal of field ornithology 2005 v.76 no.1 pp. 72-82
Quercus kelloggii, birds, breeding, habitats, hardwood, harvesting, logging, mountains, stand density, trees, California, Sierra Nevada (California)
We studied short-term responses by 16 species of breeding landbirds to group-selection timber harvest at four 21.2-ha replicated study stands in montane hardwood-conifer habitat in the central Sierra Nevada Mountains, California, 1995–2002. The group-selection timber harvest was done to enhance stand conditions for California black oak (Quercus kelloggii), the dominant hardwood. Birds were censused using point counts, and harvesting effects were assessed using the Before-After/Control-Impact Pairs (BACIP) design where the response variables were the differences in landbird abundances between paired treatment and control plots for pre- and post-treatment periods. Each stand had paired and adjacent 10.6-ha treatment and control plots, and four 0.6-ha group-selection units were randomly placed and harvested in each treatment plot in 1998 and 1999. In the treatment plots, tree basal areas and tree densities were reduced approximately 30% and snag densities were reduced approximately 45% with the harvest. Abundance differences between pre- and post-treatment periods differed among stands for 11 (69%) species. Significant differences in abundance between the pre- and post-treatment periods were found for Steller's Jays (Cyanocitta stelleri), Warbling Vireos (Vireo gilvus), and Western Wood-Pewees (Contopus sordidulus). Significant interactions between stands and treatment periods were found for Evening Grosbeaks (Coccothraustes vespertinus) and Western Wood-Pewees, indicating that responses differed among stands. Significant differences between treatment periods were due to proportionately greater decreases in post-treatment period abundance in control plots than in treatment plots (Evening Grosbeak, Steller's Jay, Warbling Vireo) or a proportionately lesser increase in post-treatment period abundance in the control plots than in treatment plots (Western Wood-Pewee). We conclude that group-selection harvesting had neutral or positive short-term effects on the species studied.