The Effects of Timber Harvesting on Breeding Birds in a Mixed-Coniferous Forest

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Abstract
Avian species composition and densities in a mixed-coniferous virgin forest and in a similar area that sustained a moderately heavy overstory removal form of timber harvesting were examined in the White Mountains in Arizona [USA] during the summers of 1973 and 1974. The unlogged plot supported significantly (P < 0.05) more individuals than did the logged plot (88.9 birds/40 ha more in 1973; 153.5 birds/40 ha more in 1974). The harvested plot supported far fewer tree-foliage searching species. Timber-gleaning species and those that nest in foliage were significantly denser in the unlogged plot. The effect on cavity nesters depended largely on their foraging behavior. Mountain chickadees, which usually nest in snag cavities and forage mainly on live vegetation and bark, were significantly less abundant in the logged plot; woodpeckers which forage on both live and dead trees were equally abundant in both plots. Aerial foragers and birds that used slash, benefited by the lumbering. This selective logging led to an increase in tree species diversity, and no appreciable change in diversity of foliage height, tree volume or bird species. The modified plot, while containing approximately the same number of avian species, supported a far smaller total population. The amount of foliage available undoubtedly exerts a strong influence on avian species composition and densities because it furnishes nesting sites and foraging substrate. The virgin forest provided substantially more foliage (113,984.0 m3/ha vs. 15,269.8 m3/ha) than did the logged plot. Along with foliage volume and configuration, presence of suitable numbers of snags and significant amounts of slash also were important.