Response of avian communities to disturbance by an exotic insect in spruce-fir forests of the southern Appalachians

The avian community of montane coniferous forests changed substantially over 21 years In response to the introduction of the balsam woolly adelgid insect (Adelges piceae) and the resulting death of endemic Fraser fir trees (Abies fraseri), These relict forests are at the southern limit of their distribution on the highest ridges of the southern Appalachian Mountains. We combined a historical study at Mount Collins in the Great Smoky Mountains with a geographic comparison of sites within five southern Appalachian mountain ranges variably affected by the adelgid At Mount Collins, fir was virtually eliminated and canopy cover reduced to half its previous level. Long-term data front Mount Collins showed that the combined density for all breeding birds also declined by half Of the common territorial species present in 1974, 10 of 11 declined, Ci by more than 50%. Some species are neat local extinction. Canopy-and subcanopy-foraging species declined more than near-ground and trunk-foraging species. In addition, invasions of birds characteristic of open and disturbed forests have diluted the boreal character of the avifauna. These changes are consistent with two other long-term studies and are not explained by regional population trends. In the other southern Appalachian mountain ranges where habitat is not as extensive, the adelgid invasion resulted in greater declines in avian abundance, stronger effects on sensitive species, and more pronounced invasions by successional species. Sensitive species in the southern Appalachian studies were also strongly affected in other studies of forest disturbance by fire and logging. The extent of relatively pristine spruce-fir forest and the population pools in other forest types in the Great Smokey Mountains appear, to hn ve buffered the effects of forest decline on the bird community.