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 substantiall y over 21 years In response to the introduction of the balsam woolly a delgid insect (Adelges piceae) and the resulting death of endemic Fras er fir trees (Abies fraseri), These relict forests are at the southern limit of their distribution on the highest ridges of the southern App alachian Mountains. We combined a historical study at Mount Collins in the Great Smoky Mountains with a geographic comparison of sites withi n five southern Appalachian mountain ranges variably affected by the a delgid At Mount Collins, fir was virtually eliminated and canopy cover reduced to half its previous level. Long-term data front Mount Collin s showed that the combined density for all breeding birds also decline d 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 characteri stic of open and disturbed forests have diluted the boreal character o f the avifauna. These changes are consistent with two other long-term studies and are not explained by regional population trends. In the ot her southern Appalachian mountain ranges where habitat is not as exten sive, the adelgid invasion resulted in greater declines in avian abund ance, stronger effects on sensitive species, and more pronounced invas ions by successional species. Sensitive species in the southern Appala chian studies were also strongly affected in other studies of forest d isturbance by fire and logging. The extent of relatively pristine spru ce-fir forest and the population pools in other forest types in the Gr eat Smokey Mountains appear, to hn ve buffered the effects of forest d ecline on the bird community.