Temporal Stability of Bird Communities in the Great Smoky Mountains

Rabenold, Kerry

"Studies focused on Mt. Collins in the park have chronicled the impact of the balsam wooly adelgid on the communities of plants and birds since the 1970s. The demise of Fraser fir was accompanied by declines in red spruce and substantial changes in the understory vegetation. Beginning in the 1980s, most bird populations indigenous to the spruce-fir declined to approximately half their original densities by the 1990s. Species not originally common in the mature spruce-fir, but characteristic of logged or burned forests, increased substantially. Forests in the smaller Balsam and Black mountain ranges changed more dramatically, consistent with the expectation that larger protected areas, with their larger population pools at lower elevations, would buffer the impact of this invasion. Some recovery of vegetation in the recent decade has occurred, although the open canopy exacerbated by spruce wind-throw continues to suppress bird populations in the Smokies. Increases in bird populations to near original levels have occurred in some species at Mt. Collins and ""core"" species present before adelgid invasion as still slowly recovering, but though ""disturbance"" species have subsided to some degree they are still abundant. Little recovery toward original species composition has occurred in the smaller mountain ranges. Recovery to the original species composition of this mature spruce-fir forest does not seem likely. Bird communities in cove hardwoods appear to have remained relatively stable over a decade, and some evidence exists that these may be sources for potential recovery of spruce-fir populations. Continuing recovery in the spruce-fir will likely be slowed by the impacts of the hemlock adelgid in these forests. PI revisited the spruce-fir field sites in 2009 to assess long-term changes in the bird communities in the spruce-fir. PI also determined that during the breeding season, Neotropical migrants account for nearly three-fourths of birds in mature cove hardwoods. PI also looked at junco migration across altitudes during the winter, comparing sexual and social dominance differences in migration with similar differences in the northern race of juncos."