Elevation-mediated effects of balsam woolly adelgid on southern Appalachian spruce–fir forests

Abstract

The pattern of distribution of endemic Fraser fir (Abiesfraseri (Pursh) Poir.) in the southern Appalachian Mountains is being affected by infestation of the exotic balsam woolly adelgid (BWA) (Adelgespiceae (Ratz.)). BWA kill mature fir trees in about 3–9 years after initial infestation. Prediction of the effects of BWA in a forest region requires an assessment of (i) the population dynamics of the BWA and the fir, (ii) the prevailing physical conditions that affect the spread of BWA, and (iii) the subsequent pattern of fir mortality. This paper predicts the patterns of fir mortality and recovery on an elevation gradient by using a population model with site-specific environmental conditions and ecological interactions. The model shows that temperature range and amplitude, which affect the survival and development rates of BWA, can have an indirect influence on the spatial pattern of living trees. The model results suggest that persistence of both species, with oscillations in numbers over time and space, is probable.