Fraser fir (Abies fraseri), an endemic species that dominates the high elevation forests of the southern Appalachians, has suffered widespread mortality throughout its native range due to a non-native insect, the balsam woolly adelgid (Adelges piceae). BWA was first found in the Great Smoky Mountains National Park (GRSM) in 1963; it is estimated that BWA was responsible for the death of 91% of all mature firs within the park. This study seeks to examine the effect of disturbance intensity due to BWA on stand composition of spruce-fir forests and to describe changes in stand structure over time. The data were collected from thirty-six 400 m2 permanent plots, stratified into four stand types established on five mountain peaks in GRSM, and data collection follows methods used in 1990 and 2000. Differences among the five mountains and the four stand types were tested using a one-way factorial MANOVA. Parameters tested for significance included: under-story fir seedling densities in five size classes, fir sapling density (>1.37 m tall and <5 cm DBH), and total basal area (m2/ha) of Fraser fir, red spruce, and hardwood species >5 cm DBH.
Results/Conclusions
No significant differences were found between 1990 stand types; additional work is underway to assess the influence of microclimate and acid deposition in stand regeneration. Mountains vary significantly in fir sapling density (DBH < 5 cm) and density of mature fir and hardwoods. Trends seen with respect to hardwood density correlate with elevation. All plots show increases in fir basal area over time; average density of stems >5 cm DBH has increased from 413 stems/ha in 1990 to 2275 stems/ha in 2010. Size distributions indicate that regeneration of Fraser fir is occurring throughout the area. However, fir seedling density has decreased over the two decades of study. Increased stress from drought, higher temperatures, acid deposition, or competition with herbs may be limiting the recovery of this species.