Long-term Landscape-scale Impact of Early 20th Century Logging on Plant Communities in the Southern Appalachians

Woodbridge, Margaret

ABSTRACT: Logging has been hypothesized to have long-term effects on plant communities throughout the world. Quantifying the effects of disturbances such as logging on patterns of plant diversity and composition is a fundamental question in ecology and conservation. In this dissertation I examined the long term (70+ year) impact of early 20th century clear-cutting on forest communities in the southern Appalachians, one of the most diverse temperate regions in North America. I investigated hypotheses about how clear-cutting has changed plant diversity, composition, functional traits, and the evergreen shrub layer. I used Generalized Dissimilarity Modelling to determine how clear-cutting has changed the relationships between environmental gradients and plant species turnover. I found that clear-cutting has changed the overall and relative long-term importance of drivers of community turnover, most notably by increasing the importance of spatial distance and decreasing the importance of topographic position. Based on perMANOVA and nonmetric multi-dimensional scaling ordination, I found that the composition of logged communities in high elevation areas and in landscape positions that accumulate water had diverged from communities with no logging history. By comparing the dispersions of clear-cut and unlogged areas in multivariate space, I also found that clear-cutting has homogenized plant communities overall. This homogenization effect was not only present compositionally but was observed in the community-weighted means of traits that are closely related to disturbance response, such as growth rate and fire tolerance. Clear-cutting also caused long-term declines in tree species that do not re-sprout and in ground-layer species with limited dispersal mechanisms. I did not find that clear-cutting increased the presence of evergreen shrub layers in general, as has been speculated in other studies in the region, but did find increased density of rhododendron at low elevations following clear-cutting. This study suggests that early 20th century clear-cutting has caused lasting plant community changes across the landscape, but the nature and magnitude of those changes varied along the many environmental gradients found in the region.