Masters Theses

Date of Award

8-2008

Degree Type

Thesis

Degree Name

Master of Science

Major

Ecology and Evolutionary Biology

Major Professor

Nathan J. Sanders

Committee Members

Aimée T. Classen, Daniel Simberloff

Abstract

Understanding how ecological communities change over time is critical for biodiversity conservation. However, few long-term studies directly address decadal-scale changes in the ecological communities of protected areas. In this study, we take advantage of a network of permanent forest plots, established in Great Smoky Mountains National Park in 1978, to investigate temporal changes in plant communities. In particular, we examine the factors that influence temporal change in species richness and composition within communities and temporal change in compositional similarity among communities. In 2007, we revisited 15 permanent plots that were logged in the late 1920s and 15 permanent plots that have no documented history of intensive human disturbance. In addition to differences in disturbance history, these plots varied in elevation and a variety of edaphic parameters. We found that understory species richness decreased by an average of 4.3 species over the 30-year study period in the logged plots, while understory richness remained relatively unchanged in the unlogged plots. In addition, tree density decreased by an average of 145 stems/ha in the logged plots but was relatively stable in the unlogged plots. Historic logging had no effect on within-site understory or tree compositional turnover. However, sites with higher soil pH had higher understory turnover and higher tree turnover than did sites with lower soil pH. In addition, sites at lower elevations and sites with lower understory productivity in 1978 had higher understory turnover than did sites at higher elevations and sites with higher understory productivity in 1978. Among-community similarity was unchanged from 1978 to 2007 in the understory communities and in the tree communities of both the logged and unlogged plots. Taken together, our results indicate that human disturbance can affect plant communities for decades following the disturbance event but that the extent of temporal change in community composition may depend more on environmental gradients than on the legacy of large-scale but short-lived historic disturbances, such as logging. In addition, our results suggest that variation in temporal turnover within communities may not necessarily translate into changes in compositional similarity among communities over time.

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