Date of Award


Document Type

Restricted Thesis

Terms of Use

© 1999 Anna Sugden-Newbery. All rights reserved. Access to this work is restricted to users within the Swarthmore College network and may only be used for non-commercial, educational, and research purposes. Sharing with users outside of the Swarthmore College network is expressly prohibited. For all other uses, including reproduction and distribution, please contact the copyright holder.

Degree Name

Bachelor of Arts



First Advisor

Roger Latham


The Pocono till barrens are shrub dominated vegetation communities that seem to be an alternative community state to forests. They are found disproportionately on flat areas underlain by glacial till, and burn frequently. This study investigated how slope, geology, fire history and proximity to forest influenced transitions from barrens to forests and each other in two historical periods: 1938-63 and 1963-92. There were frequent fires during the first period, while during the later period fire was rigorously suppressed. A combination of non-parametric statistics and Mantel and partial Mantel correlations were used to determine interrelationships between variables. From 1938-1963 slope was the only variable that showed a significant correlation with vegetation transitions. However, from 1963-1992, slope was not significantly correlated with vegetation transitions, while fire history was. The results from this study support the hypothesis that surficial geology does not affect barrens persistence, but that barrens are found disproportionately on till because of a confounding effect of slope. Slope was correlated with vegetation transitions in the earlier time period even when fires were held constant, refuting earlier hypotheses about the role of slopes and fire history. In addition the results of the earlier time period do not support the alternative community states model, while the results of the later time period support it. This indicates that both environmental constraints and positive feedback loops play an important role in the Pocono till barrens system.