Date of Award

Spring 1998

Document Type

Restricted Thesis

Terms of Use

© 1998 Robert Eberhardt. 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

Department

Biology Department

First Advisor

Roger Latham

Abstract

Time domain reflectometry (TDR) was used during summer 1997 to determine whether vegetation patterns follow predicted soil moisture gradients in the Pocono till barrens, a rare species-rich assemblage of pine barrens in northeastern Pennsylvania that occurs disproportionately on deposits of Illinoisan glacial till. The results provide insights into the relative importance of disturbance and abiotic factors in determining vegetation patterns and dynamics and have implications for barrens protection and management. Soils of barrens and adjacent forests did not differ in water content over all depths and drought conditions, and in the upper 15 cm of soil barrens on bedrock had slightly higher water contents than barrens on Illinoisan till. It can be inferred from these results, contrary to prevailing views, that xeric soil conditions do not maintain the barrens/forest distinction on the southern Pocono Plateau. Vegetation-driven processes that encourage wildfire and restrict nitrogen availability may instead be responsible for barrens maintenance. Relatively mesic conditions could explain the rapid succession of Pocono barrens into woodlands that has occurred since fire suppression—particularly in areas over bedrock. Furthermore, soils of distinct barrens types that were thought previously to follow moisture gradients did not differ in water content, although the abundance and diversity of wetland indicator plant species does vary between barrens types. Frost pockets may favor the persistence of heathlands in topographic depressions, with rhodora barrens, which support a greater abundance and diversity of wetland indicator species, occurring in areas subject to periodic flooding not apparent during summer 1997. Mesic soils and the historical importance of wildfire in the Pocono till barrens make prescribed burning a particularly appropriate management strategy for biodiversity conservation.

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