Date of Award


Document Type

Restricted Thesis

Terms of Use

© 1999 Wendy L. Lawrence. 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


Biology Department

First Advisor

Roger Latham

Second Advisor

Mark Jacobs


The factors influencing the ecosystem dynamics of Pocono till barrens and surrounding forests in Monroe County, Pennsylvania, are unknown. These heathlands are a unique ecosystem that exists not on the poor soil common to other barrens, but on soil seemingly favorable to forests. To test the hypothesis that mineral nitrogen availability is lower in heathlands than in adjacent forests, the role of ericoid mycorrhizae was studied. Unlike most non-ericaceous plants, plants with ericoid mycorrhizal associations can utilize organic nitrogen. By taking up nitrogen before it is broken down into inorganic forms which other plants can utilize, ericaceous plants short-circuit the nutrient cycle and may thus monopolize nitrogen when they are sufficiently abundant. In one field and two greenhouse experiments, I analyzed percent mycorrhizal colonization in Kalmia angustifolia and Vaccinium angustifolium grown with either organic or inorganic nitrogen, and in either barrens or forest soil. Mycorrhizal colonization did not vary quantitatively with either nitrogen or soil treatment, but the growth of Vaccinium was significantly greater in forest soil than barrens soil. The implications for the restoration of the species-rich heathlands on the Pocono Plateau are discussed.