Doctoral Dissertation Research: Maintaining Diversity in a Serpentine Ecosystem: The Role of Multiple Stable States and Stochastic Change

9406272 TAYLOR Concerns about global change and related issues draws more attention to the need to understand the complex ways through which both human and natural factors interact with each other. Of particular concern have been analyses of the respective roles of natural and human factors on changes in vegetation, particularly the succession of species in forests. This doctoral dissertation research project will conduct a case study of forest succession in the serpentine 'barrens' of southeastern Pennsylvania and northeastern Maryland. The bedrock underlying these areas makes its soils low in nutrients and higher in toxins, thereby inhibiting development of vegetative combinations like those found in surrounding areas. As a result, a complex mix of grasses and trees exists along with a number of endemic and rare plant species. Two different hypotheses have been formulated to explain the persistence of the distinctive plant communities associated with the serpentine barrens. The first posits multiple stable states, with each of the plant communities perpetuating itself in association with local soil characteristics and other factors. The second hypothesis holds that the vegetative landscape is primarily the result of stochastic factors, including fires (whether started natural or by human activity) and fire suppression. Of special interest in assessing the latter hypothesis is the way that plants regenerate immediately after a fire. In order to assess the validity of these hypotheses, this project will include analyses of the historical and human-induced disturbances in promoting the diversity of plant communities on serpentine bedrock, descriptions of the current composition and structure of serpentine vegetation and how it has responded to disturbances, and analyses of short- and longer-term responses of serpentine forests to fires. In addition to analyzing historical documents and aerial photos, intensive analyses will be made of vegetation bef ore and after controlled burns at two sites. This project will contribute to understandings of the processes and effects of human-induced and natural change, including better knowledge of the different spatial and temporal scales at which different factors are important. The project also will generate useful data, and it will contribute to knowledge about strategies that can be used to maintain populations of rare species in these areas. As a doctoral dissertation improvement award, this award also will provide support to enable a promising student to establish a strong independent research career.