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

9406272泰勒对全球变化和相关问题的关注使人们更多地注意到需要了解人类因素和自然因素相互作用的复杂方式。特别令人关注的是对自然因素和人为因素对植被变化，特别是森林中物种演替的各自作用的分析。这个博士论文研究项目将对宾夕法尼亚州东南部和马里兰州东北部蛇形“贫瘠地带”的森林演替进行案例研究。这些地区下面的基岩使其土壤营养物质含量低，毒素含量高，从而抑制了像周围地区那样的植物组合的发展。因此，草和树的复杂混合以及一些特有和稀有的植物物种存在。人们提出了两种不同的假设来解释与蛇形荒地有关的独特植物群落的持久性。第一种假设是多种稳定状态，每个植物群落都与当地土壤特征和其他因素相关联，使自己永久化。第二种假设认为，植被景观主要是随机因素的结果，包括火灾（无论是自然引起的还是人类活动引起的）和灭火。在评估后一种假设时，特别有趣的是植物在火灾后立即再生的方式。为了评估这些假设的有效性，本项目将包括分析促进蛇形岩床植物群落多样性的历史和人为干扰，描述蛇形植被的当前组成和结构及其对干扰的反应，以及分析蛇形森林对火灾的短期和长期反应。除了分析历史文献和航空照片外，还将对两个地点的控制燃烧前后的植被进行深入分析。该项目将有助于理解人为和自然变化的过程和影响，包括更好地了解不同的空间和时间尺度，在这些尺度上，不同的因素是重要的。该项目还将产生有用的数据，并将有助于了解可用于维持这些地区稀有物种种群的策略。作为博士论文改进奖，该奖项也将提供支持，使有前途的学生建立一个强大的独立研究生涯。

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.