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

9406272泰勒对全球变化及相关问题的关切提请人们更多地注意需要了解人类和自然因素相互作用的复杂方式。特别令人关切的是，分析了自然和人为因素对植被变化，特别是森林物种演替的各自作用。这一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的蛇纹状“贫瘠地带”的森林演替进行个案研究。这些地区下面的基岩使其土壤营养含量低，毒素含量高，从而抑制了像周围地区那样的营养组合的发展。因此，草和树木的复杂组合与一些特有和稀有植物物种一起存在。两种不同的假说被用来解释与蛇纹岩荒漠相关的独特植物群落的持久性。第一种假设有多种稳定状态，每一种植物群落都会随着当地土壤特性和其他因素的影响而永久存在。第二个假说认为，植被景观主要是随机因素的结果，包括火灾(无论是自然起火还是人为起火)和灭火。在评估后一种假设时，人们特别感兴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，这个项目将包括对促进蛇形基岩植物群落多样性的历史和人为干扰的分析，对蛇形植被目前的组成和结构及其如何应对干扰的描述，以及对蛇形森林对火灾的短期和长期反应的分析。除了分析历史文献和航空照片外，还将对两个地点受控燃烧前和燃烧后的植被进行密集分析。该项目将有助于理解人类引起和自然变化的过程和影响，包括更好地了解不同因素在不同空间和时间尺度上的重要性。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战略。作为博士论文改进奖，该奖项还将提供支持，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.