DISSERTATION RESEARCH: Islands of invasion: savanna oak trees and plant community structure in California grassland

在上个世纪，世界上许多草原和热带稀树草原群落的灌木和树木数量发生了重大变化。木本植物在许多不同类型的草地上急剧增加，而在其他类型的草地上则减少。鉴于这些变化以及草原上受威胁的动植物比例很高，有必要更好地了解树木对周围植物群落的影响，这些影响如何随区域气候梯度沿着变化，以及这些生态系统对进一步变化的抵抗力。特别是，树木死亡后对邻近社区产生长期影响的潜力从未得到评估。该项目将探索加州橡树稀树草原的结构在当地和区域尺度上通过时间，重点是橡树的存在和其他本地和非本地物种的多样性之间的关系。研究将集中在两个主要问题：（1）橡树对物种多样性和土壤性质的影响持续多久？和（2）稀树草原树木创造的资源斑块如何对物种丰富度做出贡献？研究人员将调查活橡树和死橡树的周围环境，用放射性碳测年法确定每棵树的死亡时间，并使用绘图软件和空间分析。在这个时候，没有总体理论预测树冠树木将有积极或消极的影响林下物种多样性。这项工作将提供一个统一的理论，了解草原树木的影响。热带稀树草原和草原是北美和全世界重要的经济牧场。 该项目将有助于了解这些栖息地现在发生的变化如何在未来影响它们，帮助社会调整管理以跟上变化的步伐。 此外，该项目还将提供机会，指导高中学生学习科学，并将与加州大学的外联方案合作，向科学代表性不足的群体的学生介绍栖息地保护和恢复。

Many of the world's grassland and savanna communities have experienced significant changes in the abundance of shrubs and trees over the last century. Woody plants have dramatically increased in many different types of grassland and declined in others. In light of these shifts and of the high proportion of threatened plants and animals that occur in grasslands, there is a need to better understand the influences of trees on the surrounding plant communities, how these impacts vary along regional climatic gradients, and the resistance of these ecosystems to further change. In particular, the potential for trees to exert long-term impacts on neighboring communities following their death has never been evaluated. This project will explore the structure of the California oak savanna at local and regional scales through time, focusing on the relationship between the presence of oak trees and the diversity of other native and non-native species. Research will focus on two main questions: (1) How long do the effects of oaks on species diversity and soil properties last? and (2) How do the resource patches created by savanna trees contribute to species richness? Researchers will survey the surroundings of living and dead oak trees, determine the time of death for each tree with radiocarbon dating, and use mapping software and spatial analyses. At this time there is no overarching theory predicting when canopy trees will have positive or negative impacts on understory species diversity. This work will provide a unified theory for understanding impacts of trees in grasslands. Savannas and grasslands are economically important grazing lands in North America and throughout the world. This project will help understand how changes taking place now in these habitats may affect them in the future, helping society adapt management to keep pace with change. In addition, the project will provide opportunities to mentor high school students in science and will work with outreach programs at the University of California to introduce students from groups under-represented in science to habitat conservation and restoration.