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

University Of California-Santa Barbara, Santa Barbara CA

Investigators

Abstract

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.