Multiple States in Grassland Systems: Invasion and Environmental Feedbacks

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When non-native plants become problem invasive species, they appear to push the entire ecosystem across a threshold, creating an alternative vegetation state that is difficult to restore. While this pattern is consistent with theoretical predictions concerning multiple stable states, there have been few empirical tests. The research will promote the understanding of restoration and multiple state dynamics in California grasslands, one of the most invaded ecosystems in the United States. Through observational studies and field experiments, it will investigate several factors that will aid in restoration and conservation: whether variation in soil nitrogen availability creates refugia for native and non-native grasses, whether intermediate levels of nitrogen supply can generate both non-native- and native-dominated states, whether interactions between vegetation and soil microbes create positive feedbacks and lead to the formation of multiple states, and whether regional colonization differences between non-native and native species overwhelm these local interactions. The project will also train young scientists through year-long experiential science programs. Students from local high schools will be involved with data collection as well as with the design and implementation of a public demonstration experiment. The project will also encourage the participation of women, particularly Hispanic women, by recruitment and outreach efforts. The results will be disseminated broadly to applied practitioners, scientists, and the general public through directed publications, workshops, and seminars.