THE SPATIAL DISTRIBUTION OF INVASIVE PLANT PRESENCE, ABUNDANCE, AND IMPACT

Across the globe, native ecosystems are increasingly threatened by the spread and negative impacts of non-native, invasive plants. While many hypotheses explore what contributes to the damage caused by invasive species, few studies have tested these hypotheses at the macroscale. My dissertation addresses this knowledge gap by synthesizing thousands of vegetation surveys from ecosystems across the United States. I leverage existing, as well as explore new macroecological methods to deepen our understanding of the spatial ecology of plant invasions. My dissertation also asks how effective management and policy has been at reducing plant invasions. The primary introduction pathway for invasive plants is the horticultural industry. Despite efforts to regulate horticultural trade, I found that 61% of U.S. invasive species were still marketed as garden plants. Consistently regulated invasive plants were sold less often, but many high-impact invaders were still available through plant trade. More policy efforts are needed to stop the spread of invasive plants. A key take-home from my research is that the environmental conditions of recipient native communities play an important role in determining invasive plant success. For example, species-rich native plant communities were more resistant to invasive plant establishment. But once an invader reaches high abundance, high richness native communities were more susceptible to diversity loss. In areas with high anthropogenic effects, invasive plants were more likely to establish as well as have greater negative impacts on native plant communities. The effect of the environment on invasive plant abundance differed by species. Some invasive plants reached high abundance in any environment where it was able to occur, whereas other invasive plants only reached high abundance in a subset of the habitats where they could occur. While some invasion processes may be species-specific, my research shows that at macroscales, top priority habitats for management should include species-rich native plant communities in high resource environments and communities facing high anthropogenic effects. These findings deepen our understanding of the spatial ecology of plant invasions