Community Change in an Arid Ecosystem

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The San Simon Valley of southeastern Arizona maintained high plant diversity over much of the past 30 years. However, during the mid-1990's, this plant community underwent a dramatic change associated with the sustained irruption of the invasive winter annual plant, Erodium cicutarium. Coincident with the increase of this invasive plant, the winter annual plant diversity dramatically declined, species composition shifted, and the seed-eating rodent community changed. This research utilizes physiological, ecosystem, community and theoretical approaches to disentangling the various environmental factors hypothesized to have led to the dominance of E. cicutarium, and its major impacts on the local ecosystem. These environmental factors include recent changes in climate (decreased winter rainfall and more frequent drought), pollution in the form of nitrogen deposition (from agricultural fields and nearby copper smelters) and changes in the rodent community (from dominance by a kangaroo rat to dominance by a pocket mouse). Results from field manipulations and growth chamber studies will form the basis of mathematical models to predict changes in the annual plant community and in the functioning of the ecosystem under future climate and nutrient enrichment regimes. These models should elucidate the roles of human drivers of change in this ecosystem. Results from this work will inform mitigation and management strategies for plant invasions in arid ecosystems, and should aid efforts to restore native plant communities. This project also has an important research training component for undergraduates and graduate students and a postdoctoral fellow. It will support the training of women and minorities in a scientific discipline where they have been underrepresented.