Fig. 11. The Central Arizona Phoenix Long-Term Ecological Research site. This project studies the interactions between ecological and socioeconomic systems in an urban desert environment. One of its goals has been to document the history of changes in land use and its role in shaping the urban, recreational, agricultural, and desert landscapes of today. The modeling group did not define one overlying model question, but did examine the resiliency of native plants to urban development and the introduction of non-native species. The model shows how human and biological processes shape the interactions between introduced and native species in urban environment. The concentric circles at the edges of the model represent urban expansion. Values and beliefs shape people's conceptions of what their residential and natural surroundings should look like, and hence may strongly influence future plant composition in this area. It is suggested that water is a key limiting factor in the future social-ecological urban environment around Phoenix.