| Urban areas are dynamic systems in which to study the anthropogenic effects on ecosystem processes. Urbanization directly destroys or fragments surrounding natural and agricultural ecosystems. Urbanization also indirectly exposes these ecosystems to altered climate, including elevated carbon dioxide levels, increased temperatures from the urban "heat island", changes in precipitation patterns, and increased nitrogen (N) availability. The effects from urban-caused climate change may result in significant change in natural ecosystem processes, such as carbon (C) sequestration or release. The magnitude of these effects can be quantified through comparisons with rural "control" sites. The ramifications of the effects of urbanization on native plant communities in desert ecosystems are unclear. The overall objective of this research is to determine the consequences of urbanization on the structure and function of desert ecosystems.; Soil carbon dioxide efflux from anthropogenically altered landscapes, automobile activity and human respiration, produced the majority of the input of carbon dioxide into the urban environment. In contrast, soil carbon dioxide efflux from the natural desert ecosystems was minimal during hot and dry periods, but increased rapidly when moisture levels increased. In the future, reductions in automobile emissions due to increased fuel efficiency standards and predicted land use changes could result in a reduction in urban carbon dioxide emissions compared to current levels.; Using an urban to rural framework, the effects of urbanization on the structure and function of creosote bush dominated desert ecosystems were evaluated. Urbanization increased soil C and N levels, but lowered annual soil respiration rates. Urban locations also showed a reduced dependence on soil temperature and moisture as predictive measures of soil respiration and a lack of spatial variability typical of Southwestern deserts in regards to soil respiration rates and N availability, suggesting that the functioning of desert ecosystems in urban setting have been altered. Additionally, soil respiration and microbial activity in urban desert ecosystems are higher in response to water and N additions than similar environments in rural locales, and the response difference is most pronounced during the summer months. This research reveals that urban location effects such as precipitation change, N deposition, temperature change and increased carbon dioxide alter desert ecosystem function. |
