Document: NAN-3-7-7

Multiple-scale analyses of ecosystem function and human-ecological interaction in an urban setting, the central Arizona-Phoenix ecosystem.

GRIMM, N.B.*, M.A.LUCK and G.D.JENERETTE

Department of Biology, Arizona State University, Tempe, AZ, USA. ¹

Abstract:
The central Arizona-Phoenix (CAP) urban ecosystem provides a striking contrast to the surrounding native ecosystem, the Sonoran Desert. The CAP ecosystem is situated in the arid Southwest, where water is a limiting factor to all growth but that of the human population. To understand ecological pattern and process in this region, a long-term study (CAP LTER) was initiated in 1998. A subset of 30 initial projects focuses on phenomena at the patch scale, such as the impact of urbanization on ecological conditions within urban patches and feedbacks between the social system and ecological system within the city. At the whole ecosystem scale, a nitrogen mass balance provides an integrative measure of ecosystem function that can be compared with other cities as well as other ecosystems. At still larger scales, the interaction of the city with its environment is described by estimating the "ecological footprint" (EF). By examining the EF for different ecological services (provision of food and water, and absorption of emitted carbon dioxide), we can begin to identify which ecological factors are most likely to constrain growth of the city. We computed the EF for the CAP system in a variety of ways that allowed exploration of potential effects of environmental heterogeneity and transportation. Size of the EF varied with ecosystem service and depended on the locations from which resources were appropriated. Compared to Phoenix, metropolitan areas like Baltimore-Washington and Chicago had much smaller contiguous EFs. Analysis of projected changes in EF size with population growth suggests that food would limit the Phoenix metropolis's population growth prior to water; however, this does not take into account institutional and other social impediments to sequestration and delivery of either resource. The ecological footprint analysis as modified in our study illustrates the need to consider the spatial extent of the demand for ecosystem services, which extends well beyond the boundaries of urban ecosystems. To understand the functioning of socio-ecological systems, a multi-scale approach is useful because it can capture the processes occurring between different urban components, the dynamics of the entire system, and the interaction of the city with larger-scale ecological and social systems.

Keywords: urban, ecosystem, human population growth, ecosystem services, scale, heterogeneity, human-ecosystem interaction

This abstract is being presented at: 2:00 PM in session:
Symposium # 11: Urban Ecology: The Eastern and Western Perspectives.