An Ecosystem Approach to Understanding Cities: Familiar Foundations and Uncharted Frontiers

Conclusions

We have presented examples from the Central Arizona-Phoenix urban ecosystem, promoting the view that we can apply familiar techniques of ecosystem ecology to cities, just as we would to any ecosystem. Given our charge to explore the intellectual frontiers of urban ecosystem understanding, it may be useful to consider whether our initial approach to mass balance should be modified. In particular, do we need to incorporate models of human behavior or economic drivers? The answer here is probably yes because the largest inputs are a consequence of human behaviors (e.g., driving patterns, fixation via combustion) and economics (e.g., imports of food, animal feed, and fuels). Would a different view of ecosystem structure improve our ability to put the mass balance to use in informing policy that will promote environmental protection? More fundamentally, would it improve our ability to predict the major points of production, accumulation, and transformation of nitrogen in the ecosystem? Again, we answer in the affirmative: Understanding how humans have manipulated paths of water flow within cities may be key to unlocking the dynamics of transport and transformation of materials.

We suggest that the next step in understanding urban ecosystems is to begin to incorporate social scientific explanations, controls, and mechanisms into our existing ecosystem models. Just as ecologists learned to speak the language of physical scientists when an understanding of climatic controls and changes was required for ecological explanations, we must now engage in a dialogue and sharing of conceptual models with the social sciences. With our new emphasis on the urban extreme along a spectrum of humandominated ecosystems, the time is right to develop a more comprehensive ecosystem theory.