Understanding the ecology of cities a key issue in world debate

provided by Arizona State University College of Liberal Arts and Sciences

s the current Johannesburg Summit has underscored, the focus of global environmentalism seems to have shifted from preserving the natural environment to concern with the human condition. At the same time, environmental science and ecology have gone through a similar change and have defined a new kind of ecosystem that may be at risk – the city.

    Increasingly, cities – big cities – are dominating the global environment. The global population is moving to them: in 2000, for the first time in history, more humans lived in urban areas than anywhere else. Across the globe, mega-cities contain tens of millions of inhabitants and sprawl across hundreds and hundreds of square miles. Is this phenomenon a catastrophic surge towards disaster and collapse, or does it reflect the emergence of a new global ecosystem?

    In Phoenix, Arizona, a massive ongoing study of the ecology of urban areas is in its fifth year and may be beginning to yield some answers. Funded by the National Science Foundation, the Central Arizona-Phoenix Long Term Ecological Research (CAPLTER) project is trying to get a grip on understanding the complex web of biological, geological and sociological interactions that govern the metropolitan Phoenix Area – one of the most rapidly growing urban areas in the world – as it spreads across the spare and biologically fragile Sonoran Desert.

    When looked at as an ecosystem, metropolitan Phoenix is far from being an ecological wasteland. In fact, the urban area has a number of surprising ecological features:

  • Urban areas are far from being dead space. Phoenix is significantly richer biologically than the surrounding desert. The city, in fact, works like an oasis in times of environmental stress for many species that normally live in the surrounding desert.
  • Local diversity and abundance of urban plant and animal populations appears to be determined more by human factors than landscape. A neighborhood's economic standing has more effect on its plants and animals than geographical features like rivers and mountains do.
  • Some native species (along with imports) actually do better in the urban environment than in the natural landscape. Abert's towhee and Anna's hummingbird, relatively rare native desert birds, thrive and are common in Phoenix because of canals and feeders.
  • Soil, water, and air chemistry are changed by urbanization. Phoenix's deep soil, most of which was agricultural land a century ago, has become salt-permeated and hard. The city's ground water has become richer in nitrogen and other minerals, which generally encourages plant growth. Urban water systems develop their own unique ecology of microorganisms in canals.
  • Phoenix is hotter and wetter than surrounding lands and generates some of its own weather.