Study: Cities Are Ecosystems in Their Own Right

If you are reading this, chances are that you live in a city – one, perhaps, on its way to becoming a megacity with a population that exceeds 10 million or more. If not, you and most of the world's population soon will be, according to global population demographics projections.

What shape could these future cities take and how will their populations meet environmental and resource challenges? An article, "Global Change and the Ecology of Cities," published in the journal Science on Feb. 8 by Arizona State University ecologist Nancy Grimm and her colleagues, addresses these questions.

Grimm's co-authors include ecologists John Briggs, Stan Faeth, and Jianguo (Jingle) Wu of ASU's School of Life Sciences; archaeologist Charles Redman, director of the ASU School of Sustainability; as well as researchers, Nancy Golubiewski from New Zealand Centre for Ecological Economics and Xuemei Bai of CSIRO Sustainable Ecosystems in Australia.

Their analyses capture some of the commonalities that will face future city planners and societies, viewing cities as both drivers of and responders to environmental change. They chart the socio-ecological challenges and changes ahead for all cities, but particularly those in rapidly developing regions, like China and India.

"Cities, and the people in them, will ultimately determine the global biodiversity and ecosystem functioning," says Wu. "Sustainable urbanization is an unavoidable path to regional and global sustainability."

Cities literally are proving to be a hotbed for environmental research. Studies by urban ecologists reveal that city centers are physically hotter. Known as the heat island effect, urban and suburban temperatures are "2 to 10 degree F (1 to 6 degree C) hotter than nearby rural areas," according to the Environmental Protection Agency. This rise in temperatures translates into "increases in peak energy demand, air conditioning costs, air pollution levels and heat-related illness and mortality."

Just a one-degree rise in temperature can bump up residential water use 290 gallons per month on average for a single-family unit. However, knowledge about heat island effects also has meant innovation and the rise of new and greener technologies, such as roofing materials with a high solar reflectance and recycled rubber/asphalt composites to pave roadways.

But not all the challenges that occur in the city stay in the city. Grimm says rural landscapes at a city's edge show changes in soils, built structures, human settlements, the diversity of plant and animal species and further impacts on fringe ecosystems. The authors invoke future thinking about cities and their effects as expressed by urban planner and policy expert Robert Lang, of Virginia Polytechnic Institute and State University. Lang believes that a city's "footprint" has ballooned so that "cities are no longer independent, but represent a limited number of dominant megapolitan regions across the globe, with coalitions of urban centers built up in the intervening areas."

 "Global emissions of nitrous oxide and nitric oxide have increased dramatically during the last century, primarily due to human activity associated with agriculture and fossil fuel combustion," notes Hall. "We are just now discovering how urban centers figure into this equation, and how cities such as Phoenix impact surrounding landscapes, as well as contribute to larger regional or global climate."

 "The relatively young and highly interdisciplinary field of urban ecology has demonstrated how well-designed cities can actually have less overall impact on the environment than equivalent dispersed rural populations," says Jonathan Fink, director of ASU's Global Institute of Sustainability. "The kind of counter-intuitive research results described in Grimm's paper show how an ecological perspective can help urban planners and engineers find ways for society to live more harmoniously with nature."

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