Population growth and the environment

December 13, 2000

Population growth and residential and commercial development are having environmental impacts in areas that are far from the nation's urban centers, according to an analysis by two University of Maine professors and a the U.S. Forest Service scientist. Their finding results from one of the first attempts to develop a theoretical framework to define and predict how population growth affects environmental qualities such as wildlife habitat.

John Bartlett (Ph.D., '99) of the U.S. Forest Service, Deirdre Mageean of the Margaret Chase Smith Center for Public Policy at UMaine and Raymond O'Connor of the UMaine Dept. of Wildlife Ecology base their analysis on U.S. nationwide demographic and environmental data. Bartlett is a former UMaine graduate student in wildlife ecology who worked with Mageean and O'Connor to study factors that tend to reduce biodiversity.

Support for the research was provided by the U.S. Environmental Protection Agency, USDA Forest Service and the National Science Foundation.

The researchers applied a method known as classification and regression tree (CART) modeling to identify what they call "a particularly damaging form of sprawl" in areas where growth is associated with non-agricultural land use changes involving "green field" building.

Such growth is strongly associated with high concentrations of endangered plants and animals, the authors report. In particular, growth threatens coastal species that depend on large blocks of sand dunes and other barren coastal habitats.

Their report titled "Residential Expansion as a Continental Threat to U.S. Coastal Ecosystems" was published last spring in Population and Environment: A Journal of Interdisciplinary Studies.

Ecologists and demographers have long known that human population growth and development affect the environment by eliminating wildlife habitat and reducing air and water quality. Indeed, in the last decade, some environmental groups have advocated steps to slow the rate of population growth in the U.S. as a means of protecting the environment.

However, a detailed model that explains how a growing population affects the environment at both local and continental scales has been lacking. In part, that is because demographers and ecologists work with different kinds of data.

"There's a lot of the work going on in human dimensions of change," says Mageean. "A lot of it is taking place in ecological hot spots around the world, such as Amazonia, Nepal, China and so on. One of the virtues of doing this research in the U.S. is that while we have a very extensive physical area to study, we also have a fairly homogenous political, social and economic structure. That can reduce the variance of those factors that tend to mediate between population and environmental impact."

In their paper, Mageean, O'Connor and Bartlett used climate data as well as information from the U.S. Geological Survey and from the U.S. Environmental Protection Agency's Environmental Monitoring and Assessment Program (EMAP). The USGS provided remotely sensed satellite data on land cover for 8 million 1km2 pixels in the conterminous United States. EMAP provided land cover pattern data and information on streams and roads for 12,600 hexagon shaped regions across the area. For population and socio-economic factors, the researchers used county level data from the U.S. Census as well as information about land ownership and building construction.

Through CART analysis, they identified specific ranges of values for environmental variables that are associated with distinct patterns of settlement. They focused on temperature averages and extremes, land use classification and listings of endangered or threatened species. They were thus able to correlate changes in population density and development with changes in vegetation and threats to wildlife.

Development in remote areas, they point out, is consistent with population increases in Sun Belt states and along sea coasts. Since it occurs in areas that are relatively pristine, such growth may drive out very rare wildlife species that cannot tolerate the presence of humans, thus contributing to a loss of biodiversity.

While the authors focused on growth impacts in coastal areas, they suggest that a similar analysis can be extended to deserts. "We have just started looking at the desert systems in some depth, and we've found some interesting patterns," says Mageean. "For example, when you look at Nevada, what self-respecting demographer or ecologist would have predicted years ago that Las Vegas would grow so fast? You have very severe constraints imposed by desert conditions. It's very interesting to see how these factors literally shape growth out there. You can see that they're being pulled to water bodies and constrained by federal land and mountain ranges."

The authors suggest that their model can assist policy makers by identifying patterns of human settlement likely to occur in different areas and predicting future environmental impacts.
Contact: Deirdre Mageean, Margaret Chase Smith Center, 207-581-1644, deirdre_mageean@umit.maine.edu
Raymond O'Connor, Dept. of Wildlife Ecology, 207-581-2880, oconnor@umenfa.maine.edu
Nick Houtman, Dept. of Public Affairs, 207-581-3777, houtman@maine.edu

University of Maine

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