Note that the data published in the 2002 State of the Nation’s Ecosystems Report as well as the 2003 and 2005 Web-Only Updates have been superseded by the 2008 Report and thus should be used with caution. For the most recent data, purchase the 2008 Report from Island Press.

Review the indicators at a glance

Thinking of America’s cities and suburbs as an ecosystem does not come automatically to many people. “Ecosystems” are usually defined by plants, animals, naturally occurring attributes like landscape type, and the interaction among these elements. People, by contrast, create cities and suburbs, and it is the built environment—houses, office buildings, factories, roads, sidewalks, piers, parking lots—that defines them. Although they occupy less than 2% of the land area of the lower 48 states, cities and suburbs are home to more than 75% of all Americans. Characterized by a great many people living in a very small area, much of it covered by a variety of hard surfaces, cities and suburbs nevertheless provide a range of goods and services not unlike those provided by the other, more “natural,” ecosystems. In fact, 20% of urban and suburban land is forest, farmland, wetlands, or grassland and shrubland; streams run through cities and suburbs, and many cities lie on the coast. It is in this unconventional ecosystem that people interact most often with nature.

What can we say about the condition and use of urban and suburban areas?

Fifteen indicators describe the condition and use of urban and suburban areas. Partial or complete data are available for six of these indicators. Only one (air quality) has a long enough data record to judge trends, while four can be compared to a regulatory standard or guideline. For five indicators, data are not available for reporting on a national basis, and four indicators require additional development before it will be possible to assess the availability of data.

After the following brief summaries of the findings and data availability for each indicator, the remainder of this chapter consists of the indicators themselves. Each indicator page offers a graphic representation of the available data, defines the indicator and explains why it is important, and describes either the available data or the gaps in those data.

System Dimensions

Five key indicators describe the dimensions of the urban/suburban system. The first and most basic is how much land these areas occupy, and how much is developed or remains as forest, grassland or shrubland, or other undeveloped land. A second indicator, still requiring development, would track conversion of land from rural to suburban. Three other indicators provide further detail on the character of urban and suburban lands. One tracks the size of the patches of forest, grasslands and shrublands, and other natural areas that provide green space and wildlife habitat; a second tallies the fraction of urban and suburban lands covered by asphalt, buildings, and other impervious surfaces that prevent the penetration of rainfall and on which plants cannot grow. A final measure will track the percentage of urban streams that are lined with vegetation, which can have a significant effect on water quality and which also serves as wildlife habitat.

• How much land do “urban and suburban areas” occupy? How much of this land is developed, and how much is forest, grasslands and shrublands, wetlands, and croplands? In 1992, urban and suburban areas, as defined by this report, accounted for about 32 million acres in the lower 48 states, or about 1.7% of total land area. About 22% of urban and suburban land in the South, Northeast, and West was undeveloped; in the Midwest, this figure was 17%.
• How are patterns of development changing at the boundary between suburban and rural areas? When suburban development expands into rural areas, the pattern of development—how dense or spread out it is; how transportation, water, sewer, and other infrastructure are integrated, and so on—can affect both wildlife and people living in and around newly developed areas. This indicator requires further development.