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Summer 2005
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USGS's The National Map Helps Calculate the Value of Natural Systems

This article has been modified from the printed version.

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One of the datasets available as part of The National Map is the National Land Cover Data, which has been mapped by conducting a nationwide land-cover classification based on Landsat satellite imagery.

This spring the Millennium Ecosystem Assessment project, an international effort engaging more than 1,300 scientists from 95 countries, released the results of its comprehensive study. The findings were bleak—more than 60 percent of the ecological functions of the global ecosystems have already been degraded by human activity. Our "ecological glass" is less than half full. The researchers' report stated, "We must learn to recognize the true value of nature—both in an economic sense and in the richness it provides to our lives. Above all, protection of these assets can no longer be seen as an option to be considered once more pressing concerns of wealth creation or national security have been dealt with."

While many individuals recognize the significance of this report, the scale of the problem is so large it is disorienting. People don't know what to do next when the context of the problem is worldwide. The famous bacteriologist Rene Dubois provided a thoughtful solution to this problem when he coined the phrase "think globally, but act locally." Fortunately, GIS provides the technology needed to understand and act to improve the local environment.

Individuals can measure the land-cover changes that have taken place over the last 10 years in their communities and use their understanding of GIS technology to provide their community leaders with the decision support materials they need to make thoughtful decisions about the local ecology. This article shows the reader how to use a free service to obtain data and information about the natural resources where they live so issues of green infrastructure can be used in decision making.

Obtaining this data and information is now easy because two of the nation's most enduring organizations, the United States Geological Survey (USGS) and American Forests (both established in the late 1800s), collaborated to make it possible. They recognized the opportunity to connect the extensive land-cover dataset created by USGS with the ecosystem service calculations developed and refined by American Forests to create an ecological model for public use. As Nick Van Driel, chief scientist for information services at the USGS National Center for Earth Resources Observation and Science, says, "This application of ecological modeling, using the data from The National Map, allows the data to become useful knowledge." GIS technology allows the data on the map to be connected to ecological models that put a value on the services nature provides (ecosystem services). ArcGIS Server technology recently gave this application the horsepower needed for Web delivery.

USGS developed The National Map in 2001 "to provide public access to high-quality, geospatial data and information to help inform decision makers," says Paul Hearn, a senior scientist in the USGS geography discipline. It is a giant warehouse of geographic data that is extensively used by GIS professionals to create the basic geographic data needed to build GIS projects. One of the data layers available as part of The National Map is the National Land Cover Database (NLCD). "The NLCD data was mapped by conducting a nationwide land-cover classification based on Landsat satellite imagery," says Van Driel. Satellite data was classified into land-cover types and deployed on The National Map for 1992. Using improved methods and more recent satellite data, NLCD 2001 has been mapped for most of the United States and should be completed by the end of 2006.

As the findings from the Urban Ecosystem Analysis reports were compiled, national trends started to emerge. The land-cover analyses showed that developed lands were growing at a rate of approximately 20 percent in 10 years while the natural systems were declining. In other words, humans are degrading the health of the local ecosystems just as the Millennium Ecosystem Assessment shows humans are degrading global ecosystems (this should not be a surprise since the two are linked).

The rate of decline is evidenced by measuring temporal tree cover change in areas where forests once flourished east of the Mississippi River and in the Pacific Northwest. Less obvious are regional ecosystem strains where urban populations have expanded and tree cover has always been sparse. On first look, it appears that Denver, Colorado, is not losing ecological services because tree cover increased by 1 percent, but the urban surfaces also increased by 20 percent, overshadowing the small increase in tree cover. Balancing the ecological equation for Denver required creative thinking by American Forests' staff and local urban foresters. The solution for cities such as Denver is to balance the gray urban surfaces with living green land cover and the most robust of the green surfaces are trees.

The findings from Denver, as well as those from a couple dozen other urban areas, inspired USGS and American Forests to collaborate on developing a Web-based version of the urban ecosytem analysis tool. USGS's Comprehensive Urban Ecosystems Studies (CUES) project, an extension of The National Map, has developed an online application to generate reports estimating the value of ecological services for any urban area in the continental United States. The application uses public-domain USGS NLCD land cover derived from 30-meter Landsat-7 imagery, and therefore provides only a rough estimate of the environmental services produced by the ecology.

By using the application provided by USGS on the CUES Web site, anyone can extract a "ball-park estimate" of the value of the ecological services produced in any urban area in the continental United States. While this public-domain data provides only a coarse view of the land cover and therefore a rough estimate of the environmental services produced by the ecology, the Web-accessible ecosystem analysis provides a compelling estimate of the value of greening urban infrastructure. Exploring the data on the CUES Web site is the first step in a longer journey to green up the local urban infrastructure.

The Web-based ecosystem analysis tool is accessible on the Web at Dozens of Urban Ecosystem Analysis reports are also available at For more information, visit and

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