By Gary Moll, American Forests

Mecklenburg County's different land covers are highlighted. Dark green represents tree cover, light green represents grass and open space, and gray designates impervious surfaces.

The Charlotte, North Carolina, metropolitan area is among the top 10 fastest growing metropolitan areas in the nation, and Mecklenburg County, which houses the city, has seen a 72 percent growth in population since 1980 according to the U.S. Census Bureau. With such a boom in population, some loss in natural vegetation is inevitable. However, the rate of urbanization and tree loss in Mecklenburg County surpasses even that of population growth. Between 1984 and 2001, the county saw a 127 percent increase in areas covered by impervious surfaces. Without a balance between impervious and tree-covered land, the county's citizens will face costly and unhealthy environmental consequences.

Consider the lessons learned about growth and development of the I-485 Outerbelt highway. An analysis of Landsat imagery from 1984 and 2001 shows a 42 percent loss in tree cover and a 194 percent increase in impervious surfaces. This change in land cover was measured using a two-mile buffer around a 12-mile section of the highway. Measuring the impact of this one section of the beltway provides community leaders with a feel for the future impact of the planned roadway. The environmental impact of the entire Outerbelt will be huge. If the highway development project continues its growth, it will push away from the city center in a sprawl pattern. The challenge to the community is how to manage growth while maintaining efficient use of its land and a robust green infrastructure. Finding a solution to this problem is the focus of this article.

Charlotte's mayor, Patrick McCrory, says, "Our trees are the city's signature." And, like John Hancock's on the U.S. Declaration of Independence, this signature is easy to read. The mayor challenged Charlotte's Tree Commission to establish a new tree ordinance for the city that would ensure the signature status of the trees in the future.

Rick Roti, citizen chairman of the Tree Commission, says, "It was a challenge that kept us busy for a year, but we now have a good ordinance."

The mayor's tree signature also appears on the regional air quality improvement effort, called Sustainable Environment for Quality of Life, centered around Charlotte's urban area and organized by the Centralina Council of Governments. The city's air quality is dangerously close to the Environmental Protection Agency's "nonattainment" designation. If the air quality deteriorates, giving the area a nonattainment status, the region stands to lose $6 billion in federal highway funding, not to mention risking the health of the area's residents. To improve the air, the area has agreed on a checklist of a dozen actions, and improving the tree canopy is one of them.

Charlotte's arboreal signature has become part of the city management fabric thanks to the power of GIS technology. A green data layer (tree theme) became part of the city's central database about a year ago. As a result of this technical action, managers throughout the city have access to the tree theme in the GIS and can include tree cover concerns in daily infrastructure management efforts. The city of Charlotte and Mecklenburg County have the technical expertise to use the green data layer effectively, but it is the Land Development Division of the Engineering Department in the city of Charlotte that has utilized the data most intensively. The department has joined the rest of city government in using the ArcGIS platform.

Laura Brewer, senior urban forestry specialist, and Nick Roberts, systems analyst with the Engineering Department, have long-time familiarity with ArcView software. Following a period of competitive analysis, they chose the CITYgreen extension from Esri Business Partner American Forests to evaluate the impact of development proposals received by the city on current and future tree cover.

For the large-scale analysis this means using ArcGIS Desktop software and CITYgreen to create a baseline of current conditions by combining land cover and land use data. The current condition is then fed into a land use projection model to establish a metric for future land cover. The future land cover includes specific measures for tree cover that are then compared to the requirements set forth in the tree ordinance. This analysis provides direction to the public policy makers so they can determine the effectiveness of the development code at controlling tree loss.

"This is accomplished by modeling the development proposals using GIS technology," says Roberts. "We use the green data layer produced by American Forests for the city's GIS, along with other growth and development data, to conduct our analysis."

The small-scale analysis allows the Land Development Division to evaluate the impact of all new development or rezoning on the tree cover and make immediate adjustments in development in keeping with the tree cover goals of the tree ordinance.

The efforts by the city of Charlotte to incorporate a green data layer into its central database and establish application of the data in the Engineering and Property Management section of the city government is a groundbreaking action that should be considered by every urban government.

For more information, contact Gary Moll, American Forests (e-mail: gmoll@amfor.org).