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Fall 2009
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Gary Moll Wants People and Nature to Work Together

GIS HeroThis article is part of an ongoing series honoring individuals who have made a difference in the world by applying a GIS solution to challenges or needs within conservation or their communities. Since these unique individuals have been selected for their innovations or special achievements in a particular field, the series is appropriately named GIS Heroes. Esri recognizes ecosystem environmentalist Gary Moll as a GIS Hero.

An advocate of using technology to integrate human and natural systems, Gary Moll has been a force in bringing the value of urban ecology to the attention of federal and local leaders and uses GIS to apply solid scientific and engineering data to decision making.

  photo of Gary Moll
Gary Moll

Along his life path as a conservationist, Moll has successfully worked with the Congress of the United States to increase funding for urban forestry and with the U.S. Forest Service (USFS) to expand urban forestry programs to 50 states. His work on the development of the GIS software program CITYgreen helps local governments measure urban forests and harness their benefits.

"The human network needs to be built with the natural system in mind," says Moll. "Urban forests and green infrastructure are part of the city ecosystem. GIS shows the relationships between social systems and ecosystems and offers a means for us to weave the city structure into the natural system." Moll is the senior vice president of the Urban Ecosystem Center at American Forests and is one of the nation's foremost authorities on urban forestry and urban ecosystems.

Community leaders traditionally make their decisions about community structures based on dollar values. Sadly, they almost always overlook the value of the natural system upon which these community structures are built. People need to be made aware that if the natural system remains intact, it can do much of the work a structure does. Moll and his team use GIS to show that the original natural system provides similar ecosystem services to those offered by expensive structures. This has huge financial value. For example, using Landsat imagery and GIS technology, Moll was able to show that the 10 counties of the Atlanta, Georgia, metro area lost $2 billion worth of storm water runoff benefits. The analysis measured the tree loss in the region between the years 1972 and 1986. The team then ran the CITYgreen analysis on both scenarios. The good news was that the area still had about $1 billion of that natural storm water benefit left. When community leaders become aware of these dollar amounts, "environmentalists" suddenly are invited to join the urban development discussion.

In the early 1990s, Moll was introduced to GIS technology while working with USFS on an urban forest research project. The agency was planning to issue two urban forest research proposals, one for tree inventory and one for cost-benefit calculations. Moll suggested these two projects should be one and successfully convinced the agency leaders to combine them before issuing the final proposal. The project introduced urban forestry specialists to GIS and proposed a new way to look at urban forests, not as street trees, but as comprehensive urban forest ecosystems.

The proposal recognizes that urban forests are a mix of street trees, yard trees, park trees, and all the other land cover that makes up a community. The national hydrologist, Don Woodward, who worked for the Natural Resources Conservation Service (NRCS) (formerly known as the Soil Conservation Service), showed Moll's team how to calculate the movement of storm water based on land cover. NRCS developed a runoff "curve number" system after monitoring streamflow for 50 years. This became the basis for the most widely used storm water planning model in the country.

  screenshot example of leaf-on image of Bellevue, Washington
This high-resolution leaf-on image of Bellevue, Washington, provides city officials with a detailed analysis of their green infrastructure. Trees (vegetation) and soils provide the basic foundation for the movement of air and water through this landscape.

Woodward helped Moll's team add the impact trees had on that curve number. As a result, for the first time, people could calculate the ecosystem services provided by tree cover. The engineering formulas provided by Woodward produced accurate volume measurements for storm water, Moll's team determined dollar values by obtaining the cost of building storm water retention structures from engineering firms, and the Environmental Protection Agency costs were calculated using cubic foot storage metrics.

Ultimately, however, USFS did not adopt the methods developed by Moll's team as a national standard. Then in 1995, Moll and his team developed an ArcView extension using this technique and, in 1996, released the desktop software CITYgreen. This program makes it possible for local communities to calculate the functions of their natural system, attach dollar values to storm water and air quality, and use this information to make better decisions about managing their communities. Along with the advances in ArcGIS software, the CITYgreen extension has since undergone six iterations.

Moll played a central role in the growth and development of the urban forestry movement and was chairman of the National Urban Forest Conference from 1984 until 2001. But his view of urban forests, not as street trees but as an ecological system, led him to organize the first National Urban Ecosystem Conference in 2003 and drop the National Urban Forest Conference altogether. Taking the broader ecological view of the places where people live has led Moll to work with nontraditional partners and rethink traditional approaches.

Along with Michael Gallis, a renowned expert in large-scale metropolitan regional development strategies, Moll and his nontraditional partners proposed the concept of coevolution, which proposes the management of the human network and the natural system in concert and in parallel. This requires a new framework for efficiently guiding economic growth and rebuilding ecosystems. (See Moll's, Gallis', and Heather Millar's series of three PeopleľNature articles in ArcNewsWinter 2006/2007, Summer 2007, and Fall 2007.)

Moll says, "An aphorism of coevolution is that the global network is the most useful framework for understanding the pressures on ecosystems and human systems around the country and around the world. Simply put, global networks are patterns of trade, transportation, and information that people use to meet their needs, such as roads, shipping routes, and economic regions."

This network forms a pattern of centers and corridors that reaches around the world like a web. Looking at the world this way makes it possible to break down problems and begin to identify goals and strategies. The idea is to start at the global scale, then come down to areas on a regional scale, putting together the natural and human networks.

Recently, Moll and his team, along with Gallis and his associates, and Dr. Michael Flaxman of the Massachusetts Institute of Technology, applied the method to the Piedmont Crescent that lies between Birmingham, Alabama, and southern Virginia, including North Carolina, South Carolina, the Appalachian Mountains, and parts of Tennessee and Kentucky. The task to collect the data and maps about the many different systems was quite involved. Using GIS to analyze data from the Army Corps of Engineers, the Census Bureau, the National Oceanic and Atmospheric Administration, USFS, and USGS, the team found the area to be much different than expected. The southern forest of the Piedmont area is 99 percent gone; the forest of the Great Smoky Mountains is 93 percent gone. The system is in total disarray. These findings have been published in a map book called Piedmont Crescent. One of the biggest surprises was that all the thousands of rivers in this Piedmont Crescent area had been altered—every single one. In reality, the area is not a natural system but actually an unnatural one.

The sobering question asks, if expansion of the human network is inevitable, how do we manage its impact? It would help if everyone stopped to take some time to determine ways the human network can move through these places without destroying them. Questions need to be asked: What economic and social patterns are driving the development of a region? Where are the transportation corridors? Where are the economic corridors? What metro areas are nearby? How are they linked? How is expansion and change happening? How do air and water move through these ecosystems?

"The solution to building better communities in the future lies in learning how to integrate the natural system with the human network," advises Moll. "The first step is to understand how the natural system functions, and the second is to understand the human network. This must be done at various scales. Once that is done, GIS technology can help people understand how the two will interact so we can develop human networks that are low impact and highly efficient."

More Information

For more information, contact Gary Moll (e-mail: Read more about American Forests at Download a free PDF version of the booklet Co-Evolution at

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