Front Range Trees Provide Millions in Benefits

American Forests
Wednesday, 18 April 2001

New Study Finds Growth in Urban Forests Not Keeping Pace with Development

Trees in Denver and seven other Northern Front Range cities of Colorado are providing services equivalent to a $44 million stormwater management system and removing 2.2 million pounds of air pollutants (such as particulate matter, sulfur dioxide, nitrogen dioxide, carbon monoxide, and ozone) valued at $5.3 million per year. The cooling shade from these same trees is saving homeowners $4.5 million per year in air conditioning costs, which also avoids the production of 1.6 million tons of carbon emissions from power plants annually. These are some of the findings of a new study presented today to Denver Mayor Wellington Webb and a number of city foresters just prior to Colorado's Arbor Day (April 20) and Earth Day (April 22) by American Forests (americanforests.org), the national conservation group for trees and forests.

American Forests analyzed satellite images from 1986 and 1998 for a 2.24 million-acre area from Denver to Ft. Collins and a more developed 425,000 acres around Denver. Thirty-nine selected sites, documented with aerial photographs and ground sampling, were analyzed in depth with CITYgreen software. The study was conducted with support and cooperation from the US Forest Service, Colorado State Forest Service, and the city forestry departments of Denver, Aurora, Wheat Ridge, Lakewood, Boulder, Louisville, Ft. Collins, and Greeley.

"Colorado is known for its mountain forests and beauty," said Gary Moll, study coordinator and vice president of urban forestry at American Forests. "But with the rapid growth of population and of urban areas here, it's vitally important to recognize and plan for the full environmental and economic value of urban and community forests."

In the regional study area, tree cover increased from just 6 percent to 7 percent over the 12-year study period, while roads, buildings, and other hard surfaces that contribute to runoff increased from 9 to 12 percent. In the more developed Denver Metro Area, tree cover increased from 4 percent to 6 percent of the area while impervious, hard surfaces, grew from 30 to 39 percent of the area and currently cover nearly six times the area that trees do (166,049 to 26,324 acres).

Unlike many other parts of the country where urbanization has meant a loss of tree cover as forests are cleared to make way for development, it is the opposite in Front Range cities established on dry prairie landscapes with little tree cover. As settlers moved into the area, they planted trees in their communities. Those who followed cared for them and planted more. Today, some older neighborhoods of Denver, Boulder, Greeley, and Ft. Collins have tree canopies of 25 to even 40 percent and these trees form the core of a green infrastructure that helps to moderate many of the negative ecological impacts of development. (more)

"The fact that forest cover in the Denver metropolitan area has increased to about 6 percent of the area is a good trend that should be continued," says Moll. "However, this is still far short of the goal of 25 to 30 percent average tree cover that we believe is optimum for healthy communities in this region."

The study also calculated urban forest benefits for a 214,000-acre contiguous area of Denver, Aurora, Wheat Ridge, and Lakewood at its current estimated 6 percent tree cover, then estimated values for an average 25 percent cover. With 6 percent cover, this Denver-area urban forest is providing the equivalent of a $21 million dollar stormwater system worth $1.5 million annually; storing 546,000 tons of carbon; sequestering 9,000 tons of carbon annually; and removing one million pounds of air pollutants at a value of $2.6 million per year. Growing this urban forest to an average 25 percent tree cover would increase these annual benefits from $7.6 million to $12.7 million.

While the Front Range's increasing tree canopy is a positive trend, trees are not being planted nearly as rapidly as they could be or should be to counteract the environmental effects of development. The population of the Denver metropolitan area has increased 40 percent in the last 20 years, from 1.4 million in 1980 to 2 million in 2000 (based on Denver Regional Council of Government figures for incorporated cities, June 2000). When urban areas expand and populations increase so does energy use, stormwater management costs, and air pollution. This makes the environmental and economic benefits provided by trees even more important.

In the Front Range study, American Forests recommends ways city leaders and planners, engineers, and policy makers can utilize trees to improve a city's "green infrastructure" such as: by including tree cover data in all natural resource and land development decision making; by increasing tree cover as cities grow to improve air quality and to help offset stormwater runoff; encouraging local jurisdictions to promote the conservation of healthy, mature trees; and by establishing local tree cover targets while determining the contributions trees make to air, water, and energy needs of the community.

CITYgreen computer software, now in its forth edition, was developed by American Forests as a tool for policy makers, planners, urban foresters, and citizens to enable them to map and measure the ecological and economic benefits of urban forests. CITYgreen software is now being used by hundreds of agencies, universities, and organizations.

American Forests is a national leader in the urban forestry movement. It combines education, action, and research into programs that improve the trees, forests, and overall environmental health of our communities. Every two years, American Forests holds the National Urban Forest Conference, which brings together planners, legislators, and others interested in improving the urban environment. The 2001 National Urban Forest Conference will be held in Washington, DC, September 5-8. This study and others can be found on the Internet in the Trees, Cities & Sprawl section of www.americanforests.org.

For more information, or to contact American Forests, see their website at: www.americanforests.org