Study Shows Benefits of Urban Trees.

The city of Garland, Texas, is saving more than $5 million per year because of its urban tree canopy, according to a new study by the Urban Forests Center of American Forests.

Officials of American Forests recently conducted an urban ecosystem analysis (UEA) of the city of Garland to map, measure, and analyze the value of tree cover for stormwater management, air quality, and energy conservation. The UEA technique conducted in Garland used geographic information system (GIS) technology along with scientific research to calculate the effects of trees on the urban environment. The analysis also used CITYgreen[R], an American Forests software designed to determine the financial savings provided by a tree canopy.

"The Garland study clearly shows the benefits trees have on cities," said Gary Moll, vice president of the Urban Forest Center. "Too often, city planners and officials look at trees only in terms of aesthetic value. This report illustrates the financial savings and positive health effects trees can have on an urban area and how these benefits increase as tree cover increases. It's especially significant since sprawl is one of the biggest environmental problems facing the nation today."

American Forests analyzed 10 sites in Garland, including residential, commercial, and industrial plots, ranging in size from about 4 acres to 21 acres. using CITYgreen, the organization found that Garland's current tree cover is saving the city $5.3 million a year.

Tree cover in Garland's residential, industrial, and commercial areas reduces stormwater runoff by 19 million cubic feet during a major storm event. The study pointed out that constructing retention facilities to deal with this runoff could cost $38 million over 30 years, or an estimated $2.8 million annually

In 1990, Garland began an innovative approach to managing stormwater by charging a stormwater utility fee to property owners based on the amount of impervious surface they have on their property. Trees help reduce stormwater runoff by allowing for absorption at the roots. Also, some drops of water that land on leaves and branches evaporate before reaching the ground. By contrast, impervious surfaces like concrete impose additional costs on municipalities that have the responsibility of channeling stormwater runoff. Flood control systems and sewer infrastructure are often needed to deal with stormwater runoff, and building such facilities costs money--sometimes millions of dollars, which many localities may not have. Localities are mandated by the U.S. Environmental Protection Agency to maintain water quality.

In 1993, Garland adopted innovative tree preservation regulations for new developments. Unlike requirements common in other municipalities that only preserve trees of certain sizes or species, Garland's regulations require that a certain percentage of the total canopy coverage and tree communities be saved.

Besides reducing stormwater runoff, Garland's tree canopy provides the city with other benefits, including the annual removal of 497,000 pounds of pollutants, a value estimated at $1.2 million per year. The city's urban forest currently stores an estimated 209,000 tons of carbon and sequesters about 531 tons of carbon each year.

Trees also help shade and cool the city. The study found that 4,400 tons of utility-based carbon emissions are avoided each year because of the cooling effects trees have on this urban environment. Long, hot summers force Garland residents to use their air conditioners at an approximate annual cost of $408 dollars per home. Residential shade trees were shown to save each home an average of $28 a year. If 95 percent of the residences have air conditioners, the estimated annual residential savings totals $1.296 million.

American Forests officials determined that increasing tree cover could bring millions more in savings. For example, one 3.86-acre residential site had eight percent canopy cover that provided a runoff reduction of three percent, energy savings of $103, and pollution removal of $76 per year. If the tree canopy increased to 35 percent, runoff reduction would reach 12.8 percent, energy savings would triple to $370, and pollution removal would grow to $341. A canopy cover of 45 percent (American Forests recommends that cities maintain a 40 percent tree cover) would bring the numbers to 16.1 percent, $431, and $438, respectively

American Forests, founded in 1875, is the oldest national nonprofit citizen conservation organization. Its three centers--Global ReLeaf, Urban Forests, and Forest Policy--mobilize people around the world to improve the environment by planting and caring for trees.