MONEY might not grow on trees, but wherever they take root in cities across the United States, trees scatter an ample windfall in greenbacks for city dwellers.
``Urban forests'' play a small but striking part in saving energy and reducing the cost of cleaning up pollution, according to a study by the US Forest Service.
A tree planted and tended by the city of Chicago will not only pay its own way over its lifetime, but will also yield several hundred dollars in savings for the city, says the three-year study, which focused on Chicago.
The findings are welcome news for mayors who must meet stringent federal standards for clean air and reduce city spending because of tight budgets.
The study goes against the grain of a view prevailing in city halls across America that trees, while loved by poets and naturalists, are mostly for the birds.
Most urban officials recognize only the conspicuous tree-related costs like planting, pruning, watering, raking, felling, and legal liability, says Cheryl Kollin, director of urban forestry at American Forests, a nonprofit organization in Washington.
``In general, policymakers, city managers, and budget directors have underestimated the economic and environmental benefits of trees,'' Ms. Kollin says.
During the recent recession, as city budgets grew tighter, many cities cut spending for trees before other departments' budgets, according to Kollin.
Yet in their solid and reticent way, trees offer city dwellers significant savings in ``the long green.'' If the metropolitan Chicago area were to plant 95,000 trees and tend them for 30 years, it would enjoy net savings of $38 million, largely because of reductions in energy use, pollution, and the runoff of storm water. Looked at another way, each tree would offer a net value of benefits worth $402, according to the forest service report.
In 1991, trees across the Chicago metropolitan area performed $9.2 million worth of pollution removal, scrubbing the air of carbon monoxide, sulfur dioxide, nitrogen dioxide, ozone, and particulate matter, according to the study.
Moreover, Chicago-area trees store 6.1 million tons of carbon dioxide, one of the leading ``greenhouse gases'' believed to trap atmospheric heat.
Also, by blocking out the summer sun and impeding winter wind, trees conserve energy for air-conditioning and heating. Three trees planted to provide maximum summer shade and winter wind protection save a typical Chicago homeowner $50 to $90 a year, or 5 to 10 percent of the typical costs in heating and cooling, the study says.
TREES also cool surrounding areas as their leaves absorb heat and transpire water. Without the trees around Chicago, fossil-fuel power plants would annually emit 12,600 tons of additional carbon dioxide, the forest service says.
``Trees won't solve pollution problems, but they'll certainly help,'' says David Nowak, one of three authors of the report and a research forester with the Forest Service's experiment station in Chicago. The Forest Service study is the most comprehensive investigation ever performed on city trees, according to its authors.
Trees also help control storm water as their leaves and branches prevent a sudden deluge of water on the ground. In turn, tree roots reduce erosion and filter out impurities from water.
Some of the benefits from trees are intangible. Neighbors on a city block easily and quickly build a sense of fellowship by planting and tending trees together, Kollin says. She formerly promoted the planting of trees block-by-block with San Francisco Friends of the Urban Forest.
``In some cases these people have only dealt with negative community problems - litter, vandalism, or crime - and tree planting their block is the first positive thing they were able to do together,'' she says.
Once the trees are in the ground and flourishing, the neighborhood group that formed to plant them often decides to take on other urban issues, Kollin says.
Tree planting ``is a very empowering kind of positive action,'' she says.
Chicago has long valued the tree. A 1909 plan for Chicago proposed a belt of forest preserves and parks around a ``city in a garden.'' The Forest Service chose Chicago for the study at the request of Mayor Richard Daley, a vocal tree fancier.