Putting trees on the payroll: here's a greener way to clean up air and water while putting your city's books in the black.

Urban forests--the trees and related resources where people live, work, and play--are as old as civilization. People have long appreciated their unique benefits: cooling shade and soothing green. Since 1970, the science and practice of urban forestry has gained credibility as researchers learned about other benefits--for increased property values, as a natural means to a sense of community, and to soften the harsh lines of our buildings and streets.

The U.S. Forest Service had the foresight to include urban forestry in its Cooperative Forestry programs legislation 25 years ago, albeit with minimal funding. In 1990 urban forestry was included in the Farm Bill and funding jumped tenfold. Congress has appropriated money for it ever since.

Clearly Congress recognizes urban trees are worth the investment. Conservative calculations done by AMERICAN FORESTS On the value of urban tree cover for reducing stormwater problems and improving air quality show that the trees in our cities are worth more than $400 billion.

It's hard to imagine any resource more valuable than the land where we live and the natural resources it holds. Satellite images show naturally tree-covered parts of the country are losing that canopy--it's declined about 30 percent in 25 years--while urban areas have expanded by about 20 percent during the same period.

It's time to turn this trend around. The urban forest is an ecological resource with an economic value. Invest wisely, and it can yield big payoffs. Most U.S. cities have huge budgets, of which urban forestry constitutes a small part; but, those dollars can be leveraged into tremendous values. The big bonus is cleaner air and water for the more than 80 percent of Americans who live in urban areas.

Trees are now recognized as assets by the U.S. Environmental Protection Agency (EPA), which regulates environmental health, and the Government Accounting Standards Board (GASB), a nonprofit that sets state and local government accounting practices.

Investing in the natural benefits of a green infrastructure can go a long way toward improving the air and water in metropolitan America. Trees sequester carbon dioxide and remove air pollutants. Trees and soil reduce stormwater runoff by slowing water flow and therefore increasing the amount of rain that soaks into the ground.

City decisionmakers need to look at the benefits of increasing their tree cover and decide on a tree cover goal. Once that's set, they can make it real by remeasuring every year. With the tools available to measure tree canopy loss or gain, we have the scientific means to make trees "green machines" that help meet EPA standards for clean air and water.

With EPA recognizing trees as official air and water cleaners and GIS software calculating dollar values for tree benefits, our arboreal neighbors can be recorded as assets in a city's books. Think of the possibilities: A city's "balance sheet" could be used when evaluating a city's "wealth" for its bond rating. Putting green infrastructure into the GASB rule will increase appreciation of and investment in the urban forest. It might even raise this green asset up on the budget priority list.

The federal investment and the hard work of U.S. Forest Service scientists and AMERICAN FORESTS' public policy experts are starting to pay off. There is a green resource available to improve the environment and compelling arguments to demonstrate it to the institutional powers that be. If we hesitate to grow and value our green infrastructure, we have no one to blame but ourselves.

Deborah Gangloff, executive director & Gary Moll, VP, urban forestry