BURLINGTON, Vt. — Increasingly, trees are the new must-have for American cities. Some prodded by environmental awareness, some by regulatory edict, they're stepping up tree plantings in hopes of improving air quality, reducing energy consumption and easing storm water flows.

And a four-man team of scientists at the University of Vermont is helping urban planners and foresters gauge the existing "tree canopy" - or cover - in their cities and set realistic goals for increasing it.

Their expertise has been tapped by public and private groups in New York, Boston, Washington, D.C., and several Maryland towns eager to green their cities with the help of private property owners.

"Everybody's trying to do their best to improve tree canopies and work with developers and urban planners to make sure they remove as little tree canopy as possible in their projects," said Mark Buscaino, executive director of Casey Trees, a not-for-profit in Washington, D.C., that works to green the nation's capital.

"The benefits are many. First, there's the environmental. Trees cool things. They remove particulates in the air. They're linked to mitigating storm water flows, which is an enormous problem in all urban areas because there's so much impervious surface."

Generally speaking, tree canopy refers to the part of a city that's shaded by trees. Quantifying size was once an elusive task.

But the UVM scientists, working with a research scientist from the U.S. Forest Service, have used computer programs and their own expertise to combine satellite images with aerial photos and tax maps to ascertain tree canopy size and break it down by parcel, determining which trees are on public land and which are on private land.

"If you don't even know what you have, you can't make any decisions," said Jarlath O'Neil-Dunne, a geospatial analyst with the team. "It wasn't that people didn't want to plant trees or didn't want a tree canopy program. But they needed the hard data to make decisions. That's where we came in."

The group consulted on a study of Baltimore's ecosystem in 2002, and word of their methods spread.

Their expertise dovetailed with a growing awareness among elected officials that trees could be more than decorations for urban areas.

In addition to giving off oxygen, they cool the air, limit sun exposure and act as sponges for precipitation, catching rainwater and releasing it gradually instead of having it flow directly into storm sewers.

Charlie Lord, executive director for the Urban Ecology Institute in Boston, has worked with the scientists.

"They help you gather the data, analyze it and help you answer the basic questions - `Where do we have trees?' `Where don't we have trees?' - and the more sophisticated ones, like `Where would we plant to improve our carbon footprint?' or `Where are the best places to plant to improve our water quality?'" Lord said.

The group's work helped the city of New York establish the goals for a 1-million-tree initiative that kicked off last fall, aiming to plant that many trees over a 23-year period.

"It really kicked off everything, from a policy perspective, a natural resource management perspective, a planning perspective. It helped us set our sights on 1 million trees," said Fiona Watt, chief of forestry and horticulture for the New York Department of Parks and Recreation.

"People used to overlook trees in cities," said Watt. "They're now viewed as increasingly important because of the work of scientists who've helped us quantify those benefits. The environmental benefits and property value benefits are quantifiable, but the social ones are harder. They make us feel good, they improve our moods, they make neighborhoods more beautiful.

"Tree canopies can make neighborhoods more cohesive and bring people together, bonding them over this common resource," she said.

The fruit of the team's work may not be visible yet, but it will be eventually. In the world of forestry, there's an old proverb: "The best time to plant a tree was 20 years ago. The next-best time is today."