The blue paisley picnic blanket was spread out just so, stretched and scrunched to fit the small and uneven shade of the American elm that served as Robin LaCasse's respite from the 97-degree heat yesterday.
"I like coming out here, under the tree for lunch," said the 28-year-old event planner, munching a cracker. "But it seems like there used to be more of them out here, bigger trees."
LaCasse's host, the 40-foot elm in McPherson Square park, is an industrious tree. Besides shading the spot for LaCasse and her two panini-eating friends, it removes 199 grams of ozone that its thin, green leaves filter from the air -- and saves the city $2.46 annually in air-equality improvement costs.
The dollars-and-cents assessment of the elm is a perspective that a group of tree advocates is trying to get wonky Washingtonians to consider when they are not willing to accept "beautification" as a reason to spend money to keep the District green.
"We would like to see the city talk about trees, think about trees in the same way they talk about transportation systems, improved schools and public housing," said Jim Lyons, executive director of the Casey Trees Endowment Fund.
"I think people associate trees with the Cherry Blossom Festival, with beautification and a cool place to sit in the shade on a day like this. But trees do so much more," Lyons said.
The Casey Foundation released a study this week that calculates stem diameter, height, crown width, species type and other attributes of the city's 1,928,000 trees, and plugs those facts into an equation that helps determine carbon storage, pollutant removal, particulate removal and many other attributes that scientists associate with trees.
The Urban Forest Effects Model, created by the U.S. Forest Service and used in the study, showed that the tree canopy covering 28.6 percent of the District saves $2.6 million annually in utility costs in buildings and that it removes 540 tons of air pollution particles each year.
The 28.6 percent of the District covered by trees is relatively high compared with 11 percent in Brooklyn, N.Y. A different study said that in 1973, the District had a canopy of 37 percent.
If those numbers are difficult to grasp, take the example of Casey volunteer Antoinette Campbell, whose pocketbook might feel the recent death of a 60-foot Pin oak on her Petworth street.
For years, on even the hottest D.C. mornings, Campbell's automated air-conditioning unit would whir to life at about 9, when the sun overpowered the oak shading the front of her home.
Since the tree was cut down, she said, her air conditioner starts at 7 a.m. "It notices the tree's not there," Campbell said.
She said she is nervous about what the extra two hours will do to her energy bill. Pepco said a shade tree near a home can save a consumer $80 annually on the cost of household electricity.
Calculations aside, sometimes the emotional attachment to trees is enough. Kathleen Zook, 27, noticed Washington's trees when she peered outside her airplane window before landing to begin her new life as a legal assistant five years ago, leaving behind the oaks, elms and farmland of her native Iowa.
"I was so happy when I looked down and saw all those trees," Zook said. She said that she spends almost every lunch hour under a sprawling elm in Lafayette Square and that it does not matter much to her that the tree removes about 300 grams of ozone a year.