Studies have shown that trees reduce air pollution and also dampen the urban heat island effect of sunlight beating down on asphalt, concrete and rooftops.

Beth Strommen, director of the city's Office of Sustainability, said the analysis by Avins' group helped planners understand better the distribution of woods, and now they're looking how best to preserve them.

Avins said she'd like to see the city strengthen its forest conservation ordinance to protect smaller patches of woods, and even individual large trees that are notable specimens of their species. Though the city officially recognizes forest patches as small as 10,000 square feet, there are no legal requirements for property owners to minimize or replace any trees cut until the area cleared exceeds 20,000 square feet, she pointed out.

Strommen said that's being looked at, but she'd prefer to start with a nonregulatory approach that enlists landowners voluntarily in caring for their forest patches.

"The best way is to educate people about the value because if they don't understand the value, it doesn't really matter what else you do because they're not going to take care of it," she said.

The Govans plot illustrates what a concentrated volunteer effort can do in a short period of time. The woods were adopted about a year ago by members of the York Road Partnership, said Helene Perry, head of the group's streetscape committee.

Perry said the group enlisted the help of the Loyola University rugby team in cleaning the place out, filling a 15-foot trash bin with trash and debris.

In clearing the forest, the Govans group discovered that a homeless man had taken up residence there. Perry said they have focused their work on the front of the plot near the street and left his camp in the back of the tract undisturbed.

Students from Friends School have since joined the effort, which included chopping down vines cloaking many trees and replacing Norway maples with native seedlings. The Friends students also contributed painted birdhouses and the entrance sign.

"They're these little gems that are hidden in the neighborhood," said Perry, a retired Loyola physics professor who said she's learning a lot about ecology these days. "You pass by them every day and you don't realize what is there."