Inside space-age laboratories in Fort Detrick, fragrant forests on Sugarloaf Mountain and tree-enshrouded public parks, scientists, entomologists and weekend gardeners wage war on the enemies of a precious natural resource: the Washington area's trees.

Imported insects, weeds and diseases, combined with natural and man-made phenomena such as Hurricane Isabel and suburban subdivisions, are eating a swath through the lush tree canopy that has been the region's pride for two centuries.

Every day, the Washington metropolitan area loses 28 acres of green space, "and that's a conservative estimate," said Brian LeCouteur, senior environmental planner and urban forester for the Metropolitan Washington Council of Governments' Department of Environmental Programs.

"We have to be aware of what's going on if we want our natural land cover to perform the functions we look to green spaces for," he said. Beyond providing a place to picnic or a shady spot to park the car, LeCouteur said, trees help clean the air, which is particularly important in light of this region's pernicious smog and ozone problems.

Thanks to a combination of heavy forest cover, renowned research facilities and concerned activists, Frederick and Montgomery counties are home to several important efforts to preserve and restore trees.

Most spring weekends, Essie and Burnie Burnworth of Potomac can be found at Sugarloaf Mountain, on the border between Frederick and Montgomery counties, gently weeding beds of chestnut tree saplings. For the Burnworths and other members of the Maryland chapter of the American Chestnut Foundation, the delicate green shoots hearken back to a time when billions of American chestnut trees covered mountain slopes from Maine to Georgia, providing food, lumber and wildlife shelter.

But in 1904, a blight, believed to have come over in a shipload of lumber from Asia, ravaged the species, leaving a mere handful of trees by the mid-1950s. It's those trees that the Burnworths target, collecting nuts from the ones located in Maryland and planting them in hopes of developing a Maryland-specific, disease-resistant American chestnut. On March 16, the group planted 2,700 nuts in beds protected from deer and squirrels. To protect their seedlings, the Burnworths and a small band of volunteers weed the beds themselves until the saplings are easily distinguishable.

"If these trees could be brought back, the impact would be really amazing," said Essie Burnworth, 64. "Chestnuts tend to grow in masses, so they sequester carbon dioxide," which helps purify water and air near them. In a region constantly trying to find new methods to fight air and water pollution, "the benefits would be economically important."

At Thorpewood, a privately funded foundation based near Thurmont in Frederick County, Chestnut Foundation members who are researchers from Hood College in Frederick are trying to crossbreed the American chestnut with the disease-resistant Chinese chestnut. They hope to develop a hybrid that's close in appearance to the American variety but without its fatal weakness.

Though it may take longer, the Burnworths continue dreaming of a purebred American chestnut, a cousin to the trees of old. "We have high hopes," Essie Burnworth said. "It's nice to do something that [reaches] beyond next week."

While Sugarloaf volunteers try to correct errors of the past, researchers such as Douglas G. Luster are attempting to thwart the plague of the future. Outfitted in protective suits and respirators and working in a high-security laboratory at Fort Detrick in Frederick, the Foreign Disease-Weed Science Research Unit, part of the Agricultural Research Service branch of the U.S. Department of Agriculture, isolates and tests native plants' resistance to a host of threats from abroad.

Invasive species "are for me a plant disease, an insect or a small animal" that hitchhikes into the U.S., usually on ships or planes, said Luster, research leader at the laboratory. Due in part to growth in foreign trade and travel, "we're seeing an increase in these species coming in, which is very worrisome," he said.

One of the chief threats being studied at the laboratory is sudden oak death, a blight that's decimating trees in Pacific coastal areas and has been found on nursery stock shipped to Maryland from California. First identified in 1995 by Matteo Garboletto, a plant pathologist at the University of California at Berkeley, the blight spores, whose DNA is similar to Irish potato blight, settle on tree leaves. Once established, the spores create red, oozing "cankers," causing the tree to wilt and die within weeks.

Despite its name, the disease doesn't only affect oaks -- the spores attack redwoods, evergreens and smaller flowering trees, as well. Scientists in California are inoculating trees against the disease, but with only limited success.

At Fort Detrick, the USDA researchers are testing the virus on young saplings and ornamental trees such as rhododendrons, azaleas and camellias. "We already know that some of them are susceptible," Luster said. But what they don't know is whether the spores can survive in the mid-Atlantic climate.

"Nothing's been found in the wild in the East," Luster said. Sudden oak death "really thrives in that coastal foggy microclimate, so people have postulated that our foggy Appalachian forests could mimic that."

"We don't know yet," Luster said. "But we're worried."

The Montgomery County Weed Warriors, the Maryland Invasive Species Council and a growing number of volunteer groups are battling nature gone wrong -- insect and plant species, usually imported to this region, that attack native plants and trees. The groups patrol thousands of acres of parkland, pulling out and destroying invasive vines and plants that choke the life out of trees and rare native vegetation, depriving them of space and food.

The Weed Warriors target invasive plants. These vines and weeds come in many varieties but have several things in common: They grow and spread quickly and mature early; they thrive in many habitats and under adverse conditions; and they have few known predators.

After a special training course in which they're taught how to identify harmful plants, the 300 volunteers in the Weed Warriors, established in 1995, patrol 28,000 acres of Montgomery County parkland, pulling the culprits and reporting what they've found. They function with special permission from park authorities; if they're stopped, they flash an identification card explaining their mission.

Kerrie Kyde, a plant pathogen researcher from Dickerson, is a founding member of the Maryland Invasive Species Council, formed four years ago to spread awareness of the threats posed by "exotic" invasive species, from beetles to vines. Members include nursery and pet shop owners, horticulturists and homeowners concerned about the problem.

On its Web site, www.mdinvasivesp.org, the group features an "Invader of the Month" and publishes "red alerts," news about new invaders from other states that may be coming Maryland's way.

Many invasive plants, such as some strains of wisteria and bamboo, are actually popular among homeowners -- until they take over. What common plant poses one of the most serious threats to trees?

"English ivy," Kyde said. "It shades out the growth" -- interrupting a tree's ability to feed itself through its leaves -- "and it actually gets heavy enough to topple trees."

Nina Shishkoff, above, a plant pathologist at the USDA's Foreign Disease-Weed Science Research Unit at Fort Detrick in Frederick, studies a pathogen responsible for causing sudden oak death. Below, plant pathologist Kerrie Kyde makes cultures of the pathogen for study.Barbara Knapp, left, weeds tree saplings as Burnie Burnworth cuts grass at Sugarloaf Mountain. Both American Chestnut Foundation members want to develop disease-resistant chestnut trees.