With apologies to Robert Frost, these woods in Northeast Baltimore are lovely and dark, if not so deep. Towering oaks screen out the sun, while fallen leaves carpet the ground of this sylvan oasis in the Chesapeake Bay region’s second largest city. A faded sign on the street corner identifies it as “HEPP Park.”

Many foresters might not call this 4-acre woodland a forest. On a recent visit, there was no escaping the brassy blare of a high school band practicing nearby. In a small clearing, a pile of beer cans and other debris suggested it’s a popular hangout.

But the surrounding urban landscape of homes, vehicles and asphalt faded from view after just a short walk among the trees. And not long ago, a pair of red-shouldered hawks found it a quiet enough spot to build their nest.

“This is a really special place,” said Miriam Avins, executive director of Baltimore Green Space, while showing it to a visitor. Her nonprofit group started out in 2007 working to help neighborhoods secure open land in the city for community gardens and pocket parks, but branched out several years ago to advocate for urban woodlands outside of parks.

For all of its concrete and asphalt, Baltimore is sprinkled with many such woodsy refuges that somehow got passed by as the city grew over the decades. Some are as small as a baseball diamond, while others cover three or four acres of land. Many are overgrown with vines and littered with trash. But a recent survey found that a significant number of them retain at least some of the natural attributes of their larger rural counterparts.

Avins’ group, with help and advice from ecologists, is working to engage city residents and urban planners to nurture and protect these so-called “forest patches,” for their environmental, cultural and recreational benefits.

Trees are certifiably green, absorbing carbon dioxide and filtering other pollutants from the air while pumping out life-sustaining oxygen. Their roots soak up nutrients that otherwise might cause water quality problems in streams, rivers and the Bay. Trees also provide food and shelter for birds and animals; for people, they offer cooling shade, especially in the paved-over “heat islands” of cities.

Forests — larger areas covered by dense growths of trees — can provide even greater environmental benefits. They can soak up large amounts of storm runoff while helping to control flooding and offer habitat for a wide variety of wildlife, especially species vulnerable in open landscapes.

In cities, though, the question persists: Do small woody places, some just a few vacant building lots in size, act like forests, or have they been too chopped up and degraded?

Working with the U.S. Forest Service and other experts, Baltimore Green Space analyzed 10 forest patches in the city last year to assess their condition. They sampled the tree species that made up the canopy, assessed the extent and types of ground cover and tested the soil for density and organic content.

The survey found that most of the tree canopy in these woodlands is native. White oaks predominate, but tulip poplar, maple and sassafras also are common.

To Avins, though, the most exciting finding is that the soils in a significant number of the patches checked were typical of woodlands, a healthy dose of organic matter capable of soaking up moisture.

“That’s actually big news,” she said, “because people keep telling us that the soils are sure to be compacted. This is the first time that we have good evidence that forests in the city are likely filtering stormwater just like their country cousins.”

Baltimore has about 2.6 million trees, according to the Forest Service, but about one-quarter of them are distressed, dead or dying. The city’s tree canopy has declined by about a third over the years to shade just 27 percent of the urban landscape. Some tightly packed blocks of rowhomes are virtually tree-less.

In recognition of trees’ varied environmental benefits, the 2014 Chesapeake Bay Watershed Agreement calls for increasing the six-state region’s urban tree canopy by 2,400 acres by 2025. Baltimore has its own goal of doubling its canopy by 2037, and the city is working with several nonprofits toward that goal by planting trees along streets and in vacant lots.

But Baltimore may not reach those goals, Avins argued, if forest patches like HEPP Park are not preserved. While the city boasts some large woodsy public spaces, including the leafy wilderness of Leakin Park, fully a fifth of its forested tracts are outside the protective boundaries of parks, and vulnerable to future development.

HEPP Park is among those at risk — it is not an official park. The sign is a relic of a time when now-defunct neighborhood groups adopted it as a community amenity.

Matthew Baker, a professor of geography and environmental systems at the University of Maryland, Baltimore County, who has studied the city’s scattered woodlots, said that many are too small or thin to provide significant benefits. Even excluding those, though, he said that there are about 700 patches that feature at least some of the attributes of forests.

HEPP Park turned out to be the healthiest ecologically of the forest patches examined. Indeed, given its small size and relative isolation, its vitality is something of a mystery, he said.

“In general, woodlands in urban areas are a good thing, and they can provide a lot of benefits,” he said. They hold carbon over time, he pointed out, collectively helping to mitigate greenhouse gas emissions from cities and suburbs. They also provide seasonal food sources for migratory birds.

“But they don’t always generate those benefits if we ignore them, if we leave them alone,” he cautioned. “A lot in Baltimore have been ignored, and they’re in need of attention.”

Indeed, the survey found many forest patches are infested with poison ivy and invasive nonnative vines, such as English ivy, and Japanese honeysuckle. If unchecked, they can grow up into a tree’s canopy, blocking the sunlight its foliage needs.

“The contents of the understory (in the survey) suggest that we are likely to lose this inheritance — unless we make a big effort at stewardship,” Avins said. “The invasive plants threaten the canopy directly, by climbing and suffocating the trees. They also make it too hard for the little trees to grow.”

Baltimore Green Space is recruiting residents to serve as stewards for their neighborhood forest patches, and working with government agencies, academics and other nonprofits to get expert help and resources for the effort.

In contrast to HEPP Park, “Fairwood Forest” is perhaps more typical of the city’s woodlands. It’s a 3.8-acre band of woods spanning 32 vacant home lots on the edge of a rocky bluff in Northeast Baltimore. Oaks and poplars dominate it as well, with some hickory and dogwood in the understory. But invasive plants, including kudzu, make up four-fifths of the ground cover.

Even so, some of the neighbors have adopted the forest, and Baltimore Green Space has secured the consent of owners of most of the tract to work to clean it up and enhance its recreational value.

“There’s two parallel trails — one higher up and one lower,” said Katie Lautar, the group’s program director, as she led a tour of the tract. “This is a site that has a lot of species diversity. It does have some dumping also.”

It also has gnomes and fairies— or at least fanciful signs tacked to tree trunks suggesting the woods are alive with little people. They’re the handiwork of Daisy Sudano-Pellegrini, who lives across the street.

“It gives you something to look for,” said Sudano-Pellegrini. She wants youngsters and adults to have fun in the woods, she explained. But there’s a lot of real nature to soak up as well among the trees, she noted. She should know — she’s a master naturalist who works at Cylburn Arboretum in North Baltimore.

“We have a fox that comes every now and then in the neighborhood. We have nesting hawks, and raccoons live in a tree across from my house. We have possums,” she said. “I know some people would rather not have these animals because they get in trash cans. We just need to learn to share the space with them.”

Sudano-Pellegrini said she and other neighbors have begun to keep a lookout for trucks that might stop to dump their debris. They’ve also worked to maintain the paths and take out some of the invasive species. One day in November, with the help of local volunteer weed warriors, they planned a day of hacking and yanking out “villainous vines.”

“It would be nice if it could be dedicated as just a natural green space,” Sudano-Pellegrini said. “People in their neighborhood walk the dogs back there. Children walk through; it’s just a safe little haven.”

The highlight of having a forest across the street, she said, occurred one summer day, when a couple of children came out of the woods with an animal they’d found. They showed it to her and asked her what it was.

“It was a salamander,” she recalled. “It was just the coolest thing; city kids had never seen it before.”

Avins and Lautar said they hope they can build on those experiences, and create networks of support for Baltimore’s forest patches, as well as persuade the city to accord them some measure of recognition and protection from removal.

“The overall lesson is — there really is nature here,” Avins said, “and we’ve got to care for it.”