Sarah Charlop-Powers was comparing New York City’s forests to its subways. The city has more than 840 miles of tracks for one
It has 10,542 acres of the other, about half as much as the Congaree Swamp in South Carolina, a small national park with an old-growth forest and, according to the website I Love National Parks, “more bugs than you can imagine.”
No doubt there are many bugs in New York’s forests, even cockroaches that have yet to find their way to somebody’s basement or bathtub. But Ms. Charlop-Powers, the executive director of a Manhattan-based nonprofit group called the Natural Areas Conservancy, is not focused on them. She sees the trees — and the forest. Most of the city’s forest is deep in parks, and on the worry spectrum, she is “concerned” about them.
“The situation is not dissimilar to the subways, in that we’re at a crucial moment,” she said.
Fortunately, urban forests appear to be at the point the subways reached decades ago, before transit policymakers decided that maintenance could be deferred.
But there is another concern for urban forests: climate change.
Ms. Charlop-Powers wants to prepare the city’s forests for a changing climate. If nothing else, forests can slow rising temperatures by reducing what foresters call urban “heat-island effects.” Trees lower the nearby temperature by up to nine degrees. There is also the worry that forests could be overrun by invasive species that can change soil conditions — another contributing factor on the climate change checklist.
Enter the Natural Areas Conservancy, which began by conducting a survey. The group hired 25 scientists to take stock of biological conditions in parks. The conservancy’s senior ecologist, Helen Forgione, said the survey found 750 species of plants in the city’s forests.
The survey-takers also interviewed 1,600 park users. Their answers led to the conclusion that the urban forest has never been more important for people.
“Half the people reported recreating in New York City parkland, never leaving to go to the Catskills or Jones Beach,” Ms. Charlop-Powers said. “Their whole experience with nature is happening right here in the five boroughs, which means that if we want people not just to experience playgrounds and ball fields but to take a hike or be in a place where you can hear birds singing, it becomes really important to invest in forests.”
So, as with the subways, it’s about money.
The legislature in Albany approved $836 million for Gov. Andrew M. Cuomo’s subway action plan after he declared a mass-transit state of emergency last year. For the forests, Ms. Charlop-Powers sees a smaller price tag and a longer timeline: $385 million over 25 years.
“Without investment, we risk losing wildlife and plants we may never be able to get back,” Ms. Charlop-Powers said.
The biological data indicated the city’s forests “are at a tipping point,” she said. The mature forests, which for the most part grew after the Civil War on land that earlier generations had logged and farmed, are “surprisingly healthy, similar to the conditions in rural forests upstate.”
The assumption had been that invasive vine species like Japanese honeysuckle and the mile-a-minute weed (Persicaria perfoliata to those in the know) were crowding out the trees foresters prefer.
Invasive species were indeed found in 56 percent of the areas in the survey, but they were less prevalent in the older forests. It was the younger forests that troubled Ms. Charlop-Powers, especially in what foresters call the midstory and understory layers, the lower levels of the tree canopy. The researchers taking the survey found the smallest proportion of native species among the 561 species they counted in the understory.
The invaders include the Norway maple and the black locust. The latter, Ms. Forgione, the ecologist, said is rot-resistant, which is good, but raises nitrogen levels in the soil, which is not. “We don’t want high-nutrient soil,” she said. “Our mature forests have evolved on low-nutrient soil.” And the higher nitrogen levels figure in climate change.
The recommendations in the plan are for what Ms. Forgione calls “future forests,” but specifically future urban forests. She said that climate change could affect urban forests a generation or two before differences begin to appear in rural areas.
Already the conservancy’s ideas are shaping a chunk of forest in Prospect Park in Brooklyn. On a recent day, Susan M. Donoghue, the administrator and president of the Prospect Park Alliance, which manages the park, led the way to the area, on Lookout Hill. Longfellow’s “forest primeval” it was not. A helicopter whipped the air overhead, and a jet climbing away from Kennedy International Airport whined in the distance.
Last summer the alliance brought in four goats to do some weeding. Their mission was to clear out invasive species — but only on one side of the path. In the grayish light of early spring, it was the greener-looking side because it had English ivy, a nonnative species. Unlike, say, poison ivy, English ivy can take over the forest floor and crowd out trees.
On the other side of the path, Ms. Forgione pointed to a sugar maple and an ash, trees that are considered desirable in the forest, although the ash is a species threatened by the Emerald ash borer, a beetle. “It’s a tree we would not recommend planting,” Ms. Forgione said. “In New York City, the days are numbered for our ash trees.”
But there are 10 trees on the conservancy’s list that will soon be planted on Lookout Hill, including three types of hickories with irresistible names — the pignut hickory, the shagbark hickory and the mockernut hickory.
“We’re thinking for the next century,” Ms. Forgione said. “That’s going to be our forest.”