In the city’s forests, Parks employees might take a more laissez-faire approach to invasive species. Some are targeted for removal, including the Norway maple, once the darling of Parks tree-planters throughout the East Coast but now known to release chemicals that discourage undergrowth. But mostly, urban foresters are comfortable with the idea that the species makeup of nature will change based on external events and that tomorrow’s forests won’t be the same as yesterday’s. They talk about encouraging the trajectory of the forest. The imminent arrival of the Emerald ash borer, an exotic beetle, may mean the destruction of thousands of ash trees in the next few years, but it also will bring about the beginning of something else.
This is a culture shift, and it has already happened in Europe, where biologists tracked plant and forest succession at bombed-out sites after the war. There, what Americans consider invasive species are tolerated as plants that thrive in the warmer, more acidic ecology of the city. “They just consider it nature, and this whole question of ‘natural or not natural’ is just a moot point,” says Peter Del Tredici, a senior scientist at the Harvard arboretum who teaches urban ecology at the Graduate School of Design.
This is not to say the Parks Department farms kudzu vine; it just means that it recognizes that invasive plants are, by definition, ecologically successful, and there’s something admirable about that. You hear this in Wenskus’s patter, as he inspects Alley Pond on a midsummer afternoon. He walks by a ten-year-old tree that foresters had planted on the top of the hill. “Okay,” he says, “maybe you shouldn’t plant a tulip tree at this elevation on a glacial hill. But then, look: That one’s doing fine.”
Nothing has helped illustrate the potential productivity of New York City’s nature more than an oil spill. In 1990, Exxon’s Bayway Refinery released 567,000 gallons of oil into Arthur Kill, a narrow tidal strait separating Staten Island and New Jersey. Arthur Kill is one of those bodies of water that people typically look in only when looking for bodies; it was assumed to be lifeless, even before the spill. Indeed, in the litigation proceedings that followed, Exxon argued that it was not obligated to provide reparations because the waterway was of no ecological value.
At its wildest, New York’s nature exists in the places humans let be, either because we mapped it as parkland and forgot about it, or we abandoned it as ruin.
The NRG’s naturalists knew that this was wrong, and the city joined state and federal bureaucrats in pursuing damages against Exxon. Traditionally, damages were valued on the number of dead birds or animals. The NRG proposed arguing that for one egret to survive, it meant that the area was habitat to small fish, which in turn depended on smaller fish, and so on down to the marsh’s bacteria. “I was sitting there at a meeting, and I thought, What about counting all the killifish at, say, 25 cents, and then counting all the bacteria in the marsh?” Matsil recalls. “Everybody said I was crazy.” But the government won a $15 million settlement, and the money moved NRG into the wetland-restoration business.
In the Middle Atlantic states and parts of southern New England, restoring wetlands has a lot to do with planting spartina grass. At first, the NRG researchers imported healthy spartina from Maryland, but it was seemingly overwhelmed by the pollution in Arthur Kill. So they took a chance on the local spartina, hoping that the grass would pump oxygen into the ground, thus re-aerating the marshes so that the bacteria in the peat would ingest the oil. The ecologists at the National Oceanic and Atmospheric Administration doubted the NRG’s plan, but the local grass survived, and after about two years, tests indicated that the total amount of petroleum hydrocarbons in the marsh had fallen. “The bacteria that was there already—they went to bat,” says Carl Alderson, who worked with the NRG at the time and is now a wetlands-restoration expert with NOAA. “The spartina had a remedial effect on the oil.”
The success at Arthur Kill changed everything among naturalists. Now, in addition to documenting how urban nature has thrived in areas we’ve left alone, they are designing projects with an eye toward actively encouraging it. Arthur Kill has been used as a model for similar remediation efforts in London and Beijing, and in New York, the NRG is focusing most of its energy on ecosystem restoration. There may be nothing on Earth as ecologically productive as our spartina marshes: The fish, crabs, mussels, copepods, and bacteria together produce ten tons of organic matter per acre per year, more than ten times the amount that deserts produce, and about twice as much as a typical forest or farm. At the moment, in addition to its work in the city’s forests and waterways, the NRG is restoring another 200 acres of salt marsh across the five boroughs.