NEW YORK - For most of her career, Christine Padoch did her environmental research in the rain forests of Amazonia and Borneo, while Steven Handel studied evolution in the Galapagos Islands.
Now Padoch, an ecological anthropologist, takes the subway from her job at the New York Botanical Garden in the Bronx to count exotic vegetables at the green markets of Queens, while Handel, a professor of evolutionary biology at Rutgers University, is studying the vegetation that grows along the tracks of the New Jersey transit railway - a true test, if ever there was one, of the survival of the fittest.
Their projects are examples of a new field of environmental studies: urban ecology.
Until recently, the only real environments thought to be worth studying were in "pristine" nature, remote areas as far as possible from the footprint of human beings. Cities, by contrast, were seen as unnatural, nonenvironments, whose parks, gardens, ornamental plants, scraggly sidewalk trees and weeds were of as little interest to ecologists as house cats and lap dogs are to big game hunters.
Now, though, ecologists are finding that cities are interesting, legitimate environments, with surprisingly high levels of biodiversity and, what's more, understanding and protecting them might be crucial to our environmental future.
From Paris, Rome and Cairo, Egypt, to New York, Baltimore and Phoenix, cities are subjects of intense ecological study. UNESCO is thinking of making several major cities, including New York, biospheres, important natural areas to be protected, joining ranks with such traditional sites as Yellowstone and Yosemite national parks.
"If Darwin were alive today, he might be studying Staten Island instead of the Galapagos," said Handel, who is working to reintroduce native North American species to a portion of what was, until recently, North America's largest garbage dump, the Fresh Kills waste site.
That ecologists have gone from studying Darwin's finches to counting papayas and mangos at the Hunt's Point market in the Bronx, as well as the nearly indestructible flora and fauna that survive inside the vacant lots and abandoned industrial sites of the world's cities, is part of a much broader maturation of the field, several environmental scientists say.
"The original idea that ecology involved trips to faraway places that people would consider to be pristine reflected a very deep-seated belief that people and nature are separate, which has been dominant in ecology," said Steward Pickett, a senior scientist at the Institute of Ecosystems Studies in Millbrook, N.Y., who is taking part in a major long-term study of the environment of Baltimore.
The foundations of ecological thinking, he said, were shaken by studies in the past 25 years that showed virtually all "pristine" environments bore clear signs of human intervention: fires, the hunting of animals, the harvesting of plants, herbs, nuts or fruits.
"There is no area left in the world that has not undergone serious human impact, and this makes the whole planet a man-made planet, and cities are only the extreme example of that," said Christine Alfsen-Norodom, coordinator of a Columbia University-UNESCO program on the biosphere and society.
The shift to urban ecology is also linked to changes in the environment itself: increased urbanization, metastasizing sprawl and global warming. "The choice is no longer between cities and wildness," Alfsen-Norodom said. "It is, in the face of increasing population, between density and sprawl."
Density is an ally
Density and verticality, the hallmarks of big cities, were once bad words in an ecologist's vocabulary but are now seen as invaluable allies. By concentrating large numbers of people in limited areas, they leave substantial areas for forests, meadows, wetlands and the wide open spaces needed for many other species to survive.
"If large numbers of people didn't live concentrated in cities, the world would be a nightmare," Alfsen-Norodom said.
As ecologists have begun to study city environments, they have been surprised at the level of biodiversity they contain. "In the New York metropolitan area, within a radius of 50 miles, we have recorded over 3,000 plant species: 2,000 native species and 1,000 introduced to the area," said Steven E. Clemants, vice president for science at the Brooklyn Botanic Garden.
As the Hudson River has made a comeback, seahorses have been spotted in the Gowanus Canal, and rare centipedes have recently been found in Central Park.
New York City is a major bird sanctuary. The marshy wetlands of Jamaica Bay near John F. Kennedy Airport are among the biggest nesting areas on the East Coast, and big patches of green such as Central and Prospect parks look like landing pads to birds migrating north and south with the seasons.
Thus, some rather unexpected species - the American white pelican, the pied-billed grebe and the red-throated loon - can be seen in New York City, while the downy woodpecker and the rock dove live there year-round.
This is not as unlikely as it might seem, Clemants said, when you consider that New York has a higher percentage of open space - some 25 percent of its land surface - than any major city in the United States.
Exotics vs. natives
As ecologists have come to accept the "impure" nature of urban environments, they have been re-evaluating the role of exotic plants, imported species that have traditionally been regarded as noxious, aggressive pests crowding out native North American species.
As a result, there is an intense debate between ecological purists who are trying to conserve and bring back native species and those who feel that exotic plants are the victims of biological xenophobia.
"If we value the composition and the diversity of native species, then we do have to be concerned about exotic species," Pickett said. "The other side of the story is that in many urban environments, the exotics are particularly good at dealing with harsh urban conditions."
Because the sidewalks, paved streets and tall buildings make the city hotter and its soil drier, plants originally from tropical environments do extremely well.
If you look through a subway grate and see a tree growing at the slimy bottom, ecologists say, it will almost certainly be an Ailanthus, known as the "tree of heaven," from China and the Korean peninsula. They grow at a rate of 6.6 feet a year and survive in soils that would kill most plants. Indeed, of the 3,000 plant species found in New York, fully a third were introduced from somewhere else.
"We owe a lot to invasive species," said Charles Peters of the botanical garden in the Bronx. "They are able to grow and reproduce in the extremely screwed-up environment. Over the decades, there is an increase of nonnative species. The natives are dying out or having trouble reproducing.
"The exotics, like the tree of heaven, are continuing to prevent soil erosion, maintaining the cycling of nutrients, pumping out oxygen and providing shade where native species don't go."
Handel, who is a co-director of the Center for Urban Restoration Ecology at Rutgers, insists that while obviously an exotic species in a place where nothing else will grow is fine, people should not be too cavalier in accepting the demise of native species. Because they are often less aggressive, they allow for a higher number of different plants in their midst, while the most successful exotic plants are so aggressive that they leave no room for others.
"The final result is a poorer, more monotonous environment," Handel said. But with care, as in Fresh Kills and in Flushing Meadows on grounds once occupied by the World's Fair, native species have made a solid comeback, he added.