A walk across the abandoned railyard in Berlin's Schöneberg district gives new meaning to the words "urban jungle." Between a noisy commuter train line on one side and apartment blocks on the other, a carpet of rare flowers with names like ladies' fingers and queen-devil hawkweed covers railroad ties and warehouse ruins. All sorts of endangered butterflies, spiders and bumblebees thrive, as does Europe's northernmost breeding colony of praying mantises. Goshawks and kestrels spy for prey overhead.
Nature has, of course, found its niches in towns and cities ever since humans built them. Pigeons and cockroaches have settled down with mankind. Escaped pets and their offspring, like the famed wild parrots of San Francisco's Telegraph Hill, have added an exotic touch to the urban fauna. Yet for some reason many of us continue to see cities as barren or worse, spreading biological destruction wherever they sprawl.
As they take a closer look, however, biologists in the nascent science of "urban ecology" are finding that cities are not just important habitats, but veritable hot spots of animal and plant life. "You can take any big city and find more species, more diverse habitats than in just about any national park or nature reserve," says Josef Reichholf, professor of ornithology at Munich's Technical University. Both in animal numbers as well as species diversity, he says, cities beat the countryside hands down.
Berlin, one of the best-studied cases, is home to two thirds of the 280 bird species existing in Germany, including peregrine falcons and ospreys--raptors that have disappeared from much of the country. What's more, biologists say, urban biodiversity seems to be on the rise--as our cities become cleaner, suburbs grow greener, and more and more species learn to adapt. These findings are challenging an old piece of orthodoxy--that urbanization is the planet's biggest environmental threat. On the contrary, it's in the open country that plants and animals have seen the most rapid decline. The main culprit, biologists say: a highly efficient but species-killing agriculture, now spreading from the developed world to southern countries like Brazil.
Vast "monocultures" of single-strain crops, maintained with powerful herbicides and insecticides, have decimated the older, more varied landscape. Many forests are now uniform tree farms supporting few species. An oversupply of fertilizers and animal wastes favors fast-growing greens that crowd out the wildflowers, grasses and weeds that were once a rich habitat for insects and animals. "The real wasteland isn't in the city, it's out in the country," says John Hadidian, head of the Urban Wildlife Program at the Humane Society in Washington, D.C. Today, biologists estimate that agriculture and forestry cause over 80 percent of explainable species deaths worldwide, versus just 15 percent caused by human settlement, pollution and sprawl.
Some biologists think flora and fauna are seeking refuge in cities, and the bigger the city, the better. For starters there are fewer guns (in general) and more sources of food in heavily settled areas, as suburban raccoons, deer and coyotes discovered long ago. In Zurich today, there are now up to ten times as many foxes, badgers and hedgehogs per square kilometer within the city as in the surrounding rural area, a recent Swiss survey found.
More important, megacities create a mosaic of habitats and microclimates, from pond-filled gardens to industrial "brownfield" sites like those dry, hot railyards in Berlin. In London, the extremely rare redstart has seen a resurgence in abandoned factory lots, and on those "green roofs" newly popular with environmentally conscious urbanites. For the birds, these spaces resemble the country meadows they can no longer find. Among skyscrapers and tall smokestacks, peregrine falcons seem to feel even more at home than in the mountains whence they came. New York City's population, 14 breeding pairs, is the highest concentration on record.
Established suburbs, with their old trees, underbrush and open space, attract ten times more species of butterflies than farmland, again because they more closely approximate woodsy meadows. In Britain, the magnificent stag beetle, which likes piles of rotting wood, has all but disappeared from the antiseptic countryside. Its biggest U.K. population now lives in the south London suburbs.
All this has happened with astonishing speed. In the past half-century, dozens of once-shy species have learned that city dwellers mean them no harm. Wild boars, hunted in the country, have become an increasing nuisance in Europe's suburbs, with occasional sightings in downtown squares. Shy woodland birds, such as goshawks, first colonized major cities a couple of decades ago. Now, each successive generation seems to adapt to shorter nesting trees in ever smaller parks, particularly in comparison with their cousins still living in the wild. "It will be very interesting to see how much farther they will go," says Rainer Altenkamp, a Berlin biologist who just ringed a nestful of hawk chicks in a small Jewish cemetery downtown. Because of this adaptation, he says, many cities now support higher raptor populations than similar-size nature reserves.
Cities are turning into vast labs for studying animal behavior and evolution. New York, Hong Kong and London rate among the world's richest spots for migratory waterfowl--especially now that cleaner water has brought back the fish and crustaceans on which some of them feed. Urban duck populations are already producing countless new variations in colors and plumage. Butterflies and moths that a century ago adapted to sooty factory districts by developing black pigment have, in recent years, lightened up again.
Because cities tend to be hotter than the surrounding countryside--brick and pavement store heat--scientists see them foreshadowing the great environmental upheavals likely to follow from global warming. Birds lay their eggs earlier, plants grow faster, and new species arrive from the south, like those praying mantises in Berlin. In the fall, once-migratory birds flutter nervously, fly once around the city and settle back down to stay for the winter, Reichholf says.
This vast urban experiment is only now grabbing significant scientific attention. For decades, mentioning "urban" and "nature" in the same sentence drew sneers from an environmentalist mainstream. Fewer than 10 percent of all biological field studies take human settlement into consideration at all. It was not until 1997 that the U.S. National Science Foundation first added cities (Baltimore and Phoenix) to its long-term ecosystem studies. Now, schools from Virginia Tech to the University of Halle in Germany have taken up urban biology studies. The first text on urban wildlife management appeared last year in the United States. Yet skepticism remains. "Academics still have this fixation that cities are artificial," says Hadidian. "They'd rather go to the tropical rain forest or the Arctic tundra, even though they've got an accelerated experiment in evolution going on right at home."
Still the explosion of urban wildlife is forcing a rethink, and not only among scientists. Environmentalists and planners have long pushed for builders to develop vacant urban land before using up new "greenfields" on the outskirts--a policy that often destroys lots teeming with life in order to protect ecologically dead farmland. "We think that's wrong," says Catherine Harris, an activist with Wild London, one of a growing number of urban wildlife pressure groups. Sprawl is fine, these urban environmentalists say, if it develops ecologically inferior land and takes pressure off biologically diverse city neighborhoods.
Of course, cities can destroy nature, especially when they pave over every last tree, or spread into or poison wetlands and wild forests. While birds, insects and plants often do well, fish and amphibians are usually decimated by settlement. But as urbanization continues--more than 60 percent of the earth's population will likely live in cities by 2030--understanding how human settlement interacts with nature will be key. Why protect dead space just because it looks like a field, when that empty lot down the street has more life?