The notion that someday nature could swallow whole something so colossal and concrete as a modern city doesn't slide easily into our imaginations. The sheer titanic presence of a New York City resists efforts to picture it wasting away. The events of September 2001 showed only what human beings with explosive hardware can do, not crude processes like erosion or rot. The breathtaking, swift collapse of the World Trade Center towers suggested more to us about their attackers than about mortal vulnerabilities that could doom our entire infrastructure. And even that once-inconceivable calamity was confined to just a few buildings. Nevertheless, the time it would take nature to rid itself of what urbanity has wrought may be less than we might suspect.
In 1939, a World's Fair was held in New York. For its exhibit the government of Poland sent a statue of Wladyslaw Jagiello. The founder of the Bialowieza Puszcza had not been immortalized in bronze for preserving a chunk of primeval forest six centuries earlier. By marrying its queen, Jagiello had united Poland and his duchy of Lithuania into a European power. The sculpture portrays him on horseback following his victory at the Battle of Grunwald in 1410. Triumphant, he hoists two swords captured from Poland's latest vanquished enemy, the Teutonic Knights of the Cross.
In 1939, however, the Poles weren't faring so well against some descendants of those Teutonic Knights. before the New York World's Fair ended, Hitler's Nazis had taken Poland, and the sculpture couldn't be returned to its homeland. Six sad years later, the Polish government gave it to New York as a symbol of its courageous, battered survivors. The statue of Jagiello was placed in Central Park, overlooking what today is called Turtle Pond.
When Dr. Eric Sanderson leads a tour through the park, he and his flock usually pass Jagiello without pausing, because they are lost in another century altogether - the 17th. Bespectacled under his wide-brimmed felt hat, a trim beard graying around his chin and a laptop jammed in his backpack, Sanderson is a landscape ecologist with the Wildlife Conservation Society, a global squadron of researchers trying to save an imperiled world from itself. At its Bronx Zoo headquarters, Sanderson directs the Mannahatta Project, an attempt to re-create, virtually, Manhattan Island as it was when Henry Hudson's crew first saw it in 1609: a pre-urban vision that tempts speculation about how a postman future might look.
His team has scoured original Dutch documents colonial British military maps, topographic surveys, and centuries of assorted archives throughout town. They've probed sediments, analyzed fossil pollens, and plugged thousands of bits of biological data into imaging software that generates three-dimensional panoramas of the heavily wooded wilderness on which a metropolis was juxtaposed. With each new entry of a species of grass or tree that is historically confirmed in some part of the city, the images grow more detailed, more startling, more convincing. Their goal is a block-by-city-block guide to this ghost forest, the one Eric Sanderson uncannily seems to see even while dodging Fifth Avenue buses.
When Sanderson wanders through Central Park, he's able to look beyond the half-million cubic yards of soil hauled in by its designers, Frederick Law Olmstead and Calvert Vaux, to fill in what was mostly a swampy bog surrounded by poison oak and sumac. He can trace the shoreline of the long, narrow lake that lay along what is now 59th Street, north of the Plaza Hotel, with its tidal outlet that meandered through salt marsh to the East River. From the west, he can see a pair of streams entering the lake that drained the slope of Manhattan's major ridgeline, a deer and mountain lion trail known today as Broadway.
Eric Sanderson sees water flowing everywhere in town, much of it bubbling from underground ("which is how Spring Street got its name"). He's identified more than 40 brooks and streams that traversed what was once a hilly, rocky island: in the Algonquin of its first human occupants, the Lenni Lenape, Mannahatta referred to those now-vanished hills. When New York's 19th century planners imposed a grid on everything north of Greenwich Village - the jumble of original streets to the south being impossible to unsnarl - they behaved as if topography were irrelevant. Except for some massive, unlovable schist outcrops in Central Park and at the island's northern tip, Manhattan's textured terrain was squashed and dumped into streambeds, than planed and leveled to receive the advancing city.
Later, new contours arose, this time routed through rectilinear forms and hard angles, much as the water that once sculpted the island's land was now forced underground through a lattice of pipes. Eric Sanderson's Mannahatta Project has plotted how closely the modern sewer system follows the old watercourses, although man-made sewer lines can't wick away runoff as efficiently as nature. In a city that buried its river, he observes, "rain still falls. It has to go somewhere."
As it happens, that will be the key to breaching Manhattan's hard shell if nature set about dismantling it. It would begin very quickly, with the first strike at the city's most vulnerable spot: its underbelly.
New York City Transit's Paul Schber and Peter Briffa, superintendent of Hydraulics and level one maintenance supervisor of Hydraulics Emergency Response, respectively, understand perfectly how this would work. Every day, they must keep 13 million gallons of water from overpowering New York's subway tunnels.
"That's just the water that's already underground," notes Schuber.
"When it rains, the amount is…" Briffa shows his palms, surrendering. "It's incalculable."
Maybe not actually incalculable, but it doesn't rain any less now than before the city was built. Once, Manhattan was 27 square miles of porous ground interlaced with living roots that siphoned the 47.2 inches of average annual rainfall up trees and into meadow grasses, which drank their fill and exhaled the rest back into the atmosphere. Whatever the roots didn't take settled into the island's water table. In places, it surfaced in lakes and marshes, with the excess draining off to the ocean via those 40 streams - which now lie trapped beneath concrete and asphalt.
Today, because there's little soil to absorb rainfall or vegetation to transpire it, and because buildings block sunlight from evaporating it, rain collects in puddles or follows gravity down sweepers, or it flows into subway vents, adding to the water already down there. Below 131st Street and Lenox Avenue, for example, a rising underground river is corroding the bottom of the A,B,C, and D subway lines. Constantly, men in reflective vests and denim rough-outs like Schuber's and Briffa's are clambering around beneath the city to deal with the fact that under New York, groundwater is always rising.
Whenever it rains hard, sewers clog with storm debris - the number of plastic garbage bags adrift in the world's cities may truly exceed calculation - and the water, needing to go somewhere, plops down the nearest subway stairs. Add a nor'easter and the surging Atlantic Ocean bangs against New York's water table until, in places like Water Street in lower Manhattan or Yankee Stadium in the Bronx, it backs up right into the tunnels, shutting everything down until it subsides. Should the ocean continue to warm and rise even faster than the current inch per decade, at some point it simply won't subside. Schuber and Briffa have no idea what will happen then.
Add to all that the 1930s-vintage water mains that frequently burst, and the only thing that has kept New York from flooding already is the incessant vigilance of its subway crews and 753 pumps. Think about those pumps: New York's subway system, an engineering marvel in 1903, was laid underneath an already-existing burgeoning city. As that city already had sewer lines, the only place for subways to go was below them. "So," explains Schuber, "we have to pump uphill." In this, New York is not alone: cities like London, Moscow, and Washington built their subways far deeper, often to double as bomb shelters. Therein lies much potential disaster.
Shading his eyes with his white hard hat, Schuber peers down into a square pit beneath the Van Siclen Avenue station in Brooklyn, where each minute 650 gallons of natural groundwater gush from the bedrock. Gesturing over the roaring cascade he indicates four submersible cast-iron pumps that take turns laboring against gravity to stay ahead. Such pumps run on electricity. When the power fails, things can get difficult very fast. Following the World Trade Center attack, an emergency pump train bearing a jumbo portable diesel generator pumped out 27 times the volume of Shea Stadium. Had the Hudson River actually burst through the PATH train tunnels that connect New York's subways to New Jersey, as was greatly feared, the pump train - and possibly much of the city - would simply have been overwhelmed.
In an abandoned city, there would be no one like Paul Schuber and Peter Briffa to race from station to flooded station whenever more than two inches of rain falls - as happens lately with disturbing frequency - sometimes snaking hoses up stairways to pump to a sewer down the street, sometimes navigating these tunnels in inflatable boats. With no people, there would also be no power. The pumps will go off, and stay off. "When this pump facility shuts down," says Schuber, "in half an hour water reaches a level where trains can't pass anymore."
Briffa removes his safety goggles and rubs his eyes. "A flood in one zone would push water into the others. Within 36 hours, the whole thing could fill."
Even if it weren't raining, with subway pumps stilled, that would take no more than a couple of days, they estimate. At that point, water would start sluicing away soil under the pavement. Before long, streets start to crater. With no one unclogging sewers, some new watercourses form on the surface. Others appear suddenly as waterlogged subway ceilings collapse. Within 20 years, the water-soaked street columns that support the street above the East Side's 4,5, and 6 trains corrode and buckle. As Lexington Avenue caves in, it becomes a river.
Well before then, however, pavement all over town would have already been in trouble. According to Dr. Jameel Ahmad, chairman of the civil engineering department at New York's Cooper Union, things will begin to stall apart during the first month of March after humans vacate Manhattan. Each March, temperatures normally flutter back and forth around 32 degrees Fahrenheit as many as 40 times (presumably, climate change could push this back to February). Whenever it is, the repeated freezing and thawing make asphalt and cement split. When snow thaws, water seeps into these fresh cracks. When it freezes, the water expands and cracks widen.
Call it water's retaliation for being squished under all that cityscape. Almost every other compound in nature contracts when frozen, but H20 molecules do the opposite, organizing themselves into elegant hexagonal crystals that take up about 9 percent more space than they did when sloshing around in a liquid state. Pretty six-sided crystals suggest snowflakes so gossamer it's hard to conceive of them pushing apart slabs of sidewalk. It's even more difficult to imagine carbon steel water pipes built to withstand 7,500 pounds of pressure per square inch exploding when they freeze. Yet that's exactly what happens.
As pavement separates, weeds like mustard, shamrock, and goosegrass blow in from Central Park and work their way down the new cracks, which widen further. In the curent world before they get too far, city maintenance usually shows up, kills the weeds, and fills the fissures. But in the post-people world, there's no one left to continually patch New York. The weeds are followed by the city's most prolific exotic species, the Chinese ailanthus tree. Even with 8 million people around, ailanthus - otherwise innocently known as the tree-of-heaven - are implacable invaders capable of rooting in tiny chinks in subway tunnels, unnoticed until their spreading leaf canopies start poking from sidewalk grates. With no one to yank their seedlings, within five years powerful ailanthus roots are heaving up sidewalks and wreaking havoc in sewers - which are already stressed by all the plastic bags and old newspaper mush that no one is clearing away. As soil long trapped beneath pavement gets exposed to sun and rain, other species jump in, and soon leaf litter adds to the rising piles of debris clogging the sewer grates.
The early pioneer plants won't even have to wait for the pavement to fall apart. Starting from the mulch collecting in gutters, a layer of soil will start forming atop New York's sterile hard shell, and seedlings will sprout. With far less organic material available to it - just windblown dust and urban soot - precisely that has happened in an abandoned elevated iron bed of the New York Central Railroad on Manhattan's West Side. Since trains stopped running there in 1980, the inevitable ailanthus trees have been joined by a thickening ground cover of union grass and fuzzy lamb's ear, accented by stands of goldenrod. In some places, the track emerges form the second stories of warehouses it once serviced into elevated lanes of wild crocuses, irises, evening primrose, asters, and Queen Anne's lace. So many New Yorkers, glancing down from windows in Chelsea's art district were moved by the sight of this untended, flowering green ribbon, prophetically and swiftly laying claim to a dead slice of their city, that it was dubbed the High Line and officially designated a park.
In the first few years with no heat, pipes burst all over town, the freeze-thaw cycle moves indoors, and things start to seriously deteriorate. Buildings groan as their innards expand and contract; joints between walls and rooflines separate. Where they do, rain leaks in, bolts rust, and facing pops off, exposing insulation. If the city hasn't burned yet, it will now. Collectively, New York architecture isn't as combustible as, say, San Francisco's incendiary rows of clapboard Victorians. But with no firemen to answer the call, a dry lightning strike that ignites a decade of dead branches and leaves piling up in Central Park will spread flames through the streets. Within two decades, lightning rods have begun to rust and snap, and roof fires leap among buildings, entering paneled offices filled with paper fuel. Gas lines ignite with a rush of flames that blows out windows. Rain and snow blow in, and soon even poured concrete floors are freezing, thawing, and starting to buckle. Burnt insulation and charred wood add nutrients to Manhattan's growing soil cap. Native Virginia creeper and poison ivy claw at walls covered with lichens, which thrive in the absence of air pollution. Red-tailed hawks and peregrine falcons nest in increasingly skeletal high-rise structures.
Within two centuries, estimates Brooklyn Botanical Garden vice president Steven Clemants, colonizing trees will have substantially replaced pioneer weeds. Gutters buried under tons of leaf litter provide new, fertile ground for native oaks and maples from city parks. Arriving black locust and autumn olive shrubs fix nitrogen, allowing sunflowers, bluestem, and white snakeroot to move in along with apple trees, their seeds expelled by proliferating birds.
Biodiversity will increase even more, predicts Cooper Union civil engineering chair Hameel Ahmad, as buildings tumble and smash into each other, and lime from crushed concrete raises soil pH, inviting in trees, such as buckthorn and birch, that need less acidic environments. Ahmad, a hearty silver-haired man whose hands talking in descriptive circles, believes that process will begin faster than people might think. A native of Lahore, Pakistan, a city of ancient mosaic-encrusted mosques, he now teaches how to design and retrofit buildings to withstand terrorist attacks, and has accrued a keen understanding of structural weakness.
"Even buildings anchored into hard Manhattan schist, like most New York skyscrapers," he notes, "weren't intended to have their steel foundations waterlogged." Plugged sewers, deluged tunnels, and streets reverting to rivers, he says, will conspire to undermine subbasements and destabilize their huge loads. In a future that portends stronger and more frequent hurricanes striking North America's Atlantic coast, ferocious winds will pummel tall, unsteady structures. Some will topple, knocking down others. Like a gap in the forest when a giant tree falls, new growth will rush in. Gradually, the asphalt jungle will give way to a real one.
The New York Botanical Garden, located in 250 acres across from the Bronx Zoo, possesses the largest herbarium anywhere outside of Europe. Among its treasures are wildflower specimens gathered on Captain Cook's 1769 Pacific wanderings, and a shred of moss from Tierra del Fuego, with accompanying notes written in watery black ink and signed by its collector, C. Darwin. Most remarkable, though, is the NYBG's 40-acre tract of original, old-growth, virgin New York forest, never logged.
Never cut, but mightily changed. Until only recently, it was known as the Hemlock Forest for its shady stands of that graceful conifer, but almost every hemlock here is now dead slain by a Japanese insect smaller than the period at the end of this sentence, which arrived in New York in the mid-1980s. The oldest and biggest oaks, dating back to when this forest was British, are also crashing down, their vigor sapped by acid rain and heavy metals such as lead from automobile and factory fumes, which have soaked into the soil. It's unlikely that they'll come back, because most canopy trees here long ago stopped regenerating. Every resident native species now harbors its own pathogen: some fungus, insect, or disease that seizes the opportunity to ravish trees weakened by chemical onslaught. As if that weren't enough, as the NYBG forest became an island of greenery surrounded by hundreds of square miles of gray urbanity, it became the primary refuge for Bronx squirrels. With natural predators gone and no hunting permitted, there's nothing to stop them from devouring every acorn or hickory nu before it can germinate. Which they do.
There is now an eight-decade gap in this old forest's understory. Instead of new generations of native oaks, maple, ash, birch, sycamore, and tulip trees, what's mainly growing are imported ornamentals that have blown in from the rest of the Bronx. Soil samplings indicate some 20 million ailanthus seeds sprouting here. According to Chuck Peters, curators of the NYBG's Institute of Economic Botany, exotics such as ailanthus and cork trees, both from China, now account for more than a quarter of this forest.
"Some people want to put the forest back the way it was 200 years ago," he says. "To do that, I tell them, you've got to put the Bronx back the way it was 200 years ago."
As human beings learned to transport themselves all over the world, they took living things with them and brought back others. Plants from the Americas changed not only ecosystems in European countries, but also their very identities: think of Ireland before potatoes, or Italy before tomatoes. In the opposite direction, Old World invaders not only forced themselves on hapless women of vanquished new lands, but broadcast other kinds of seed, beginning with wheat, barley, and rye. In a phrase coined by the American geographer Alfred Crosby, this ecological imperialism helped European conquerors to permanently stamp their image on their colonies.
Some results were ludicrous, like English gardens with hyacinths and daffodils that never quite took hold in colonial India. In New York, the European startling - now a ubiquitous avian pest from Alaska to Mexico - was introduced because someone thought the city would be more cultured if Central Park were home to each bird mentioned in Shakespeare. Next came a Central Park garden with every plant in the Bard's plays, sown with the lyrical likes of primrose, wormwood, lark's heel, eglantine, and cowslip - everything short of Macbeth's Birnam Wood.
To what extent the Mannahatta Project's virtual past resembles the Manhattan forest to come depends on a struggle for North America's soil that will continue long after the humans that instigated it are gone. The NYBG's herbarium also holds one of the first American specimens of a deceptively lovely lavender stalk. The seeds of purple loosestrife, native to North Sea estuaries from Britain to Finland, likely arrived in wet sands that merchant ships dug from European tidal flats as ballast for the Atlantic crossing. As trade with the colonies grew, more purple loosestrife was dumped along American shores as ships jettisoned ballast before taking on cargo. Once established , it moved up streams and rivers as its seeds stuck to the muddy feathers or fur of whatever it touched. In Hudson River wetlands, communities of cattail, willow, and canary grass that fed and sheltered waterfowl muskrats turned into solid curtains of purple, impenetrable even to wild life. By the 21st century, purple loosestrife was at large even in Alaska, where panicked state ecologists fear it will fill entire marshes, driving out ducks, geese, terns, and swans.
Even before Shakespeare Garden, Central Park designers Olmstead and Vaux had brought in a half-million trees along with their half-million cubic yards of fill to complete their improved vision of nature, spicing up the island with exotica like Persian ironwoods, Asian katsuras, cedars of Lebanon, and Chinese royal paulownias, and ginkgos. Yet once humans are gone, the native plants left to compete with a formidable contingent of alien species in order to reclaim their birthright will have some homegrown advantages.
Many foreign ornamentals - double roses, for example - will wither with the civilization that introduced them, because they are sterile hybrids that must propagate through cuttings. When the gardeners that clone them go, so do they. Other pampered colonials like English ivy, left to fend for themselves, lose to their rough American cousins, Virginia creeper, and poison ivy.
Still others are really mutations, forced by highly selective breeding. If they survive at all, their form and presence will be diminished. Untended fruits such as apples - an import from Russia and Kazakhstan, belying the America Johnny Appleseed myth - select for hardiness, not appearance or taste, and turn gnarly. Except for a few survivors, unsprayed apple orchards, defenseless against their native American scourges, apple maggots, and leaf miner blight, will be reclaimed by native hardwoods. Introduced garden plot vegetables will revert to their humble beginnings. Sweet carrots, originally Asian, quickly devolve to wild, unpalatable Queen Anne's lace as animals devour the last of the tasty orange ones we planted, says New York Botanical Garden vice president Dennis Stevenson. Broccoli, cabbage, Brussel sprouts, and cauliflower regress to the same unrecognizable broccoli ancestor. Descendants of seed corn planted by Dominicans in Washington Heights parkway medians may eventually retrace their DNA back to the original Mexican teosinte, its cob barely bigger than a sprig of wheat.
The other invasion that has accosted natives - metals such as lead, mercury, and cadmium will not wash quickly from the soil, because these are literally heavy molecules. One thing is certain: when cars have stopped for good and factories go dark and stay that way, no more such metals will be deposited. For the first 100 years or so, however, corrosion will periodically set off time bombs left in petroleum tanks, chemical, and power plants, and hundreds of dry cleaners. Gradually, bacteria will feed on residues of fuel, laundry solvents, and lubricants, reducing them to more benign organic hydrocarbons - although a whole spectrum of man-made novelties, ranging from certain pesticides to plasticizers to insulators, will linger for many millennia until microbes evolve to process them.
Yet with each new acid-free rainfall, trees that still endure will have fewer contaminants to rest as chemicals are gradually flushed from the system. Over centuries, vegetation will take up decreasing levels of heavy metals, and will recycle, redeposit, and dilute them further. As plants die, decay, and lay down more soil cover, the industrial toxins will be buried deeper and each succeeding crop of native seedlings will do better.
And although many of New York's heirloom trees are endangered if not actually dying, few if any are already extinct. Even the deeply mourned American chestnut, devastated everywhere after a fungal blight entered New York around 1900 in a shipment of Asian nursery plants, still hangs on in the New York Botanical Garden's old forest - literally by its roots. It sprouts, sends up skinny shoots two feet high, gets knocked back by blight, and does it again. One day, perhaps, with no human stresses sapping its vigor, a resistant strain will finally emerge. Once the tallest hardwood in American eastern forests, the resurrected chestnut trees will have to coexist with robust non-natives that are probably here to stay - Japanese barberry, Oriental bittersweet, and surely ailanthus. The ecosystem here will be a human artifact that will persist in our absence, a cosmopolitan botanical mixture that would never have occurred with us.
Which may not be bad, suggests New York Botanical Garden's Chuck Peters. "What makes New York a great city now is its cultural diversity. Everyone has something to offer. But botanically, we're xenophobic. We love native species, and want aggressive, exotic plant species to go home."
He props his running shoe against the whitish bark of a Chinese Amur cork tree, growing among the last of the hemlocks. "This may sound blasphemous, but maintaining native biodiversity is less important than maintaining a functioning ecosystem. What matter is that soil is protected that water gets cleaned, that trees filter the air, that a canopy regenerates new seedlings to keep nutrients from draining away into the Bronx River."
He inhales a lungful of filtered Bronx air. Trim and youthful in his early fifties, Peters has spent much of his life in forests. His field research has revealed that pockets of wild palm nut trees deep in the Amazon, or of durian fruit trees in virgin Burneo, or of tea trees in Burma's jungles, aren't accidents. Once, humans were there, too. The wilderness swallowed them and their memory, but its shape still bears their echo. As will this one.
In fact, it has done so since soon after Homo sapiens appeared here. Eric Sanderson's Mannahatta Project is re-creating the island as the Dutch found it - not some primordial Manhattan forest no human had set foot on, because there wasn't one. "Because before the Lenni Lenape arrived," explains Sanderson, "nothing was here except for a mile-thick slab of ice."
About 11,000 years ago, as the last ice age receded northward from Manhattan, it pulled along the spruce and tamarack taiga that today grows just below the Canadian tundra. In its place came what we know as the temperate eastern forest of North America: oak, hickory, chestnut, walnut, hemlock, elm, beech, sugar maple, sweet gum, sassafras, and wild filbert. In the clearings grew shrubs of chokecherry, fragrant sumac, rhododendron, honeysuckle, and assorted ferns and flowering plants. Spartina and rose mallow appeared in the salt marshes. As all this foliage filled these warming niches, warm-blooded animals followed, including humans.
A dearth of archeological remains suggests that the first New Yorkers probably didn't settle, but camped seasonally to pick berries, chestnuts, and wild grapes. They hunted turkey, heath hens, ducks, and white-tailed deer, but mainly they fished. The surrounding waters swarmed with smelt, shad, and herring Brook trout ran in Manhattan streams. Oysters, clams, quahogs, crabs, and lobsters were so abundant that harvesting them was effortless. Large middens of discarded mollusk shells along the shores were the first human structures here. By the time Henry Hudson first saw the island, upper Harlem, and Greenwich Village were grassy savannas, cleared repeatedly with fire by the Lenni Lenape for planting. By flooding ancient Harlem fire pits to see what floats to the top, Mannahatta Project researchers have learned that the Lenni Lenape cultivated corn, beans, squash, and sunflowers. Much of the island was still as green and dense as the Bialowieza Puszcza.. But well before its famous transfiguration from Indian land to colonial real estate, price to sell at 60 Dutch guilders, the mark of Homo sapiens was already on Manhattan.
In the millennial year 2000, a harbinger of a future that might revive the past appeared in the form of a coyote that managed to reach Central Park. Subsequently, two more made into town, as well as a wild turkey. The rewinding of New York City may not wait until people leave.
That first advance coyote scout arrived via the George Washington Bridge, which Jerry Del Tufo managed for the Port Authority of New York and New Jersey. Later, he took over the bridges that link Staten Island to the mainland and Long Island. A structural engineer in his forties, he considers bridges among the loveliest ides humans ever conceived, gracefully spanning chasms to bring people together.
Del Tufo himself spans an ocean. His olive bespeak Sicily; his voice is pure urban New Jersey. Bred to the pavement and steel that became his life's work, he nonetheless marvels at the annual miracle of baby peregrine falcons hatching high atop the George Washington's towers, and at the sheer botanical audacity of grass, weeds, and ailanthus trees that defiantly bloom, far from topsoil, from metal niches suspended high above the water. His bridges are under a constant guerrilla assault by nature. Its arsenal and troops may seem ludicrously puny against steel-plated armor, but to ignore endless, ubiquitous bird droppings that can snag and sprout airborne seeds, and simultaneously dissolve paint, would be fatal. Del Tufo is up against a primitive but unrelenting foe whose ultimate strength is its ability to outlast its adversary, and he accepts as a fact that ultimately nature must win.
Not on his watch, though, if he can help it. First and foremost, he honors the legacy he and his crew inherited: their bridges were built by a generation of engineers who couldn't possibly have conceived of a third of a million cars crossing them daily - yet 80 years later, they're still in service. "Our job," he tells his men, "is to hand over these treasures to the next generation in better shape than when we accepted them."
On a February afternoon he heads through snow flurries to the Bayonne Bridge, chatting with his crew over his radio. The underside of the approach on the Staten Island side is a powerful steel matrix that converges in a huge concrete block anchored to the bedrock, an abutment that bears half the load of the Bayonne's main span. To stare up directly int o its labyrinthine load-bearing I-beams and bracing members, interlocked with half-inch-thick steel plates, flanges, and several million half-inch rivets and bolts, recalls the crushing awe that humbles pilgrims gaping at the soaring Vatican dome of St. Peter's Cathedral: something this mighty is here forever. Yet Jerry Del TUfo knows exactly how these bridges, without humans to defend to them, would come down.
It wouldn't happen immediately, because the most immediate threat will disappear with us. It's not, says Del Tufo, the incessant pounding traffic.
"These bridges are so overbuilt, traffic's like an ant on an elephant." In the 1930s, with no computers to precisely calculate tolerances of construction materials, cautious engineers simply heaped on excess mass and redundancy. "We're living off the overcapacity of our forefathers. The GW alone has enough galvanized steel wire in its three-inch main cables to wrap the Earth four times. Even if every other suspender rope deteriorated, the bridge wouldn't fall down."
Enemy number one is the salt that highway departments spread on the roadways each winter - ravenous stuff that keeps eating steel once it's done with the ice. Oil, antifreeze, and snowmelt dripping from cars wash salt into catch basins and crevices where maintenance crews must find and flush it. With no more people, there won't be salt. There will, however, be rust,, and quite a bit of it, when no one is painting the bridges.
At first, oxidation forms a coating on steel plate, twice as thick or more as the metal itself, which slows the pace of chemical attack. For steel to completely rust through and fall apart might take centuries, but it won't be necessary to wait that long for New York's bridges to start dropping. The reason is a metallic version of the freeze-thaw drama. Rather than crack like concrete, steel expands when it warms and contracts when it cools. So that steel bridges can actually get longer in summer, they need expansion joints.
In winter, when they shrink, the space inside expansion joints opens wider, and stuff blows in. Wherever it does, there's less room for the bridge to expand when things warm up. With no one painting bridges, joints fill not only with debris but also with rust, which swells to occupy far more space than the original metal.
"Come summer," says Del Tufo, "the bridge is going to get bigger whether you like it or not. If the expansion joint is clogged, it expands toward the weakest link - like where two different materials connect." He points to where four lanes of steel meet the concrete abutment. "There, for example. The concrete could crack where the beam is bolted to the pier. Or, after a few seasons, that bolt could shear off. Eventually, the beam could wake itself right off and fall."
Every connection is vulnerable. Rust that forms between two steel plates bolted together exerts forces so extreme that either the plates bend or rivets poop, says Del Tufo. Arch bridges like the the Bayonne - or the Hell Gate over the East River, made to hold railroads - are the most overbuilt of all. They might hold for the next 1,000 years, although earthquakes rippling through one of several faults under the coastal plain could shorten that period. (They would probably do better than the 14 steel-lined, concrete subway tubes beneath the East River - one of which, leading to Brooklyn, dates back to horses and buggies Should any of their sections separate, the Atlantic Ocean would rush in.) The suspension and truss bridges that carry automobiles, however, will last only two or three centuries before their rivets and bolts fail and entire sections fall into the waiting waters.
Until then, more coyotes follow the footsteps of the intrepid ones that managed to reach Central Park. Deer, bear, and finally wolves, which have reentered New England from Canada, arrived in turn. By the time most of its bridges are gone, Manhattan's newer buildings have also been ravaged as wherever leaks reach their embedded steel reinforcing bars, they rust, expand, and burst the concrete that sheaths them. Older stone buildings such as Grand Central - especially with no more acid rain to pock their marble - will outlast every shiny modern box.
Ruins of high-rises echo the love song of frogs breeding in Manhattan's reconstituted streams, now stocked with alewives and mussels dropped by seagulls. Herring and shad have returned to the Hudson, though they spent some generations adjusting to radioactivity trickling out of Indian Point Nuclear Power Plant, 35 miles north of Times Square, after its reinforced concrete succumbed. Missing, however, are nearly all fauna adapted to us. The seemingly invincible cockroach, a tropical import, long ago froze in unseat apartment buildings. Without garbage, rats starved, or became lunch for the raptors nesting in burnt-out skyscrapers.
Rising water, tides, and salt corrosion have replaced the engineered shoreline, circling New York's five boroughs with estuaries and small beaches. With no dredging, Central Park's ponds and reservoir have been reincarnated as marshes. Without natural grazers - unless horses used by hansom cabs and by park policemen managed to go feral and breed - Central Park's grass is gone. A maturing forest is in its place radiating down former streets and invading empty foundations. Coyotes, wolves, red foxes, and bobcats have brought squirrels back into balance with oak trees tough enough to outlast the lead we deposited, and after 500 years, even in a warming climate the oaks, beeches, and moisture-loving species such as ash dominate.
Long before, the wild predators finished off the last descendants of pet dogs, but a wily population of feral house cats persist, feeding on starlings. With bridges finally down, tunnels flooded, and Manhattan truly an island again, moose and bears swim a widened Harlem river to feast on the berries that the Lenape once picked.
Amid the rubble of Manhattan financial institutions that literally collapsed for good, a few bank vaults stand; the money within, however worthless, is mildewed but safe. Not so the artwork stored in museum vaults, built more for climate control than strength. Without electricity, protection ceases; eventually museum roofs spring leaks, usually starting with their skylights, and their basements fill with standing water. Subjected to wild swings in humidity and temperature, everything in storage rooms is prey to mold, bacteria, and the voracious larvae of a notorious museum scourge, the black carpet beetle. As they spread to other floors, fungi discolor, and dissolve paintings in the Metropolitan beyond recognition. Ceramics, however, are doing fine, since, they're chemically similar to fossils. Unless something falls on them first they await reburial for the next archaeologist to dig them up. Corrosion has thickened the patina on bronze statues, but hasn't affected their shapes. "That's why we know about the Bronze Age," notes Manhattan art conservator Barbara Appelbaum.
Even if the Statue of Liberty ends up at the bottom of the harbor, Appelbaum says, its form will remain intact indefinitely, albeit somewhat chemically altered and possibly encased in barnacles. That might be the safest place for it, because at some point thousands of years hence, any stone walls still standing - maybe chunks of St. Paul's Chapel across from the site of the World Trade Center, built in 1766 from Manhattan's own hard schist - must finally fall. Three times in the past 100,000 years, glaciers have scraped New York clean. Unless humankind's Faustian affair with carbon fuels ends up tipping the atmosphere past the point of no return, and runaway global warming transfigures Earth into Venus, at some unknown date glaciers will do so again. The mature beech-oak-ash-ailanthus forest will be mowed down. The four giant mounds of entombed garbage at the Fresh Kills landfill on Staten Island will be flattened, their vast accumulation of stubborn PVC plastic and of one of the most durable human creations of all - glass - ground to powder.
After the ice recedes, buried in the moraine and eventually in geologic layers below will be an unnatural concentration of a reddish metal, which briefly had assumed the form of wiring and plumbing. The next toolmaker to arrive or evolve on this planet might discover and use it, but by then there would be nothing to indicate that it was us who put it there.