The charge that the passenger pigeon is a false symbol of past abundance is not new; observers at least as far back as the 1800s note that the earliest American colonists made no mention of pigeon flocks as spectacular as those witnessed later. The birds’ bones also do not turn up in great numbers in the prehistoric garbage heaps known as middens, considered to be among the best available records of what people ate ahead of European arrival. “The simplest explanation for the lack of passenger pigeon bones,” comments one midden-searching archaeologist, “is a lack of passenger pigeons. Prior to 1492, this was a rare species.”
The simplest explanation for any phenomenon, though, is often an oversimplification. Enrique Bucher, an Argentine expert in colony-forming birds, reviewed the competing theories about how the passenger pigeon went extinct. He concluded that it was impossible for the pigeons to have been rare in indigenous North America, because sheer abundance was the birds’ survival strategy. Their primary foods were the beechnuts, acorns and chestnuts that are collectively known as “mast.” Mast forests are curiously unpredictable, often producing nuts in a boom and bust pattern that shifts over time. The passenger pigeon had adapted by forming flocks of millions that could line out over huge areas of countryside in search of the trees that were bearing that year’s crop. A special call alerted other birds to the loaded trees, and the famously dense roosts were meeting places from which hungry birds could follow others that had found food. In other words, passenger pigeons had the paradoxical ability to be both numerous and uncommon: The huge flocks were only occasional visitors to any one place, and years could pass before they returned. They were only perceived to be widespread after European settlers themselves had dispersed widely.*
It’s certainly possible that the nineteenth-century flocks grew even larger as they benefited from a lack of competition for mast, which had been a staple food among indigenous nations. But the flocks in 1491 would still have been mind-boggling to a time-traveller from today; at the least, they were probably comparable to the passenger pigeon’s little-known living relative, the eared dove. In South America, these doves continue to form colonies of over ten million birds, and for decades have both competed with humans for their crops and been the target of eradication efforts far more unrelenting than anything indigenous communities could have mustered, including poisoning, trapping and unregulated hunting—all without any lasting effect on dove populations. Only recently have the birds begun to decline, apparently due to the destruction of their grassland habitat. Passenger pigeons probably faded for the same reason. By the 1860s, four-fifths of the forest they relied on had been levelled. Suddenly, no amount of searching could turn up sufficient mast, and the pigeon population—still heavily hunted—went into freefall. They were such highly social animals that the last scattered flocks and breeding pairs may have starved to death even in the presence of food, simply from the stress of isolation. One of the last passenger pigeons seen in the wild was among a flock of domestic pigeons.
The belief that North America before Columbus was an unspoiled Eden is unfounded, but there is no reason to declare that the continent’s most natural condition is one in which most species have been hunted into scarcity. There clearly were densely populated areas, such as the Mississippi Valley, where the first European visitor, Hernando de Soto, in around 1540 reported many Native American cities but not a single buffalo. But there were also those places less hospitable to human presence. The first European to cross the Texas Panhandle, Francisco Vásquez de Coronado, in 1541, witnessed uncountable bison and was never once out of sight of the animals. The anthropologists Torben C. Rick and Jon M. Erlandson surveyed the evidence that ancient peoples depleted and otherwise altered coastal areas from Alaska to the Gulf of Maine to California’s Channel Islands, and found the proof was “overwhelming” that they “often” did. The two researchers also speculate, however, that the struggle to survive in increasingly degraded surroundings may have given rise to the conservation values that many indigenous nations gave voice to at the time of European contact. If so, then 1492 was a clash of shifting baselines: European nations revelling in the discovery of apparently infinite natural riches just as the Americas’ original cultures were formulating a widespread understanding of ecological limits.
There have always been corners of the globe where the human influence fades and a more ancient order asserts itself. In some cases, these are simply places too high, too dry, too cold or too barren for long-term human survival. But there are many other examples. Throughout history, large areas have been set aside as the hunting grounds or pleasure gardens of kings, queens and other social elites, preserving the trees, plants and wildlife against the ordinary onslaught of settlement—at one point, royal “forests and chases” covered one-fifth of England. At the turn of the year 1000 BC, Europe was home to forests in which every human activity but the worship of gods was forbidden. In western North America, no-man’s-lands between hostile indigenous nations were far richer in game than zones where people hunted freely. Today, of course, we have parks and protected areas, but more particular traditions continue as well. Fly over the small African country of Malawi, for instance, and you see a landscape dotted with the remaining groves of an otherwise vanished forest; these miniature jungles are the graveyards of Chewa villages and the sacred ground of all-male secret societies called upon to communicate with the dead.
Wilderness has long been understood as the original, wholly natural condition of any landscape. It has been celebrated by writers, artists and philosophers, and inspired generations of environmental activists. Yet while popular wisdom holds that every place on earth has a single, wild condition that it will maintain unless altered by human hands, science has moved in the opposite direction. Nature has proved harder to pin down than expected.
The turning can be traced to a competition of ideas in the early twentieth century, beginning with the American botanist Frederic Clements. Clements grew up on the tallgrass prairie of Nebraska just as the stands of bluestem and switchgrass, up to eight feet high and with roots nearly as deep, were making way for tilled fields. The last buffalo herds had vanished while he was a boy, though he would have heard them remembered, or even walked the animals’ old migration routes, some tamped so hard by beating hoofs that their imprint is still visible from the air today. He would have known pronghorn antelope, prairie dogs, rattlesnakes and the rasping call of the sandhill crane, so raw and unformed to our ears that it seems to cry out from prehistory. He would have known all of these, and the loss of them.
In 1916 Clements published Plant Succession, one of history’s most influential books of ecological ideas. In it, Clements proposes that the mature condition of every landscape is fixed—predetermined by soil conditions, climate, rainfall and other limiting factors. Disturbances could set the process back, but the land would then recover through a predictable series of stages. Nature was always on a path to perfection.
While Clements’s pure science was little known outside of scholarly circles, his basic idea took hold in the popular imagination. With the Dust Bowl in the 1930s, when the overworked soils of America’s drought-struck plains were sucked up by the wind to dirty the sails of yachts off the Atlantic seaboard, it seemed clear that a timeless and durable natural order had been disrupted. Clements even recommended a place to look for the original prairie: in cemeteries, one of the few places where native plants and grasses had not been completely ploughed under.*
The challenge to Clements’s view arose when researchers went looking for landscapes that had reached their ultimate climax states. Another American botanist, Henry Gleason at the University of Michigan, observed in the 1920s that while plant communities generally do become more complex over time, they rarely if ever do so in the same way. Oxford ecologist Arthur Tansley, meanwhile, found that many different combinations of species appear on landscapes that otherwise share the same soils and climates. Tansley also pointed out that in Britain and much of Europe, stable, fully matur
e ecosystems had developed that were entirely the result of human influence—climax states of disturbance.
It was decades before these counter-arguments overthrew Clements’s theories. Today, the Clementsian idea that every place on earth has a single, predictable state of nature that it will eventually achieve if left undisturbed has been discarded. This would appear to spell doom for the notion of a natural baseline, but in fact: not so much. Nature may be a more complex blend of chaos and order than Clements believed, but that doesn’t mean that human impacts are just another signal lost in the noise. By human-scale timelines, the ordinary rate of change on many wild landscapes is so slow, patchy and incremental as to be imperceptible without dedicated study. To say that change occurs in nature is not the same as saying that every change that occurs in nature is equal, a fact that we recognize in our most day-to-day observations: a farm is not a forest, after all, and a parking lot is not a farm. There is an ever more urgent need, as the environmental historian Donald Worster puts it, to hold fresh “the memory of a world by which civilization could be measured.” Research today considers new questions: How much balance is normal in nature, and how much change? At what point does change become damage? In what ways is natural change different from the changes wrought by human influence?
One place to look for answers is in “macro time,” or time that is measured in millions of years and renders the whole of human history to the blink of an eye. We know that the earliest signs of life on this planet date back 3.5 billion years. But is there a point along the timeline where we can say that this thing we call “nature” began?
In fact, there is. The story begins in the late Permian period, approximately 250 million years ago. At a glance, nothing Permian would seem recognizable today. The world was hotter and drier and had a single supercontinent known as Pangaea, which was probably home to the world’s first warm-blooded vertebrates. What passed for big, charismatic wildlife was typified by the gorgonopsids, vaguely dog-like creatures that could stand as tall as a modern-day bear but with much more impressive teeth. Among their prey were the cynodonts, which were something like oversized, prehistoric badgers. Life since the Permian has never been easy—the period ended with a poorly understood mass extinction that erased more than 90 percent of marine species and 70 percent of creatures on land. But from the Permian forward, nature has always re-emerged in a recognizably similar form, with warm- and cold-blooded animals; a mix of carnivores, herbivores and omnivores; and a steady tilt toward diversity of life.
At least five major changes have taken place in that multi-million-year-old pattern since our own species began its spread around the globe. For one, we have largely eliminated the megafauna of our age. For at least 250 million years and through every variation in global climate, life on earth was not so empty of large and fierce beasts as it is today except during periods of cataclysmic mass extinction. The same is true of “keystone species,” or the animals and plants with the greatest influence over the structure of their environments; no ordinary force in deep time has ever tended to erase them in the way that humans have. Until the human era, other species also enjoyed the freedom to move, unbound by the fences, highways, cities and other barriers that restrict them today. Nonetheless, they tended to arrive in new places at a pace that permitted gradual adaptation. There was no possibility, for example, of a species like the rabbit appearing suddenly as a breeding population on a new continent, as occurred several times when they were introduced by Australian colonists; with no natural predators, the rabbit population exploded in the mid-1800s, causing such devastation through overgrazing that it was among the leading contributors to native animal and plant extinctions on that continent.* Lastly, we now live in a time in which the actions of a single species—us—appear to be dramatically changing the climate. While not unheard of in prehistory (luckily for us, single-celled algae helped bring about an oxygenated atmosphere 800 million years ago), it is fair to say this is extremely rare.
There is, in other words, a fundamental difference between background patterns of change and cataclysmic change—and we, human beings, belong in the cataclysmic camp. Us and killer asteroids. Us and glaciers two miles deep and as wide as continents. If nature’s complexity has been described as “noisy clockwork,” then the singular tone of the human era has been that of a pendulum slowly winding down. Taken together, these alterations to the patterns of nature are less the “environmental challenges” that we speak of today than they are breaches in the space-time continuum.
In September 2004, fourteen leading conservation thinkers—described by an organizer of the group as “National Academy, silverback, rock-star scientists”—gathered in a century-old stone-and-mortar house on the Ladder Ranch, a property in New Mexico belonging to media mogul and philanthropist Ted Turner. The goal was to draw a radical new baseline for the way we look at nature.
The group had been influenced by the concept of “rewilding.” The term was coined in the early 1990s by Dave Foreman, a founder of the direct-action Earth First! environmentalist network, writing in Wild Earth magazine. Foreman used rewilding in the general sense that the word evokes: “to make a place wild again.” In 1998, conservation biologists Michael Soulé and Reed Noss applied the term to science, defining rewilding as the effort to restore wilderness on a large scale. Once again, the familiar question arises: Restore to what?
The Ladder Ranch workshop’s answer appeared the following year in the science journal Nature. The baseline state of nature for any given place on earth, they declared, should not be drawn in 1492 or even the dawn of civilization. Instead, it should be drawn at that point in time when the most complete web of life existed during the current climate cycle in geological time. That would be the end of the last ice age, also known as the Pleistocene epoch, when the glaciers receded to reveal the landforms that we know today, while the planet warmed to produce the climate that has endured ever since.
The last continent on earth to be populated at the end of the Pleistocene was North America, some fifteen thousand years ago. At that time, the land was home to a hair-raising assortment of megafauna. Most of us are familiar with some of these giant animals, like the mammoths and mastodons that look like woolly elephants and, like elephants in some parts of Africa today, may have roamed grasslands in densities of more than three animals per square kilometre. But North America was also home to pampatheres, which resembled armadillos the size of overturned rowboats, and another armoured family, the glyptodonts, at their largest the size of a subcompact car. There were ground sloths—amiable-looking herbivores that often stood up on their hind legs and could weigh nearly three tonnes. There were herds of wild horses, some as heavy as today’s Clydesdales, and tapirs rooting through the wetlands, and an antelope called the saiga, with a pouchy snout that acted as a dust filter.* Wild oxen drank at waterholes alongside camels that would tower over today’s dromedaries. There were giant moose, giant llamas, giant elk, giant boars. There was a beaver nearly the size of a bear.
There were monsters. Packs of dire wolves were widespread, the animals outweighing modern wolves by twenty pounds apiece but still far from the most fearsome predators in the Pleistocene wilderness. That title probably goes to the short-faced bear, a flesh-eater large enough to look you in the eyes while still on all fours. The greatest feline, still haunting the pop-up-book nightmares of children, was the sabre-toothed cat, with serrated fangs as long as chef’s knives and a body twice the heft of a modern lion’s. There were lions, too—prides of American lions that were like today’s African and Indian lions in every way but one: they were larger.
The list goes on, from scavenging birds with wingspans of fifteen feet to beetles adapted to rolling the dung of giant animals. Then, North America’s megafauna began to disappear. Scientists have debated the cause of the mass extinction for decades, but evidence increasingly points to the spread of humans around the globe at a time of intense climate change. Go to any corner of the planet, and the moment tha
t Homo sapiens first shows up in that place will be roughly the time that many of its largest species begin to fall toward the void of extinction. Africa is the exception, where megafauna such as elephants, giraffes, lions and hippopotamuses evolved alongside people. Otherwise, the pattern holds. Fifty thousand years ago, humans reach Australia and twenty-one entire genera (groupings of species with similar characteristics) disappear over the following millennia; every land-based species with an average weight above one hundred kilograms is wiped out. Thirty thousand years ago, modern humans settle in Europe, and nine genera vanish. North America loses thirty-three, with the Americas as a whole shedding 75 percent of their big beasts. Most compelling is the fact that the die-offs taking place on continental mainlands were often postponed on offshore islands, for the simple reason that humans had not arrived on them yet. The biggest animals in the Caribbean, including sloths and various oversized rodents, survived the extinctions going on in North and South America only to go extinct themselves when our species reached the islands just six thousand years ago. Despite being Australia’s neighbour, New Zealand didn’t lose its large fauna—eleven species of flightless moa—until just eight hundred years ago, with the arrival of the Maori culture.
What the Ladder Ranch group proposed was an attempt to revisit that older world—“Pleistocene rewilding,” they called it. A series of experiments could be undertaken, they wrote, in which existing species from one part of the planet—say, elephants—might be carefully “reintroduced” to places where similar species—like mastodons—went extinct in the Pleistocene. The end point, described as “the ultimate in Pleistocene rewilding” for North America, would be a free-living population of lions somewhere on the Great Plains, limited only by perimeter fencing. Without megafauna, the scientists argued, the planet’s landscapes would forever be ecologically incomplete.
The Once and Future World Page 6