The Artificial Wilderness


Until about 200 million years ago Eurasia and the Americas were lashed together in a single landmass that geologists call Pangaea. Pangaea broke into pieces, sending the continents drifting like barges across the ocean floor. For millions of years, the separate fragments of Pangaea had almost no communication. Evolution set their species spinning off on separate trajectories, and the flora and fauna of each land diverged so far from each other that the astounded Columbus remarked that “all the trees were as different from ours as day from night, and so the fruits, the herbage, the rocks, and all things.”

Columbus was the first to see the yawning biological gap between Europe and the Americas. He was also one of the last to see it in pure form: his visit, as Alfred Crosby put it, initiated the process of knitting together the seams of Pangaea. Ever since 1492, the hemispheres have become more and more alike, as people mix the world’s organisms into a global stew. Thus bananas and coffee, two African crops, become the principal agricultural exports of Central America; maize and manioc, domesticated in Mesoamerica and Amazonia respectively, return the favor by becoming staples in tropical Africa. Meanwhile, plantations of rubber trees, an Amazon native, undulate across Malaysian hillsides; peppers and tomatoes from Mesoamerica form the culinary backbones of Thailand and Italy; Andean potatoes lead Ireland to feast and famine; and apples, native to the Middle East, appear in markets from Manaus to Manila to Manhattan. Back in 1972 Crosby invented a term for this biological ferment: the Columbian Exchange.

By knitting together the seams of Pangaea, Columbus set off an ecological explosion of a magnitude unseen since the Ice Ages. Some species were shocked into decline (most prominent among them Homo sapiens, which in the century and a half after Columbus lost a fifth of its number, mainly to disease). Others stumbled into new ecosystems and were transformed into environmental overlords: picture-book illustrations of what scientists call “ecological release.”

In ecological release, an organism escapes its home and parachutes into an ecosystem that has never encountered it before. The majority of such escapees die rapidly, unable to thrive or reproduce in novel surroundings. Most of the survivors find a quiet niche and settle in, blending inconspicuously with the locals. But a few, finding themselves in places with few or none of their natural enemies, look around with the hopeful incredulity of juvenile delinquents who discover the mall’s security cameras are broken—and wreak havoc. In their home ecosystems these species have, like all living things, a full complement of parasites, microbes, viruses, and insect predators to shorten and immiserate their lives. Suddenly free of this burden, they can burst out and overwhelm the landscape.

The Japanese grind the roots of a low vine called kuzu (Pueraria lobata) into a white powder that thickens soup and is alleged to have curative properties; they also plant the species on highway shoulders as erosion-preventing ground cover. In the 1930s the U.S. Civilian Conservation Corps planted millions of kuzu seedlings to fight soil loss, a major fear in the era of the Dust Bowl. Renamed “kudzu,” the vine prevented so much erosion that villages across the U.S. Southeast celebrated kudzu festivals and crowned kudzu queens. People harvested it like hay and fed it to cows; entrepreneurs marketed kudzu cereal, kudzu dog food, and kudzu ketchup. In the early 1950s rural areas suddenly awoke from their trance and discovered that kudzu was eating them alive. Without its natural enemies the plant grew so fast that southerners joked they had to close their windows at night to keep it out. Worse, the plants themselves grew bigger than is usual in Japan—nobody knows why. Engulfing fields in dense mats of root and vine, kudzu swarmed over entire farms, clambered for miles along telephone lines, wrapped up trees, barns, and houses like a green Christo. The roots sank so deep that the vine was nearly impossible to remove. In 1996 the federal government estimated that kudzu had swallowed seven million acres. The figure is now much larger.

What happened after Columbus was like a thousand kudzus everywhere. Throughout the hemisphere ecosystems cracked and heaved like winter ice. Echoes of the biological tumult resound through colonial manuscripts. Colonists in Jamestown broke off from complaining about their Indian neighbors to complain about the depredations of the rats they had accidentally imported. Not all the invaders were such obvious pests, though. Clover and bluegrass, in Europe as tame and respectable as accountants, in the Americas transformed themselves into biological Attilas, sweeping through vast areas so quickly that the first English colonists who pushed into Kentucky found both species waiting for them. Peaches, not usually regarded as a weed, proliferated in the southeast with such fervor that by the eighteenth century farmers feared that the Carolinas would become “a wilderness of peach trees.”

South America was hit especially hard. Endive and spinach escaped from colonial gardens and grew into impassable, six-foot thickets on the Peruvian coast; thousands of feet higher, mint overwhelmed Andean valleys. In the pampas of Argentina and Uruguay, the voyaging Charles Darwin discovered hundreds of square miles strangled by feral artichoke. “Over the undulating plains, where these great beds occur, nothing else can now live,” he observed. Wild peach was rampant in South America, too. Peachwood, Darwin discovered, had become “the main supply of firewood to the city of Buenos Ayres.” Some invasions cancel each other out. Peru’s plague of endive may have been checked by a simultaneous plague of rats, which the sixteenth-century writer Garcilaso de la Vega reported “bred in infinite numbers, overran the land, and destroyed the crops.”

A phenomenon much like ecological release can occur when a species suddenly loses its burden of predators. The advent of mechanized fishing in the 1920s drastically reduced the number of cod from the Gulf of Maine to the Grand Banks. With the cod gone, the sea urchins on which they fed had no enemies left. Soon a spiny carpet covered the bottom of the gulf. Sea urchins feed on kelp. As their populations boomed, they destroyed the area’s kelp beds, creating what icthyologists call a “sea urchin barrens.”

In this region, cod was the species that governed the overall composition of the ecosystem. The fish was, in ecological jargon, a “keystone” species: one “that affects the survival and abundance of many other species,” in the definition of Harvard biologist Edward O. Wilson. Keystone species have disproportionate impact on their ecosystems. Removing them, Wilson explained, “results in a relatively significant shift in the composition of the [ecological] community.”

Until Columbus, Indians were a keystone species in most of the hemisphere. Annually burning undergrowth, clearing and replanting forests, building canals and raising fields, hunting bison and netting salmon, growing maize, manioc, and the Eastern Agricultural Complex, Native Americans had been managing their environment for thousands of years. As Cahokia shows, they made mistakes. But by and large they modified their landscapes in stable, supple, resilient ways. Some milpa areas have been farmed for thousands of years—time in which farmers in Mesopotamia and North Africa and parts of India ruined their land. Even the wholesale transformation seen in places like Peru, where irrigated terraces cover huge areas, were exceptionally well done. But all of these efforts required close, continual oversight. In the sixteenth century, epidemics removed the boss.

American landscapes after 1492 were emptied—“widowed,” in the historian Francis Jennings’s term. Suddenly deregulated, ecosystems shook and sloshed like a cup of tea in an earthquake. Not only did invading endive and rats beset them, but native species, too, burst and blasted, freed from constraints by the disappearance of Native Americans. The forest that the first New England colonists thought was primeval and enduring was actually in the midst of violent change and demographic collapse. So catastrophic and irrevocable were the changes that it is tempting to think that almost nothing survived from the past. This is wrong: landscape and people remain, though greatly altered. And they have lessons to heed, both about the earth on which we all live, and about the mental frames we bring to it.

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