1491_ New Revelations of the Americas Before Columbus - Charles C. Mann [179]
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