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Rants from the Hill: Pleistocene rewilding

In a 2006 article [PDF] in The American Naturalist, a small herd of perfectly respectable conservation biologists advocates a bold ecological restoration project they call “Pleistocene Rewilding.” The concept itself is outrageously wild. First of all, “rewilding” is the process of reintroducing species to ecosystems from which they have been extirpated—usually by that big bully, Homo Notsosapiens. Think wolves in Yellowstone. Pleistocene rewilding, by contrast, is the incredible idea that we can enhance ecosystem health by reintroducing many of the large mammals that were driven to extinction between 10,000 and 13,000 years ago. The so-called “pre-Columbian benchmark” of 1492 is the commonly used target for restoration efforts. To achieve this benchmark we just figure out how the world looked on the day Chris Columbus made landfall—say, at about cocktail hour—and then restore North American ecosystems to that condition by extirpating exotic species, reintroducing natives, and rehabilitating habitat. It isn’t easy to do, but at least it’s easy to understand. Then along come these provocative Pleistocene Rewildatators, who ask why we’re so stuck on 1492. In fact, it was about 13,000 years ago that humans showed up in North America, where they wasted no time poking spears into everything that moved—a habit that probably contributed to the disappearance of large mammals. And the mass extinction of megafauna during the Pleistocene—along with a secondary wave of extinctions resulting from the disappearance of those keystone species—caused severe damage to the fabric of North American ecosystems, which have been slowly fraying and unraveling ever since. Since the fossil record gives us a pretty good idea of what beasts roamed here 13,000 years ago, before the arrival of human hunters, why not select an ecological restoration benchmark that is closer to Pleistocene cocktail hour? Why not acknowledge that North American ecosystems are full of holes—ecological niches that have gone unoccupied for 10,000 years—and then do our best to fill those holes by reintroducing large mammals? Now here’s the fun part. It turns out that by the time Columbus arrived, most of the cool stuff was long gone—and in this sense the usual pre-Columbian restoration benchmark actually describes a world in which biodiversity was already radically impoverished. Pleistocene North America was in fact home to a living bestiary of outrageous creatures, including various species of horses, donkeys, camels, muskoxen, sloths, tapirs, peccaries, cheetahs, lions, and Proboscideans (mammoths and mastodons), not to mention giant short-faced bears, ferocious saber toothed cats, and fierce dire wolves (and, to depart from mammals for a moment, the nine-foot long sabertooth salmon and the ten-foot tall terror bird as well). Among the charismatic megafauna that made it through the bottleneck of Pleistocene extinctions are animals every westerner knows to be equally fantastic: coyote, wolf, bison, grizzly, cougar, and pronghorn antelope, to name a few. Read more.