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America's Least Wanted > Executive Summary Introduction An invasion is under way that is undermining our nation's economy and endangering our most precious natural treasures. The intruders are alien species—non-native plants and animals introduced into this country either intentionally or by accident. Attention to the problem of alien, or exotic, species often centers on their costs to agriculture, ranching, forestry, and industry. The price they exact on the nation's forests, grasslands, and waterways, however, is at least as great. The Problem Alien species now are one of the leading threats to U.S. species and ecosystems. Of the approximately 4,000 exotic plant species and 2,300 non-native animal species in the United States, most cause few problems. Unfortunately, some alien species are proliferating unfettered, causing severe environmental or economic damage; just 79 of them have cost the U.S. economy $97 billion. Infestations of introduced pest species also are changing the very fabric of our natural ecosystems and pushing endangered species even further toward the brink of extinction. Indeed, exotics have contributed to the decline of 42 percent of U.S. threatened and endangered species. The Dirty Dozen This rogues' gallery represents some of America's least wanted intruders. These 12 plants and animals exemplify the range of problems caused by exotic species. Some, such as tamarisk and Chinese tallow, degrade ecosystems by altering their physical or chemical properties. Others, including the rosy wolfsnail and brown tree snake, deplete native wildlife by preying on them. Yet others, such as the zebra mussel or balsam wooly adelgid, set off cascading biological changes in the natural systems they invade. What Can Be Done? Containing the onslaught of exotic species will not be easy or quick, but it is not impossible. This effort requires work on four fronts:
Our nation's native plant and animal species, and the ecosystems on which they—and we—depend, are too important to sacrifice to alien invaders. This is an issue of both ecological and economic survival. Containing these invasions requires shared commitment and action. And although the problem may be expensive to address now, the cost will be far higher if we delay—both in dollars and diversity. With prompt attention and action, though, we still have time to safeguard our nation's unique natural heritage. |
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