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Foreign Species: They're Here, And They're Taking Over


Environment: Ecology

Foreign Species: They're Here, and They're Taking Over

And they're invading the U.S.--and costing plenty

In the mid-1980s, the Taylor family abandoned their 1,360-acre ranch in Klamath County, Ore., because it was overrun with leafy spurge, a deep-rooted invader from Eurasia that chokes out the native grasses on which cattle prefer to graze. At the time, the estimated value of noninfested land was around $125 an acre. The best the Taylor family could get was $22 an acre--an 83% loss in value. Sadly, the story of the Taylor ranch is not an isolated incident. With no natural predators, leafy spurge now infests about 2.7 million acres, mostly in the northern Great Plains and southern Canada, at a cost to agriculture of $144 million a year.

This is more than a scare story about killer weeds. Leafy spurge is only one of an army of foreign plant and animal invaders that are infesting every region of North America. They are riding the wave of a rapidly swelling global trading system that brings cargo--along with hidden seeds and bugs--from the most exotic corners of the earth. Bioinvasion, the spread of nonnative species, is fast becoming one of our most costly ecological problems as it disrupts food and agriculture, destroys wetlands, interferes with shipping, and drastically alters natural habitats. "Every ship, every plane, every truck is a potential carrier," warns Faith T. Campbell, an invasive-species specialist with the America Lands Alliance.

In a report to be published later this year in the journal Bioscience, Cornell University ecologist David Pimentel estimates that invasive species cost the U.S. more than $122 billion annually. The list of troublemakers includes noxious weeds ($35 billion), harmful insects ($25 billion), and organisms, such as the AIDS virus and cholera, that cause human disease ($6.5 billion). Randy G. Westbrooks, the noxious-weed coordinator for the U.S. Agriculture Dept., figures that invasive plants already infest 1.2 billion acres and each year take over 3 million more. "If this keeps up we will become the planet of the weed," says Westbrooks.

There is also a huge untallied cost. Exotic species destroy the ecosystems that support native species, leaving them nowhere to go. According to the Pimentel study, purple loosestrife, a European plant with brilliant magenta flowers, has invaded wetlands in 48 states, crowding out 44 native plants. In Guam, the brown tree snake has eradicated 9 lizard species and 10 types of forest bird. In all, the Environmental Defense Fund reports that roughly 400 of the 958 species listed as threatened or endangered by the U.S. Interior Dept. are at risk from invasive species.BAD ZEBRAS. Environmentalists have worried for decades about the ecological threat that invasive species represent, but it has been hard to marshal government or public support. Attitudes are changing, though, due in large part to an aggressive, bean-sized mollusk that has taken over the Great Lakes. The zebra mussel arrived in 1986 in Lake St. Clair from Eastern Europe, via a freighter's ballast water. Today it's found in every river in the Mississippi watershed, and water and power plants spend an estimated $3 billion annually trying to keep it from clogging their works. "If nothing is done, these mussels could one day be in every lake, river, and stream all the way to the West Coast," says Charles R. O'Neill Jr., director of Sea Grant's aquatic nuisance species clearinghouse.

There is another threat arriving over land: the dreaded Asian long-horned beetle, which hitched from China on wooden pallets and packing materials. Since it landed three years ago, this wood-boring insect has decimated more than 2000 trees in Brooklyn, New York. A similar infestation now plagues Chicago. Because the beetle has a huge appetite for a variety of trees, the Agriculture Dept. warns it could cause more than $41 billion in damages if it becomes widely established.

In many ways, bioinvasion is the dark side of globalization. With more and more goods entering the country, it's easier for pests to stow away. Christopher J. Bright, a researcher at the Worldwatch Institute, says booming tourism also opens the way for invasions. Every day, some 2 million people cross an international border around the world; every week, a million people move between developed and developing nations.

Efforts to control the menace have been far too fragmented. There are 24 federal agencies with some authority to regulate non-native species, and it has been difficult to coordinate their efforts. "The usual approach has been an ad hoc attack on a particular problem," writes environmental analyst M. Lynne Corn in a recent Congressional report.

An executive order issued Feb. 3 goes part way toward rectifying the situation. It calls for a coordinated federal effort and the creation of an Invasive Species Council that will develop, by September, 2000, a comprehensive plan to address the growing economic and environmental threat.WHITE LIST? Although the executive order is a good first step, ecologists say the laws need strengthening to stop access in the first place. "There's been a lot of talk but no real rolling up of sleeves," complains Andrew N. Cohen, a marine biologist with the San Francisco Estuary Institute. Under the current system, an import is deemed safe unless it's on a list of organisms known to be harmful. Often, by the time federal regulators have the evidence to blacklist a particular species, it's too late. "The burden of proof is so high and our resources so small that it is tough to get things on the list," says Westbrooks.

Ecologists would prefer a "white-list" law, one that bans entry of plants and animals until they're proven innocent. New Zealand and Australia already have such laws, but some U.S. officials worry that such a policy could alienate trading partners. Still, there is a growing sense that it may be worth the risk. Already this year, Senators Daniel K. Akaka of Hawaii and Larry E. Craig of Idaho have introduced bills that would strengthen Agriculture's power to protect native plant species. And Interior Secretary Bruce Babbitt is calling for comprehensive entry controls that reverse the burden of proof. "We need to enact national legislation and put principle into practice," he says.

David Pimentel agrees. "The true challenge lies in preventing further damage," he says. "No matter how you slice it, invasives are costing us significant money." Just ask the Taylors.Return to top


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