A weed by any other name would spread as fast

According to the authors of "Nature Out of Place," the Garden of Eden is becoming a lawn full of dandelions.

The human penchant for moving people and goods over ever-greater distances in ever-lesser times is wreaking havoc on the earth's most precious characteristic: biodiversity.

For instance, the zebra mussel, a thumbnail-size bivalve that carpets miles of Midwestern waterways, was unknown in this country 20 years ago, and probably survived a transoceanic trip in a tank full of ballast water. The gypsy moth, Dutch elm disease, and the sea lamprey all received similar assists.

The problem with such immigrants, ecologically speaking, is that the locals often aren't prepared for them. Held in check in their countries of origin by predators or parasites that co-evolved with them, they may multiply geometrically in new environments.

Their advent can be particularly explosive in habitats like oceanic islands, where isolation can foster a palmy lifestyle ill-prepared for continental sophisticates. Australia's brown tree snake, for instance, drove 12 of Guam's 16 unique bird species to extinction in the last 50 years simply by eating them.

The authors call this fraying of barricades "the globalization of nature," and have no trouble itemizing a huge bill of economic and ecological costs. Evolution takes millenniums to integrate species into ecosystems; invaders can turn these communities into ghost towns overnight.

If you like Queen Anne's lace on a sandy roadside, or wild mustard on a cobble beach, you may feel a bit guilty, since both are foreigners. But only a small percentage of introductions are truly invasive, or able to displace natives wholesale. Indeed, about a third of the plants currently growing wild in the US were not here before Columbus, and yet most do no damage.

Part of the challenge of defending local ecosystems is the difficulty of predicting which newcomers might cause trouble.

Federal law focuses on pests liable to impact livestock or agriculture. The authors recommend a broader approach, "cleanlisting," which would deny entry to all foreign species except those already determined to pose no threat.

"Nature Out of Place" is full of such prescriptions, and it develops a medicinal flavor. Cowritten by an ecologist at the University of Massachusetts and his graduate-student son, the chapters alternate between theoretical overviews by Van Driesche Sr. and eyewitness accounts by Van Driesche Jr. from hot spots like Hawaii, California, and the Eastern forests.

The book has a heft and authority not often found in popular-science accounts. It is highly organized, well edited, bristling with photos, maps, and tables, and it justifies its arguments in a convincing, businesslike manner - indeed, it could serve as a state-of-the-art manual for preventing and confronting invasions.

There are horror stories here, but also hopeful developments. The authors follow current thinking in emphasizing the importance of matching local support to outside expertise in order to craft effective action. They also have a winning faith in the willingness and ability of ordinary citizens to become ecological stewards.

Tom Palmer is an environmentalist and writer in Milton, Mass.

(c) Copyright 2000. The Christian Science Publishing Society

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