When aliens attack

Should we battle invasive species of plants and animals? Maybe. But in his provocative new book, "Out of Eden," Alan Burdick argues that we are only doing so for ourselves.

By Andrew O'Hehir

May 27, 2005 | Like an increasing number of New York City's summer migrants, I spend part of each year in the Catskills, an ancient, crumbling range of hills and mountains that wanders across central New York state from the Hudson River to the Delaware. No one pretends that this is a pristine natural environment. Abandoned resorts and crumbling farmhouses dot the landscape, and the grand hemlock forests that once covered these peaks were hewed down 150 years ago, replaced largely by oaks and maples that moved in from the south and west.

Still, you have to get to know the Catskills to appreciate how fundamentally they have been changed by the presence of man. The area is sparsely populated to this day, and the woods are alive with animals and birds. Wild turkeys cross our meadow in the morning; white-tailed deer sleep there at night. It sure feels like wilderness, at least at first. But see those drifts of lavender and white flowers my wife transplanted to a few different spots, assuming they were native phlox? That's dame's rocket, a wildflower of the English countryside viewed by many American gardeners as a hostile invader. The tenacious, creeping green vine with the spade-shaped leaves? That's buckwheat, brought to America by the Dutch almost 400 years ago.

When I bought some garage-sale fishing gear and taught myself to fly-cast, I entered the even murkier arena of North America's freshwater life. Modern dry-fly fishing was pretty much invented in the Catskills, and the region's rivers are said to teem with trout. Well, sure, but the big native brook trout pursued along the Neversink River by angling legend Theodore Gordon a century ago exist only as a shrunken backwater population; you're far more likely to catch a brown trout (native to Germany) that was born in a bucket and stocked in the river as a fingerling. You might also come across rainbow trout, smallmouth bass or carp -- all introduced here, by accident or on purpose, from somewhere else.

These low-rent examples of "invasive species" just scratch the surface, and it's a surface that Alan Burdick, the author of "Out of Eden," aims to dig deep beneath. His tour through the burgeoning discipline of invasion ecology is nuanced, judicious and often delightful; in the finest tradition of science writing, Burdick delivers the hard stuff on a granular level while also pursuing a more philosophical and personal muse. In search of the plant and animal species that move around the world at an ever-accelerating pace -- and in search of possible answers to the quandaries they pose for us, the species that has made their pilgrimages possible -- Burdick travels to Guam and Hawaii and Tasmania, to the shores of San Francisco Bay, Chesapeake Bay and Long Island Sound, and across the north Pacific aboard one of the world's biggest oil tankers.

Burdick, a senior editor at Discover magazine and a widely published freelance writer, would tell you that the Catskills are more typical than not. You've probably heard about one or more of the invasive species that has assumed celebrity status in the United States: kudzu, the Asian vine that has become an unstoppable weed of the American South; the zebra mussel, a Eurasian shellfish responsible for tremendous ecological and economic damage to Great Lakes waterways; the Asian snakehead, a voracious freshwater fish that can actually crawl from one pond or river to another. But for each one of these invaders there are dozens, perhaps hundreds, that attract attention only from scientists, if at all.

Most of the ecologists and biologists Burdick meets don't use the word "invasive" for the same reason many gardeners no longer talk about "weeds." Those are value judgments, used only to differentiate species we like from those we don't. But however you frame the question, the cascade of introduced or non-indigenous species -- invaders "from anywhere, going everywhere," as he puts it -- is causing major and permanent ecological change all over the world. How do we understand this change, and what does it tell us, Burdick wonders, about the fundamental nature of nature itself?

Some species invasions have had clearly catastrophic results, at least on a local level. Burdick goes to Guam to meet the brown tree snake, an Australia native that arrived on the remote Pacific island after World War II, aboard ships or in the wheel wells of airplanes or both. There were no other predatory snakes on Guam, and the island's docile species (many found nowhere else) made easy pickings. In 40 years, the snake had essentially exterminated Guam's native bird population -- the island's national bird, a flightless rail called the koko, now exists only in captivity. In Hawaii, on the other hand, tourists encounter no shortage of colorful birds and tropical vegetation -- but in the lowland areas most frequented by visitors, these are almost all non-native. Those mynah birds, canaries, finches, waxbills, cockatoos and mockingbirds you heard outside your Maui beachfront hotel are imported species, as are the lantana shrubs, banana poka vines, Himalayan raspberry bushes and more than 400 other "local" plants. Only in the Aloha State's highlands, principally in Hawaii Volcanoes National Park on the Big Island, can you find some facsimile of the original Hawaiian rain forests.

Next Page: San Francisco Bay: The most invaded marine ecosystem anywhere

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