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.
The case of Guam might seem to support the classical idea of an ecosystem as an interlocking mechanism finely honed by millennia of evolution, where each organism occupies a niche crucial to the whole, and where the addition (or subtraction) of a single species can wreak havoc up and down the system. One serpent arrived in Eden, and now the forest is silent. But dire case histories like the brown snake's are more the exception than the rule. As Burdick puts it, "Most successful invaders simply blend into the ecological woodwork."
San Francisco Bay, as he learns late in his impressive nine-year odyssey, supports more than 200 non-native species, making it the most-invaded marine ecosystem anywhere in the world. Only a handful of those new arrivals have caused conspicuous problems, and as yet there have been no mass extinctions, no ecological catastrophe. As in the Hawaiian example (and probably in the Catskills too) the net result has been more species living in the bay, rather than fewer. In other words, local biological diversity has actually increased, which -- again, according to classical ecology -- is supposed to be a good thing.
Yet surely something has been lost when the nature most of us see most of the time is a collage of native and non-native species, thrown together haphazardly in very recent historical time, even if it presents the appearance of relative stability and -- for want of a better word -- naturalness. For an environmental purist like writer Bill McKibben, such a landscape isn't nature at all, just a sort of human-centric golf-course fakery. Burdick takes a more nuanced and longer view, arguing that the central tragedy of the human condition is that we are both inside and outside nature, doomed to alter it and to observe ourselves altering it. In this he finds a kind of obscure hope.
How one thinks about the jumbled quality of nature on a planet constantly being circumnavigated by Homo sapiens and all its planes, ships and automobiles lies at the very heart of the still-young science of invasion ecology, which, as Burdick discovers, is only beginning to move away from anecdotal evidence and conjecture toward grappling with hard data. Generations of environmentalists, for example, have blamed the feral pigs of Hawaii (descended from 18th century English imports) for ravaging native plant life. Native Hawaiians, who conduct ritual pig hunts, argued that the porcine invaders did only cosmetic damage to the forest -- and they now appear to have been right.
Indeed, leading scientists in the field have grown skeptical of the idea that an ecosystem is a well-balanced, self-regulating and internally calibrated natural machine (and some now reject the word as well). Instead, they say, the only constant in nature is change. In one of his most breathtaking passages, Burdick elaborates on this "nonequilibrium model":
"Nature does not function precisely like clockwork, a tapestry, a cathedral, a pyramid, an airplane, or an international bank; metaphors are drawn from the world of human invention and knowledge, whereas nature is far larger than either of those things and has hardly begun to be understood ... Species disperse and invade, come and go, evolve and go extinct. Any organism can be an invader somewhere. Every ecosystem -- or whatever one calls it -- can be invaded by something. This is true even in the absence of humankind. An ecosystem is stable over time not because the list of species remains forever the same, but because it varies -- not in spite of disturbance, but because of it."
What is this, you may be wondering -- the Dick Cheney school of laissez-faire ecology? Are we supposed to accept that the human-enabled distribution of microorganisms, seeds, spores, bugs, fish, birds and insects from one place to another is just the natural process, speeded up a few thousand times? If the entire state of Hawaii becomes a tropical fantasyland plantation, and the zebra mussel chokes out the Mississippi River's native life forms, and the European green crab kills off the native shore crabs of the Pacific Northwest, well, that's life in the fast lane, right? (As one of Burdick's scientists has demonstrated, both mussel and crab almost certainly arrived in ballast water, the huge doses of seawater oceangoing cargo ships suck up in one location and then discharge in another.)
Not exactly. Burdick, like most of the ornithologists, entomologists, soil ecologists and marine biologists in his book, believes in trying to control the unlimited flow of ecological invasion, whenever and wherever that's possible. But he suggests that, first of all, we have to be realistic. One theme repeated throughout "Out of Eden" is that resources are often squandered on expensive and dubious attempts to save critically endangered species, when it would be more practical and cost-effective to protect as much wilderness habitat as possible and face the fact that some individual species won't survive.
Even more important, Burdick thinks that if we decide it's critical to save diverse kinds of ecosystems all over the world -- that we value the ecological distinctions between Hawaii and Australia, India and California -- we must recognize that we're doing it for our own reasons, not for any objective scientific reason to be found in nature itself. Nature, Burdick insists, is "not a reliable model for wilderness conservation." Instead, it is "heartless, mindless, raw, and insatiable; it is red in tooth and claw. However much we care about it or its more attractive artifacts, it does not care for us, or even for itself."
This may rock your world if you're the holistic New Age type, or for that matter if you believe in God. But whether or not you admire the tone of his language, Burdick is trying to get to an essential problem, which could be framed in a variety of ways: Do we want to live in a world where everything is familiar, or a world where many things remain strange, alien, even completely unknown? God or evolution or the turning of the cosmic wheel has empowered human beings to make this choice, and if we choose the latter option -- which is less convenient and more difficult to manage -- then why?
Hawaiian entomologist David Foote, one of Burdick's star witnesses, tells him that human life all over the world is increasingly accompanied by a handful of plants and animals we all know: domestic animals and livestock; scavenger species like squirrels, coyotes and raccoons; a few familiar shrubs and trees; rats, pigeons, sparrows, roaches. "If that's what you want to live with -- a small suite of a dozen, maybe two dozen species -- then you can live with that, I suppose. You can argue that biodiversity has a utilitarian value. But it's an aesthetic issue for me."
It's extraordinary to hear a scientist -- let alone one whose professional career has largely been devoted to the genus Drosophila, the fruit flies -- fall back on aesthetics. But what could more clearly define the separation, partial and conditional as it may be, between man and nature? As another scientist points out, you could also call this a moral or a spiritual question, but whatever it is, you can't quantify it by collecting data or see it under a microscope. Burdick is struck by the idea "that the strongest argument for preserving biodiversity might rest on something so mercurial, so subjective, so intimate as a personal desire to live in a world that is biologically rich."
In a sense, Burdick's journey along the cutting edge of ecological science points us back in time, to the early years of the environmental movement and the old-fashioned sentiment that wilderness preservation had psychic and spiritual benefits for human beings, irrespective of its meaning for "nature." No one ever put it better than novelist Wallace Stegner, in his 1960 "Wilderness Letter":
"Something will have gone out of us as a people if we ever let the remaining wilderness be destroyed; if we permit the last virgin forests to be turned into comic books and plastic cigarette cases; if we drive the few remaining members of the wild species into zoos or to extinction; if we pollute the last clean air and dirty the last clean streams and push our paved roads through the last of the silence, so that never again will Americans be free in their country from the noise, the exhausts, the stinks of human and automotive waste. And so that never again can we have the chance to see ourselves single, separate, vertical and individual in the world, part of the environment of trees and rocks and soil, brother to the animals, part of the natural world and competent to belong in it. Without any remaining wilderness we are committed wholly, without chance for even momentary reflection and rest, to a headlong drive into our technological termite-life, the Brave New World of a completely man-controlled environment."
Amid all Burdick's amusing and amazing factoids (there's a Hawaiian leaf-hopper named in honor of country singer Loretta Lynn; the London Underground is home to not one but three distinct species of mosquito), his appealing portraits of nerd-hero scientists (one exclaims in wonder: "These Balanus improvisus have just released nauplii into my sample!"), his brain-stretching vocabulary (not just "nauplii," but also "propagule," "reticule" and "stochasticities"), his taxonomic lists and his sometimes overly rhapsodic asides on the circular life cycle of the barnacle or the mating habits of the sea scallop, one moment stood out for me.
Burdick's only encounter with the dreaded brown tree snake of Guam comes when an animal control officer presents him with a captured 6-foot specimen (despite its prevalence on the island, the snake is notoriously difficult to find in the wild). The snake wraps itself around him, "squeezing with a gentle, almost clinical indifference, like the blood pressure gauge in a doctor's office." Burdick becomes aware of the obvious difference between them -- "I could both consider the snake and consider my considering of the snake, whereas the snake could only consider me as lunch."
Beyond that, Burdick finds himself gripped by a perverse admiration. "The snake was a marvelous work of biology -- powerful, elegant, efficient," he writes. "As agents of homogenization go, it was not without appeal. I sympathized with it. I even felt a little sorry for it -- guileless, cursed, outcast."
Referring to Bill McKibben's notion that nature no longer exists as a separate realm, now that the most remote wilderness has been tainted by human civilization, Burdick asks: "But if nature was finished, what now was this thing that had wrapped itself so firmly around me, doing its Sisyphean best to finish me? Was it not nature? Was I not nature? ... If the line we've drawn to distinguish natural from unnatural serves some human purpose, it is a line to which the snake -- and every living inhabitant of the world, save ourselves -- is entirely oblivious."
Something like Burdick's epiphany, his collision with the ambiguous margins of the natural world, comes to many of us, even without stalking a fearsome snake through the Guamanian jungle. A few years ago, after fumbling through a few fly-fishing expeditions, I caught my first brown trout just before sunset one evening. I was standing up to my waist in the West Branch of the Delaware River just east of Hamden, N.Y., where it's not much more than a glorified farm stream with Holstein cows chewing grass along its banks.
I had made a cast at nothing in particular with a little fly called a beadhead nymph, meant to imitate a larval insect. I was just practicing, letting the nymph drift downstream until it was time to reel it in. At the last second, when the fly was about to jerk to a stop in the water, it hung suspended in the current for a magical moment and a fish took it. Every fly fisher knows that shuddering, electrical sensation of life at the end of your line; it's that, rather than the prospect of a fish dinner, that makes the sport so addictive. (Many fly fishermen, perhaps most, don't keep or kill their catch.)
It was a young male, barely of legal size and not big enough to fight me for long. But as I guided it into my net, I was amazed at this angry little cold-water predator I had momentarily outsmarted -- despite its nondescript name, the brown trout is often golden in rivers, and spotted in black and deep orange. I thought it was the most beautiful animal I'd ever seen, as if I were its mother, or God admiring one of his sixth-day creations. Around me the river seemed intensely alive. Swallows flew from under a highway bridge as the light faded, dipping to the water. A wood duck swam past with her brood of ducklings, quacking her keep-away warning at me. Tiny riverine snails began their nightly journey upward through the forest of reeds.
Neither of us was native to that place, or entirely comfortable there. I was a weekend angler, born 3,000 miles away. The fish was probably reared in a barrel, fed Purina Trout Chow and chucked in the river by a fourth-grader. It didn't occur to me until later that one of my ancestors, in the dim European past, could have caught and eaten one of its ancestors. But there we were, and for the moment we both seemed "part of the natural world and competent to belong in it." I unhooked him and he was gone in a quarter of a second. I waded back to my car.