More than ever before, exotic species are knocking at our state’s door. That’s a bad thing, right?
One day last winter, at Interstate State Park on the Minnesota–Wisconsin border, Scott Noland supervised a DNR crew spraying herbicide on a tangle of buckthorn. Spread mostly by birds that eat its berries, the European shrub grows into broad dense thickets, often overwhelming the underlying native plants and wild-flowers. “It’s definitely causing a problem,” says Noland, a DNR parks-area resource specialist. “It’s changing the natural communities. It’s starting to shade out the understory.”
Minnesotans are waging a war against non-native wildlife and plants. The state bans the import and transport of more than two-dozen “prohibited invasive species,” from Asian raccoon dogs to water chestnut. But hundreds of exotic species are already established here and potentially thousands more are at the door. Asian carp, European buckthorn, zebra mussels, purple loosestrife, Eurasian water milfoil, spiny water fleas, gypsy moths—as many as 50,000 animals, plants, and disease organisms have been introduced to the United States, including Minnesota.
Many are agricultural pests. Others threaten forests. Their management costs us more than $138 billion each year, according to one commonly cited estimate. Last year, a consortium of conservation groups warned Congress that “invasive species are one of the worst threats to native biodiversity, inflicting damage to ecosystems, and they are a great threat to our local economies. They can push native species to extinction, and harm a wide variety of industries, including fisheries and water supplies.”
But do they really? Do alien species threaten extinction and the “health” of ecosystems? Is that why we hate carp and starlings? Some biologists and scholars believe there’s something else at work here. While they don’t welcome exotic species at our lakes, woodlands, and farms, they don’t see the arrival of such organisms as a sign of environmental apocalypse, either. Yes, some exotic species cause problems. But others can be beneficial.
EXOTICS, ALIENS, non-natives—we use all these words to describe organisms from somewhere else. (If the species proliferate beyond control, we may call them invasive, a term that also applies to such natives as sumac—or white-tailed deer, for that matter.) But most organisms come from somewhere else. In Minnesota, wiped clean by the last glaciers, virtually everything that lives here walked, flew, crawled, swam, or drifted in from somewhere else.
When ecologists talk about exotics, they usually mean things that humans, especially Europeans, have brought with them. David Andow, a professor of insect ecology at the University of Minnesota, sums up the view this way: “The ones that get here naturally are somehow more legitimate.”
The distinction makes sense. For millennia, animals, plants, and microorganisms had only modest success in surmounting such natural barriers as oceans, deserts, and mountain ranges. Ecosystems flourished with only occasional intrusions by new organisms. But then came fleets of ocean-going ships from Europe, facilitating vigorous trade that shuffled animals, crops, pests, diseases, and other organisms across entire oceans and continents. Suddenly, Old World species flooded the New World (and vice versa).
Many species were introduced to North America deliberately. The ring-necked pheasant, originally from Asia, proved adaptable and popular with hunters. The apple, native to Kazakhstan, cultivated in Europe, and spread across the United States by an itinerant named John Chapman, was packed into American lunches and baked into American pies. Their environmental impacts—not to mention their effects on U.S. agriculture, business, and tourism—were widely considered a boon.
But other non-natives were a different story. The prolific carp had a habit of stirring up sediment and is reviled to this day. Kudzu, imported from Japan as a decorative plant and then promoted as a tool to combat soil erosion, became the vine that ate the South.
Other species were clearly unwanted from the get-go and their damage has been lasting: We’re still paying the consequences of importing rats, white-pine blister rust, and Dutch elm disease, which has cost urban forest departments across the country an estimated $100 million a year simply for tree removal. Controlling weeds (most are exotics) costs U.S. farmers, ranchers, and homeowners billions of dollars a year.
POPULAR ACCOUNTS of exotics rely on well-worn clichés. A recent opinion piece in the New York Times described several Asian carp species collectively (they apparently all look alike) as a “voracious invader” that “eats half its body weight in food in a day... [and has] outcompeted all native species.” But native fish of equal size consume roughly the same amount, depending on what they eat. And though many Asian carp species inhabit the Mississippi, the effect on native species isn’t clear.
National Geographic tells of an angler in Maryland who “caught an air-breathing, land-crawling, voracious predator.” The fish was a northern snakehead, no more or no less voracious or predatory than any native northern pike or walleye of similar size (though the snakehead’s ability to crawl on land certainly gives people the creeps).
Banu Subramaniam, a professor at the University of Massachusetts–Amherst, says the “xenophobic rhetoric” used to describe exotic species echoes the heated language used in discussions about immigration in the United States. There are worries about “invasions” and uncontrolled “reproduction.” Foreigners are blamed for disruption and disorder, overshadowing problems of our own making. Such words and concepts distort our view, and even our management, of exotic species. “The solution becomes stopping these alien species and to focus on them rather than [focusing] on things such as development and what we are doing about habitat,” says Subramaniam. Blaming exotics for environmental problems, she notes, mostly “adds to the hysteria without doing anything that is actually going to help.”
For a half-century, ecologists believed that ecosystems were tightly knit, highly adapted organizations. Exotics weren’t part of this evolution. So an ecosystem free of aliens was healthy. Invaded ones were not.
But now some ecologists disagree. Communities of plants and animals are not tightly organized systems, honed by eons of evolution, as scientists once thought, says Mark Davis, professor of biology at Macalester College. “It is clear that functioning ecosystems and communities can be established quite quickly even with species that have not shared a long evolutionary history.”
Surely, if exotics are so disruptive and harmful to the ecosystem, scientists can somehow quantify how they differ from natives or to tell one from the other on the basis of how they play with others, so to speak. But when you get down to it, says Mark Sagoff, an environmental-ethics scholar at the University of Maryland, “They can’t, and no one could tell how you would tell the difference.” In this respect, ecologists are a lot like wine experts who fail in a blindfolded taste test to distinguish a cheap California wine from the expensive French. While many ecologists vigorously disagree, others concede that little distinguishes exotics from natives except their history. “I have always argued,” Mark Davis wrote in a recent e-mail, that it would be “unlikely that an ecologist could tell the difference.”
For example, argues Sagoff, if we didn’t know that zebra mussels were introduced to Minnesota waters by humans (and therefore are unnatural), we would believe them to be a vital benefit to the ecosystem. While they clog water intake pipes and smother native mussels, they also filter algae and nutrients—in effect, removing human-caused pollutants.
Both Sagoff and Davis point out that as prolific and disruptive as some exotic species can be, they haven’t driven native species to extinction, except in small insular environments, such as landlocked lakes and islands.
AT U.S. BORDERS and international airports, government inspectors check our luggage for farm products that may contain diseases or pests. In summer, the DNR chides us to scrape weeds off our boats to prevent the spread of Eurasian water milfoil as we travel from lake to lake, river to river. This policing has its costs—not just the expense of staffing, but also in delaying the introduction of species that may prove beneficial. How much regulation can we afford and where should we focus our efforts?
Davis suggests starting with “nonnative species that threaten human health.” Good examples are West Nile virus and avian influenza. Next, he says, are agricultural pests and aliens that threaten economic harm, such as soybean aphids, gypsy moths, and emerald ash borers. Also important are a few creatures that are “truly threatening native species with extinction,” though none seem to pose such as threat in Minnesota for the time being.
“Last on the list, in my view, are other species causing other ecological impacts that we don’t like,” Davis says. “Whether allocating resources to such things as pulling up buckthorn is a good thing…depends on what is valued in the landscape and how much the community is willing to spend to make the landscape the way they want it.”
At the University of Minnesota, a program supported by the National Science Foundation is recruiting students to research the effects of globalization on the spread of exotic species. Which species are potentially beneficial? Which are likely to harm existing crops or native species? Which are likely to reproduce and spread? If a particular species, such as an insect, is introduced to control another species—a pest—is it likely to solve the problem or create a new one? Many ecologists concede they still have trouble answering these questions. “We’ve gotten a lot better at predicting whether a new species that arrives here will survive and spread,” says Anne Kapuscinski, a University of Minnesota fisheries professor, “but we still have a lot to learn in order to make good predictions about what effect it’s going to have.”
Meanwhile, new species of Asian carp are swimming up the Mississippi. Minnesota officials have asked Congress for $4 million to start building a barrier of high-pressure bubbles to hold the carp at bay. Kapuscinski is skeptical. “A fence across the Mississippi River? I’m not convinced that will work.” It’s not even clear, she says, what harm the carp will cause. “I’m not a fan of them coming here, but before we overreact, we need to think through what is the most strategic way to use our limited resources.”
Greg Breining is a frequent contributor to Minnesota Monthly.