Are invasive species really that bad for the environment?

News and commentary about environmental issues.
Nov. 4 2009 1:30 PM

Don't Sweat the Invasion

Why foreign plants and animals may not be that bad.

Illustration by Charlie Powell. Click image to expand.

Tamarisk, a Eurasian shrub, is your classic invasive species—designated one of America's "least wanted" plants by the National Parks Service. In recent decades, it has spread along Southwestern riverbanks, replacing native trees such as willows and cottonwoods. For nature lovers in the region, tamarisks (also known as saltcedars) rank somewhere between Land Rovers and James Inhofe. Measures to thwart them include burning, herbicides, and "tammy whacking" (physical removal sometimes done by freelance volunteers). A few years ago, the USDA let loose thousands of leaf-eating Asian beetles in order to sic them on tamarisks, which die from the defoliation.

But these efforts to oust the intruder have encountered a glitch. It turns out that a charismatic endangered bird—the southwestern willow flycatcher—is known to nest in the offending shrubs. Last March, the Center for Biological Diversity sued the government, charging that indiscriminately killing tamarisks jeopardizes the flycatcher. A recent article in the journal Restoration Ecology goes even further in the weed's defense. Tamarisks are widely thought to hog water and drive out other vegetation, but the authors dispute that theory. In their view, the newcomer may just be better suited than the natives to an environment altered by human activities.

These controversies highlight a broader debate within "invasion biology," a field that emerged in the 1980s. Some scientists—such as Matthew Chew, Dov Sax, and Mark Davis—are challenging what they consider old prejudices about "alien" species. They point out the inevitability of change and the positive roles that non-natives can play in ecosystems, while describing eradication projects as often wasteful and even counterproductive.

Advertisement

The outlook of the more traditional camp goes something like this: While most non-natives are harmless, a minority—about 10 percent—cause serious damage. Some pose threats to human health (H1N1 is an invasive species), while others, such as agricultural pests, wreak economic havoc. A third category dramatically changes landscapes. (Think kudzu, the creeping vine that has conquered the Southeastern United States.) And since these effects are unpredictable—sleeper species can seem benign for decades—all exotics are suspect. The hard-liners promote a "guilty until proven innocent" approach to biological foreigners, including a strict "white list" of those allowed to enter each country. As globalization accelerates the movement of species, vigilance is more important than ever. Climate change adds another wildcard, making the behavior of organisms all the harder to foresee.

Now a growing contingent of scientists is advocating a more neutral attitude. Certainly, they say, non-native plants and critters can be terribly destructive—the tree-killing gypsy moth comes to mind. Yet natives such as the Southern Pine Beetle can cause similar harm. The effects of exotics on biodiversity are mixed. Their entry into a region may reduce indigenous populations, but they're not likely to cause any extinctions (at least on continents and in oceans—lakes and islands are more vulnerable). Since the arrival of Europeans in the New World, hundreds of imports have flourished in their new environments. Common wildflowers such as Queen Anne's lace and certain kinds of daisies are "naturalized" aliens. The storied apple tree originally hailed from Asia.

Even when species are destructive, there's the tricky question of what to do about them. We may all agree that a particular plant or animal is loathsome, but eradication isn't innocuous. Such plans tend to cost millions of dollars and often rely on toxins that bring collateral damage to other species. Biological solutions—like leaf-eating beetles and root-boring weevils—are usually considered more benign, but as the case of the tamarisk shows, they, too, can pose problems. Once an ecosystem has absorbed a new species, any targeted intervention is likely to have significant ripple effects. 

The past few years have also seen active debates about the field's terminology. Some criticize the term "invasive" as too value-laden and imprecise. One widely cited definition comes from a 1999 executive order, issued by President Clinton, that aimed to ward off "alien species whose introduction does or is likely to cause economic or environmental harm or harm to human health." But what exactly constitutes "environmental harm"? It's easy to see when a power plant is hemorrhaging pollutants into the air and water—but how do you make the call when the agent of harm to nature is … also nature? Critics such as Mark Davis say we need to distinguish "harm" from "change." If an introduced species causes natives to become less abundant, does that constitute harm? Many people would say yes, but Davis doesn't think so. 

TODAY IN SLATE

Politics

The Democrats’ War at Home

How can the president’s party defend itself from the president’s foreign policy blunders?

Secret Service Director Julia Pierson Resigns

Piper Kerman on Why She Dressed Like a Hitchcock Heroine for Her Prison Sentencing

Windows 8 Was So Bad That Microsoft Will Skip Straight to Windows 10

Homeland Is Good Again! For Now.

Politics

Cringing. Ducking. Mumbling.

How GOP candidates react whenever someone brings up reproductive rights or gay marriage.

Music

How Even an Old Hipster Can Age Gracefully

On their new albums, Leonard Cohen, Robert Plant, and Loudon Wainwright III show three ways.

The U.S. Has a New Problem in Syria: The Moderate Rebels Feel Like We’ve Betrayed Them

We Need to Talk: A Terrible Name for a Good Sports Show by and About Women

Trending News Channel
Oct. 1 2014 1:25 PM Japanese Cheerleader Robots Balance and Roll Around on Balls
  News & Politics
Crime
Oct. 1 2014 4:15 PM The Trials of White Boy Rick A Detroit crime legend, the FBI, and the ugliness of the war on drugs.
  Business
Moneybox
Oct. 1 2014 2:16 PM Wall Street Tackles Chat Services, Shies Away From Diversity Issues 
  Life
Gentleman Scholar
Oct. 1 2014 4:55 PM Blood Before Bud? Must a gentleman’s brother always be the best man at his wedding?
  Double X
The XX Factor
Oct. 1 2014 4:05 PM Today in GOP Outreach to Women: You Broads Like Wedding Dresses, Right?
  Slate Plus
Behind the Scenes
Oct. 1 2014 3:24 PM Revelry (and Business) at Mohonk Photos and highlights from Slate’s annual retreat.
  Arts
Brow Beat
Oct. 1 2014 3:02 PM The Best Show of the Summer Is Getting a Second Season
  Technology
Future Tense
Oct. 1 2014 4:46 PM Ebola Is No Measles. That’s a Good Thing. Comparing this virus to scourges of the past gives us hope that we can slow it down.
  Health & Science
Science
Oct. 1 2014 4:03 PM Does the Earth Really Have a “Hum”? Yes, but probably not the one you’re thinking.
  Sports
Sports Nut
Sept. 30 2014 5:54 PM Goodbye, Tough Guy It’s time for Michigan to fire its toughness-obsessed coach, Brady Hoke.