Mounting a defense against biological invaders
by Tim Steury | © Washington State University
Whatever its impact on trade, the World Trade Organization has opened the doors to biological invasion, says Dick Mack. A professor of botany at Washington State University, Mack is a leading authority on invasive species and lead author of Predicting Invasions of Nonindigenous Plants and Plant Pests, a report recently published by the National Research Council.
Invasive species are those that are introduced, whether deliberately or not, only to find their new home much too accommodating. Whereas a plant might be an inconspicuous face in its home crowd, it could become the ubiquitous bully in a new ecological crowd with no defense against its aggressiveness. A prime example in the intermountain West is cheatgrass (Bromus tectorum), the focus of much of Mack's research. Introduced to the U.S. in the 19th century, perhaps as forage, cheatgrass has dramatically transformed the ecology, even the landscape, of much the West. Like most invasive species, cheatgrass has few predators or competitors in its adopted home and spreads across the landscape unchecked.
Other invasive species include the zebra mussel, which probably snuck into the county on the hull of an ocean ship and has since spread throughout the Great Lakes and beyond, crowding out native species, voraciously consuming the food supply of native species, virtually changing the entire lake ecosystem.
One estimate places the cost of invasive species from lost crops and control measures at $137 billion a year. Moreover, says Mack, "The indirect and ecological costs of losing native species because of attacks by or competition with invasive species may be incalculable."
So how do you keep every foreign species out of the country? You don't.
First of all, says Mack, not every foreign species is necessarily invasive. Most intruders simply can't make it on their own in foreign territory. It might be too cold or too dry, or the species may simply die before it's able to establish a viable breeding population.
Furthermore, most of this country's agriculture and much of its horticultural industry is based on introduced species. Most of these species are perfectly content in their allotted and cultivated space. However, a new cheatgrass or kudzu could wreak havoc with a vulnerable agricultural-or natural-niche.
Raising the specter of an unprecedented wave of invasion is the global movement toward free trade. Trade restrictions have often served double duty, protecting domestic industry and also keeping out potential invaders-or the invisible pathogens that might accompany imported produce or commodities.
Now those safeguards are gone, says Mack.
"We can't keep things out anymore based simply on intuition," he says. "The WTO has now said that for a member nation to keep something out, they have to have a scientific basis for doing so."
One example is the running battle between Japan and Washington over soft fruit. Japan has effectively kept Washington cherries out of its markets by claiming the threat of disease. Whether or not that threat is legitimate is not the point, as Japan used it as a trade barrier.
Now, says Mack, if Japan is going to turn back our cherries, the WTO requires a scientific basis for doing so. And that information requires expertise and money.
Introduction of species is currently overseen by APHIS (Animal and Plant Health Inspection Service). However, APHIS has resources to conduct spot checks of less than 2 percent of all incoming shipments at borders and air- and seaports.
In response to the increasingly open borders, Mack and his committee recommend a multiple-tier screening process at the border. "For some you give them a clean bill of health, they're already here, or there's nothing that we know about their background that's been a problem. Others would have to go through a filter process.
"There are different ways of going about this," he says. "One, there are categories of species that we could say are problems right off the bat."
For example, anything that's parasitic is a potential problem. Also, plants that have brightly colored fruits, seeds that are very attractive to birds, are potential problems, as birds are absolute experts at moving seeds about the landscape. Such plants cannot be automatically restricted, says Mack, but they should raise a red flag.
Mack then recommends a second line of defense, early detection and rapid response.
"Any invasion-whether zebra mussel or cheatgrass or yellowstar thistle-probably started out with a very small population. You could have stamped it out in an afternoon. "It's not insurmountable," he says. "But the task is, a lot of species are involved we've never encountered before, and we have to start doing it right now."
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