© 1999 Streamline Publications

The newly-created National Invasive Alien Species Council faces an ecological challenge that, taken as a whole, exacts an annual cost of more than $122 billion. According to a study released in January, 1999 by Cornell University ecologists, more than 30,000 nonnative species—plants, mammals, birds, amphibians and reptiles, fishes, invertebrates and microbes—have been introduced to the United States since Columbus landed in North America.

Spreading Threat

Now, an estimated 5,000 imported plants, introduced as food, fiber or ornamentals, have escaped into the environment. A tenth of these have become weed pests and are displacing native wildlife habitat (LEAF-let, September/October 1998, Green Aliens).

One of these—the purple loosestrife (Lythrum salicaria) spreads at a rate of 284,050 acres a year. This one plant alone has reduced the biomass of 44 native plants in wetlands where it has taken over, thereby denying forage for the animals that depend on the native plants.

Star Power

Nearly 10 million acres of northern California grasslands have been overrun by the yellow star thistle, a native of Eurasia. According to Joe Di Tomaso, Department of Weed Science at the University of California, Davis, "The star thistle has become the most common plant in the state, and it is out of control." The weed will dominate an area quickly and out-compete native plants. There is belief among some scientists that the thistle attacks nearby plants with an "allelochemical" that stunts their growth. As if such behavior isn't bad enough, the star thistle is poisonous and, if eaten in large quantities in the spring before spines have grown, it can kill horses. The sharp spines are a danger to people and animals both when the plant is alive and after it dies.

State government estimates put the star thistle's coverage at 20 million acres—about one-fifth of California's area. The state legislature is studying possible methods that may be used to control the thistle.

Ants and Termites

Red fire ants are now making inroads into California after first getting established in Alabama in the early 1950s. These South American ants are believed to have arrived aboard ships. Now they are responsible for both human and animal deaths and damage to irrigation systems and farm machinery. Scientists are hoping to stall the spread of the ants using some natural predators and a parasitic fly larve.

The Formosan termite is a truly ravenous import from China. Typically huge colonies can cause a wooden home to collapse in two years. They attack dead and live wood and can penetrate soft metals with acid they produce.

Invisible Invaders

Over 100 accidentally-introduced microbes are major crop pests, accounting for $23 billion in annual losses. That is in addition to the $13 billion loss from native pathogens. Scientists estimate that non-indigenous plant pathogens cause about $2 billion in annual losses to lawns, gardens and golf courses. There is an equal loss in forest products.

While the bare numbers might suggest that the addition of 30,000 nonnative species to the North American environment might help achieve biodiversity, that conclusion would be difficult to support.

Indeed, many of these introduced species have been beneficial:

• 100 species of nonnative microbes are used in processing beer, wine and food
• 50 nonnative microbes control pest caterpillars, beetles and mosquitos
• corn and wheat are introduced crops.

Conversely, though, the success of those pest species—by their uncontrolled addition to the environment—reduce biodiversity. Fewer natives survive and thrive when invasive exotics, like purple loosestrife and the star thistle, take over.

Mounting the Defense

The National Invasive Alien Species Council's primary effort will be to bring some order to the policies and programs of disparate government agencies.

Elimination of many existing nonnative pest species may not be possible once established. The counter attack must consider both elimination and prevention, but success will be reflected in both environmental and economic terms.

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