A Unified Defense Against Invasive Species

Long ago, the word "weed" crept into our vocabulary. It identified plants that grew where we didn't want them. Little did we realize, when we were young, that everything we learned was a weed was most likely an alien plant. These included the dandelion (Taraxicum officinale), ox-eye daisy (Chrysanthemum leucanthemum), white clover (Trifolium repens), and sweet honeysuckle (Lonicera japonicum) of the typical American suburban yard, brought from another continent intentionally or by accident. Homesick colonists brought their favorite flowers, medicinals, and edibles from the Old World. Lodged in the hooves of livestock were seeds from European pastures. By the time we recognized these plants as a problem, most Americans assumed they had always been here.

Now we recognize that invasives (alien species whose introduction causes or is likely to cause harm to the economy, environment, or human health) are not just an inconvenient affront to our landscaping efforts. Federal agencies spent $631.5 million on invasive species issues in FY 2000, with about $31 million coming from the Department of the Interior. The spread of invasives is estimated to cost Americans as much as $138 billion annually in crop, timber, and commercial fishing losses; human health problems; navigational (e.g., boating) interference; and damage to structures. Add to that the immeasurable damage caused by introduced organisms that injure or kill people or cause native species to go extinct, such as West Nile virus, smallpox, Africanized bees (Apis mellifera scutellata), and brown tree snakes (Boiga irregularis), and you get a problem of incalculable dimensions across North America.

In 1904, a fungus (Cryphonectria parasitica) from Asia that was first discovered in New York City cost us our precious American chestnut trees (Castanea dentata). These trees, giants among the eastern deciduous forests from Maine to Georgia and west to the Ohio River Valley, were a staple of the Appalachian settlers. Their straight trunks, sometimes branchless for 50 feet (15 meters), could grow to ten feet (3 m) in diameter and provided ample rotresistant lumber. The chestnuts nourished the locals and their livestock, provided cash from their sale to big cities by the box car, and fed such game species as bears, deer, squirrels, and turkeys. The blight swept through nine million acres (3.6 million hectares) of eastern woodlands, killing all adult chestnut trees in the United States. Now, only an occasional sprout appears from a stump, only to die when its bark is old enough to fissure. A few large healthy trees remain in Canada. The economic hardship to homesteaders can't be estimated, nor can the loss of the mast crop to wildlife.

Since the early Spanish explorers released pigs into Florida in the 1500s, alien species have been arriving on our shores virtually nonstop. An estimated 50,000 species of plants and animals have been introduced into the United States. More than 200 species, such as hydrilla (Hydrilla verticillata), were from the aquarium industry alone.

Approximately 35-46 percent of the species on the endangered species list are there partly or entirely because of the effects of invasive species (Wilcove et al. 1998). This doesn't even count species like the American chestnut, which functionally died out before the Endangered Species Act was passed and therefore is not listed. The threats posed by some species are obvious; for example, Norway rats (Rattus norvegicus) are decimating seabird colonies on islands in Alaska where mammalian predators were naturally absent. Zebra mussels (Dreissena polymorpha) are clogging intake pipes, encrusting ship hulls and propellers, and smothering native mussels. Other examples are subtle; endangered southwestern willow flycatchers (Empidonax trailii extimus) are heavily dependent on willows, which are being displaced by non-native saltcedars (Tamarix spp.) in the Southwest.

What is the Federal government doing to stop this flood of new introduced species and control the spread of existing ones? Many applicable laws, such as the Plant Quarantine Act, the Animal Damage Control Act, the Federal Plant Pest Act, National Environmental Policy Act, the Endangered Species Act, and the Federal Noxious Weed Act, have been in effect for decades. Since 1990, the Service and National Marine Fisheries Service have co-chaired the Aquatic Nuisance Species Task Force, established by the Non-Indigenous Aquatic Nuisance Prevention and Control Act. This Act was designed to prevent the introduction of and to control the spread of aquatic species and the brown tree snake. Furthermore, the Federal Interagency Committee for Management of Noxious and Exotic Weeds, focuses on integrated ecological approaches on Federal lands.

More recently (on February 3, 1999), President Clinton signed Executive Order 13112 on Invasive Species, which requires all Federal agencies whose actions may involve invasive species to join in the war to control their spread. The order created an Invasive Species Council that is chaired by the Secretaries of Interior, Agriculture, and Commerce, and includes the Departments of State, Treasury, Defense, and Transportation and the Environmental Protection Agency. On October 2, 2000, the Council released a draft National Invasive Species Management Plan outlining a coordinated strategy by the Federal agencies. This working document will be updated every two years.