Nonnative Invasive Species

Nonnative invasive species, also called invasive exotic species or biopollutants, are important threats to forest health in the southern Appalachians. Invasive plants (kudzu, privet, Japanese honeysuckle), invasive insects, (European gypsy moth, hemlock wooly adelgid), and invasive pathogens (chestnut blight, Dutch elm disease, dogwood anthracnose) have become established in the region; they are affecting watershed integrity and sustainability, biological diversity, economics, and human health and safety.

Introduction and Spread of Nonnative Species

As many as 50,000 nonnative species are estimated to have been introduced; of these, at least 4,500 are established. Approximately 675 species in the United States cause severe economic or environmental harm. Of 370 identified nonnative invasive species of insects in the United States, 17 are highly invasive to forests and have caused or could cause serious environmental and economic impacts. On National Forest System rangelands, 6 to 7 million acres are infested with noxious weeds and invasive plants. Infestations are increasing at an estimated rate of 8% to 14% per year. Estimates of the economic losses due to nonnative invasive species are as high as $125 billion per year (USDA Forest Service 2000).

The unintentional introduction of nonnative invasive species into the United States is a byproduct of travel, immigration, and global commerce. Invasive species may enter:

• In timber, produce, seeds, or nursery stock.

• In wood used for packing crates. The Asian gypsy moth and the Formosan termite were introduced in this manner.

• In freight via railway cars, tractors, aircraft, automobiles, bicycles, ships, and other vehicles.

• In ballast water dumped from ships.

• On hiking boots, camping equipment, and lawn furniture.

• In or on soil.

Although State and Federal plant quarantine laws slowed the rate of introduction of insect pests and plant pathogens after 1912, rates have been higher throughout the 20th century than in the preceding one (USDA Forest Service 2000). Once introduced, the domestic spread of invasive species occurs naturally, and often with (intentional or unintentional) human assistance. Once in a new environment, a nonnative invasive organism may simply die; it may become established with little noticeable effect; or it may become established and spread, often with devastating environmental and economic results. Populations of many nonnative invasive species expand rapidly upon reaching new habitats where the competitors, predators, pathogens, and parasites that formerly kept them in check are no longer present. Without natural enemies to limit reproduction and spread, some nonnative species grow, adapt, multiply, and disperse to unmanageable levels over time (SAMAB 1996).

Negative impacts of invasive species

Established nonnative species become harmful by destabilizing existing ecosystems. Deforestation or conversion of tree species or both may occur. Riparian forests may be altered, causing deterioration of water quality and wildlife habitat. Fire danger may increase. Habitats of indigenous species may be modified and degraded. In fact, nonnative invasive species are the second largest cause of decline in 42% of the threatened and endangered species listed today. Only habitat destruction is a greater cause of loss or decline for native species (SAMAB 1996).

• Invasive species control describes basic strategies available for solving exotic species problems.