Invasive threats to the American homeland

Parameters, Spring, 2004 by Robert J. Pratt

"Defending our nation against its enemies is the first and fundamental commitment of the federal government. Today, that task has changed dramatically. Enemies in the past needed great armies and great industrial capabilities to endanger America. Now, shadowy networks of individuals can bring great chaos and suffering to our shores for less than it costs to purchase a single tank."

--President George W. Bush, National Security Strategy of the United States, September 2002

Before 11 September 2001, when American leaders prepared for war they envisioned enemies using bombs, tanks, guns, military force, and other traditional armaments. The attacks on that fateful day forever changed the way the United States and the world would view the nature of war. Using four hijacked commercial jetliners, terrorists attacked the United States, killing some 3,000 men and women. This surprise attack was not a symmetric attack, but an asymmetric one. Furthermore, a non-state entity conducted this attack at a relatively low cost of under $500,000. (1) However, that may have been just the beginning. The success of the attack, and the devastation inflicted on the nation at a relatively low cost, will doubtless inspire our adversaries to continue to employ asymmetric methods to threaten and weaken the United States. Among those methods may be the introduction of an invasive species, a disease pathogen, or some other biological threat.

Introducing Invasive Species

Presidential Executive Order 13112 defines invasive species as "a species that is (1) non-native (or alien) to the ecosystem under consideration and (2) whose introduction causes or is likely to cause economic or environmental harm or harm to human health." (2) An invasive species can be a microbe, plant, animal, or other organism. These invaders may be moved from their natural habitat and introduced to a new environment either purposefully or by accident. The simple act of moving a nonindigenous species to a new habitat does not make it invasive. For centuries people have moved species around the world for agricultural and other purposes. Examples of noninvasive species are numerous--from livestock to grain crops to ornamental plants. Most of these species are nonthreatening and benign, but some species can be threatening because of their adverse impact on their new environment. Their introduction may threaten the natural balance in the ecosystem because of their competitive nature, may threaten human and agricultural plant and animal health, and may cause economic damage through the cost of controlling or managing the species. These threatening species are "invasive species."

Historically, the introduction of an invasive species has not been intentional, nor has it been the purposeful act of an adversary to weaken or attack the United States. Typically, invasive species have been accidentally introduced when they were imported for ornamental purposes, escaped from captivity, or were carelessly released into the environment. Often invasive species arrived by means of ocean vessels' ballasts, or in pallets, produce, or plant nursery stock. Additionally, animals and other agricultural products have transported them to the United States. (3)

The new species may flourish and rapidly expand, as they typically have few or no natural enemies in their new environment. Parasites, pathogens, or predators that would inhibit or limit their spread may be few or nonexistent. In addition, the new environment often provides a better medium for growth and reproduction than the species' original surroundings. (4) With these advantages, native species may find it difficult to compete and survive against a new, more energetic and prolific neighbor.

A 1999 study by Cornell University estimated that approximately 50,000 foreign species have invaded the United States since the 1700s, and the number in the last 30 years has increased at an alarming rate. (5) Ten to 15 percent of these foreign species are considered threatening or invasive. Their effects range from being a nuisance to causing economic damage, health problems, and endangerment of native species; 42 percent of "endangered" or "threatened" species are at risk because of invasive species. (6) One hundred million acres of the United States are covered by invasive plants, and the rate of spread is 14 percent per year--an area twice the size of Delaware. (7) Since 1985, the US Department of Agriculture's Animal and Plant Health Inspection Service (APHIS) has intercepted 7,400 species of plant pests at our country's borders. (8) The US Department of Transportation estimates that every day 4,600 acres of land are colonized by invasive species in the United States. (9) Every 60 seconds, oceangoing vessels release 40,000 gallons of foreign ballast water in American waters, often releasing invasive species. (10)

Historical Examples

History offers many examples of invasive species damaging their new parent environment. Four revealing examples include the invasion of multiple species in San Francisco Bay, the glassy-winged sharpshooter, "foot-and-mouth" disease (aphthovirus), and the brown tree snake.