Many harmful invasive species impair biolog- 
ical diversity by causing population declines, 
species extinctions, shifts in predator-prey 
dynamics, shifts in species niches, changes 
in habitat, and reductions in ecosystem com- 
plexity. The establishment of invasive species 
destroys the uniqueness of habitats, making 
all areas biologically alike. 
In 1993, the Congressional Office of 
Technology Assessment reported that devas- 
tating invasions of plants, insects, aquatic 
invertebrates, pathogens, and other organ- 
isms have changed ecosystems and perma- 
nently diminished the biological diversity 
associated with them. Examples of these in 
the United States include melaleuca (a wet- 
lands tree), Sypsy moth, spruce bark beetle, 
zebra mussel, larch canker, chestnut blight, 
and Japanese beetle. Concern about the 
incursion of other harmful invasive species, 
such as the brown tree snake, is increasing. 
Conservation experts have found that in 
the United States, invasive alien plant 
infestations cover 100 million acres and are 
spreading at a rate of 14 percent per year. 
Recent studies have also revealed that the 
San Francisco Bay is invaded by a new 
exotic species on the average of once every 
12 weeks. 
Naturally occurring movement of species 
into the United States is uncommon. Most 
invasive species arrive in association with 
human activities or transport. Species can be 
brought into the country and released inten- 
tionally, or their movement and release can 
be an unintentional byproduct of cultivation, 
commerce, tourism, or travel. 
Many species enter the United States each 
year as contaminants of commodities. 
Agricultural produce, nursery stock, cut 
flowers, and timber can harbor insects, 
plants pathogens, slugs, and snails. Weeds 
continue to enter the United States as seed 
contaminants. Plant pathogens arrive as 
unintended contaminants of plant materials. 
Fish and shrimp pathogens and parasites 
have been introduced into the United States 
on infected stock for aquaculture. Crates and 
containers can harbor snails, slugs, mol- 
lusks, beetles, and micro-organisms. Military 
cargo transport also brings in harmful 
species, such as the Asian gypsy moth and 
the brown tree snake. Ballast water that is 
released from ships as cargo is loaded or 
unloaded has brought in several destructive 
aquatic species. 
A 1999 Executive Order mandated the 
enhancement and coordination of Federal 
activities to control and minimize the eco- 
nomic, ecological, and human health 
impacts caused by invasive species. That 
Order also established a National Invasive 
Species Council to oversee a management 
plan detailing the goals and objectives of the 
efforts of the involved Federal agencies. 
APHIS is an active participant on the 
Council since the basic work performed by 
APHIS already helps to keep pests and dis- 
eases that threaten our biological resources 
from being introduced into and becoming 
established in the United States. 
Both ecosystems and the individual species 
within them are vulnerable to invasive pests 
and pathogens. APHIS is responsible for 
excluding and managing invasive species 
that can potentially affect plant and animal 
health, either directly or indirectly. Through 
its activities, APHIS protects not only agri- 
culture but also forest, rangeland, and wet- 
land ecosystems. APHIS works closely with 
USDA's Forest Service and the U.S. 
Department of the Interior’s Bureau of Land 
Management, National Park Service, and 
U.S. Fish and Wildlife Service. APHIS con- 
trols certain types of invasive species and 
vertebrate pests that affect native ecosystems 
rather than agricultural resources. Other 
activities focus on protecting and managing 
endangered species as well as migratory bird 
populations. 
As more and more 
countries enter the 
world marketplace, 
the United States 
needs to look 
forward in order 
to prevent the 
continued 
introduction of 
invasive species 
into the country. 
Future Trends in Agncultural Trade 
