96 



trol but later caused unexpected harm. And some enter illegally — via first class mail 

 or in travellers' baggage. 



Because our actions are responsible for the majority of introductions, we have 

 many opportunities to make improvements. However, continuing changes in pat- 

 terns of international travel and trade may make this job more difficult. 



Almost every part of the Nation faces at least one highly damaging NIS — like the 

 zebra mussel, gypsy moth, or yellow star thistle. Now, NIS account for 25 percent 

 of U.S. fish; 17 percent are U.S. species moved outside their natural ranges. In a 

 number of States, non-indigenous plants account for 10 percent, 20 percent, or 30 

 percent of all plants. In Hawaii, at least one-half the State's wild plants and ani- 

 mals are non-indigenous. 



Certainly harmful non-indigenous species are in our backyards — ^Asian clams are 

 abundant in the Potomac River. European starlings and English sparrows are daily 

 companions — and responsible for declines of eastern bluebirds. Five non-indigenous 

 vines are toppling trees and eliminating wildflowers in Rock Creek Park and along 

 the C&O Canal and George Washington Parkway. A Maryland suburban nursery 

 sells several varieties of a wetland weed that, between 1987 and 1991, Minnesota 

 spent $500,000 to control. 



Economic Losses 



Unfortunately, Minnesota's expenditures are just the tip of an iceberg. From 

 1906-1991, just 79 NIS caused documented cumulative losses of $97 billion, mostly 

 in control costs and direct losses of marketable goods. For example, 



• In 1990, leafy spurge caused direct losses of livestock production of $110 million 

 over 1.5 million acres in the northern Great Plains. 



• The European gypsy moth caused $764 million in forest and other losses in 

 1981, its all-time high. 



• Removal of salt cedar along the lower Colorado River and restoration of indige- 

 nous vegetation is estimated at $45 to $450 million. 



Our $97 billion total includes only 14 percent of the species known to be harmful 

 and excludes one of the most costly groups — agricultural weeds. Thus, it likely rep- 

 resents only a fi^action of the total costs because so many species and kinds of pri- 

 mary and secondary impacts are uncounted. For example, economic impacts on in- 

 dustries other than agriculture, on human health, and on protection of natural 

 areas are seldom quantified. 



However, we can conservatively estimate that harmful NIS annually cause losses 

 of hundreds of million of dollars for agriculture, fisheries, forest, and rangelands. 

 Losses can reach several billion dollars or more in high-impact years. A worst case 

 scenario for 15 high-impact species adds another $134 billion in potential future eco- 

 nomic losses. 



Environmental Impacts 



Botany professor Clifford Smith drives the 12 miles to work at the Univer- 

 sity of Hawaii. His trip fi'om one side of the island to the other takes him 

 past what Hawaii's visitors see: a lush green paradise. But what Dr. Smith 

 sees are plants virtually all fi"om elsewhere. Only four native species grow 

 along that 12-mile stretch, and only one of those is moderately common. 



Like 80 many seemingly Hawaiian plants, populations of NIS can spread like 

 wildfire in new habitats where their former competitors, predators, pathogens, and 

 parasites no longer keep them in check. Asian clams are believed to have arrived 

 on the West Coast before 1924. As of 1986, these clams could have come from 6 of 

 the 14 states that the Committee represents. We each helped pay the estimated $1 

 billion in losses Asian clams caused the power industry in the early 1980s. 



At their worst, harmful NIS cause declines of indigenous species and contribute 

 to extinctions. The most destructive species also can transform entire ecosystems. 

 Some, like chestnut blight in eastern forests, radically shift species composition. 

 Other, like the zebra mussel, drastically modify an ecosystem's basic features. 



The popular press and environmentalists frequently stress the role of harmful 

 NIS in species extinctions but — except for islands — much of the supporting evidence 

 is anecdotal or equivocal. Over-emphasizing extinctions tends to divert attention 

 from other significant and unambiguous environmental damage. Biological commu- 

 nities can be radically and permanently altered without extinctions occurring. The 

 United States can experience a significant decline in the abundance, diversity, and 

 aesthetic value of its indigenous species, also without extinctions. Both kinds of 

 changes are common now: 



