Transporting Problem Plants

CHAPEL HILL, N.C. - Whether they're anthrax, West Nile virus or some other species, biological organisms moving from one region to another are big news these days and pose not only environmental, but political and social concerns as well.

Transport of pest plants, which attract less attention because they don't usually make people sick beyond allergies, are nonetheless important, explained Peter S. White, director of the North Carolina Botanical Garden. Such plants can crowd out native species, radically alter their new environments and eventually damage agriculture and other economics and aesthetic interests.

"No matter where you are in the world - Japan, Australia, South America, North America, Hawaii - pest plant invaders are coming from other places to compete with and sometimes wipe out native species," White remarked.

Examples of problem plants are easy to find, he said. One is privet, an evergreen oriental shrub planted as hedges throughout the South that escaped and crowded out numerous indigenous species. Privet has formed impenetrable thickets and become almost the only plant in the understory of many Southern bottomland forests.

Another is the Brazilian pepper, which transpires so much water into the atmosphere compared with native vegetation, that is has lowered the water table in South Florida and made subsequent fires more intense and destructive.

A third is a shrub in Hawaii, Myrica, which adds excessive nitrogen to soil and kills off native plants able to tolerate low nitrogen by promoting growth of species that thrive on that element.

To raise awareness of this problem, White spearheads an international effort to protect native varieties form aggressive foreign flora. In 1996, the N.C. Botanical established a policy on alien species that present potential environmental threats. Two years later, it adopted strict guidelines governing distribution of seeds and plants to other institutions and people.

"Many gardens have what's called an index seminum, which is catalogue of seeds that they exchange with other gardens worldwide," White said. "Seed exchange has been a tradition for several centuries among gardens. One way plants are accidentally released into the environment is through this kind of trading and distribution."

In spite of this trading distribution, botanical gardens and nurseries should asses potential risks before introducing plants into the public domain, White advised. The best way to combat this problem, he explained, is to cease distributing known pest species, to replace them with non-invasive species and to raise public awareness about the problem.