CHAPEL HILL – 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, says Dr. 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 economic 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,” said White, a University of North Carolina at Chapel Hill biology professor. “Kudzu, sometimes called ‘the plant that covered the South,’ is the poster child of aggressive invaders, and it is by no means the worst.”
White spearheads an international effort to protect native varieties from aggressive foreign flora. Earlier this month, with colleagues Sarah Reichard and John Randall of the universities of Washington and California, and Pat Duncan Raven of the Missouri Botanical Garden, he helped mount a unique conference in St. Louis titled “Linking Ecology and Horticulture to Prevent Plant Invasions.” Experts from Europe, Africa, Australia and elsewhere met at the St. Louis garden, the nation’s premiere such facility, whose director, Peter Raven, hosted the event with London’s Kew Gardens staff.
“We organized the conference around plant invaders and specifically plants brought purposely through horticulture to new areas,” he said. “The aim was to get the horticulture industry to adopt voluntary codes of conduct as a way of trying to turn down the volume of potential pest species released into the environment.”
In 1996, the N.C. Botanical Garden was the first North American garden to establish 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 a 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 1998, we were the first garden to purposely restrict our distribution of plants that might be invasive elsewhere.”
The following year, the N.C. Botanical Garden released what White called the “Chapel Hill Thesis,” a statement of eight principles aimed at persuading horticulturists to be more responsible about such an important environmental issue.
“Like Martin Luther, who nailed his ‘thesis’ to a church door, I nailed our statement to a tree, an alien invader princess tree from Japan,” he said. “The statement became the inspiration for the St. Louis meeting and led to a series of five codes we call the Missouri Consensus.”
Representatives came from such organizations as the American Association of Botanical Gardens and Arboreta, the American Association of Landscape Architects, the American Nursery and Landscape Association, the Garden Clubs of America and the Federated Garden Clubs of America.
“This issue has similarities to air pollution and second-hand smoke in the sense that the activity occurs in one place and time, but the effects are felt later somewhere else,” White said. “The voluntary codes we developed cover actions by botanical gardens, plant nurseries, landscape architecture, public gardeners and governments.”
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 it has lowered the water table in South Florida and made subsequent fires more intense and destructive.
A third is brome grass of the American Southwest, which alters the way fires sweep through the ecosystem. Still another 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.
“Examples of invasive aquatic weeds include Salvinia, duckweed, water millfoil -- an underwater feather-like plant that totally clogs some northern lakes -- and water hyacinth, which totally covers some ponds and rivers,” White said. “Species like these affect businesses and recreational facilities and cost society millions of dollars to control.”
Although identical in spirit, principles in the various codes developed at the conference differ somewhat and are tailored to each group’s specific roles, he said. For example, home gardeners are encouraged to ask about plants’ invasive behavior when buying from nurseries.
Botanical gardens and nurseries are encouraged to assess potential risks before introducing plants into the public domain. Three principles all codes have in common are to cease distributing known pest species such as Chinese wisteria, to replace them with non-invasive species and to raise public awareness of the problem.
“The conference was a great, upbeat meeting,” White said. “Participants from gardens, nurseries, landscape architecture and the gardening public all contributed constructively to a consensus. We think it represents a real landmark in the history of this major environmental concern, and we are proud the Chapel Hill Thesis played such a large role in inspiring it.”
Materials provided by University Of North Carolina At Chapel Hill. Note: Content may be edited for style and length.
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