6 May 1998

US Warning On Invasive Plants

Before Columbus, seeds travelled slowly, in the baggage hold of migrating birds. Now, with international travel and commerce, the United States is being swamped by hardy newcomers. "The invasion of noxious weeds has created a level of destruction to America's environment and economy that is matched only by the damage caused by floods, earthquakes, wildfire, hurricanes and mudslides," says Secretary of the Interior Bruce Babbitt. "This is truly an explosion in slow motion."

A multi-agency committee in the United States will issue a report this summer on the devastation caused by immigrant species, in a book titled Invasive Plants: Changing the Landscape of America. The report claims that non-native species comprising between 8 and 47 per cent of the total flora in most states, are invading western wildlands at a conservatively estimated rate of nearly 5000 acres per day.

Termed "biological pollution", the invaders behave like a cancer: "It starts with a single individual or seed and then is carried to other places by people or nature where nodes get established or proliferate, eventually affecting entire ecosystems," explains Thomas Casadevall, acting director of the U.S. Geological Survey.

Introducing plants into an environment in which they did not evolve means they have no natural enemies to limit their reproduction. They spread easily, jeopardizing native - and often rare - species, as well as the animals that depend on them for food and habitat.

Statistics compiled by the International Union for the Conservation of Nature indicate that 1 in 8 plant species globally are threatened with extinction. Robert G Stanton, National Park Service director says: "Although vast fields of flowering plants may look attractive to the visitor, many of these plants are actually silent, green invaders, slowly destroying the native, living natural heritage the parks are supposed to preserve." Plants such as kudzu, Japanese honeysuckle and the aptly named mile-a-minute weed are completely draping forested areas.

The report's authors lay the blame on increasing human population, disturbing the land through travel, farming and other commercial purposes. The authors pull back from providing a clear solution to the problem, perhaps because of the powerful agricultural lobby and the immense difficulty in implementing an effective national strategy. Perhaps finely-targeted systemic or genetic weedkillers are the answer to the problem, but what will the organic lobby say? Rachel Carson's Silent Spring may come to pass - through neglect of chemical treatment rather than because of it.