"Alien" pests wreak vast economic damage: U.N.

Alister Doyle, Reuters 21 May 09;

OSLO (Reuters) - Many governments are ignoring alien invasive species such as weeds or rats that may be causing $1.4 trillion damage a year to the world economy, the head of the U.N. Environment Program (UNEP) said on Friday.

"Time to get tough on alien species," UNEP head Achim Steiner wrote of insects, fungi, algae and other plants or animals often taken unwittingly by humans to new habitats, for instance in grain exports or in ships' ballast water.

Alien species may be "one of the least known threats to biodiversity and economies," he wrote in a statement to mark International Biological Diversity Day on May 22.

"Far too many countries have failed to grasp the threat or are far too casual in their response," he said, praising countries including South Africa for eradication programs or New Zealand for imposing tough customs controls.

He noted that one study put the cost of alien invasive species at $1.4 trillion a year -- almost 5 percent of the world economy -- split between losses from introduced pests in crops, pastures and forests and other environmental damage.

"The $1.4 trillion ... is still credible today," David Pimentel, a professor at Cornell University in the United States who led a 2001 study that came up with the number, told Reuters when asked if he might now revise the figure.

"I would rank agricultural weeds as number one and rats as number two," he wrote in an e-mail, asked to name what he reckoned the most destructive aliens, which can thrive in new habitats when freed of natural predators.

CHOKING HYACINTH

Among examples, Steiner pointed to the water hyacinth, a native of the Amazon basin with large violet flowers that has exploded in numbers since it was brought to Africa as an ornamental plant.

In Uganda alone, the hyacinths cause annual costs of perhaps $112 million, by forming a floating mat choking parts of Lake Victoria since 1990. Impacts include reduced fish catches and clogging propellers of ships.

And in sub-Saharan Africa, the invasive witchweed causes annual maize losses totaling about $7 billion a year, he said.

A project to curb invasive species in Europe, DAISIE, reckons there are more than 11,000 invaders of which 15 percent cause economic damage.

Aliens species "are spread from one continent to another via the global agricultural, horticultural and pet trades or by hitch-hiking lifts in ballast water and on ship's hulls," Steiner wrote, saying the "free ride" had to end.

"Globalization and international trade will, when the world economy recovers, increase the chances of new aliens to travel from one part of the world to another," he added.

(Editing by Jon Hemming)