Once rooted, eupatorium adenophorum can cover 100 percent of a hectare of grassland within two years, experts say.

Each hectare of grassland invaded by this toxic species produces no more than 1 kilogram of grass but 78,000 kilograms of eupatorium adenophorum.

This grass has a unique odor and toxin that makes it unattractive to cattle and sheep. However, a multitude of livestock have already died after eating this poisonous grass by mistake.

In the Liangshan Yi Autonomous Prefecture in Southwest China's Sichuan Province, this kind of grass now occupies more than 500,000 hectares of natural grasslands, accounting for over 20 percent of the total, according to statistics from the local government.

According to local government reports, the toxic grass costs the Liangshan region more than 20 million yuan (US$2.5 million) each year.

Xie Yan, an expert from the Chinese Academy of Sciences, said the grass originated from Central America and later spread to Southeast Asian countries like Myanmar and Viet Nam.

In the early 1950s, eupatorium adenophorum moved into Southwest China's Yunnan Province and created a disaster in the region.

Statistics provided by the Chinese Academy of Sciences show that eupatorium adenophorum had expanded to over 24.7 million hectares in Yunnan Province by the end of 1998, endangering a multitude of species there.

Xie pointed out this toxic grass will bring "a much bigger disaster" to the country if it spreads upwards to the northern parts of fertile Sichuan Province and even the central parts of the country.

Local governments in southern China have been fighting against eupatorium adenophorum for nearly a decade, exploring varied methods to counter its spread including regular weeding, using insects to control the growth and scattering chemical weedicide.

But none of these methods, all of which have negative side effects, can remove eupatorium thoroughly or at least control its expansion because of the toxic grass's hardiness.

Eupatorium adenophorum absorbs most of the nourishment in soil to support rampant expansion while producing a certain toxin that prevents other species from growing.

So far, no effective solution has been found to control the grass's spread.

China suffers from a number of alien, or invasive species - those that are found outside their natural range - which have wreaked havoc on local ecology.

These invasive species, which often are introduced by imported products or through natural mediums such as being blown in by the wind, reduce the number of native species and cripple the local ecology's ability to resist pests.

China boasts nearly 400 million hectares of grasslands which comprise 40 percent of the country's total land area.

However, 90 percent of the grasslands has been degraded and now is vulnerable to such biological invasion.

(China Daily November 13, 2001)