Officials and researchers based in Beijing are calling for an investigation of species from outside China that have been settling in the capital.

They must be properly documented to assess any possible negative impact on the environment and economy.

At present, 56 foreign species are known to be living in Beijing, with some dubbed "quite invasive," the Beijing Morning Post reported on Wednesday.

The newspaper said the alien flora and fauna include about 30 types of plants and more than 20 different animals.

Liu Quanru, an associate professor of life sciences at Beijing Normal University, told the newspaper that while these plants beautify the capital and some of the animals make delicious meals, the damage they may cause should not be forgotten.

There are no figures available to indicate the economic losses suffered by Beijing as a result of these uninvited guests, but national statistics show how destructive they can be.

According to Zhu Xiuyan, chief economist at the Ministry of Agriculture, more than 400 types of harmful alien plants cause annual losses of more than 57.4 billion yuan (US$7.1 billion) in the country's agriculture, forestry, animal husbandry and fishery industries.

Rhus typhina L, a type of tree that is prevalent in fields between the Fourth Ring Road and Fifth Ring Road, and Solanum rostratum or "buffalobur nightshade" with banana-shaped anthers on its flowers, have both been invading other plants' space.

Liu said they tend to absorb neighbors' nourishment due to their ability to spread even in barren places.

Amaranthus retroflexus L is a weed that is poisonous to some animals, while the weed Ambrosia tritida L threatens human health, the professor warned.

Though delicious, red crayfish, Ampullaria Crossean a type of mollusc and bullfrog are aggressive, grabbing the resources of other species.

Hyphantria Cunea, a type of moth known as "Fall Webworm," harms crops, Liu said.

Zhao Wenxia, an associate research fellow from the Chinese Academy of Forestry, told China Daily yesterday that scientific tests have shown "not all alien species are bad," citing some types of pine and locust trees that exist alongside other flora without damaging the environment.

"However, random spreading of unknown alien species to crop land or wild areas can be dangerous," she said.

Zhang Runzhi, a researcher at the Chinese Academy of Sciences, outlined measures that could help halt the random spread of harmful exotic species.

They include a pre-warning system for detecting invasive species, restrictions through quarantine and examination channels, eradication programs and blockades, and a legal framework for forbidding improper imports or transport means with a view to quick detection.

(China Daily November 4, 2005)