Invasive species have reduced the output of rice, wheat, corn, sweet potato and lettuce in some areas of China by 19 to 63 percent, said Ding Jianqing, a researcher with the Wuhan Botanic Garden of CAS.

Water hyacinth is also posing a serious problem in rivers, lakes and ponds in south and southeast China's Guangdong and Fujian provinces, southwest China's Yunnan Province, east China's Jiangsu and Zhejiang provinces and in Shanghai, said Ding.

He said invasive plant species include both Chinese and foreign species, which have been introduced into an area where they are not native by human activities and have established a self-reproducing population in a local natural or artificial ecosystems. Some of them will change and even damage the natural ecosystem.

There are more than 280 foreign invasive species of plants and animals in China, with 18 aquatic plant species and 170 terrestrial plant species. Half of the species are form America and about one-fifth from Europe.

Statistics show that invasive species have caused a total economic loss of 14.45 billion U.S. dollars in China between 2001 and 2003, with direct and indirect economic losses accounting for 16.5 and 83.41 percent.

"A national monitoring system should be set up to observe economic losses that invasive species bring about to agriculture, forestry, stockbreeding, fishery and human health," said Ding.