China has taken preventive measures to control the number of invasive species in order to maintain a safe and healthy ecological environment.

A three-year national census of invasive species is looking into the density, distribution and damage caused by invasive species in China. It was proposed by the Ministry of Agriculture and Rural Affairs with other ministries and administrations last year and is to end by 2023.

Mao Runping, who got her doctorate in invasion biology and now works at the Wuhan Institute of Landscape Architecture in Hubei province, is a member of the Wuhan expert group that is working on the national census.

"Invasive species usually enter one country from another through introduction for the purpose of animal feeding and as ornamentals, or introduction by accident during trade, tourism or war.

"In a foreign country, the species can reproduce quickly because no natural enemy species can restrict it like it does in their original environment," she said.

She said, for example, that in the 1930s, alligator weed originating from South America was introduced into China as swine feed. However, later it was found to have good reproductive ability and got out of control.

Canada goldenrod was introduced as an ornamental plant but later it was realized that it could produce a huge number of seeds, and is not easy to uproot, she said.

These weeds will inhibit plants, especially those underwater, from getting enough sunlight, moisture, fertilizer and space to grow, she said.

"Concerning regulations, Australia and New Zealand did better in the beginning since many invasive species have caused greater ecological disasters to them. Asia and Europe have been following the trend but at a slower pace compared with countries in the southern hemisphere," she said.

China has seen increasing numbers of invasive species and damage caused by them.

According to the 2020 Communique on the Status of China's Ecology and Environment released last year, more than 660 invasive species have been found across the country, of which 71 pose or are potentially a threat to natural ecosystems.

For example, monitoring data from the Ministry of Agriculture and Rural Affairs showed that red fire ants imported from South America have spread to 12 provinces, causing damage to crops.

"Human activities have greatly sped up species reaching new environments. A long time ago, it may take hundreds of years for wind or water to bring new seeds to an area. Human activities cut the time to just a few years, enhancing the chance for invasive species to travel and cause damage to the ecosystem. Curbing the trend is urgent," Mao said.

Last year, the Biosecurity Law came into force, defining the invasive species in order to protect biodiversity, and urging strengthened monitoring and treatment of the species.

In May, the central government released the Measures for the Management of Invasive Species, calling for preventing such species from the root.

"Species assessed to pose a risk of invasion shall not be allowed to enter the country.

"Treatment measures for them include physical control, artificial removal, biological control, chemical control and other preventive methods," it said.