The campaign manager of Greenpeace China said Thursday that transgenic poplars planted in northern China could pose an unpredictable threat to the environment.

Sze Pang Cheung said that their pollen could spread over great distances, allowing modified genes to spread to their unmodified relatives, a situation with unknown ecological results.

Experts and officials denied that the poplars, modified with genetic material from a bacterium, pose a threat, and that their use is bound to increase to meet surging demand for timber.

"There are many natural and artificial restraints in China to prevent them imperiling bio-safety," Lu Mengzhu, a chief scientist at the Chinese Academy of Forestry.

Poplars are one of China's most common species of tree. In the late 1990s poplar plantations stretched to 66,600 hectares, said Han Yifan, a senior researcher at the academy.

Lu, vice director of the academy's Research Institute of Forestry, said that the north's aridity means the trees stand little chance of reproducing or contaminating natural forests.

So far China has approved commercialization of two transgenic poplars, Poplar-12 and Poplar-741, Fang Xiangdong, director of the Ministry of Agriculture's Office of Genetically Modified Organism Safety, told China Daily. They have been engineered to resist leaf-eating insects.

Han, involved in GM tree studies since the early 1980s, said that so far only 200 hectares of insect-resistant Poplar-12 have been planted.

The natural pesticidal qualities of a bacterium called Bacillus thuringiensis are exploited to give the trees in-built resistance to insects, she said, and they are now scattered across areas including Hebei, Beijing, Liaoning and Ningxia.

Poplar-741 has been planted over less than three hectares in nine provinces and municipalities including Hebei, Beijing, Tianjin and Shandong, said Professor Zheng Junbao, who worked on its development.

Han and Zheng said both poplars are female with altered fertility, meaning they should be unable to release pollen into the air.

Lu said that a dry climate means that, if seed is produced, shoots would unlikely be able to survive. "Even in some rare cases where transgenic poplars yield sprouts, the chances are that the shoots will be eaten by sheep or cattle, or destroyed by farming activities," he said.

He added that they have been planted away from natural poplar forests, the majority of which lie in the west of the country.

Zhi Xin, who works for the State Forestry Administration's Genetic Engineering Safety Office, said he believed biotechnology research, including transgenic studies, should be encouraged. "In some ecologically fragile areas, it is very difficult to plant forests without using biotechnology."

"It is extremely difficult to control pests through conventional means, such as crossbreeding," Han said, adding that pesticides can have a negative environmental impact and insects can become resistant to them.

Huang Minren, from Nanjing Forestry University and vice chairman of the National Poplar Committee, said rapid economic development has stoked demand for lumber and fast-growing poplars will play an increasing role in meeting it.

Drifting pollen and vegetative propagation have been cited as major concerns by environmentalists, and there is disagreement among scientists about the risks involved. Many of them say pest-resistant transgenic plants could also promote resistance among the insects being targeted.

(China Daily April 1, 2005)