Only trees in downtown areas and major parks get chemical injection

Problematic plumes from millions of willow and poplar trees in Beijing began falling off last week but city officials say there is no citywide plan to use technology to bring the "natural ecological process" under control.

"The government is not promoting technologies to stop catkins. Such things are only used in populated areas including parks and residential areas," said Li Xuan, a press officer with the from the forestry bureau.

Fluffy catkins, from blooming willows and poplars, are an annual annoyance for many people who suffer from allergies and respiratory diseases. They also reduce visibility on city roads.

Official statistics show 128 million "female" willow and poplar trees - about 40 percent of the total number - are responsible for producing catkins.

Fewer than 1 percent of the 128 million trees have been treated with chemicals or surgery to stop them producing catkins. Some media reported the government has not managed to treat all trees because of a lack of funds and reported that it would cost 56 million yuan.

"It's expensive but this is not the key reason we don't promote it on a large scale," Li told METRO. He said the production of catkins is a normal ecological phenomenon once the average temperature reaches 15 C and shows that the trees have begun their blossoming period.

"It is against the laws of nature if we force them to change," Li told METRO.

Yu Shunli, an associate research fellow from the ecology center of the Institute of Botany with the Chinese Academy of Sciences, said catkins contains no pollen and thus are incapable of aggravating people's allergies.

"Catkins only carry the seeds from the trees," said Yu. "Allergies suffered by many residents can be caused by mildew and pollen from other flowers, which are all active in the spring."

The snowy-looking tree blossoms are usually a feature in Beijing in late April, but the unusually warm weather this spring has pushed the period forward by a couple of weeks.

Since 2003 the municipal government has been investing in research looking for ways to control catkins, resulting in two ways being put into practice since 2008, according to Che Shaochen, an engineer from the Beijing Institute of Landscape Science.

Che said one solution is to inject a liquid growth inhibitor into the trunks of poplar trees that halts reproduction but still encourages the vegetative growth of the trees.

"About one to two grams are used on each tree," said Che. "It makes the trees grow stronger branches with more leaves, but they produce much less or no blossoms."

He said the process is harmless to the trees and also the environment because the liquid used is something that already exists inside the trunks and horticulturists are simply increase the concentration.

"The method used on willow trees is top grafting, which means they undergo sex changes by pruning high branches and splicing male branches," said Che.

He said the new tree crown will need another two or three years to grow. Both solutions take at least a year to take effect.

He leads a research team of more than 20 experts on the chemical injection process against catkins. The team's workload this year calls for them to inject about 15,000 trees in large parks and residential areas before the end of May, starting from the Temple of Heaven, which was finished last week.

Che said their work has seen some good results. Each year at this season, he and his colleagues receive a deluge of phone calls from people complaining about catkins but the number of calls have been falling each year.

China Daily

(China Daily 04/19/2011 page33)