Every morning, Pu Jianyuan stands by the window, gazing at the lush forests covering the billowing mountains surrounding Xichang, Sichuan province. The 75-year-old has an endless stock of stories about the trees, which he planted from the airplane half a century ago.

Pu got the task of experimenting with aerial seeding in the spring of 1958. He was appalled by the state of the loss of green cover around the Donghe and Xihe rivers where he and other colleagues of the Sichuan provincial forestry bureau would plant trees.

"There was no tree at all. Rain had carved the banks into deep gullies and nearby Xichang city would be inundated whenever it rained," Pu recalls.

In the first half of the 20th century, Xichang suffered 58 major landslides, causing 2,400 deaths. This was caused by indiscriminate felling of trees and cattle grazing in the mountains.

In the 1950s, the local government's focus was on curbing floods and soil erosion. The provincial forestry bureau wanted to try scattering seeds from the air as it was very difficult to plant tree seedlings in deep mountains. They had a precedent in Wuchuan county, Guangdong province. They had tried aerial seeding in 1956.

Pu recalls that he and a dozen colleagues carried out field research over two weeks, sleeping in local farmers' or hunters' homes at night. The rains arrived around the same time that they finished studying the landscape. It was the best time to spread seeds from the air. But it wasn't until September 1958 when an Il-14 plane finally landed in Xichang.

Pu and four others carried out the mission. The plane had a narrow opening in its belly and they had to throw some 500 kg of seeds in less than 3 minutes.

"We hardly had a moment to breathe, the plane was flying so fast," Pu says.

They put a funnel in the opening in the plane, using a switch to control its movement, which greatly improved the efficiency. In three days, Pu and his colleagues spread pine seeds over an area of 11 sq km. Pu says he was anxious to see the seeds budding - just like a father would be, watching over his child's growth.

However, when they climbed the mountains the following spring, they found few seedlings on the barren slopes. A major reason for the first experiment's failure was the delay in aerial seeding, which left the seeds little time to take root and survive the spring drought.

Despite the setback, the provincial government was determined to improve the environment and carried out aerial seeding on a bigger scale in the following years.

The planting began promptly in the rainy season. Pu and his colleagues hammered wooden poles on the slopes to mark the areas for the pilot to see more clearly. This time pines and several other species were planted on nearly 70 sq km.

When the dry season followed, Pu was thrilled to find the slopes turning green. Clusters of short but sturdy saplings had taken root on the soil.

Pu says that compared with traditional ways of planting trees, aerial seeding effectively lowers the cost and reaches areas people can hardly access.

By 1965, Pu and other forestry workers had planted trees over some 650 sq km of Xichang and the nearby areas. In a 1972 survey, they found nearly half of the area they had covered had grown into woods.

Pu was especially proud that the aerial seeding technology in Sichuan won the Technology Advance Award in 1979 at the National Science Conference. Many international experts visited the area. An expert from the UNESCO remarked that the afforestation at Xichang was an "unprecedented achievement".

However, when the local government prepared for aerial seeding in 1994, Pu strongly opposed it.

"The climate has changed. The dry season comes a month later than before," Pu explains. Even if the seeds take root, the seedlings won't have enough time to penetrate the dry layer of soil, they'd wither before the dry season ends.

In the wake of the global warming, says Pu, aerial seeding in Xichang should be carried out in areas 2,500 m above sea level where the dry season is shorter.

What worries him the most is that the increasing population is threatening the forests he had planted decades ago. Every year about 5 sq km of forests are being burned or axed, says Pu, who has been trying to attract public attention to protect the environment.

In 1995, a regulation on protecting the forests in Liangshan Yi autonomous prefecture, with Xichang as the prefectural capital, went into effect. This gives Pu and other environmental workers another legal weapon to protect the green cover.