ZHENGZHOU, May 9 (Xinhua) -- As the rays of the morning sun shine through the tree branches landing on the shoulders of Dong Yunlan, an 85-year-old retired expert on forestry, he lays his hand on the tree's trunk and looks up to observe the growth of the leaves while taking notes from time to time.

Wearing a flat cap, a pair of sports shoes and a cross-body bag, Dong, with his 66 years of experience in forestry research and protection of ancient trees, is so glad to meet his old friends again -- the 272 oriental plane trees along Weiyi Road in Zhengzhou, capital of central China's Henan Province.

Weiyi Road "hides" itself in the downtown area of Zhengzhou's Jinshui District, where thick and straight oriental plane trees stand neatly on both sides, with branches extending upward in a "Y" shape to hold palm-sized leaves.

"Zhengzhou lies on the southern bank of Yellow River, China's second-longest river, and the sand from around the river used to turn the city into dust," Dong said, adding that to prevent sand storms, street trees were planted on a large scale in Zhengzhou in the 1950s.

The oriental plane trees, due to their well-developed root system, rapid growth and strong resistance to harmful gases, were quickly widespread across the city.

In early April each year, the new leaves on the trees usher in their budding stage, when clusters of bright yellow leaves top gray bare branches. Then, as the temperatures rise, the new leaves can be seen in May.

"As the weather gets hotter, the leaves are unfolding, bringing a slight chill in the air," said Zhi Yuxiang, a 72-year-old resident who spends most of her time living in a community near Weiyi Road. "We don't need to open umbrellas when it drizzles, since the trees could shade pedestrians from the sun and rain."

Statistics from the municipal parks and forestry bureau show that air humidity under the oriental plane trees can increase by about 50 percent, with temperatures more than 3 degrees centigrade lower than surrounding areas. The trees can also absorb urban noises by 10 to 30 decibels.

"When we planted these trees back then, they were as thin as the handle of a spade. Now, even two or three people can't hold hands around the trunk," Dong said. "I grew up with them and witnessed the development of Zhengzhou and the changes of the times."

In 1948, Zhengzhou had only a few dozen street trees and was known as the "city of wind and sand." Through the unremitting efforts of several generations, about 2 million oriental plane trees had been planted in downtown Zhengzhou by the end of 2021, when over 90 percent of sidewalks and bike paths had been covered with green space.

Everything turns golden as the sun sets, when the elderly carrying vegetable baskets and children who have just learned to ride bikes and runners pass by each other in the shades cast by the trees. The ancient city on the bank of the Yellow River is now embracing another green summer.

"Only by giving the green back to cities can people enjoy more beauty of life," Dong said. The old man observes these trees gently one by one, while the trees look at him in silence like tacit old friends.