Isaac Newton had to sit under a tree and be hit on the head by a falling apple to discover his famous law of gravity in 1687.

But Zhao Huaiqian, a Chinese botanist, had to lie under a tree to ascertain where the peach borers hid during winter.

Zhao's discovery may not have been as significant as Newton's, but it was a breakthrough, nonetheless. Because in the 1950s, when he made his finding, the country's modern botanical studies were still at an embryonic stage, and the habits of peach borers remained an enigma for orchid managers.

"People used to wonder where the swarms of borers came from every spring only to totally disappear with no trace of even their nits in the winter," said Zhao, 80, recalling his days working in a Beijing nursery 50 years ago.

"To find out the answer, I lay down on the ground and fixed my eyes on the snail-like borers on a nearby tree for days one chilly autumn. I did not even dare to blink for fear that the bug that I gazed at might disappear in a split second until I found that they tucked themselves away in the tips of the branches, not very deep, to turn into pupae."

Thanks to that discovery, gardeners learnt how to easily wipe out such borers, then a major pest to peach trees, by cutting down the tips of branches during the regular trimming session before the arrival of spring, instead of using pesticides, which also averted environmental hazards.

But the borer discovery is not Zhao's only one under the trees. He made a career under them, especially the ancient trees that are now assigned numbers and regarded as part of the "living heritage" of Beijing.

In half a century's time, Zhao said, he visited practically every ancient tree in the urban area, just like a doctor who visits his patients to check their conditions, treat their diseases, eliminate pests and help them regain their health.

According to figures from the Municipal Gardening and Forestry Bureau of Beijing, more than 50,000 trees in the city are more than 100 years old, about 10,000 of which are more than 300 years old.

"They are the oldest living objects in the capital, dating to the Liao (907-1125), Yuan (1206-1368), Ming (1368-1644) and Qing (1644-1911) dynasties," Zhao said. "A few date back to the Tang Dynasty (618-907) and maybe even earlier.

"These trees bear testimony to our history, and are enmeshed in our folklore, handed down from one generation to another. Some of them give unique impressions of our city's landscape."

Zhao listed several ancient trees that are older than 1,000 years, such as the Chinese scholar tree (Japanese pogoda tree) in Beihai Park, the pine trees in Jietai Temple, the ginkgo "Tree God" at Badaling, and a cypress from the Liao Dynasty in Zhongshan Park.

Having a deep affection for ancient trees, Zhao said he once watched a veteran Chinese scholar tree for 130 days straight to count the varieties of bugs climbing on its trunk.

"I stood, sat or lay under the tree all day long and counted the bugs one by one," Zhang recalled. "You may think such a move is stupid, but it was important to get to know the habits of the bugs, such as when they start to come out in spring, when they appear the most in number, and how far they can climb."

After careful observation, Zhao found that the bugs usually crept out from the bases of walls or cracks in bricks, where they spend the winter, in mid-February every year.

Zhao invented a new method to kill such bugs, which suck juice from the trees. "I found that the bugs fall to the ground if they encounter obstacles as they climb up, because they don't know how to make a detour," he said. "So I tried to place a plastic hoop around the bottom of the trunk, making it stick closely to the bark, and found that the bugs under the hoop could no longer climb up and all fell down.

"The bugs attempted to climb again and again but all in vain. Then they moved to other trees nearby, but the longest distance that such bugs can creep on ground is about 21 metres. Then I put such hoops on every tree nearby, and the bugs found no place to climb and starved to death."

"The idea was proved effective and then spread throughout the city," Zhao said, thumbing through a dog-eared notebook, which records the 5-month-long close contact Zhao had with the old trees and the bugs.

The notebook is just one of dozens of writing pads that Zhao used as his work diary during the past 50 years. He recorded the date, weather and the stories almost every day. Zhao said he had sorted out his notebooks and published several books on the control of plant diseases and pests.

China's botany study has progressed in the past 50 years, and now Zhao's pupils are working on the front line. "The younger generation knows more high technology than our elderly people, and there are many new ways to treat diseases and rejuvenate old trees," Zhao said. "I still need to learn more."

Although he has been retired for a long time, Zhao is still active in ancient tree protection and is one of the senior advisers to the city's gardening and forestry bureau. Every time he heard an old tree had fallen ill, he would go to see the tree for himself.

Zhao said veteran trees can be found throughout the city, but there are particular concentrations in certain landscapes.

Imperial gardens, temples, emperor's mausoleums and scenic spots on the northwest outskirts are the four major areas that contain an abundance of veteran trees, including scholar trees, pines, cypresses and ginkgoes.

Individual impressive old trees may be found on village greens, in orchards, in churchyards, associated with historic buildings, or simply in people's courtyards.

"Different kinds of ancient trees have their own characters, and we should use different ways to rejuvenate them," Zhao said, citing such examples as the pine, whose growth depends highly on soft soil so people need to loosen the soil frequently, and old scholar trees, which usually have big hollowed areas in their trunks, so people need to use a kind of synthetic resin to fill them up.

"Hollows in the trunk seriously threaten the safety of scholar trees," Zhao said, recalling an extremely strong wind several years ago that blew down eight old scholar trees in Dongcheng District.

"I could not help crying when I saw the old trees being torn up by the roots. It was our fault for failing to fill up their hollows in time. They were all more than 100 years old, older than most of our human beings."

Drawing lessons from the tragedy, Zhao said the gardening and forestry bureau stepped up its census on the city's ancient trees and in 2002 started making a digital map to show the living heritage. That project is now finished.

Wang Zhongying, a bureau official engaged in the project, said each of the ancient trees in the urban area was recorded on the map, with detailed information about its age, height, girth, medical history, and location marked using the global positioning system.

Even the wormholes have been archived, and digital pictures of the tree are taken from different angles, Wang said.

She also mentioned that the digital map is included in the database of the Beijing Municipal Commission of Urban Planning so that the commission can take tree protection into consideration when it evaluates and approves construction projects.

Zhao likes the digital map because "in case any tree becomes ill, we can look up its medical records and give timely treatment."

Having been friends with trees for his entire life, Zhao said he has benefited from the friendship, as well. "My eyesight is still perfect, and I have neither myopia nor presbyopia. For that I give thanks for the long time I've spent tree watching."

And apparently, his silent friends have compared notes with him on history and philosophy.

"They have seen the turning of the many chapters of our history, the come-and-go of emperors and empresses, heroes and villains, war and peace," Zhao said.

"Now, in a time of the obsession with style and superficiality in appearance, their beauty, and their green color, are just like classical music. They let you know what eternal quality is."

(China Daily April 12, 2006)