Beijing, as just about everybody knows, is full of ancient things. Palaces and royal mansions have graced the capital for centuries, as have some of the city's winding hutong lanes, courtyard houses and time-honored shops.

And some grinning, wrinkled Beijingers seem pretty ancient too, as they sit sunning themselves in parks, push mahjong tiles around the board, chat with neighbors and play with grandchildren or great-grandchildren.

While few Beijingers, even the truly old ones, are 100 years old, the capital does have many living residents - its trees - that are several centuries old.

The image Beijing often projects to the international community is of a mix of ancient and modern structures - the bending steel ribs of the Bird's Nest, the blue bubbly exterior of the Water Cube, the CCTV tower and the vast open sweep of Tian'anmen Square contrasted with the stately red hues of halls in the Forbidden City and the Summer Palace. But this image leaves out the capital's surprising greenness, one of its most endearing characteristics.

The capital is full of thousands of trees and many of them are gloriously big, with wide-spreading branches. Some of Beijing's older, shaded streets, such as Guloudongdajie and Nanchizidajie, are a joy to walk down simply because they seem like long green tunnels.

True, the city doesn't seem too green in the bitter grip of winter, when the leaves are gone, or in the smoggy haze of summer. But if you get up on an elevated vantage point in the downtown area in spring or fall, you can see the foliage spreading across the old streets, parks and hutong like a refreshing green blanket.

Beijing has at least 40,000 officially ancient trees, according to the Beijing Municipal Administration Center of Parks, most of them are scholar trees, pines, junipers, gingkoes and cypresses and are in gardens, palace grounds and parks.

The authorities have put a green tag on every tree in the city verified as being older than 100. Those older than 300 have a red tag.

There are, according to the center, more than 3,600 300-year-old trees throughout the capital.

There are even a few 1,000-year-old cypresses, each about 20 meters high, in the parks and gardens at the southwestern edge of the Forbidden City.

Near the south gate of Beihai Park there are two 800-year-old, 30-meter-high whitebark pines.

Even though the trees are not trumpeted as heavily as the city's eye-catching monuments and buildings, local residents, officials and park managers are clearly concerned about keeping them in good health.

Those new to Beijing are often touched, if also a bit startled, to see workers wrapping or screening trees in parks with heavy burlap or cloth at the onset of cold temperatures, to keep winter sunscald at bay and protect delicate branches and roots.

Such winter damage, as well as drought in the summer, has taken its toll on some of the capital's old trees and Beijing's rapid development has reportedly affected the groundwater supply they rely on, leaving 20 percent of the city's ancient trees in declining health and 2 percent endangered.

So it's heartening to see Beijing officials recently spend millions of yuan on a program to rejuvenate ancient trees across the city. It is not cheap to treat these ailing old trees (sometimes as much as 500,000 yuan for a single one), but it is money well spent.

Beijing's scientific community is also helping preserve the city's legacy of ancient trees.

The genetic variety of the old trees is much less varied than that of the city's ordinary trees, according to the Beijing Science and Technology News. Efforts are already underway to clone 100 of the ancient trees using test tube tissue culture, to ensure the survival of the genes that help the trees live so long.

Such efforts are welcome because, without its pleasant foliage, downtown Beijing would lose some of its ancient charm.