Ancient Lacebark “General” gives up secrets of the past

In 2001, an 800-year-old Lacebark pine that showed signs of poor health inadvertently led park authorities to discover the existence of an unusual irrigation system built into the foundations of the Round City, an ancient site of devotion and contemplation in Beijing's Beihai Park.

To casual observers of Beijing's history, the existence of something wise and ancient in one of its parks should not have seemed surprising. The park, as with much of the city's ancient imperial infrastructure, has had a colourful past.

Beihai Park History

Dating from the middle of the 11th century, Beihai Park is the largest of Beijing's municipal parks situated a stone's throw from the back door of the Imperial Palace in the Forbidden City. In the course of its 1,000-year history, the park has been used as an imperial pleasure park, particularly by emperors of the Ming and Qing dynasties, and their families, which included groups of wives, relatives and offspring. Each of the emperors left their mark with ever more fanciful large-scale projects. In 1651, under the instruction of Emperor Shunzhi, the White Dagoba Temple, the park's trademark symbol, was built on the site of the Palace of the Moon, a Yuan Dynasty devotional site of worship. The surrounding island was renamed White Dagoba Hill. The Dagoba was badly damaged in the Beijing earthquake of 1679 but was rebuilt the following year.

Emperor Qianlong (1736-96) added several new structures during the Qing Dynasty. In 1900, the eight-power allied invasion force damaged many parts of the park. It was fully rebuilt by the central government in 1953.

 The collapse of the Qing Dynasty in 1911 brought changes in the administrative control of imperial property, and the park was placed in the hands of the people. It was formally opened as a public park in 1925.

Round City

The history of the Round City, a walled, elevated landform situated at the southern end of Beihai Park, immediately to the east of Great Marble Bridge, dates from the Liao Dynasty (916-1125). It came to prominence during the Jin Dynasty (1115-1234) when rulers planted trees from many parts of China there and built a devotional pavilion they called the Hall of Received Light.

The Round City was then a small island in the park's Taiye Lake.  During the Ming and Qing dynasties, the Round City was often used by imperial families as a site for devotion and contemplation, since it was close to the imperial quarters in the Forbidden City. The 5-metre-high circular Round City wall, rebuilt during the Ming Dynasty, was reputed to have previously protected the residence of Kublai Khan, the first emperor of the Yuan Dynasty (1271-1368), on the same site.

In 1669, during the reign of Emperor Kangxi, the Hall of Received Light collapsed because of an earthquake, but it was later rebuilt. The learned and energetic ruler Emperor Qianlong (1736-96), who filled his palace with scientists and inventors to satisfy his curiosity and pursue his ambitions, reconditioned the Hall in 1764. The present buildings and layout date from about this time.

Today the Round City is a shaded, stone-terraced edifice with courtyards, buildings and its many ancient trees that have survived scourges of war, invasions and earthquakes.

Emperor Qianlong is said to have granted titles to these majestic old trees that are now as much as 800 years old. A white Lacebark pine that dates to the Jin Dynasty was entitled the "General in White Robe" by the emperor, and a twisting, knotted, arthritic-looking pine, which stands to the side of the Hall of Received Light and which is just as old, was named the Marquis of Shade by the humorous emperor.

Ancient Irrigation System

In 2001, the poor health of the old Lacebark "general" -- it had developed two withered branches -- alerted park authorities and a research team to the existence of an unusual irrigation system that had been built into the foundations of the City.

The ill health of the ancient pine was a matter of such concern for park workers that they decided to lift an ornate cover off a drain near the tree and take a look. They had no idea what they might find. An intrepid member of the team tied a rope around his waist and descended through the opening. Torchlight revealed a drop of about 1.5 metres into a brick-roofed tunnel of about 1.5 metres high and just less than a metre wide. The worker crouched in the space and knelt lightly on the water-soaked earthen floor. His torch shone along a curve of bricks that disappeared into the darkness ahead of him.

Although the existence of the tunnel was known to park authorities, its purpose had never been ascertained and the workers were genuinely surprised with their find.

Park authorities enlisted the help of specialists. Experts in ancient underground structures were called in, and they used computers to build a profile of the size and shape of what lay beneath the terrace. Their work revealed a C-shaped tunnel that was connected with each of the drain openings positioned every couple of metres around the trees.

Dating experts were next. They lifted old worn bricks from the grounds of the terrace and noted unusual differences in their sizes and shapes. Even more surprising, radio carbon dating techniques suggested they were of the Ming Dynasty, from about 1411. Less surprising though was that bricks found in different parts of the City's terrace showed different ages, having been replaced during different periods, with the newest dated to about 1821 during the late Qing Dynasty.

Irrigation specialists worked to analyse the data. They discovered that because each brick was uneven, with a wider diameter at its top than at its base, water was able to trickle between the triangular shapes between each brick and flow freely into the earth. Their estimates indicated that about 10 percent of water falling on the bricks evaporated from the surface of the ground, but that the remainder was absorbed into the earth.  The water soaked into the earth until it reached the tunnel, where, experts argued, it was cannily collected, particularly after heavy rainfalls. The tunnel conserved the water that later slowly seeped through the tunnel's floor feeding the pines.

The experts agreed that the tunnel was a sophisticated and efficient irrigation system and that the workers had been right to look for the source of the Lacebark pine's troubles underground. They found that damage to a part of the tunnel beneath the tree's roots had resulted in a blockage of the flow of water in the system.

Experts also agreed that the discovery of a sophisticated ancient irrigation system that had fed water to the imperial trees unaided for hundreds of years was still functioning, and that they regarded this as something of a miracle.

Fortunately, even though the damage to the General in White was severe, it was restored to health after careful surgery. Today, the irrigation system is under the care of the Beijing Municipal Bureau of Parks, and workers keep a watchful eye on the trees as if they were greatly loved elderly relatives, which, in a way, they are.