Christopher Nixon Cox (front), grandson of former US president Richard Nixon, plants a southern yew tree at the Hangzhou Botanical Garden in 2013. PHOTO PROVIDED TO CHINA DAILY

In February 1972, as winter was giving way to spring in Hangzhou, a young redwood arrived at the city's botanical garden from across the Pacific.

The tree was small then, just 2.4 meters tall. More than half a century later, it has grown to nearly 20 meters — and become a living marker of a relationship that has grown since the day it was planted.

It was a diplomatic gift, carried to China at a moment when the relationship between Beijing and Washington was beginning to thaw.

In 1972, then US president Richard Nixon arrived in Hangzhou, where the two sides discussed the Joint Communique, an agreement that would help set the two countries on a path toward normalized relations.

Wang Jinshun, who was responsible for security at the botanical garden, recalled in an archival account that when the tree arrived at the Hangzhou Botanical Garden, it was still wrapped in its original packaging. Inside was a redwood accompanied by instructions on how to plant and care for it.

Keeping the tree alive in Hangzhou would prove to be a challenge. The city's subtropical monsoon climate is very different from the cool, humid conditions of the redwood's native range along the West Coast of the United States.

"When the redwood first came here, it needed to adapt to a climate different from that of the West Coast of North America," said Wang Hongyi, an engineer at the botanical garden.

Workers installed artificial misting equipment to increase humidity. During the hot summer months, they used woven reed screens to shade and cool the tree.

The precautions went further. "After the redwood was planted, the botanical garden surrounded it with a very tall bamboo fence," Wang Jinshun recalled. "A small house was also built next to it, and people were assigned to watch over it day and night."

Later in 1972, horticultural workers propagated the redwood from cuttings. Seven years later, through artificial pollination, they obtained mature seeds from three cones and raised the first seedlings.

As the tree grew, generations of visitors came to see it.

In 1982, Nixon returned to Hangzhou, this time as a former president. By then, the redwood had reached more than 7.7 meters. Its second-generation offspring were also growing well. In 1993, he returned again to see the redwood.

Nixon said redwoods could live for 2,000 years and hoped the friendship between the two peoples would endure just as long.

Another generation came to the tree in 2013. By then, the people who planted it had grown old, and some had already passed away. That year, Christopher Nixon Cox, Nixon's grandson, led a 42-member delegation from the Nixon Foundation to Hangzhou.

Beside the redwood, the delegation planted two southern yew trees, a protected species native to China.

The tree's descendants have also spread far beyond Hangzhou.

"Today, more than 20 provinces, municipalities and autonomous regions across China have introduced redwoods propagated from the Hangzhou Botanical Garden," Wang Hongyi said.

Some have grown remarkably tall. A redwood at the Yunnan Academy of Forestry and Grassland, he said, has reached more than 30 meters in an environment well-suited to the species. Redwoods are also being propagated in Zhoushan and Qiandao Lake areas in Zhejiang province.

"In many of these places today, residents may come across them almost without realizing that it is a descendant of the tree that came to Hangzhou more than 50 years ago," Wang Hongyi said.

At the original tree in Hangzhou, care has continued. Last year, the Hangzhou Botanical Garden installed new monitoring equipment around it to track soil moisture, nutrients, pests, and disease.

"They can grow to between 90 and 110 meters and live for 1,200 to 1,800 years," Wang Hongyi said. "The oldest known specimens have lived to about 2,200 years."

For a tree that can live for more than a millennium, the story of this redwood is still only beginning, he said.