Tashi Chophel crouched beside a thin-tall pine, pulling aside a few weeds. "This is a 'third-generation' sapling, three years old," he said.

Planted in Nanshan Park in Lhasa, capital of southwest China's Xizang Autonomous Region, the first generation of trees has matured and dropped seeds, giving rise to a second generation.

"Now the second generation has produced a third one," noted the 46-year-old Tibetan. "I take care of every tree as if it were my own child."

Tashi Chophel has worked as a forest ranger at Nanshan Park for 14 years, and is responsible for planting, patrolling, preventing fires and performing other tasks related to planting and tending trees.

Thursday marks China's National Tree Planting Day.

Perched at an altitude of around 3,700 meters, Nanshan was once a barren, sandy slope. Since 2012, when the Nanshan Park afforestation project started, Tashi Chophel has witnessed the mountain turn into a lush green park that now attracts both local residents and tourists.

Planting the first generation of trees was never easy. "At first, we had to dig pits into the rock, bring soil from afar, and channel water from the river," Tashi Chophel recalled.

The slopes average 60 degrees -- too steep to stand without slipping. Before planting, they had to replace the rocky soil with fertile earth. The holes had to be dug deeper, with basins reserved to hold water.

Getting one tree to grow takes 37 steps, including selecting saplings, lifting them, transporting them, replacing the soil, backfilling and fertilizing. Each step demands care and patience.

Today, although some tree species regenerate on their own in certain areas, plantations in a much wider range continue every year. Saplings from other provinces must first grow for a year in nurseries around Lhasa before being transferred onto the mountain.

"Only after they shed their old bark and sprout new buds are they ready to be moved the following spring," he said.

To deliver saplings more easily up the mountain, Tashi Chophel has acquired an agricultural drone license.

To take good care of the trees, he consults experts and meticulously documents sunlight exposure on every slope, while researching which tree species thrive at different elevations.

He also reads the "vital signs" of trees -- yellowing leaves signal thirst, while abnormal bark may indicate pests or disease. From observing just a handful of soil, he knows which trees will thrive there, and by counting branch layers, he can estimate a tree's age. "My colleagues call me a 'tree expert,'" he said.

As he patrols every day, he often purses his lips and whistles, echoed by a bird tweeting in the tree. "An old friend is saying hello," he said with a smile, adding that he also has "pals" like a stray cat he has named Xiaomi and foxes that dart through the brush.

During the dry season from November to April, even a gentle night breeze keeps Tashi Chophel awake.

"My ears are busier than my eyes, for every whisper of wind sounds like a fire alarm," he explained. "Safeguarding the trees is even more important than planting them."

Figures show the park now has over 1 million trees consisting of more than 100 species, covering an area of 235 hectares. The number of visitors reached 590,000 last year.

Nanshan Park is part of an afforestation project in the mountains to the north and south of Lhasa. According to a white paper issued last year, the project has led to 705,333 hectares of forests being planted and 255,333 hectares tended.

The afforestation effort has reduced sandstorm days and contributed to cleaner air. Since 2016, the annual proportion of days with excellent or good air quality in Xizang has reached over 99 percent, with Lhasa ranking first among the 168 key cities in China in 2024 in terms of air quality.

Standing atop the hill, Tashi Chophel had a clear panoramic view of Lhasa. The Potala Palace in the distance glowed in the spring sunshine, while tender new shoots sprouted on the willows along the river valley.

"I hope my son, who is studying at university, can take over my job one day," he said, gazing into the distance.