More than 400 years ago, the upper slopes of Tai Mo Shan were covered in lush, green forest.
Then humans arrived on Hong Kong's highest peak, cutting down indigenous and pioneer tree species to make way for tea plantations.
Hill fires in more recent times have further reduced much of the former mountain forest to barren, sparsely grassed rock.
But now a conservation group has embarked on an ambitious plan to replant the forest - and is calling for more such efforts across Hong Kong.
Kadoorie Farm and Botanic Garden's flora conservation department says mountain forests are an important component in the ecosystem and also in supplying clean drinking water.
"The dense vegetation of forested mountains acts as a water catchment, almost like a sponge," department head Gunter Fischer said.
"The forest takes up rainfall, filters it and slowly releases it as clean drinking water all year round," he said.
Forested mountainsides also help prevent soil erosion, landslides and provide habitats for animals.
Since its planting programme began in 1998, the group has planted more than 50,000 trees, including 40 to 50 new seedlings, on the hilltop this month.
If all goes according to plan, closed-canopy forest will develop in less than a decade.
But reforestation is as time-consuming as it is laborious. The first generation of trees will need 50 to 100 years to reach full maturity. Oaks could take 500 years.
Growth will be at the mercy of soil conditions, harsh weather and threats from hill fires, heavy rains, winds and overgrown grass competing for nutrients.
Blue plastic tree guards are being used to keep the seedlings in controlled climates. The guards also convert sunlight into blue light, increasing the radiation needed for photosynthesis.
Professor Derrick Lai Yuk-fo of Chinese University's Department of Geography and Resource Management said urban development and hill fires were the biggest threats.
"Hill fires in Hong Kong tend to be man-made and if forests are not designated in country parks, they are harder to protect.
"We understand that once soil use is changed, say for development nearby, the ecosystem's overall functionality will also be reduced."
He said forests had the ability to regenerate on their own but would take decades. "Growing some trees manually could help accelerate this process," he said.
There were 33 hill fires inside or threatening country parks last year, double the number of the year before, according to the Agriculture, Fisheries and Conservation Department.
The United Nations' recent State of the World's Forests report identified forests, home to 80 per cent of global biodiversity, as vital to livelihood, food, health and energy security.