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Veronica Qi

The uprooting of numerous trees across Hong Kong during Typhoon Noul last weekend has sparked safety concerns among residents, with an expert warning that restrictive planting methods had left some unable to withstand strong winds.
Two government hotlines received a total of 331 reports of fallen trees during the typhoon, which triggered No 8 and No 9 signals on Saturday and Sunday. Of the fallen trees, eight were banyans at Wan Tau Tong Estate and another of the same species was reported near Tai Po Mega Mall in Tai Po.
At Wan Tau Tong Estate, residents said the loss of trees that had stood there for more than three decades had left them upset and concerned about the area’s safety.
Leung Po-chu, 65, who has lived in the estate’s Wan Loi House since 1991, said she had watched the trees grow over the years.
“Could the typhoon really have been powerful enough to bring down so many trees at once?” she said.
“I was very upset to see so many of them fall. This is a route I take to the shopping centre every day. There are so many memories tied to these trees.”
Leung said she felt the trees had received insufficient attention over the years.
“There used to be many trees in front of Wan Loi House, but the relevant parties rarely maintained or looked after them. That was my impression,” she said.
Chan Ah-hung, 79, who lives in nearby Yat Wing House and has been in the area since 1991, said he believed the trees had been planted too shallowly.
“It is such a shame. They had been here for more than 30 years,” he said.
“These trees were even shielded by buildings, but the damage was still so serious. They should have been planted deeper so the roots could take hold more firmly.”

Professor Jim Chi-yung, an urban forestry expert at the Education University of Hong Kong, said the trees appeared to have been left with insufficient space for their roots to spread, making them vulnerable to strong winds as their crowns grew over the decades.
“The key is not simply whether soil is present, but whether there is enough rootable soil,” he said after examining photographs of the fallen trees.
Jim said many of the trees had been confined to small pits surrounded by hard paving.
“The soil beneath hard paving has to be heavily compacted. Otherwise, the pavement will subside,” he said. “But once the soil is compacted, tree roots cannot penetrate it.”
As a result, their crowns grew larger above ground while their roots remained trapped within a limited area underground, leaving the trees top-heavy, with a high centre of gravity and inadequate anchorage, he added.
Jim said standard planting practice should involve loosening a volume of soil measuring about 1 metre (3.3 feet) long, 1 metre wide, and 1 metre deep, allowing young roots to penetrate the surrounding ground.
“I have not seen anyone doing this in Hong Kong,” he said. “They just dig a tiny, tiny hole.”
He said undersized root balls could further weaken trees. A root ball is the mass of roots and soil kept together when a tree is planted or transplanted.
If the root ball was not fully excavated and was prepared too small, fewer roots would be retained, he said. While this reduced the labour required and lowered handling and transport costs, it also limited the tree’s ability to establish a stable root system.
Jim added that a healthy root system should generally spread over an area two or three times the width of a tree’s crown.
“The crown above ground became bigger and bigger over more than 30 years, but the roots underground were not able to expand accordingly,” he said. “The trees became top-heavy and the anchorage was unstable.”

He was particularly critical of the planting method at Wan Tau Tong Estate. Unlike a narrow roadside location, the estate had open space where soil could have been left less compacted and roots allowed to spread naturally, he said.
“They were planted against nature,” he said. “That is why they failed in exactly the same way as roadside trees.”
At a separate location near Tai Po Mega Mall, Leung Ho-ling, who is in her seventies and has lived in the area for more than 40 years, said she was shocked that such a large tree had fallen towards the pavement.
“The wind did not seem strong enough to bring down a tree like this,” she said. “I would not have been surprised if branches 5cm [two inches] or 6cm thick had fallen, but seeing the whole tree come down was shocking.
“The tree fell directly towards the pavement. It was very dangerous. In future, even if the wind is not that strong, I may not dare to go out.”
The Leisure and Cultural Services Department said the banyan outside Tai Po Centre on Tai Wo Road was under its care and was toppled by strong winds during Typhoon Noul.
It added that the tree was outside the scope of earlier road improvement works on Tai Wo Road and that its collapse was unrelated to the project.
In response to inquiries, the Housing Authority said it could not trace the history of the trees at Wan Tau Tong Estate. The estate was included in the first phase of the Tenants Purchase Scheme in 1998, and the authority said responsibility for tree-related matters had rested with the estate management since then.
Residents said the trees had been planted when the estate was built in the early 1990s and had stood for more than three decades.
The Development Bureau said the estate was private property and responsibility for maintaining its trees rested with its owners’ corporation and appointed property management company, rather than a government department.
The bureau said its Tree Management Office wrote to owners’ corporations and property management companies before the wet and typhoon seasons each year, reminding them to hire registered tree management personnel to inspect trees and carry out necessary maintenance.
It also provided private property owners with a tree management handbook and organised regular talks.


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A fallen tree in Tai Po amid a T9 signal. Photo: Sam Tsang

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The remains of a tree outside Wan Lam House of Wan Tau Tong Estate. Photo: Elson Li

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A tree near Tai Po Centre uprooted by Typhoon Noul. El Nino could turn the four to seven tropical cyclones expected to come within 500km of the city this year into super typhoons. Photo: Sam Tsang

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Urban forestry expert cites restrictive planting methods for fallen banyan trees at Wan Tau Tong Estate and near Tai Po Mega Mall


Urban forestry expert cites restrictive planting methods for fallen banyan trees at Wan Tau Tong Estate and near Tai Po Mega Mall.


Extreme weather

Hong Kong environmental issues

Education University of Hong Kong

Estate residents question why Typhoon Noul uprooted so many trees

.css-1c6uqr6{color:inherit;font-weight:inherit;font-size:inherit;font-family:inherit;line-height:inherit;overflow-wrap:break-word;}Urban forestry expert cites restrictive planting methods for fallen banyan trees at Wan Tau Tong Estate and near Tai Po Mega Mall

Urban forestry expert cites restrictive planting methods for fallen banyan trees at Wan Tau Tong Estate and near Tai Po Mega Mall