SINGAPORE: After a tree fell and killed two tourists in Bali earlier in December, authorities said the plant had been healthy and that the incident was caused by "strong winds and extreme weather conditions beyond human control".
Similar accidents involving falling trees have caused deaths, damaged property and disrupted traffic in other parts of Asia, including Singapore.
Environmental conditions could be a factor, said senior horticulturist and arborist Athi Ramesh from landscaping firm Prince's Landscape.
Horticulturists are experts in garden cultivation and management while arborists are tree surgeons.
Prolonged wet weather could affect a tree's stability when too much rain leads to stagnant water, reducing soil particles attached to the tree's roots.
The tree could also end up retaining more water in its canopy, increasing the weight on its branches and trunk and resulting in a collapse, said Mr Ramesh.
Trees which grow in consistently wet weather also tend to develop shallow roots, as they don't need to extend deeper in search of water, he added.
At the other extreme, drought and dry weather can also cause soil to disintegrate and crack, reducing its ability to firmly anchor tree roots.
"It also hinders the growth of young feeder roots, which play a vital role in binding the soil together," Mr Ramesh said.
Another common issue is nearby construction as well as vehicular or even human traffic.
These can damage roots and compact the soil, restricting root growth and the ability to absorb nutrients and water - as well as to support the weight of the tree's crown or canopy.
A tree's own characteristics can also play a part.
Fast-growing species often develop weaker stems and branches, according to Mr Ramesh.
And those with codominant structures - where the stem from a single point of origin branches out into more than one - are more prone to falling.
Others have shallow root systems or brittle branches and twigs, making them more vulnerable to external forces.
Mr Ramesh pointed out that trees with shallow roots and heavy crowns - such as the Falcataria falcata and African Tulip - are commonly found in Singapore's forested areas.
A tree at risk of falling may show signs of structural weakness. These include leaning, cracks or splits in the trunk, soil lifting around the roots or decay and infestations, said Mr Ramesh.
The latter can occur below ground, making it undetectable without specialised methods. One of these is root exploratory trenching, which involves excavating the soil around the tree base to examine the condition of the roots.
It's not possible to predict exactly when a tree may fall. But there are events that heighten the risk of that happening, said Mr Ramesh.
Inclement weather like lightning strikes, strong winds or monsoon and rainy seasons, are examples.
In an urban setting, trees located between buildings could also face increased wind exposure due to a wind tunnelling effect.
Unpredictable conditions such as microbursts - strong downward rushes of wind - can also topple trees, even healthy ones.
Through a combination of proper care, maintenance, regular inspections and environmental management, said Mr Ramesh.
At Mr Ramesh's landscaping firm, visual tree inspections are conducted every six months alongside pruning.
Here, an arborist evaluates the tree height, trunk girth and overall health and structure.
Based on observations, the arborist will then recommend steps such as removing parasites, fertilisation and chemical treatments.
It's not too different for Singapore's National Parks Board (NParks), which manages 6 out of 7 million trees in the country.
About 2 million overseen by NParks are urban trees along roads, in parks and gardens, and on state land. The rest are further away from human traffic.
The statutory board has a regime of inspection which involves assessing the trees' overall form, roots, trunks, branches and crown; and pruning to improve structure and balance.
Group director of NParks' streetscape division Oh Cheow Sheng said trees are inspected every six to 24 months, with the frequency depending on location and age.
"This is stepped up during periods of adverse weather conditions to reduce the risk of tree failure incidents," he told CNA.
Ahead of adverse weather periods, NParks also reduces or thins the crowns of mature trees to manage their height and reduce wind resistance in the canopy.
The remaining 1 million trees are managed by town councils, private landowners and other entities.
To cope with climate change, which may lead to more frequent and intense rainfall if not prolonged dry weather, authorities select hardier and drought-tolerant trees that are also able to withstand the harsher growing conditions in Singapore's urban environment.
NParks has also been replacing diseased and more vulnerable trees.
More of hardier species such as the Sea Gutta and Shore Laurel have been planted at parks, gardens and roadside verges, with their numbers increasing from around 25,400 in 2017 to 46,500 in 2023.
Mr Oh added that planting trees in a way that mimics a forest structure helps to increase their resilience.
"Trees are (then) able to provide mutual support, such as roots intertwining with nearby trees, and improved buffering against strong wind gusts," he said.
This forest structure also doubles up to make Singapore’s streets cooler and shadier for pedestrians.
NParks also uses technology to monitor tree movements or to model the impact of strong winds on the stability of trees. This then helps to guide the thinking on intervention measures to take.
Authorities cited such measures in helping to lower the number of tree incidents in Singapore, from about 3,100 in 2001 to around 430 in 2023.
Want an issue or topic explained? Email us at digitalnews [at] mediacorp.com.sg. Your question might become a story on our site.
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Similar accidents involving falling trees have caused deaths, damaged property and disrupted traffic in other parts of Asia, including Singapore.
What could cause a tree to fall?
Environmental conditions could be a factor, said senior horticulturist and arborist Athi Ramesh from landscaping firm Prince's Landscape.
Horticulturists are experts in garden cultivation and management while arborists are tree surgeons.
Prolonged wet weather could affect a tree's stability when too much rain leads to stagnant water, reducing soil particles attached to the tree's roots.
The tree could also end up retaining more water in its canopy, increasing the weight on its branches and trunk and resulting in a collapse, said Mr Ramesh.
Trees which grow in consistently wet weather also tend to develop shallow roots, as they don't need to extend deeper in search of water, he added.
At the other extreme, drought and dry weather can also cause soil to disintegrate and crack, reducing its ability to firmly anchor tree roots.
"It also hinders the growth of young feeder roots, which play a vital role in binding the soil together," Mr Ramesh said.
Another common issue is nearby construction as well as vehicular or even human traffic.
These can damage roots and compact the soil, restricting root growth and the ability to absorb nutrients and water - as well as to support the weight of the tree's crown or canopy.
A tree's own characteristics can also play a part.
Fast-growing species often develop weaker stems and branches, according to Mr Ramesh.
And those with codominant structures - where the stem from a single point of origin branches out into more than one - are more prone to falling.
Others have shallow root systems or brittle branches and twigs, making them more vulnerable to external forces.
Mr Ramesh pointed out that trees with shallow roots and heavy crowns - such as the Falcataria falcata and African Tulip - are commonly found in Singapore's forested areas.
Related:
Are there signs to look out for?
A tree at risk of falling may show signs of structural weakness. These include leaning, cracks or splits in the trunk, soil lifting around the roots or decay and infestations, said Mr Ramesh.
The latter can occur below ground, making it undetectable without specialised methods. One of these is root exploratory trenching, which involves excavating the soil around the tree base to examine the condition of the roots.
It's not possible to predict exactly when a tree may fall. But there are events that heighten the risk of that happening, said Mr Ramesh.
Inclement weather like lightning strikes, strong winds or monsoon and rainy seasons, are examples.
In an urban setting, trees located between buildings could also face increased wind exposure due to a wind tunnelling effect.
Unpredictable conditions such as microbursts - strong downward rushes of wind - can also topple trees, even healthy ones.
Related:
How are the risks mitigated?
Through a combination of proper care, maintenance, regular inspections and environmental management, said Mr Ramesh.
At Mr Ramesh's landscaping firm, visual tree inspections are conducted every six months alongside pruning.
Here, an arborist evaluates the tree height, trunk girth and overall health and structure.
Based on observations, the arborist will then recommend steps such as removing parasites, fertilisation and chemical treatments.
It's not too different for Singapore's National Parks Board (NParks), which manages 6 out of 7 million trees in the country.
About 2 million overseen by NParks are urban trees along roads, in parks and gardens, and on state land. The rest are further away from human traffic.
The statutory board has a regime of inspection which involves assessing the trees' overall form, roots, trunks, branches and crown; and pruning to improve structure and balance.
Group director of NParks' streetscape division Oh Cheow Sheng said trees are inspected every six to 24 months, with the frequency depending on location and age.
"This is stepped up during periods of adverse weather conditions to reduce the risk of tree failure incidents," he told CNA.
Ahead of adverse weather periods, NParks also reduces or thins the crowns of mature trees to manage their height and reduce wind resistance in the canopy.
The remaining 1 million trees are managed by town councils, private landowners and other entities.
What else does NParks do for trees?
To cope with climate change, which may lead to more frequent and intense rainfall if not prolonged dry weather, authorities select hardier and drought-tolerant trees that are also able to withstand the harsher growing conditions in Singapore's urban environment.
NParks has also been replacing diseased and more vulnerable trees.
More of hardier species such as the Sea Gutta and Shore Laurel have been planted at parks, gardens and roadside verges, with their numbers increasing from around 25,400 in 2017 to 46,500 in 2023.
Mr Oh added that planting trees in a way that mimics a forest structure helps to increase their resilience.
"Trees are (then) able to provide mutual support, such as roots intertwining with nearby trees, and improved buffering against strong wind gusts," he said.
This forest structure also doubles up to make Singapore’s streets cooler and shadier for pedestrians.
NParks also uses technology to monitor tree movements or to model the impact of strong winds on the stability of trees. This then helps to guide the thinking on intervention measures to take.
Authorities cited such measures in helping to lower the number of tree incidents in Singapore, from about 3,100 in 2001 to around 430 in 2023.
Want an issue or topic explained? Email us at digitalnews [at] mediacorp.com.sg. Your question might become a story on our site.
Continue reading...