Trees surrounding fallen Tembusu in Botanic Gardens are safe: NParks

Channel NewsAsia 12 Feb 17;

SINGAPORE: The National Parks Board (NParks) on Sunday (Feb 12) said it completed a detailed check on the trees in the Singapore Botanic Gardens' Palm Valley, a day after a massive Tembusu tree in the area fell, killing a woman and injuring four other people.

In a media statement, Commissioner of Parks and Recreation Dr Leong Chee Chiew said that the checks showed that the other trees in the area were safe, and added that NParks officials are in the midst of checking more trees in the Palm Valley vicinity.

Palm Valley remains closed to the public while investigations continue and the fallen tree is being cleared.

Dr Leong added that the rest of the Botanic Gardens remains open and is safe for the public to visit.

The Tembusu tree that fell was more than 270 years old and predates the establishment of the Singapore Botanic Gardens. It was 40m tall with a 6.5m girth, and brought down surrounding palm trees when it fell. The tree was last inspected in September 2016, NParks said, adding that such inspections include checks on the root collar, anchoring roots, crown, trunk and signs of soil movement.

One tree expert told Channel NewsAsia that the tree most likely toppled because the recent heavy rain had caused the soil to become waterlogged and to loosen.

"We want to assure the public that we share concerns about the safety of our trees in the Singapore Botanic Gardens, especially in view of the recent spate of intense weather conditions," said Dr Leong, adding that NParks has, over time, stepped up inspections in response to "increasingly unpredictable and severe weather conditions".

Dr Leong noted that previously, trees along expressways and major roads were inspected once every 12 to 18 months, and that since 2012, NParks has increased the frequency of inspections to once every six to 12 months. Since November 2016, trees more than 4m in girth are also subject to yearly detailed second-level inspections, he said.

Besides inspections, NParks also takes measures like routine mulching to supplement the regular application of fertilisers, and pruning techniques to improve the structure and balance of trees, he said.

"Going forward, we are already developing modelling techniques to better understand the structural behaviour of trees under varying environmental conditions like rain, wind and soil," said Dr Leong.

He also urged the public not to speculate on why the Tembusu fell, saying that NParks is still investigating the incident and its priority now is to help the families of the woman who was killed as well as those who were injured.

- CNA/am/dt


No effort will be spared to ensure Botanic Gardens remains safe: Lawrence Wong
Channel NewsAsia 12 Feb 17;

SINGAPORE: No effort will be spared to ensure that the Botanic Gardens remains safe for the public, said National Development Minister Lawrence Wong on Sunday (Feb 12), a day after a massive Tembusu tree toppled, killing a woman and injuring four others there.

Mr Wong noted in a Facebook post that it is unusual for a Tembusu tree, especially one recently assessed to be healthy, to fall without any warning, and that NParks has asked arborists and experts to investigate the matter.

The tree had been inspected last September and given a clean bill of health.

Mr Wong added that the gardens remain open although the affected area has been cordoned off while the fallen tree is cleared.

"The Botanic Gardens is our national treasure - we will spare no effort to ensure that it remains safe for all to enjoy," he said.

NParks earlier said it completed a detailed check on the trees in Palm Valley, where the Tembusu had fallen, and concluded that the other trees in the area were safe.

38-year-old Radhika Angara was killed when the tree fell on her and her family. Her husband and twin children are among those injured.

Mr Wong said he was shocked and saddened by the accident. "My deepest condolences to the family of the victim; and my prayers go out to the injured for a speedy recovery."

- CNA/dt


Despite safety fears, most want big trees to stay
TAN WEIZHEN Today Online 13 Feb 17;

SINGAPORE — Visitors to the Botanic Gardens on Sunday (Feb 12) said they were concerned about safety, given the fatality caused by the Tembusu tree that had fallen, but were against chopping down other large Tembusu trees to prevent a similar occurrence — an opinion echoed by nature experts.

Mdm Angie Ng, 76, a frequent visitor to the Gardens, was at the scene of the fallen tree to see the progress of the clean-up on Sunday morning.

“I’m concerned because, lately, the winds have been very strong, and it can be dangerous. However, I’m not in favour of chopping down the trees. Rather, more should be done to prune the trees properly,” said the retiree.

“I’m quite scared, I guess, and will avoid sitting under big trees for now,” said Mr Aaron Ong, who visits the Gardens weekly.

“However, there are so many old trees in Singapore, so we shouldn’t be chopping them down, but we should be doing more safety checks instead,” said the 30-year-old, who works in sales.

A 38-year-old woman from India was killed and four other people were injured when the 40m-tall Tembusu collapsed in the Singapore Botanic Gardens on Saturday afternoon. The tree, with a girth of 6.5m, was uprooted at 4.25pm at the edge of the Botanic Gardens’ Palm Valley, near the Shaw Foundation Symphony Stage.

Many visitors were flummoxed as to what could have caused the old tree — which had stood for more than 270 years — to fall.

“I’ve been wondering why, as precautions had been taken, and the trees were checked regularly. Also, if it could withstand weather conditions for the last 200 years, surely it could withstand strong winds!” said Mr Manendra Chaudhari, 55.

Experts say that generally, the National Parks Board (NParks) would have a string of comprehensive measures and regular checks in place, and that this could have been a one-off, freak accident that was hard to predict. They were also caught by surprise as Tembusu trees are known to be hardy.

Botany expert Shawn Lum, who is also the Nature Society president, said, “It’s about knowing which species are vulnerable, monitoring them frequently, and pruning them to keep them from becoming too top-heavy.”

He said some species of trees that are prone to breaking would be removed, where possible, to pre-empt incidents of them falling and potentially injuring people.

For example, trees from the genus albizia, wherever they are found close to human activity, would be removed by the authorities unless they grow in forested areas. But regardless, he said, incidents may occur.

“In Singapore, there are bursts of heavy wind, and they sometimes bring chunks of forests down. Through their sheer force, they can even bring down old, sturdy trees if the wind strikes them at their vulnerable parts,” he said.

Arborist Ng Tze Ping of TP Arbo Care, which provides tree consultation services, added that there are now many advanced technologies for monitoring trees.

“For older trees, more advanced equipment should be used. Now, there are ultrasound technologies, for instance, which can detect any internal decay. But NParks should be well equipped with the range of technologies needed,” he said.


After detailed checks, NParks declares trees in Botanic Gardens’ Palm Valley safe
Today Online 13 Feb 17;

SINGAPORE — The National Parks Board (NParks) has completed a “detailed check” on all the trees in Palm Valley in the Botanic Gardens, where a Tembusu heritage tree fell on Saturday — killing one person — and has found them to be safe.

And it is now conducting more checks on other trees in the vicinity, as well as all the heritage trees in the Gardens, it said on Sunday (Feb 12). There are now 63 heritage trees left in the Gardens.

In its latest update, NParks also gave more details of the inspection regime for the tree that fell. For example, its twice-yearly inspections included checks on the anchoring roots, crown, trunk and signs of soil movement.

“We want to assure the public that we share concerns about the safety of our trees in the Singapore Botanic Gardens, especially in view of the recent spate of intense weather conditions,” said NParks Commissioner of Parks and Recreation Leong Chee Chiew. “As we’re still investigating the tree fall incident, we should not speculate on the cause of the tree fall and allow the due process to take its course. Our priority now is to accord assistance to the families of the deceased and the injured.”

A 38-year-old woman from India was killed and four others were injured when the tree, 40m tall and 6.5m in girth, collapsed on Saturday afternoon near the Shaw Foundation Symphony Stage.

In response to the “increasingly unpredictable and severe weather conditions”, inspections of trees along expressways and major roads have been stepped up, said Dr Leong.

Previously done once every 12 to 18 months, depending on tree species, size and location, the frequency of inspections has been increased to once every six to 12 months since 2012.

And yearly “detailed second-level inspections” of old trees more than 4m in girth have been in place since November.

Experts said the definition of old trees varies from species to species, as each species matures at a different pace. According to arborist Ng Tze Ping of TP Arbo Care, Tembusu trees in Singapore older than 50 years can be considered old.

Measures to improve the general health of NParks’ trees have also been undertaken, added Dr Leong — for instance, pruning techniques to improve the structure and balance of trees. NParks has had an enhanced maintenance regime in place since last May, with further measures such as crown reduction and pruning before periods of severe weather conditions.

For heritage trees, pruning should be done twice a year if they are located in areas with high human traffic, said Mr Ng. According to NParks, which manages 5,000 Tembusu trees, the last time the fallen Tembusu tree was pruned was in August.

“Going forward, we’re already developing modelling techniques to better understand the structural behaviour of trees under varying environmental conditions like the rain, wind and soil,” said Dr Leong.

On Sunday morning, visitors clustered around the scene of the incident, taking pictures and speculating on the cause of the fall. While Palm Valley remained cordoned off from the public, the rest of the Gardens was open.

Workers at the fallen tree were sorting out bunches of branches and leaves and moving them away. At press time, workers were still cutting the trunk from its roots as lorries continued to remove portions of the tree from the Gardens.


Botanic Gardens tragedy: 'Not likely' tree fell owing to lack of space
Audrey Tan, Straits Times AsiaOne 13 Feb 17;

SINGAPORE - The 40m-tall tembusu tree that on Saturday (Feb 11) uprooted and killed a 38-year-old woman and left four others injured was unlikely to have fallen due to the lack of space, said Mr Lahiru Wijedasa, a former senior arborist at Singapore Botanic Gardens.

The 270-year-old tembusu tree had already been there when the Gardens was established in 1859, Mr Lahiru told The Straits Times.

"It has been standing in the Gardens for more than a century since the Gardens was built. If its roots had not been able to adapt to the development, we would have seen tree failure ages ago.

"If restricted rooting was the issue, the tree would have long adapted, as there hasn't been any developments around the tree except building the road 160 years ago," said Mr Lahiru, who is now pursuing a doctorate at the National University of Singapore.

Mr Lahiru, who was a senior arborist at the Gardens between 2006 and 2009, was responding to speculation that the tree had failed because it did not have enough space to spread its roots.

He urged members of the public to await the results of final investigations and not to jump to conclusions, adding that he had decided to speak up to clarify some of the speculations raised since the incident happened.

On suggestions that the tree might have been affected by the recent winds and rain, Mr Lahiru said the weather conditions could cause a "compromised" tree to be uprooted.

"But like a chair with four legs, one of which has been hollowed out by termites, there may not have been visual clues.

"The point is that even if measures are taken to reduce the risk by 99 per cent, there is always a one per cent chance of something happening," Mr Lahiru said, adding that NParks has done its due diligence to ensure tree health.

On another suggestion of having mature trees inspected monthly, Mr Lahiru said this may not help in identifying the cause of the problem, if symptoms did not manifest in other parts of the tree.

He pointed out that there is already a system in place to look out for such red flags. The National Parks Board (NParks), which manages the Singapore Botanic Gardens, does detailed, twice-yearly routine inspections, in addition to the daily visual checks by arborists patrolling the grounds, he said.

NParks Commissioner of Parks and Recreation Leong Chee Chiew said in a statement on Sunday that it adopts a systematic regime of inspection checks based on the tree care standards prescribed by the International Society of Arboriculture in the United States, which is of the highest international standards.

A 2015 document on NParks' website said such Visual Tree Assessments are a non-invasive method of evaluating diagnostic symptoms of internal defects and measuring probability of tree failure.

"Further investigations using diagnostic decay instruments will sometimes be required to quantify these defects and determine if a tree actually poses a hazard," said the document, which The Straits Times has seen.

Mr Lahiru explained that when a tree fails due to defects either in its crown, trunk, or roots, there are usually symptoms. These could include having a receding crown, leaves turning colour, or more leaves falling off than usual.

Crown or trunk damage can be assessed easily as they are above ground. If there is a termite infestation, for example, there would be track marks. Crown failure due to excessive branching is also prevented by NParks' practice of regular pruning.

But even if the roots are damaged, by rot or fungal infections, symptoms would be manifested above ground, by dying leaves, for example. This is because the roots of trees take in water, which is vital for the nutrition of the plant and survival of the whole tree, he said.

"In this case, there did not appear to have been such signs," said Mr Lahiru. NParks had determined the tree healthy during its last routine inspection in September 2016.

If a red flag had been detected, the next step in tree inspection would be to use technology such as ultrasound scans. But this is not the first line of defence for arborists, as such scans are invasive - they would require metallic sensors to be drilled into the trunk. Doing so could introduce viruses and fungus into the tree, said Mr Lahiru.

Even if no red flags are detected, there are measures in place to ensure tree health, Mr Lahiru said.

NParks has said it conducts routine mulching to supplement the regular application of fertilisers, as well as pruning techniques to improve the structure and balance of trees.

The Board has also since May 2016 taken additional steps in tree pruning, such as by undertaking crown reduction and pruning prior to periods of more severe weather conditions.


Inspection of trees in Singapore in line with global standards: NParks
Justin Ong Channel NewsAsia 15 Feb 17;

SINGAPORE: The inspection and care of trees in Singapore is in line with global standards, and in some areas exceed the best practices of the International Society of Arboriculture (ISA), the National Parks Board (NParks) said on Wednesday (Feb 15).

Group director Oh Cheow Sheng said NParks takes an “adaptive approach” to tree management. More stringent inspections have been implemented over time in response to unpredictable and severe weather patterns, he said.

He was speaking at a media briefing held in the wake of two separate incidents where trees toppled, causing injuries and killing one person.

Last Saturday, a woman was killed and four others injured when a large, 270-year-old heritage tree toppled at the Singapore Botanic Gardens. Two days later, another woman was put in intensive care after a tree at Yuan Ching Road fell on her.

The Tembusu tree in the Gardens case - which stands at 40m tall with a girth of 6.5m - was last inspected in September 2016. Due to its heritage status, it receives two checks a year - more frequently than other trees in the Gardens.

NParks said it could not discuss the reasons for the tree toppling as police investigations were still ongoing.

But Mr Oh said: "Trees react to changes in environmental, site and soil conditions. Tree care can mitigate risks but healthy trees can be affected by strong wind gusts and rainfall.

"On top of mitigation, a preventive measure against poor weather is to plant the right tree species in the right place - for example some are not suitable to be planted in waterlogged areas. Another possible measure is to increase the drainage around an area which is prone to being waterlogged by rainfall," he added.

TREES INSPECTED REGULARLY: NPARKS

According to NParks, trees along expressways and major roads are inspected once every six to 12 months. Trees more than 4m in girth are also subject to yearly detailed second-level inspections.

This compares to ISA standards of an inspection every one to two years.

A second-level inspection can be of invasive nature and involve diagnostic equipment, versus a visual first-level check for defects and vitality.

A visual inspection process involves assessing the general condition, inspecting the root collar and roots, inspecting the trunk and inspecting the branches and crown.

Second-level checks employ a resistograph and tomography setup. The former sees a drill bit penetrate the wood to take readings, while the latter measures time taken for sound to travel though wood - the slower, the more decayed.

Tree care staff also undergo arborist certification exams within two to three years of service, said Mr Oh.

Other measures are taken to improve the general health of trees, such as routine mulching to supplement the regular fertilisers and pruning techniques to better their structure and balance.

Pruning is done for reasons such as tree health, vehicular height clearance and to control tree growth. Crown reduction for tall trees with dense crowns is necessary to improve its ability to withstand inclement weather, said Mr Oh. He added that pruning takes place prior to periods of more severe weather conditions such as squalls and monsoons.


Windy conditions on day of Tembusu tree accident 'not unusual': Met Service
Channel NewsAsia 14 Feb 17;

SINGAPORE: It has been windy in Singapore the past week - something that is not unexpected as the National Environment Agency (NEA) had said in its latest advisory last Thursday (Feb 9) that there would be "windy conditions with widespread rain" on some days.

The weather conditions have prompted questions about whether they were a factor in toppling the large Tembusu tree at the Singapore Botanic Gardens last Saturday, which killed one person and injured four others. On Monday, a woman was sent to a hospital's intensive care unit after she was hit by a falling tree at Yuan Ching Road.

In response to queries, the Meteorological Service Singapore (MSS) said that on Feb 11 at about 4.30pm - around the time the Tembusu tree toppled - the wind sensor at Paya Lebar station, which is closest to the Botanic Gardens, recorded wind gusts of 27.8km/h.

That is lower than the 38.5km/h recorded earlier in the afternoon at about 2.20pm at the same weather station. These conditions are "not considered unusual", said MSS.

It added that strongest winds on Feb 11 were at East Coast Park, with the maximum wind gust at 58.3 km/h at around 5.30pm.

Experts told Channel NewsAsia on Tuesday (Feb 14) that the strong winds are normal at this time of the year.

According to the National University of Singapore's Assistant Professor of Geography Winston Chow, February is usually the windiest month of the year so breezy conditions are expected islandwide.

"The windy conditions are due to a monsoon surge of strong winds coming from the South China Sea that started Saturday morning and should last until tomorrow at least," he explained, adding that some places may be windier depending on microsite conditions such as the presence of buildings or slopes.

A similar assessment was given by atmospheric scientist Koh Tieh Yong, an associate professor at SIM University. "This is a typical seasonal weather pattern, evidenced within the same period in the previous years," he said. "The monsoon surge condition typically lasts for a few days up to two weeks. So occasional windy conditions can be expected during this period."

The cause of the Tembusu tree fall is still being investigated by the National Parks Board. The tree had been inspected last September and was given a clean bill of health.

- CNA/gs