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 Seng 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.
National Parks Board group director Oh Cheow Seng. (Photo: Justin Ong)
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.
