Incidents of fallen trees and branches at their lowest since 2001: NParks

Samantha Boh Straits Times 6 Dec 17;

SINGAPORE - Despite online chatter, which suggests the opposite, incidents of falling trees and branches have dropped to their lowest level since recording began 16 years ago.

Though at least five cases of toppled trees and falling branches were fingered for causing traffic jams and damaging vehicles last month (November), the 361 incidents reported this year is a decline of more than 85 per cent from 3,000 in 2001, the National Parks Board (NParks) said.

The number is also less than half of the 800 recorded last year, and involved mostly snapped branches, rather than uprooted trees, NParks added.

NParks credits the plummeting figures to its tree management programme, in which trees are inspected and pruned rigorously, and those in danger of falling are replaced.

"We are also currently developing modelling techniques to better understand the behaviour of trees under varying environmental conditions, said Mr Oh Cheow Sheng, group director of streetscape at NParks, which manages about two million trees along streets, in parks and on statelands.

NParks has also been replacing storm-vulnerable species, such as the rapidly-growing Albizia and Spathodea trees, in forested areas next to roads.

For instance, a plot opposite the Bukit Batok Nature Park was cleared recently by the agency over safety concerns. It had been covered with Albizia trees, which are vulnerable to storms and more prone to falling because of their brittle wood structure and shallow roots. NParks is replanting the plot with native plants.

Other enhancements to the tree management programme, introduced in May last year, include pruning and crown reduction before periods of more severe weather events, such as the storms which slash the island during December's northeast monsoon. This is done on top of normal tree pruning.

The critical role of tree maintenance was brought to the fore after a 40m tall tembusu heritage tree in the Singapore Botanic Gardens fell and killed a woman in February. St George's Church at Minden Road had a 30m tall tembusu tree on its premises inspected after the incident, and had it chopped down when it was deemed unhealthy.

During tree inspection and pruning, a detailed visual tree assessment is first carried out of the root collar - where the stem and roots meet - trunk, and canopy of the individual tree.

Where necessary, a second-level advanced tree inspection is then conducted involving the use of specialised diagnostic equipment such as the resistograph and tomograph.

A resistograph is a tool used to drill into the tree's trunk. The resistance the drill meets is an indication of whether there is decay - decayed wood would offer less resistance.

A sonic tomography measures the speed sound travels through the wood. Sound travels slower through decayed wood than healthy wood.

"We will continue to review our tree management regime to ensure that it remains robust and comprehensive," said Mr Oh.

Botanist Shawn Lum, a senior lecturer at Nanyang Technological University's Asian School of the Environment, said even with regular inspections and maintenance, an accident can still happen due to unexpected natural elements, such as a sudden strong gust of wind, or a long bout of heavy rain that loosens the soil.

"There are so many variables that it would be impossible to have zero tree falls or fallen tree branches...but what can be done is to keep them to a minimum, he said.

"The alternative is to have a treeless city."