NParks razed vegetated plot in Bukit Batok for public safety but some experts are concerned

Audrey Tan Straits Times 19 Nov 17;

SINGAPORE - A once-vegetated plot of land opposite the Bukit Batok Nature Park was last month razed by the National Parks Board (NParks) over public safety concerns.

The plot of land had been covered with Albizia trees, which are considered vulnerable to storms and more prone to falling due to their brittle wood structure and shallow roots. NParks is now replanting the plot with native plants.

But the move has drawn concerns from conservationists, who worry that a blanket removal of vegetation could result in rarer species being cut down too, and also have an impact on wildlife.

Environmental consultant Tony O'Dempsey said: "I support the removal of potentially dangerous trees and I applaud the move to immediately replant the areas.

"However I would like to see a more analytical approach to tree removal where trees are assessed and removed only where necessary and with care so as not to damage the remaining vegetation...This is particularly important in areas such as this, where native animals such as the colugo, civet cat and flying squirrels are likely to be affected."

NParks' group director of streetscape Oh Cheow Sheng said decisions to remove trees are made in the interest of public safety after careful consideration.

In the Bukit Batok case, the Albizia trees with a treefall zone overlapping the road were removed together with a smaller number of dead trees and those in poor health. Three big, sturdy and healthy trees growing in the area were retained.

A treefall zone refers to the area that will be affected by a tree when it falls, said botanist Shawn Lum, a senior lecturer at the Nanyang Technological University's Asian School of the Environment. He noted that a falling tree may also cause collateral damage.

If a tree is, say, 30m tall, its potential treefall zone will be a circle of at least 30m around the tree in all directions, said Dr Lum, who is also president of the Nature Society (Singapore). "Factor in the extra distance a tree may fall or slide to if it is on a slope, or the fact that a falling tree may knock over other trees in its path...then a conservative radius of a treefall zone may be considerably wider than the height of the tree."

The importance of tree maintenance in Singapore was highlighted 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 recently felled a 30m-tall tembusu tree on its premises after an arborist deemed it unhealthy. The church decided to have the tree inspected following the February incident.

Asked if NParks had taken more steps to reduce the chance of trees falling since the February case, Mr Oh said that the board has had a comprehensive tree management programme in place since the early 2000s.

"With the continued strengthening of our tree management regime over the years, the annual number of cases of fallen trees and branches has been reduced from about 3,000 in the year 2000 to about 800 cases in 2016," he said.

The Albizia, one of the fastest-growing species of trees in the world, can reach a height of more than 40m - about 11 storeys.

However, its rapid growth means that lower branches are shed quickly as they get shaded out by the branches above, said Dr Lum. "Given how massive the branches can be, falling Albizia branches are a real danger in areas used by people, in parks, for example."

However, Dr Lum said Albizia trees could be important to wildlife such as eagles that roost or nest only in very tall trees.

"While there is a real need to manage Albizia where people and property are at excessive risk, allowing Albizia, perhaps even encouraging it, in certain circumstances could be part of a holistic, ecologically aligned strategy for vegetation and wildlife management in Singapore" he said.