After a heavy storm on June 25, 25 trees fell but NParks says it is stepping up measures to cut down such incidences
Huang Huifen Straits Times 11 Jul 10;
The trees along the road provide shade and beautify the surroundings but recent thunderstorms turned some into 'instant killers'.
On a single day last month - June 25 - torrential rainfall toppled 25 trees. The result was massive highway jams, hefty property damage and at least four people injured.
Two of them were hurt when a Khaya Senegalensis tree fell across four lanes of traffic on the Central Expressway (CTE).
In response to queries, National Parks Board (NParks) told LifeStyle that it is a myth that 'instant' trees - a common name for grown trees that are transplanted from nurseries - are more susceptible to collapse in rainstorms.
'Transplanted trees are not more vulnerable in storms,' says director of NParks' Streetscape Simon Longman. There are more than a million trees under NParks' care.
He explains that transplanted trees are supported with sticks attached along the stem till they stabilise.
Sceptics may argue that transplanted trees may have shallow and weak root systems, and are thus easily uprooted.
But Mr Longman points out that the trees are grown in bags to prevent damage to the roots during the transplanting process, 'hence increasing their stability in their new environment'. He adds that a new soil mix consisting of organic matter and sand helps transplanted roots to grow better.
Instead, he attributes the recent spate of toppling trees to saturation of the soil with a huge volume of accumulated rainwater underground. The soil becomes soft and the tree cannot anchor itself to it.
NParks is taking steps to reduce falling trees in storms. These include inspecting trees more often. Those along expressways will be inspected once every nine months instead of once a year now. Trees along major roads will get annual checks instead of once every 18 months.
Crown reduction - a process where branches and leaves are trimmed to reduce the weight of a tree's foliage - will also be carried out on more trees.
Ultrasound and radar technology are used to assess unhealthy-looking trees for signs of decay. Roots are checked using a Tree Radar Unit which shows a clear layout of the tree's underground root system.
Stormy weather is not the only reason trees keel over. Some experts whom LifeStyle spoke to blame urbanisation.
Trees have to co-exist alongside roads and infrastructure, which can intrude into the space they have to grow in, says landscaping projects manager Chan Hon Mun.
Mr Chan, who works at landscaping firm Horti- Flora Services, adds: 'As a result, roots are not anchored properly. When these trees experience atypical wind conditions, they will be more likely to tip over.'
This is especially true for trees planted on roadsides and centre dividers. Rapid construction works, such as road widening, cable laying and pipelining, are also believed to be taking a toll on the trees' health.
The area these trees can set down roots in is already limited, says Mr Veera Sekaran, managing director of arboriculture consultancy firm Greenology. 'They cannot venture much beyond the limits of the concrete kerb or tarmac.'
He adds that many trees have roots no deeper than 80cm to anchor them.
NParks' response to this is that a 2m-wide road coast designated for tree-planting is allocated whenever new roads are built - and that is sufficient.
'There is also no limit to how deep the root can grow. If the road curves above canals or underground MRT stations, we will make sure that there is at least 2m of soil depth,' says Mr Longman.
But he agrees with the experts that soil compaction could affect tree stability. Soil compaction is when the soil is pressed down tightly by heavy weights such as vehicles or constant trampling, reducing its ability to allow the roots to absorb nutrients essential for growth.
It can be solved by using organic matter to break down the soil.
NParks' view is that one can only do so much when it comes to preventing trees from falling.
Mr Longman says: 'Trees are living things, unlike street signs where you can apply engineering solutions to prevent them from falling over. Our job is to keep falling trees to a minimum.'
Storm-vulnerable trees
What: Albizia (Paraserianthes falcataria)
Why: The fast growing tree has soft branches which are likely to snap.
Location: On vacant land and slopes along the Pan Island Expressway and Bukit Timah Expressway
What NParks has done: 650 trees have been removed or replaced over the last three years in areas with public access.
What: Andira inermis
Why: The fast growing tree tends to rot at the pruning points and fall off in storms.
Location: Most have been culled.
What NParks has done: The trees along roads were removed over the last six years.
What: Tabebuia rosea
Why: Borer beetle, a species of wood worm, tends to eat the bark of the tree and weaken the branch attachment, causing it to snap.
Location: North Buona Vista and Beach Road
What NParks has done: Insecticide is used to kill the borer beetles.
What: Angsana (Pterocarpus indicus)
Why: Heavy foliage at the end of the branch may cause it to snap.
Location: Orchard Road, Upper Serangoon Road, Ang Mo Kio housing estate, Changi Village and Yishun
What NParks has done: Regular crown reduction has reduced such incidences common in the 1980s.
The Khaya Senegalensis on the CTE near Ang Mo Kio Avenue 1 fell on June 25 because a huge volume of rain water had accumulated underground, saturating the soil. The soil became too soft and the roots of the tree were loosened. When strong winds blew, the tree was easily uprooted.
NParks to up checks and even plant sturdier ones
Wee Ling, Lynda Hong Channel NewsAsia 10 Jul 10;
SINGAPORE: The National Parks Board will increase checks on Singapore's trees and even plant sturdier ones to reduce the incidence of fallen trees.
The sight of fallen trees was evident during the recent heavy rains resulting in traffic woes for motorists and Singaporeans in general.
In fact, 68 trees were uprooted in a three-week period last more than double the number for the whole month of June last year.
NParks said it will increase the number of checks on trees especially those along the expressways from once a year to once every nine months.
Tree crowns will also be trimmed to ensure they can withstand the weather and trees found to be too fragile will be replaced with sturdier species.
Over the past three years, NParks has replaced some 850 such fragile trees. - CNA/vm
