Mature Khaya, sea apple trees being replaced around Singapore for safety reasons: NParks

SINGAPORE – Khaya trees introduced here in the 1980s have become a common streetside feature, their dense canopies providing shade and greenery.

But these trees, along with sea apple trees, are now being felled in HDB estates and other areas, to some residents’ dismay.

Bukit Panjang resident Christina Lee, 45, observed the Khaya trees in her HDB estate being cut down last month. She said she was unaware of the reasons behind their removal, although she had surmised that they were removed out of safety concerns.

“Since the trees were quite old, it’s a bit heartbreaking to see them go,” she added. “It’ll take a very long time for the trees to grow to that size.”

Khaya trees, also known as Senegal mahogany, are native to Africa. They were first used for roadside planting because of their rapid growth rate and ability to tolerate dry urban environments. They can reach 30m tall.

National Parks Board group director for streetscape Oh Cheow Sheng said Khaya (Khaya senegalensis) and sea apple (Syzygium grande) trees have been observed to be susceptible to basal rot – a fungal disease that causes decay at the base of a tree.

Damage to a tree’s anchoring roots can lead to tree failure – the breakage of the trunk, branches or roots – which may damage the tree’s surroundings or injure passers-by.

Such trees are now being removed in HDB estates and spaces managed by NParks for safety reasons.

“Planted decades ago, many of these trees have also outgrown their growing spaces, which now limits continued root growth and affects their long-term health,” Mr Oh said, in response to queries from The Straits Times.

“Trees that show signs of disease, are in poor health or structural condition, or are growing near areas with high human traffic or in limited growing spaces are prioritised for replacement.”

Associate Professor Adrian Loo, deputy director at the NUS Centre for Nature-based Climate Solutions, explained that as the natural habitat of Khaya trees is drier than Singapore, the trees may become susceptible to disease or vulnerable to tropical storms as they age.

“With climate change, more adverse weather conditions during the monsoons might also cause more tree falls in this tree species with a weakened root support,” added Prof Loo, who has a background in botany.

Mr Oh said NParks has been progressively replacing the trees with both introduced and native species deemed better suited to Singapore’s environment, such as the rain tree (Samanea saman), shore laurel (Neolitsea cassia) and sea gutta (Planchonella obovata).

“Trees assessed to pose a lower risk to public safety – such as those located in forested or open areas away from buildings or human traffic – will be retained,” he added.

“In some places, where possible, replacement planting will be carried out prior to tree removal to mitigate the loss of greenery.”

NParks engages in the selective replacement of trees and the introduction of greater species diversity to sustain a healthy, resilient urban forest while ensuring public safety, said Mr Oh.

He added: “This approach becomes increasingly important with climate change, as we can expect more frequent and intense weather events that may bring increased wind speeds, higher rainfall, and potentially greater risks of tree incidents in urban environments.”

NParks has also advised town councils to replace some of the affected trees in their estates.

Jurong-Clementi-Bukit Batok and Holland-Bukit Panjang Town Councils are among those that have done so.

West Coast-Jurong West Town Council and Bishan-Toa Payoh Town Council have also posted explainers on their social media accounts regarding the replacement of Khaya trees around HDB estates.

Prof Loo said that the felled trees should be replaced quickly and substantially to minimise the impact of a lost tree on the benefits people receive from nature, such as shade, inspiration and cooler surroundings.

“Non-native trees that have been the fabric of our urban landscape are also useful in providing shade and may be less storm-vulnerable,” he added, raising the example of rain trees which originated from Central and South America but are now found across South-east Asia. 

Trees planted in urban environments also often undergo interventions and constraints such as pruning and restricted root zones, which may influence their stability, said forestry expert Lahiru Wijedasa. 

“Urban trees are planted for specific functions such as shade and microclimate regulation, and exist within an engineered and intensively managed environment,” he added. “In that sense, they are part of an engineered system, and over time, replacement becomes part of that lifecycle.”

Dr Lahiru, an ecologist at environmental consultancy and agroforestry firm ConservationLinks, added that many of Singapore’s large roadside trees were established decades ago, and Singapore has warmed substantially over time, which may introduce uncertainties regarding the performance of both existing and newly planted trees. 

However, managing the transition during the replacement of these trees is important, he said.

He said: “The key consideration when removing large mature trees is that they provide significant ecosystem functions – shading, cooling, carbon storage and habitat – that may take decades to replace. While new planting is essential, there will always be a temporal gap before younger trees can deliver similar benefits.”

This was echoed by former NParks divisional director of streetscape Simon John Longman, who also stressed the need for clear communication to the public over the removal plans of the Khaya trees.

“The trees provide public housing communities with shade, urban heat amelioration, and provide conducive community spaces for residents’ interaction, relaxation and recreation,” he said. “Their removal may also increase surface run-off, resulting in rainwater clogging drains and leading to floods.”

He added that depending on the percentage of Khaya trees affected by basal rot, increasing monitoring and only removing affected individuals might be a more proportional response.

Residents ST spoke to said they were unaware of why the trees in their HDB estates were removed, but saw safety precautions as a valid reason. There were also mixed reactions about the removal.

Jurong East resident Yeo Hee Kiow, 68, said that she was sad to see the trees go as they provided shade and helped to reduce noise from the road next to her block.

“I wish they could have kept the trees,” she said, adding that they had been around since she moved in more than 30 years ago. “But I guess it can’t be helped if the trees are suffering from diseases.”

Fellow resident Fatimah Ahmad, 68, said the removal of the trees allowed for more sunlight in her estate, adding that the trees required a fair amount of maintenance due to the leaves shed.