The secondary forests on both sides of Mandai Lake Road will soon make way for the Bird Park, which will move from Jurong, and the new Rainforest Park.

But developer Mandai Park Holdings (MPH) wants to preserve some of the decades-old trees and has engaged a tree expert to do the assessment. "We determine which trees to preserve based on a number of factors, including their size and species," said arborist Derek Yap.

They will be preserved in a way that ensures they remain healthy for years to come, he said yesterday, on the sidelines of an event held by MPH to brief the media on its environmental protection strategies.

"The development plans set out tree protection zones that are more than the bare minimum... As this is a forested context, we also preserve trees in clusters, and there will be a buffer around to ensure work does not encroach into these tree protection zones," Mr Yap said. A protection zone gives a tree room to grow, so its health is not impaired and its roots do not become unstable.

His assurance comes after a 270-year-old tembusu tree fell in the Botanic Gardens in February, killing a woman.

Evidence presented this month at a coroner's inquiry showed that the tree was decaying from the inside, although signs of the rot had not been visible to inspectors.

Mr Yap, the expert who took the stand, told the court that the rot could have started with the roots, and raised the possibility that this could have set in as far back as 1859, when the roots were last cut.

Yesterday, he noted that there have been major advances in arboriculture over the years. "When an arborist determines that works would result in a predictable failure of a tree, there has to be a dialogue between the parties involved," he said.

"Either the works are moved elsewhere, or the tree is removed. It is important to work with the contractor and designers - everyone has to come on board with the right mindset."

Audrey Tan