Tembusu tree that killed woman had no visible signs of decay

SIAU MING EN Today Online 18 Jul 17;

SINGAPORE — The Tembusu heritage tree that toppled and killed a woman at the Singapore Botanic Gardens earlier this year had decaying roots. However, there were no visible signs that warranted more intensive checks.

The weather conditions in the days before and on the day of the incident could have also contributed to the toppling of the 40m-tall tree, which was more than 270 years old.

These were the views of two arborists who testified at yesterday’s Coroner’s Inquiry into the death of Indian national Radhika Angara, 38.

She was with her French husband Jerome Rouch-Sirech and their one-year-old twins at the Singapore Botanic Gardens near the Shaw Foundation Symphony Stage on Feb 11 to attend an outdoor concert when the accident happened. Ms Angara was killed when the tree fell on her while four others, including her husband and children, were injured.

Among the witnesses who testified at the one-day hearing was arborist Derek Yap, a private consultant at Camphora. Mr Yap, who had spent a decade working for the National Parks Board (NParks) previously, said about 70 per cent of the tree trunk at its 2m point — measured from the ground level — was decayed, and this amount of decay would have affected the tree’s structural integrity.

Based on his inspection of the tree after it fell, coupled with information from Google maps in 2014, among other things, he said there were no signs of cracks or cavities on the tree. “The inspector would not have any signs to tell him that the tree had issues that would need additional mitigating measures. My opinion is that the tree failure was unpredictable,” he added.

It was likely that the tree had to bear an increased load from “a localised increase in wind speed” that day which, together with the “asymmetrical canopy” of the tree, caused it to topple, he said.

He also agreed with State Coroner Marvin Bay that there was a possibility that the decay had festered from 1859 — the last time the tree’s roots were cut when the Singapore Botanic Gardens was created.

Arborist Richard Gordon Thomas from ArborCulture noted that several factors could have contributed to the toppling of the tree, including the decayed roots and the rain in the preceding days which had softened the soil and made it harder for the roots to support the tree. “Tree failures, rarely or if ever, happen in an instance,” he said.

Unlike Mr Yap, Mr Thomas said it was not clear that the roots had been cut. However, the roots facing the road were stunted as the conditions under the road were not as conducive for root growth.

On the intensity of checks for the tree, both arborists agreed that signs of decay have to be observed from the visual tree assessments before calling for further checks, such as a resistograph and ultrasound to test for decay. Mr Yap added that as Tembusu trees are sensitive, it would be reflected in their canopies if the tree was having issues.

Several of Ms Angara’s family members were present at the hearing, including Mr Rouch-Sirech (above) and her sister Aarti Angara. Ms Aarti raised several questions, including whether older trees should be subjected to more checks. In response, Mr Yap said that while the maintenance schedule of the trees would be best answered by the NParks, the yearly inspections were adequate if there are no external signs of decay.

On her question if there should have been better risk management at the Gardens as it experiences more human traffic with its status as Unesco World Heritage Site, Mr Thomas said there could be more regular inspection of trees for such areas. But the levels or intensity of inspection does not depend on the age or size of the tree, he added.

Adjourning the inquiry to a closed-door session tomorrow, Mr Bay asked for the inspection schedule for the Tembusu tree — following changes to NParks’ inspection regime in November last year — and more recent images of the tree.