Written Answer by Ministry of National Development on whether NParks can consider inspecting all trees more regularly, in light of heavy winds and rains occurring more frequently causing many trees to uproot and fall

May 10, 2021

Ms Joan Pereira: To ask the Minister for National Development in light of heavy winds and rains occurring more frequently causing many trees to uproot and fall onto cars, roads and public amenities, whether NParks can consider (i) inspecting all trees more regularly than the current practice and (ii)  providing a guide for the public to help spot signs of a tree that is rotting, diseased or in need of inspection so that they can contact the authorities to conduct further checks.

Answer:

NParks has a rigorous tree inspection and maintenance regime that is aligned with the Best Management Practices of the International Society of Arboriculture. Regular tree inspections are carried out by trained inspectors every six to 24 months, depending on the location and size of the tree. Trees that are close to areas with high pedestrian or traffic activity are inspected more frequently. 

Over the years, NParks has strengthened its tree inspection regime in response to changing weather patterns. For instance, when tree inspections were first introduced, trees along expressways and major roads were inspected once every 12 to 18 months. Since 2012, the frequency of these checks has increased to once every six to 12 months. As a precautionary measure in response to changing weather conditions, NParks also introduced an annual in-depth inspection for trees of more than four metres in girth since 2016, which is over and above the Best Management Practices of the International Society of Arboriculture. 

Besides tree inspections, NParks has other measures to mitigate the risks of tree failure due to strong winds and heavy rains. First, NParks prunes trees regularly to remove weak, dry or overgrown branches, to improve their structure and balance, and ability to withstand severe weather conditions. It also undertakes targeted crown reduction and pruning of trees prior to seasons of wet weather. Second, NParks is progressively replacing storm-vulnerable tree species with hardier species. Third, NParks uses technology to analyse risks and improve inspection processes. For instance, it is piloting modelling techniques to understand the impact of adverse environmental conditions, such as strong winds, on the structural integrity of trees. This will help NParks to better determine the pruning required to improve tree stability. 

With this comprehensive tree management programme, NParks has reduced the number of tree failure incidents by almost nine-fold, from 3,100 in 2000 to 339 in 2020. However, even with these efforts, it is not possible to completely prevent tree-related incidents. Even healthy and structurally-sound trees can still be affected by exceptionally strong winds or heavy rainfall. Nonetheless, NParks will continue to review its tree management programme to ensure that it remains robust and comprehensive, and that our trees do not pose a safety hazard to the public.  

Lastly, I thank the Member for her suggestion to rope in the public to help NParks in these efforts. Recognising potential tree hazards requires assessing the health and structural integrity of trees. This is best carried out by trained personnel with the requisite experience and expertise, as this requires a good understanding of tree anatomy and physiology, including the various ways that disease and decay can manifest in trees. Nevertheless, members of the public who spot some obvious hazards, such as a snapped branch hanging from a tree after a storm, or a dead tree following a period of severe drought, or who have feedback on public trees, can contact NParks via its hotline, 1800-471-7300, or through the OneService mobile application. NParks will follow up on the feedback to inspect the trees.