LCQ21: Strengthening tree management

     Following is a question by Dr the Hon Lo Wai-kwok and a written reply by the Secretary for Development, Ms Bernadette Linn, in the Legislative Council today (October 26):

     In the middle of last month, a tree beside the carriageway of Perth Street, Ho Man Tin suddenly collapsed, hitting four vehicles. On strengthening tree management, will the Government inform this Council:
(1) whether the authorities stepped up inspection on trees located in areas with high pedestrian and vehicular traffic flows over the past three years; if so, set out the following information by year: the number of inspections conducted, the number of problematic trees identified and the percentage of trees followed up or removed;

(2) whether it will step up the application of smart technology, including making wider use of tilt sensors, so as to enhance the efficiency of tree inspection and strengthen tree risk management; if so, of the details; if not, the reasons for that; and

(3) whether it will expeditiously review and revise the "Guidelines for Tree Risk Assessment and Management Arrangement" and the "Street Tree Selection Guide" to improve the policy on tree planting and strengthen the coordination work for territory-wide tree management; if so, of the details; if not, the reasons for that?



     The Government is committed to the proper management of trees to ensure healthy tree growth and with safeguarding public safety as the prime objective. In respect of the questions raised by Dr the Hon Lo Wai-kwok, the reply is as follows:

(1) The Government adopts an "integrated approach" in conserving and managing our tree, under which departments responsible for maintaining the government facilities or land allocated to them are responsible for taking care of the trees thereon in accordance with the requirements and guidelines promulgated by the Development Bureau (DEVB). This approach allows the departments, while observing standing rules and regulations, to carry out appropriate routine tree maintenance effectively having regard to their specific work plans and internal arrangement.

     The Tree Management Office (TMO) of the DEVB co-ordinates departmental tree management work at the policy level. In order to systematically conduct tree risk assessments to reduce the risk of tree collapse, the TMO promulgated the "Guidelines for Tree Risk Assessment and Management Arrangement" (the Guidelines) in 2010 and has been revising and enhancing the content continuously as necessary. The latest version (9th version) of the Guidelines was formulated in 2020 to provide practical methods for tree management departments and the public in tree risk assessment and management.

     Before the onset of wet season every year, the tree management departments conduct tree risk assessment in areas with high pedestrian and vehicular flow according to the Guidelines issued by the TMO. The Guidelines list and describe various types of overall health and structural condition of trees to be attended to, the items to be assessed and the assessment tools to be used, for the inspection officer to make reference to, so that the tree risk assessment can be conducted correctly. The tree management departments will take appropriate mitigation measures according to the results of the tree assessment, including crown pruning and removal of dead branches. If the tree with risks of failure is identified, the tree management departments will remove it as soon as possible to ensure public safety.

     In the past three years, the number of tree inspections conducted by the tree management departments in areas with high pedestrian and vehicular flow, the number of problematic trees and the number of trees handled or removed are given in the table below:   
Year Number of tree inspections
(Generally, each inspection covers multiple trees, and the number of inspections does not represent the inspection efforts)
Number of problematic trees Number of trees handled
Mitigation measures completed Trees Removed
2021-22 43 562 20 955 14 596
6 359
2020-21 43 386 18 529 12 313
6 216
2019-20 47 961 20 823 13 023
7 800
     ‚ÄčApart from conducting tree risk assessment and follow-up treatment for about one million trees in urban areas with high pedestrian and vehicular flow every year, tree maintenance also forms part of the routine management duties of the relevant facilities. The number of this kind of routine tree inspection and maintenance work have not been recorded separately.
     In order to strengthen tree inspections, the TMO set up the Inspection Squad in October 2019 to systematically inspect and audit the tree inspection reports completed by the departments every year. This work ensures that the tree risk assessment work is carried out in a professional manner. Every year, the Inspection Squad randomly selects five per cent of the tree inspection reports completed by the departments for auditing to ensure departments have observed the Guidelines in conducting their work. In addition, the Inspection Squad proactively inspects trees in no less than 100 locations with high pedestrian and vehicular flow every year. In case a problematic tree is identified, the Inspection Squad will immediately request the relevant department to take follow-up actions to ensure public safety.
     Proper tree maintenance and systematic tree risk assessment are effective means to reduce the risk of tree failure. However, like other living organisms, trees will go through stages of a life cycle, including growth, aging, sickness and death. Numerous physiological and environmental factors may interact and affect tree health and stability. Unforeseeable variables inevitably exist. In the past three years, the number of fallen trees accounted for an average of about 0.03 per cent of the total number of trees in locations of high pedestrian and vehicular flow in Hong Kong. We will continue to work closely with departments to reduce the risk of tree failure and ensure public safety.

(2) The TMO has been actively exploring the application of various smart technologies for tree management. Regular meetings with departments were arranged to share and exchange the development and application of various tree management technologies and various trial studies among departments were conducted. At present, departments have widely used resistograph and tomograph technology to detect the internal decay of trees. In addition, we have also tried tree tilt sensors, tree labels with QR codes, tree management common platform, remote sensing multispectral images, 3D LiDAR sketching, mobile mapping systems, and the use of drones to assist in tree inspections. The TMO is also working with departments to study the use of penetrating radar devices to inspect tree roots, and the use of aerial photos and remote sensing technology for tree health monitoring, etc., in order to enhance efficiency of tree inspections and strengthen tree risk management.

(3) The DEVB has set up a Task Force chaired by the Permanent Secretary for Development (Works) in September this year to review the existing tree management guidelines, including review of the Guidelines, methods of tree inspection (including application of technology and instruments), tree species planted by the roadside, aboveground and underground growth spaces for trees, soil quality management requirements, etc. The Task Force will also monitor the work and implementation by departments after tree inspections, and consider whether the relatively large trees along the existing roads are compatible with the current environment and explore the direction of treatment, and will put forward appropriate enhancement and improvement suggestions on the above-mentioned issues. The Task Force plans to submit a report to the Secretary for Development at the end of this year.
Ends/Wednesday, October 26, 2022
Issued at HKT 15:00