LCQ9: Sealing up the gaps between paving blocks around the trees on pavements
Following is a question by the Hon Chan Chi-chuen and a written reply by the Secretary for Development, Mr Michael Wong, in the Legislative Council today (February 7):
According to paragraph 6(iv) of the Guideline on Pavement Renovation Works and Tree Stability issued in April 2013 by the Greening, Landscape and Tree Management Section of the Development Bureau, the authorities recommend that for the healthy growth of trees in paved area, removable and permeable paving blocks should be used on the sand base around trees. However, I have recently received complaints from members of the public that certain government departments often apply glue to seal up the gaps between paving blocks (gap sealing) around the trees on pavements. They were concerned that this practice will hinder the tree roots from absorbing sufficient rainwater and air, thus jeopardising the health of the trees. In this connection, will the Government inform this Council:
(1) among the gap sealing works carried out in the past two years by various government departments, of the number of those the scope of which covered paving blocks within the canopy spread of trees, with a breakdown by reason for carrying out the works;
(2) whether it conducted in the past three years any study on the impacts of sealing up the gaps between paving blocks around trees on the health of the trees; if so, of the details; if not, the reasons for that; and
(3) whether it will issue guidelines to various government departments to provide that the gaps between paving blocks within the canopy spread of trees must not be sealed up in order to avoid jeopardising the health of the trees?
The Greening, Landscape and Tree Management Section of the Development Bureau promulgated the Guideline on Pavement Renovation Works and Tree Stability (the Guideline) in April 2013. Paragraph 6(iv) of the Guideline recommends that flexible and permeable paver blocks, instead of concrete cover, should be used for tree pits. The intention of this provision is to facilitate removal of the pavers around the tree pits to allow more room for the growth and spread of tree roots, and not to provide an alternative means of air and water supply for tree growth.
My reply to the various parts of the Hon Chan Chi-chuen's question is as follows:
(1) In the past two years, Joint Stabilising Sealant (JSS) was applied to seal up the gaps between paver blocks at 67 street locations with trees within the territory (see Annex). JSS was applied as part of routine maintenance works to strengthen paver blocks in order to address different pavement issues, such as preventing uneven settlement that would affect pedestrian safety, avoiding sand loss caused by cleansing with high-pressure water jets and forestalling the growth of moss and weeds in the gaps between paving blocks. We have not compiled statistics on the application of JSS by the reasons outlined above.
(2) and (3) Openings are provided around a tree pit before actual tree planting to supply water and air needed for its healthy growth. While water and air may seep through the gaps between paver blocks, these are not the primary sources of water intake for trees. Application of JSS would not jeopardise the health of trees. The practice is consistent with paragraph 6(iv) of the Guideline as sealed paver blocks can be removed as and when trees grow in size. At present, we have no plan to conduct study on the possible impact of sealing the gaps between paver blocks on tree health. Sealing the gaps between paver blocks can prevent uneven ground settlement and sand loss, and help protect pedestrian safety. This method is also used around the world. We will continue to adopt this method in the maintenance of paved areas as and when appropriate and necessary.
Ends/Wednesday, February 7, 2018
Issued at HKT 17:12