Case 3
This was a tree planted in a rectangular tree pit along a public pavement. It located at Oxford Road, Kowloon, Hong Kong (Figure 17).
The tree had a single trunk with 2 stems remained. Its diameter at breast height (DBH) measured at 1.3 m (AFCD, 2006) was 480 mm and the age class was mature. It was 7 m tall with around 5.5 m crown spread. The tree crown was not evenly spread as there was another tree on its west. (Figure 18)
The tree was actually had three stems but unfortunately, one of the stem was damage by super typhoon Mangkhut on 16 September 2018. A tearing wound around 4m above ground level (AGL) was found after the typhoon attack and fungal attack and ineffective CODIT was observed. Furthermore, severe twig dead back was found on one of the stem with no sign of living. And the live crown ration was very low as only one stem had chlorotic leafs remained and the size of leaf was relatively small comparing with other D. regia in the same street at the time of inspection. (Figure 19)
Apart from the tree crown, abnormal longitudinal cracks with bark peeling were found on trunk at about 2m to 4m AGL. They appeared from the North to the West. Furthermore, sap flow was also found on the trunk near the cracks. (Figure 20)
Although buttress root could be formed, abnormal bulging were found on the buttress root which indicated that the tree was under stress (Figure 21-22).
With the poor health and structural condition, a reisistograph was conducted (Figure 23-26). The measuring level was 50 cm and 100 cm AGL respectively as the arborist wanted to know the structural integrity in the lower trunk and the upper trunk was already in a poor structural and health condition. According to the measurement, the amplitude of wood strength was fluctuated abnormally and with a suspected internal decay at 50cm AGL.
As the tree was located at a pavement with high usage and near some primary school, considering its brittle nature (GLTMS) and the targets cannot be removed, the subject tree was planned to be felled with the following measures and suggestions in long term.
Short term action
- To remove the dead branches such that the likelihood of failure of branches will be decreased. (Figure 27)
- To apply tree felling application from the respective Tree Preservation Authority in Hong Kong for sake of public safety.
Long term action
To review the compensatory planting at the subject location and subject species. As the subject pavement is narrow (about 1.8m in width), the management party should evaluate the necessity of planting. Furthermore, as D. regia has buttress roots, it is not recommended to plant along narrow pavement according to the Street Tree Selection Guide published by GLTMS, HKSAR in 2018.
Tree Risk Management 