Tree Risk Assessment Case 1 Canarium album 橄欖(白欖)

1. Tree species and size

The assessed tree was a mature Canarium album. The tree had 810mmdiameter at breast height (measured 1.3m above ground), 1 no. of trunk. Height was 12m and crown spread was 10m.

2. Target and location

The site is a public urban park in Yuen Long Park, Hong Kong. Frequently use recreation area by citizens. It has a vegetated slope located next to walking pathway and the slope toe was a road. Frequently pedestrians and vehicles passed through. The occupation of this area by pedestrian and vehicles‘Targets’ as well as the proximity of pedestrians and vehicles brings a high probability of risk. The existing target situation is summarized in below table 2.1:

Table 2.1 Existing target situation:

Target existing (Y/N)	Target removable (Y/N)	Site use restricted (Y/N)	Frequency of use
Y	N	N	High

The existing Targets cannot be removed from the garden or road area or be restricted in their access. Tree Risk Assessment on an Area Basis defines a high use area as having high risk and is considered under Category 2.

3. General Condition

Foliage density, leaves color and size were normal. Average tree vigor without leaning. Crown load was fair with medium live crown ratio. Only 5% dieback and few dead branches were observed.

4.Tree Defects

longitudinal splits from included bark to trunk base

Sap flow from wound and opening for pest and fungal disease attack causing decay.

Co-dominant branches were observed with included bark. A new longitudinal crack 1.5m long was found from co-dominant joint split along to trunk base. Bleeding flow appeared in the split area. Root conflicted with the adjacent tree.

5. Site Condition

The tree was planted in 1.5m area with sandy soil. Tree emerged the canopy and exposed to prevailing wind.

6. Conclusion and Mitigation Measure

Branch union with the longitudinal crack of 1.5m was observed with the associated defect of included bark which is not observed in the last inspection dated 2018/03/23. It is suspected that the new crack was caused by strong wind under Super Typhoon Mangkhut. The forks had a relatively high diameter ratio between their two branches, so consequently the incidence of branch failures was low in the test specimens. (Slater 2014) Disease, pest and fungal infection would intrude in the wound opening. Sap flow was found inside the crack indicating a decline in the wood structure was identified. Stubs and hanger were observed. Installation of cobra and a bracing rod was recommended to secure the codominant branches, crown reduction to reduce loading, crown cleaning to remove stub and hanger and reinspection within 3 months is proposed to monitor the situation. Signage was posted to alert the public the condition of the tree.

In this case, the tree is beloved by citizens. In fruiting seasons, they will come and collect the fruits. If remove the tree, will arouse public attention. Raise transparency of assessment report and communicate with the public is essential to prevent their emotional issue from conflicts. On the other hand, establish tree regulations may help to solve this kind of conflicts. If defective trees or pose high-risk trees could be removed mandatory. Arborists are authorized and permitted to carry out tree removal. Tree risk can be reduced.

Crown reduction and cleaning proposed to remove stubs, hangers and loading. Keep the tree form balance.

Propose to apply Cobra cable and bracing rod to stabilize the structure and prevent further split up the co-dominant branches from wind load.

7. Tree Plan

8. Citation

Duncan Slater and Prof, Roland Ennos. (2014). The level of occlusion of included bark affects the 2 strength of junctions in hazel (Corylus avellana L.), 27, 28.