Analysis And Research On The Risk Assessment Of Urban Green Space Trees In Hong Kong

The trees in the city are closely related to people’s daily lives.The health of the trees and the safety of the tree structure are very important of the city.Although the tree grows slowly,the health can also cause problems with different factors.There is a probability that the tree trunk or branches may break or be damaged by diseases and insects.Therefore,timely inspection and assessment of tree risks,and the implementation of different maintenance measures can reduce the risk of tree collapse and ensure the safety of the surrounding environment.In this study,non-destructive testing methods were used to investigate the health status of trees with DBH≥95 mm on 10 types of green spaces in Hong Kong cities.Assessing tree risk levels,studying potential risk factors of different tree species,tree risk capability ratings,and measures to reduce potential risks.The main findings of the study include:(1)A total of 13,916 trees with a DBH of 95 mm or more and 187 species of 126 genera in 56 families were recorded on the green space surveyed.The tree species are mainly concentrated in the Arecaceae,Moraceae,Caesalpiniaceae,Euphorbiaceae,Myrtaceae,Mimosaceae,Magnoliceae,Apocynaceae,Bignoniaceae and Rutaceae,accounting for 53.68%of the total.Arecaceae has the most species,with a total of 20 species.The number of trees in the green space is the highest in Arecaceae,with a total of 2,250 trees,accounting for16.17%,followed by Caesalpiniaceae,with a total of 1,954 trees accounting for 14.04%,and Moraceae with 1,564 trees accounting for 11.23%.56 families of 187 species of trees can be divided into 7 distributions,mainly tropical,accounting for 85.37%.The 126 genera are divided into 12 distributions,also mainly tropical,accounting for 84.06%.(2)The degree of maintenance of trees arranged from high to low after 10 green spaces:main road> regional parks> secondary schools> community halls and social welfare facilities>regional open parks> primary schools> residential land> neighborhood open space> roadside greening> tertiary college.(3)The health and structural conditions of trees on green space generally accounted for93.60%.Followed by poor,accounting for 2.46%.The best condition was the least,accounting for 3.42%.72 dead trees,accounting for 0.52% of the total.(4)Among the trees surveyed,343 trees had a potential risk of 2.47% of all trees.The trees with potential risks belong to 28 families,and the 5 families with the largest number of plants are Caesalpiniaceae,Moraceae,Mimosaceae,Euphorbiaceae and Lauraceae.Among them,there are 226 trees concentrated in the high risk category,accounting for 65.89% of all potential risk trees.(5)In the different height degree statistics of trees with potential risk,the trees of Caesalpiniaceae、Mimosaceae and Moraceae are all the families where the main potential tree species are concentrated.Evergreen and deciduous trees occupy 62.39% and 34.69% of the number of potential risk trees respectively.The most potential risk evergreen trees are Mimosaceae trees,accounting for 20.09%,and the most potential risk deciduous trees are Caesalpiniaceae,accounting for 30.25%.The number of green and deciduous trees accounted for 12.54% and 0.87% of the total potential risk respectively,and Caesalpiniaceae accounted for 7.29% and 10.50%.Native and exotic trees occupy 27.70% and 72.30% of the number of potential risk trees respectively.The most potentially risky native trees are Moraceae trees,accounting for 34.74%,and the most potentially risky exotic trees are Caesalpiniaceae,accounting for 19.76%.The number of Moraceae trees accounted potential risks of native trees and exotic trees for 9.62% and 4.96% of the total potential risk.Caesalpiniaceae accounted for 3.50% and 14.29%.(6)Tree removal and canopy pruning are the main methods to address the potential risks of trees.The main reasons for the removal of trees are leaning trunks,accounting for 38.87%of all removed trees,19.03% of tree cavity,18.22% of wood decay,5.26% of uprooting,5.26%of restricted root growth,and other diseases and pests Accounting for 2.43%.Caesalpiniaceae、Moraceae and Euphorbiaceae trees were removed at a higher rate,accounting for 72.22%,88.89% and 60.00% respectively.Crown pruning can solve the potential risk of tree unhealthy branch breaks.The crown pruning ratio of Moraceae trees is higher,accounting for 70.45%.This study found that Caesalpiniaceae and Moraceae trees are planted in the largest number,and the relative potential risk ratio will also be high.Among them,the Bauhinia ×blakeana in the Bauinia is a city flower of Hong Kong.Therefore,in addition to the large number of plants planted in the green space,they also like to plant same genu.The Bauhinia spp.always has a wide crown,fast growth,and the branches are easy to break and crack.The Ficus spp.tree in the Moraceae has a wide crown,which is easy to form a shading effect and grows well in Hong Kong.However,since the trees are tall,the planting area is often insufficient that makes the potential risks high.