How to Precisely Detect and Assess the Street Trees Risk ？ Risk Assessment Based on Precise Diagnosis Technology and Its Application

Traditional visual tree assessment is suitable for the rapid, large-scale assessment of urban tree risks, but it cannot precisely determine internal decay in trunks and underground root systems, may leading to highly subjective evaluation results. A risk matrix-based street tree risk assessment system was established by combining VTA method, nondestructive detection techniques, information acquisition and data analysis using GIS. The method was used to conduct risk detection and assessment on 1,001 street trees with a diameter at breast height greater than 40 cm in a Historic Features Protection Area of Shanghai. The result showed that: 1) The branch and the trunk risk possibility of the majority of street trees were at level 2 or below, while the root risk possibility of more than1/3 of the trees was at level 3 or above. 2) The risk level of 23% street trees was moderate or above, while that of other trees was at an acceptable level. 3) The street tree risk level shows a strong correlation with the presence of tree cavities, diseases and insect pests, the depth and range of root distribution, leaning, and internal decay in trunks, and the risk points are concentrated in the trunk and root system. Risk assessment of street trees based on precision diagnosis techniques can provide a new assessment system for the trees risk assessment in important urban areas, and the approach is conducive to the refined management of urban trees.