Urban tree management is a long existing challenge for highly populated cities. In Hong Kong, there were several fatal accidents due to tree failure. However, traditional methods for tree risk assessment are non-real time, wireless monitoring. Trees are living species which might change over time. Adopting tree sensing technologies to monitor the health condition of trees becomes necessary, facilitating urban forestry and minimizing the manpower. However, power consumption and cost are the two major challenges for current tree sensing technologies. Hence, the main objective of this research is to implement a LoRaWAN-based, wireless, real-time and low power tree monitoring system, called Internet of Tree Things (IoTT), for studying the tree falling process in a quantitative manne...[ Read more ]

Urban tree management is a long existing challenge for highly populated cities. In Hong Kong, there were several fatal accidents due to tree failure. However, traditional methods for tree risk assessment are non-real time, wireless monitoring. Trees are living species which might change over time. Adopting tree sensing technologies to monitor the health condition of trees becomes necessary, facilitating urban forestry and minimizing the manpower. However, power consumption and cost are the two major challenges for current tree sensing technologies. Hence, the main objective of this research is to implement a LoRaWAN-based, wireless, real-time and low power tree monitoring system, called Internet of Tree Things (IoTT), for studying the tree falling process in a quantitative manner from biomechanics point of view; and to find a precursory signal to predict the tree failure.

Super typhoon Mangkhut, one of the strongest typhoons in the Hong Kong’s history, brought us hurricane wind, toppled more than 60,800 trees in Hong Kong. The performance of IoTT system was fully examined, recording valuable data sets of tree motion and tree falling processes in response to dynamic wind load. Four types of tree failure are captured. No universal tilting angle before tree failure can be determined because trees are living species, which are unique among each other, giving different response during typhoon.

A newly wind tipping curve, temporal wind tipping curve, is proposed to study movement of tree before failure. The transition from elastic to elastoplastic responses of a tree structure can be readily seen before the final failure state is reached. Within the elastic range, the tree tilting responses increases linearly with the wind speed, symmetrically vibrating along the linear elastic loading path, and no permanent tilting is measured after the typhoon. If the tree structure has entered the stage of elastoplastic responses, the associated vibration responses gradually become asymmetrical and greater, and greater tilting angles can be found concentrated along the tree leaning direction. When the tilting angle continues to increase, the tree finally collapses.

After the typhoon Mangkhut, there are lots of damaged trees which did not topple during the strike of typhoon Mangkhut. These trees might recover itself, but also might fail due to pest and fungus infection or adverse loadings induced by extreme weather events. Therefore continuous monitoring on these trees should be carried out, giving additional information for arborists to analysis the health condition of the trees such that proper tree treatments can be provided, not only protect the public against tree failure, but also safe the trees.