Monitoring of tree tilt motion using lorawan-based wireless tree sensing system (IoTT) during super typhoon Mangkhut

Managing urban forests in densely populated cities with narrow streets and compact environments is chal-lenging. This paper describes a city-scale, low power-consumption, and real-time tree monitoring system, called the Internet of Tree Things (IoTT). The IoTT system includes tree motion sensors for capturing tree movement in terms of the tilt angle, LoRaWAN gateways for wireless data transmission established in an economical way, and servers for data storage, big data analysis capability, and data visualization. The performance of IoTT under extreme weather conditions was fully examined during the devastating strike of super typhoon Mangkhut in September 2018. In addition, trees having different failure modes, such as uprooting, trunk fracture, and root ball sliding, were recorded by the IoTT and are presented in this paper. The corresponding biomechanistic behavior of the trees can be better revealed using the newly proposed temporal wind tipping curves and associated polar diagrams of the tilt angles. At the beginning of the passage of Mangkhut, the trees exhibited elastic responses, and the swaying gradually increased with the wind speed. After the wind speed continued to get stronger and once the elastic limit of the tree was exceeded (yield), clustered plastic deformation developed parallel to the dominant wind direction. This behavior can be considered as a meaningful indication of tree damage, indicating a potentially hazardous tree situation and, most importantly, can be used as real-time, supplemental information to support arborists in better decision-making in urban forest management.