PiCUS Sonic Tomograph: A Case Study of Crimson Bottlebrush Tree (Melaleuca citrina (Curtis) Dum.Cours)

Abstract

Trees with a decreasing level of health and structure can become a threat to life and property if they are not properly managed. Thus, a regular visual tree assessment (VTA) is essential to monitor the trees’ conditions. A recent assessment, July 2022, by VTA on an existing Melaleuca citrina in the Forest Research Institute Malaysia (FRIM) showed poor canopy growth colonised by parasitic plants with the emergence of fruiting bodies (conk or mushroom) on its trunk, indicating internal wood decay. Tree inspection using an advanced approach of PiCUS Sonic Tomograph (PiCUS) was performed to evaluate the severity of the decayed trunk. As a non-invasive method, PiCUS measures the wood deterioration in trees using sound wave velocity that moves through the density of the wood. The thicknesses of the residual wall of trees with internal defects were recorded as colour-coded tomograms. The results were then compared with previous observations in the year 2017. The soil penetration test, pH and “The Jar Test” were also adopted to analyse soil properties and condition around the tree. The tomogram images showed an increased percentage of decay from 2017 to 2022 of approximately 2 to 78%, respectively. The sound wood also decreased from 82 to 14% for the respective period. The soil is categorised as silt loamy with pH value of 5.6 to 6.4 while the soil penetration test exceeds a value of 2.06 MPa, which restricts the root growth. This information is vital for further maintenance of urban trees and very useful for managerial decisions.