Ambient vibration of mature Hopea odorata trees

Using a triaxial accelerometer, tree movement was recorded on five chengal pasir [Hopea odorata (Dipterocarpaceae)] trees growing in a residential landscape in Singapore. On each tree, ambient movement was recorded using a triaxial accelerometer (AL100, Oregon Research Electronics, Tangent, Oregon, USA) attached to the trunk immediately below the crown. The accelerometer recorded movement continuously at 10 Hz within a range of +/- 2g over a one-week period. Attached to the trunk using two elastic cords, the sensor was oriented with its x-axis parallel to the longitudinal axis of the trunk, and the y- and z-axes of the sensor were oriented perpendicular and parallel, respectively, to a cross-sectional radius between the pith and bark. Using the same sensor, the trees were monitored sequentially over separate periods lasting approximately one week. The corresponding wind conditions were not measured during the study, and the dynamic mechanical behavior of each tree may reflect differences in environmental loads during each monitoring period. During installation, the morphometric characteristics of each tree were measured, including the trunk diameter at breast height (1.37 m above ground), DBH (m) and tree height, HTREE (m). At the same time, the height of the measurement location, HACC (m), and trunk diameter at the corresponding height, DACC were also recorded. After measurement, the data were combined into a single file containing time (s) in the first column and acceleration (g) measured along the x-, y-, and z-axes in the second, third, and fourth columns, respectively. To remove artefacts associated with the sensor installation process, the first 60 seconds and last 300 seconds were removed from each time history.