An Investigation of Fraxinus Americana Branch Sway Using a 3 Dimensional Motion Capture System

Abstract Wind is a dominant abiotic factor that a tree experiences throughout its lifetime and can cause severe tree damage, resulting in risk of injury to humans, and economic and ecological losses. It is thought that trees develop structural properties and architectures that help withstand loading conditions by dissipating wind energy through damping mechanisms. The role of branch motion in reducing potential dangerous wind loads has been the focus of relatively few studies. Even fewer studies have examined tree sway response to natural wind loaded conditions. In this investigation, branch frequencies were calculated for three Fraxinus americana using a three-dimensional motion capture system for both wind loading and hand loading conditions. Individual branch frequencies and phase angle values were calculated after portions of the tree crown mass were removed. Wind loaded branch sway frequencies ranged between 0.2 and 1.1 Hz while the pull and release test induced mean frequencies of 0.2 Hz. There was no significant difference between phase angle shifts or frequencies after the removal of tree crown mass. The hypotheses tested require further investigation as the interference with neighboring tree crowns prevented desired tree sway dynamics to occur