Sway Measurement of a Large Array of Trees Coupled With Canopy Turbulence - An Overview

Tree sway is widely acknowledged to influence the wind flow field inside and above a forest canopy, yet sway behavior and wind influences have not been quantitatively linked. Measuring the large-scale dynamics of tree sway is essential for validating how feedbacks between wind flows and forest stability operate. Monitoring the detailed motion of an array of trees large enough to capture the size of the coherent gusts that input energy into the canopy is unprecedented and only recently technologically possible. This field measurement campaign is underway in a mature coniferous forest canopy at the AmeriFlux forest site in Howland, Maine. Measurements are designed to quantify the elastic and aerodynamic properties of a large array of trees, and the temporal and spatial characteristics of tree-sway motions and their aerodynamic interactions with coherent turbulence wind fields in a forest canopy. Biaxial clinometers have been installed to measure the sway of an array of 150 trees and this dynamic and spatial information is coupled with corresponding sonic anemometer measurements from two towers. This paper will present an overview of the installation of the field site along with the first results linking tree sway to atmospheric phenomena.