抄録
We developed a method of measuring the turning moment for standing trees in natural wind. We used strain gauges attached to stems 1.3m in height to measure the strain to which they were exposed while swaying in the wind. The turning moment of the trees was obtained by multiplying the measured strain with coefficients determined by pulling tests of the trees.
We considered an adequate sampling frequency to detect the strain fluctuation peaks and pulling heights of tree stems to obtain coefficients in the pulling tests of trees. In our case, more than 10Hz of sampling frequency was needed to detect the peaks of the turning moment fluctuation. Pulling heights at the gravity center of wind were required to measure the coefficient due to the height dependency. We measured the turning moment for four trees in a coastal pine forest ( Pinus thunbergii ) in Aichi prefecture. The recorded maximum turning moment were estimated in 100Nm-600Nm for sample trees under strong wind conditions in 8 to 10m/s. Developed method is expected to use in evaluation of wind damage risk and ecological researches to clarify the effects of wind force to trees and forests.
