Continuous monitoring of water loading of trees and canopy rainfall interception using the strain gauge method

A non-destructive continuous monitoring technology was developed for documenting diurnal changes in branch weight using resistance strain gauges. The capacity of rainfall interception by the canopy can be directly measured by attaching strain gauges to the branch. The amount of water loaded in tree reaches a maximum in the early morning, and a minimum in the afternoon. Thus, the branch is the heaviest in the early morning, and the lightest in the afternoon. Differences between the weight in the morning and in the afternoon can represent as the daily change in water loading of the branch. The branch can be considered as an elastic cantilever in response to the changes in weight of water carried by the branchlets and leaves, and the changes in strain are caused by the change in the bending stress of branch. Thus, the branch increases its weight when rainfall interception occurs, that also changes the stress of branch. The technique reported in this paper will provide an effective approach to investigating biological biometrics.本研究开发了一种采用电阻应变片（resistance strain gauges）的无损连续监测技术，用于记录枝条重量的日变化特征。将应变片粘贴于枝条后，可直接测定林冠的降雨截留容量。树木承载的水量于清晨达到最大值，午后降至最小值，因此枝条重量在清晨最大、午后最轻。枝条早晚的重量差值可表征其载水量的日变化情况。枝条可被视为弹性悬臂梁（elastic cantilever），能够响应小枝与叶片所承载水量的重量变化；而应变变化则由枝条弯曲应力的改变所引发。因此，当发生降雨截留时，枝条重量会增加，其内部应力也随之改变。本文所报道的监测技术将为生物计量研究提供一种有效途径。