Tree mechanics and wind loading

Abstract

The response of trees to applied wind loads ranges from minor movement of leaves, branches and stems through to catastrophic failure in the form of stem breakage and uprooting. Catastrophic wind damage is a major source of economic loss in managed forests but is also an important ecological process in natural forests. Exposure to chronic wind stress results in a number of thigmomorphogenic responses including changes in tree shape and internal wood properties. In order to better understand the impacts of wind on trees, knowledge is required on wind loading of trees and their response to these loads. In this chapter, we provide an overview of the mechanics of wind loading of trees, starting with the drag force acting on trees for a given wind speed and how this wind speed varies within forest canopies. We then discuss how this load is resisted by the stem and root system, including tree dynamic response to fluctuating wind loads. Throughout the chapter, we focus on advances in instrumentation and modelling techniques that have aided our understanding of this complex phenomenon. We also highlight some of the key gaps in our knowledge and suggest future directions where research advances could be made. An improved knowledge of the mechanics of wind loading on trees aids the better management of the risk of damage to forests and a better understanding of the thigmomorphogenic responses of trees to wind stress and the biomechanical benefits these confer. It can also aid our understanding of the effects of wind exposure on wood properties and the potential consequences for the wood products sector.