Wind-induced forces in the near-surface lateral roots of radiata pine

Abstract

The wind-induced movement within near-surface lateral roots of a radiata pine ( Pinus radiata D. Don) tree were investigated to determine whether relationships exist between the resistive bending moment at the base of a tree and stresses in the near-surface lateral roots. The primary instrumentation consisted of four load cells split between windward and leeward roots, and two extensometers set at right angles to record stem deflection in the x– y plane. All instrument output signals were controlled by a data logger, and triggered at pre-set wind velocities to target data collection during specific storm events. The tree was calibrated by winching to obtain the forces that produced the range of stem deflections measured during storm events. After data collection, the test roots were calibrated in a laboratory to obtain the forces required to produce the wind-induced root deformation. The calibrations gave an estimation of relationships between root and tree movement, and root force and bending moment. A comparison of the forces measured in the leeward and windward roots during a storm event indicated a ratio of between 1:2 and 1:3 as the relative contribution to the strength of root anchorage provided by these roots.