Stability of Coniferous Tree Stems in Relation to Damage by Snow

In this work both conical and paraboloidal conifer stems are taken to bend along curves calculated to produce uniform strain in the outer wood. Such curvature has been observed in wind tunnel tests. From these curves for various displacements the resistive bending moment produced by the elasticity of the stem may be calculated. The maximum value of this is related to the breaking stress of the timber. The bending moments applied by the weights of stem, crown and snowload are calculated by obtaining the appropriate lever arms from the stem bending curves. Applied and resistive bending moments are compared for 20m-high trees of various types. Densely grown trees of low taper are least stable. Open grown trees with conical stems and high taper are most stable. The effects on tree stability of wind, a leaning stem, an asymmetrical crown and basal bowing are also investigated.