An Assessment of the Incidence and Significance of Spiral Grain in Young Conifer Trees

Spiral grain is a typical feature of timber growth and, whenever present, influences timber quality by causing a reduction in strength and affecting dimensional stability and finishing characteristics. Grain inclination may be appreciable in young growth timber, and, in establishment and tree improvement studies, estimates of spiral grain are of particular interest for selection purposes. Grain inclination, however, changes over relatively short periods in young growth, and, since the pattern of grain change commonly varies from tree to tree, comparative assessments based on single observations are of uncertain value. Where changes are appreciable, an estimate of spiral grain needs to be based on a series of observations, and a weighted average, which for disk material is called a spiral grain index, is proposed. The spiral grain index has a close relation to certain aspects of wood behavior attributed to spiral grain, notably twist on drying and some surface tearing. Besides being a measure of such technological characteristics, however, the index, by reducing a series of observations to a single figure, is particularly useful in comparative studies of spiral grain.

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