On the Measurement and Interpretation of Surface Growth Strains

Abstract

An important stimulus to growth stress research has been the development in recent years of a number of growth strain measurement techniques. A whole range of techniques have been used for different purposes. The need for simple nondestructive measurements of surface strain in standing trees has been met by mechanical and electrical methods carried out on small isolated elements. The methods of plank-stripping and disk-cutting previously used to estimate internal residual strain distributions have been extended to obtain far more specific information. The data obtained indicate that residual growth strains and stresses over the tree surfaces are the result of regular and systematic induction of growth strains in the developing cambial zone. It will be seen that growth strains are closely related to variations of elastic modulus, basic density, shrinkage, fiber class, and other factors connected with tree form and crown positioning. Thus, for some species where severe growth stress problems are encountered, it may be possible to combine genetic selection and silvicultural practices based on a knowledge of growth stresses to produce a more uniform and homogeneous wood product. A recent review (Kubler 1986) gives a very complete discussion of the literature on growth strain measurements in trees.