RELATIONSHIPS AMONG GROWTH STRAIN, DENSITY AND STRENGTH PROPERTIES IN 2 SPECIES OF EUCALYPTUS

An examination of eleven, nominally straight and vertical, 36-year-old trees of Eucalptus regnans and ten, similarly orientated, eight-year-old trees of E. nitens demonstrated differences between the species in terms of relationships between growth strain (epsilon-g) or growth stress (sigma-g) and other wood properties. Whereas in E. regnans growth strain and stress were highly significantly related to density (gamma) and inversely related to maximum crushing strength (M(s)) after adjustment for density, in E. nitens these relationships did not apply, or did so only at a low significance level. M(s) was not significantly related to density in E. regnans but in E. nitens M(s) and gamma were highly positively correlated. Exclusion of strain values in E. regnans higher than the highest value meausured for E. nitens (modified E. regnans) tended to reduce or eliminate such differences between the two species. The presence of tension wood was discussed as a factor possibly contributing to initial differences. In no instance was growth strain significantly correlated with modulus of elasticity (E). However, in all cases E was significantly correlated with both density and maximum crushing strength. The relationship between E and gamma became more highly significant after exclusion of high strain values in E. regnans. After all adjustments, there were no significant differences between species for either growth strain or density; growth stress, initially near significance before omission of high strain values, thereafter showed no suggestion of a significant difference. Similarly, maximum crushing strength, initially significantly greater for E. nitens, generally was not significantly different from modified E. regnans data. However, modulus of elasticity was significantly greater for E. regnans both before and after exclusion of high strain values, a fact reflected by differences in published mechanical properties between the species and suggesting different conformation in the type and/or disposition of their respective cellular structure.