Collapse, volumetric shrinkage, specific gravity and extractives in Eucalyptus and other species

Summary

An examination of shrinkage behaviour in a range of tree species has demonstrated clear differences between eucalypts and other species with respect to the volumetric shrinkage (S)/specific gravity (ϱ) ratio. The equation S=fϱ proposed by Stamm (1935a, 1952) to relate this ratio to the fibre saturation point (f) was inapplicable in eucalypts, both before reconditioning, where a highly negatively significant linear correlation was observed between S and ϱ, and after reconditioning where the correlation was not significant and the regression line indicated S to be nearly constant. Collapse was found to be highly negatively correlated with specific gravity in the eucalypt species and evidently was primarily responsible for the negative S/ϱ relationship before reconditioning.

In non-eucalypts S and ϱ were highly positively correlated, but the regression line did not pass through the origin and the slope was 10 to 14% less than the value of 28% suggested by Stamm for f. Only when the regression line was artificially forced through zero did the slope approach postulated fibre saturation point values. A power function was proposed as representing a more reasonable fit of the data.

In line with these analyses, unit shrinkage (S_u) was shown not to be equivalent to ϱ. This lack of equivalence was expressed as S_u divided by basic density (γ) which was termed the R-ratio and which was shown to be equal to the change in volume during shrinkage (or swelling) divided by the associated change in the weight of an equivalent volume of water. R was seldom equal to one, as required by the Stamm formula, and was negatively correlated with specific gravity in both eucalypts and non-eucalypts. A comparison of regression equations showed R values for eucalypts to be significantly different from those of non-eucalypts. Possible uses for the R-ratio were considered.