Shrinkage and collapse in thin sections and blocks of Tasmanian mountain ash regrowth

Summary Shrinkage and moisture content measurements for thin sections of Eucalyptus regnans have shown that although total volumetric shrinkage was positively correlated with specific gravity, the relationship did not conform to the general equation s = f (Stamm 1935, 1952) in that the straight regression line was significantly different from a line passing through the origin. This contrasted with the relationship between shrinkage from 17% EMC to 0% moisture content and specific gravity which, in principle, complied with the Stamm formula. The discrepancy arose because shrinkage from the green condition to 17% EMC was negatively related to specific gravity owing to the high variability of the measured fibre saturation point and its negative correlation with specific gravity. These observations were affirmed in a comparison of unit shrinkage-specific gravity regressions where relationships were positively significant but the regression constants were not.Shrinkage behaviour in blocks of E. regnans did not comply with the Stamm formula although the average fibre saturation point (41.8%) was not significantly different from that for sections (38.2%). The near similarity derived from a significantly greater unit shrinkage in blocks (0.49) than that in sections (0.30). It was suggested that the much greater external shrinkage in blocks contained a significant increment of cell collapse induced by drying stress below the fibre saturation point.The authors wish to thank Dr. Allan Miller for statistical assistance and Dr. Aleck Hunter for mathematical assessment