Author(s): FS Malan
In South Africa existing knowledge on the properties of the juvenile wood of Eucalyptus grandis, their variation and intercorrelation is seriously lacking and not in accordance with the species commercial importance. Such information is important because of the fact that a large proportion of this species is grown under intensive short-rotation management for the production of mining timber and pulpwood. In this study the intercorrelation between wood properties, the variation among families and the effect of growth rate on these properties were studied in 216 young trees sampled from a full-sib diallel progeny trial consisting of 72 families established in the Eastern Transvaal by the Department of Environment Affairs. Results of a factor analysis indicated that the variation in the basic wood properties of young E. grandis is adequately described by studying wood density, fibre lengths and vessel properties such as size, frequency and fractional volume. All these properties vary significantly among families suggesting some genetic influence. Heritability estimates obtained for density, fibre length and vessel diameter are more or less similar in magnitude to those found in previous studies. This, as well as a number of other studies, indicated no significant or practically important phenotypic correlation between growth rate and wood properties. On the other hand, significant negative genetic correlations of rate of growth with wood density and fibre length were found, although the estimates obtained were considerably less than previously calculated.