Wood Density Variation in Four Trees of South African Grown Eucalyptus grandis (Hill ex Maiden)

SYNOPSIS Two radial samples were randomly taken from each of seven height levels in four 27-year-old trees of Eucalyptus grandis (Hill ex Maiden) to study the within and between tree variation in basic wood density. Analyses of variance were carried out to examine those radial positions common to all height levels and trees according to the criterion of core and sheath sequence. In the core analysis (using data from the inner 11 radial positions) both the effect of distance from the pith and height above ground level were highly significant. Density exhibited a strong linear increase with increasing distance from the pith and increasing height. The significance of the latter suggests that wood formed by cambia of approximately the same physiological age but formed in successive years, varies with height above ground level. The effect of height and radial position accounted for about 60% and 8% of the actual variability respectively. In the sheath analysis (using data from the outer 11 radial positions) the effect of height above ground level was significant at a probability level of only 5% which suggests that the density of wood formed in the same year, but from a cambium of younger age, does not vary greatly with height above ground level. In both analyses (core and sheath) the interaction between trees and height levels were not significant, which means that the pattern of density variation with height above ground level does not vary significantly from tree to tree. Multiple regressions incorporating linear, quadratic as well as the interaction effects of distance from the pith and height levels were computed. For all trees pooled, the best model accounted for 72,2% of the total variation. For individual trees, the same model explained 74,2% to 87,3% of the total variation. This implies that a large proportion of the total variation among samples is caused by between-tree differences.