INTERCLONAL, INTRACLONAL AND WITHIN-TREE VARIATION IN WOOD DENSITY OF POPLAR HYBRID CLONES

Twenty-eight nine-year-old trees from ten clones of the hybrid Populus x euramericana at one site in south-central Quebec were sampled to determine the pattern of wood density variation within stems, within clones, and between clones. Sample disks were taken from each tree to examine the variation at four heights, whereas an increment core of 10 mm in diameter was extracted at breast height. Clones, trees, and heights have a highly significant effect on wood density, and the individual-tree broad-sense heritability is 0.64. The wood density of this hybrid tends to be high at the bottom of the tree, decreases to a minimum at mid-height, then increases again near the top of the merchantable stem. There is also a highly significant correlation between the weighted average wood density of the merchantable stem and the wood density of the increment core taken at breast height. Finally, wood density decreases as growth rate increases. However, the correlation is weak (r = -0.49) but statistically significant.