An early progeny trial in Pinus radiata. 4. Wood density

Variation in the density of the wood of Pinus radiata D. Don was studied in a progeny trial comprising 26 open-pollinated families arranged in nine randomised blocks. Samples of wood taken from different radii at breast height on 692 trees were divided into inner, middle, and outer segments, each containing five annual rings. The density of each segment and a mean for all 15 rings were determined for each tree. Analyses of variance showed highly significant differences between families and between blocks. Point estimates for heritability ranged from 0.51 to 0.72. On the basis of common knowledge, it may be assumed that on average each radial sample within a stem showed a consistent trend of density increasing with age, as xylem was deposited further and further from the pith. If, then, the variance of density is regarded as that of a point anywhere within the breast-height cross-sections of some 600 trees, a large part of the statistical effect of this trend may be extracted from the data as a linear regression component