Wood density was studied in 18 clones of radiata pine (Pinus radiata
D. Don) replicated within and between four contrasting sites.
Clonal repeatabiiities were high, generally 0.75 or greater, and it appears that the standard deviation of genotypic values is about 6-10% of the population mean. Notwithstanding appreciable clonal differences in the density gradient, clonal correlations were high between density in the first and second five rings from the pith.
Site effects were large, but not altogether consistent among different parts of the tree. Expression of site and genotypic differences was generally greater at breast height than higher up.
Clone-site interactions, although statistically significant, were minor, the most important involving a phosphate-deficient site and elsewhere. The clones which were severely distressed on this site showed a slightly greater density increase, in relation to another site, than the remainder.
Within sites density was very little affected by non-genetic differences in ring width, which accounted for less than 5% of the phenotypic variance at standard sampling positions.
Evidence for clonal relationships between density and growth rate in general is inconclusive. However, it appears that outside the first five rings there is a positive effect of height coupled with a negative relationship with diameter. This accords with mechanical considerations.