Clonal variation and repeatability of microfibril angle in Pinus radiata

Microfibril angle was measured at breast height on growth rings 1,5,10, and 15 from the pith, for two trees from each of 11 clones of Pinus radiata D. Don. Average breast-height values for both trees and clones were calculated by weighting individual ring values by relative growth ring area. Significant variation was observed both among clones, and within and between trees for each clone. The clonal repeatability (an estimate of broad-sense heritability) of unweighted microfibril angle was 0.7. The corresponding single ring values were high for rings 1 and 15 but were much lower for rings 5 and 10. Differences between trees within clones could be attributed to the presence of compression wood in some cases. Compression wood was associated with larger angles on average, although this was a variable effect for individual ring comparisons. Microfibril angle in ring 5 was the best predictor of average weighted breast-height microfibril angle for individual trees, indicating a potential for screening of young trees if required. The poor correlation of ring 15 values with weighted tree means suggests that outerwood microfibril angle is independent of corewood microfibril angle, or that the relationship varies among clones