Özet:

Density is a key wood quality trait, which is moderately to highly heritable, and has been the focus of selective breeding efforts in radiata pine (Pinus radiata D.Don) in New Zealand. Forest managers require information on realised gain in wood density in order to help them make decisions about which tree stocks to plant, how to manage stands and when to harvest in order to achieve certain wood quality outcomes. The aim of this study was to quantify realised genetic gain in radiata pine wood density and to incorporate it into existing modelling systems for predicting growth and wood quality. Methods: A national model of radiata pine wood density, which predicts wood density at breast height as a function of ring number from the pith and a “local parameter”, was modified to account for the effects of genetic improvement. The value of this local parameter was estimated for 679 radiata pine families with differing levels of genetic improvement (as quantified by their GF Plus rating for wood density) that were growing in 18 trials established by the Radiata Pine Breeding Company. The value of Wood Density Index (defined as the breast height outerwood density at age 20 years) was calculated from the estimate of the local parameter. Simulations were performed to show the impact of genetic improvement on whole-log average density and the variation in density within a log. Results: There was a strong positive relationship between GF Plus rating for wood density and Wood Density Index (R2 = 0.73), with a one-unit increase in GF Plus corresponding to a 2.16 kg m−3 increase in wood density. An increase in GF Plus density rating from 18 to 27 would result in an increase in breast height outerwood density at age 20 years of 18.5 kg m−3. Over the same range of genetic improvement, average whole-log density is predicted to increase by 14–16 kg m−3. Validation of the model using independent data from older trees showed that it was able to correctly predict the effect of genetic improvement. It also indicated that the assumption that the expression of genetic gain is constant across sites with different wood density potentials is valid, although data from additional trials located across a wider range of sites is required to confirm this. Conclusions: The effect of genetic improvement on wood density has been quantified and included in growth and yield modelling systems. This enables forest managers to estimate wood density in radiata pine plantations for any site and management regime established using tree stocks with a specific wood density rating.

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