Valuing Breeding Traits for Appearance and Structural Timber in Radiata Pine
Degree GrantorUniversity of Canterbury
Degree NameDoctor of Philosophy
The aims of this thesis were; firstly, to obtain economic values for radiata pine traits to produce appearance and structural lumber, and secondly to analyze the selection of efficient logs and profitable trees to substantiate the development of breeding objectives for solid wood quality. The thesis included three approaches to value wood attributes: hedonic models, partial regressions and stochastic frontiers. Hedonic models generated economic values for pruned and unpruned log traits to produce appearance grades. Values for small end diameter were 0.33, 0.19 and 0.10 US $/mm, and for form 2.6, 1.4 and 0.63 US $ for the first, second and third log respectively. The value of mean internode length was 0.19 US $/cm. Branch size traits were non-significant to explain the log conversion return (p>0.05). The economic value of log traits to produce structural lumber with stiffness of 8, 10 and 12 GPa was estimated with a partial regression. The values were 1.1, 29.7, 0.3 and -0.4 NZ $/m3 for small end diameter (cm), stiffness (GPa), basic density (kg/m3) and largest branch (mm) respectively. Small end diameter and stiffness explained 73% of the variation of log conversion return. The economic values for structural attributes were also derived from a Cobb Douglas stochastic frontier, resulting in 2.1 NZ $/cm for small end diameter and 15.8 NZ $/GPa for stiffness. The change of values between approaches can be attributed to differences of model formulation. The stochastic frontier used aggregate volume of lumber with stiffness of 8 GPa or higher. The partial regression used the economic value of every lumber product derived from the logs, making it more sensitive to changes in wood quality. Data envelopment analysis (DEA) used structural traits and their economic values to assess the technical and economic efficiency of logs to produce lumber with stiffness of 8, 10 and 12 GPa. The most efficient logs had 1:4 ratios between stiffness and small end diameter, whereas logs that did not generate structural lumber had ratios closer to 1:8. Trait economic values from the partial regression analysis were used as attribute prices to estimate cost efficiency. Efficiency measures were significantly correlated with stiffness and log conversion return; however, they were non-significantly correlated with small end diameter and log prices. The technical efficiency of logs to produce structural lumber was also determined using a Cobb Douglas stochastic frontier which determined that the most efficient logs were characterized by a 1:5 ratio between stiffness and small end diameter. Selection of trees for deployment was analyzed with a portfolio model, where risk was represented as the mean absolute deviation of tree returns due to the variability of volume, stiffness and resin defects. Under high variability (risk), the model selected structural trees with large stiffness and high return. These results suggest an opportunity for narrowing genetic variability (via clonal or family forestry) to make the returns from radiata pine structural grades lumber less risky. As variability decreased the portfolio model opted for trees that produced appearance and structural lumber. These trees had a stabilizing effect on their returns, as there were phenotypic tradeoffs between stiffness and volume under optimistic and pessimistic growing scenarios. These results showed the benefits of product diversification at the tree level.