Calculating the potential increase in Pinus radiate stem value through selection for higher stiffness

Abstract

New Zealand grown Pinus radiata is limited in its application for structural purposes by its stiffness deficiencies. This dissertation aims to estimate potential improvements in stem value through selection for improved stiffness. A new method to model and value volumes of structural wood grades within a stem was used to calculate these value improvements. Data for each stem from a stand in Kaingaroa Forest bred for improved wood quality was used to perform this analysis. This data was from a stand bred for improved wood quality and included information on the stiffness, density and width of each growth ring for each stem. The data was in the form of cores. Height and volume data was not recorded and therefore needed to be modelled. The volumes of MSG8, MSG11 and MSG13 wood were estimated by modelling the stem volume at the age when wood is produced that is stiff enough to qualify for each grade. The majority of stems had merchantable volumes between 1-2.5m3 with the largest stems containing 3.6m3. Average stiffness ranged between 5.2GPa and 11.3GPa with the stand average being 8.4GPa. There was no relationship between average stiffness and merchantable volume. Stem values were found to range between $60-$131/m3 with the stand average being $91/m3. The 10 most valuable stems had a total stem value ($318) twice that of the stand average ($157). The most valuable stem ($411) showed a 160% increase in stem value from the average. The increases in value/m3 were caused by large increases in the proportion of MSG11 and MSG13 wood held within the merchantable volume. These potential gains in stem value could help tree breeders assign an accurate economic weighting to stiffness improvements. Forest managers wanting to justify using a more expensive, improved stiffness seedlot may also find these results valuable.