Genomic selection is expected to enhance the genetic improvement of forest tree species by providing more accurate estimates of breeding values through marker-based relationship matrices compared with pedigree-based methodologies. When adequately robust genomic prediction models are available, an additional increase in genetic gains can be made possible with the shortening of the breeding cycle through elimination of the progeny testing phase and early selection of parental candidates. The potential of genomic selection was investigated in an advanced Eucalyptus nitens breeding population focused on improvement for solid wood production. A high-density SNP chip (EUChip60K) was used to genotype 691 individuals in the breeding population, which represented two seed orchards with different selection histories. Phenotypic records for growth and form traits at age six, and for wood quality traits at age seven were available to build genomic prediction models using GBLUP, which were compared to the traditional pedigree-based alternative using BLUP. GBLUP demonstrated that breeding value accuracy would be improved and substantial increases in genetic gains towards solid wood production would be achieved. Cross-validation within and across two different seed orchards indicated that genomic predictions would likely benefit in terms of higher predictive accuracy from increasing the size of the training data sets through higher relatedness and better utilization of LD.

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Background: Density is an important wood property due to its correlation with other wood properties such as stiffness and pulp yield, as well as being central to the accounting of carbon sequestration in forests. It is influenced by site, silviculture, and genetics, and models that predict the variation in wood density within and among trees are required by forest managers so that they can develop strategies to achieve certain wood density targets. The aim of the study presented here was to develop a wood density model for radiata pine (Pinus radiata D. Don) growing in New Zealand. Methods: The model was developed using an extensive historical dataset containing wood density values from increment cores and stem discs that were obtained from almost 10,000 trees at over 300 sites. The model consists of two sub-models: (1) a sub-model for predicting the radial variation in breast-height wood density and (2) a sub-model for predicting the distribution of density vertically within the stem. Results: The radial variation in breast-height wood density was predicted as a function of either ring number or both ring number and ring width, with the latter model better accounting for the effects of stand spacing. Additional model components were also developed in order to convert from annual ring density values to a whole-disc density, predict log density from disc densities, and account for the variation in wood density among individual trees within in a stand. The model can be used to predict the density of discs or logs cut from any position within a tree and can utilise measured outerwood density values to predict the density by log height for a particular stand. It can be used in conjunction with outerwood density to predict wood density distributions by logs for stands of any specified geographic location and management regime and is designed to be able to incorporate genetic adjustments at a later stage. Conclusions: The analysis has confirmed and quantified much of the previous knowledge on the factors that affect the variation in wood density in radiata pine, particularly the influences of site factors and silviculture. It has also quantified the extent and patterns of variation in wood density within and among trees.

Biosolids have been applied to a 1000 ha Pinus radiata D. Don plantation in Nelson, New Zealand, since 1996. A research trial was established in a 6-year-old stand in 1997 with three stocking rates (300, 450, and 600 stems·ha–1), and biosolids were applied at ages 6, 9, and 12 years at three application rates based on total nitrogen loading at each application of 0 (control), 300 (standard), and 600 kg N·ha–1 (high). The aim of this study was to evaluate the responses of tree growth rate and wood properties to biosolids application at midrotation. Since the trial was established, tree diameter and volume increment in the biosolids-treated plots have increased markedly. This increase in growth is being maintained at midrotation, with the year 13–14 volume increment being 40% greater in the standard treatment than the control, and 46% greater in the high treatment than the control. The response in growth has occurred across all stockings in the trial, although there has been a tendency for the difference in growth between the standard and high rates to be greater at higher stockings. A small but significant reduction of basic wood density and standing-tree sonic velocity in P. radiata was found in the biosolids treatments. Although the reductions in wood density and stiffness may slightly decrease the average log value in biosolids treated trees, this will be greatly outweighed by the large increase in wood volume.

Background: To understand the underlying control of patterns of important wood properties is fundamental to silvicultural control of wood quality and genetic selection. This study examines the influences of site, silviculture and seedlot on diameter growth, wood density and estimated wood stiffness in mid-rotation radiata pine (Pinus radiata D Don) stands across New Zealand.