Genetic Parameters of Diameter Growth Dynamics in Norway Spruce Clones

The breeding of Norway spruce in northern Europe has substantially contributed to the production of high-quality wood. The vegetative propagation of robust elite clones could help to sustain the provision of high-quality timber in the face of changing climates. For the adequate evaluation of genetic gains, the altered tree growth dynamics of the clones need to be understood, yet essential information about the long-term growth dynamics of improvedboreal trees is still lacking. We examined a 50-year-old clonal plantation in Latvia to distinguish the clonal effects on diameter growth function parameters and estimate the genetic parameters. A mixed-effect modelling approach was used, in which the clones were applied as random effects on the parameters of the Chapman-Richard equation. All model parameters showed significant variance in the genotypic coefficients of variation CVg which ranged between 11.0 and 17.1%, with the highest being for the growth rate. The heritability (H-2) of the diameter at breast height (DBH) reached 0.35 at the age of 40, while CVg decreased from 12.9% to 7.8% between the ages of 20 and 45. Age-age genotypic correlations were positive and were strong or very strong (>0.76). The realised genetic gain varied from -6.3 to +24.0% around the trial mean. A substantial improvement in DBH was indicated when elite clones were selected for vegetative propagation based not only on early measurements, but also considering the genetic variance in the model parameters.