Maximizing growth without compromising wood density: Selecting superior Norway spruce clones

The study examined a free-growing (initial stand density 400 trees ha–1), 50-year-old grafted clonal Norway spruce plantation in Eastern Latvia to assess the genetic control and variability of growth traits and wood density. The latter was used as a proxy for structural timber strength. Results showed moderately high heritability in growth traits and moderate variability in wood density among clones, with an estimated genetic coefficient of variation CVg, of 8.6%. Even when grown at a very low density on nutrient-rich soil, 85% of the trees met the density requirements for construction timber (C18 in accordance with EN 338). The negative correlation between growth traits and wood density was weak at both individual tree and clonal levels (–0.08 < rP < –0.06; –0.16 < rG < –0.09), making it feasible to select fast-growing clones with wood density required for structural timber. The observed variation underscores the importance of selective breeding to ensure optimal timber quality, with implications for enhancing sawn wood strength grades and promoting climate-resilient forestry practices. Keywords: tree breeding; structural timber; clonal forestry; wood properties; plantation forestry; climate-smart forestry