Effects of Genetics and Silviculture and Their Interactions on Loblolly Pine and Norway Spruce Growth and Wood Properties

Effects of genetics on important growth and wood quality traits were investigated in a 26-year old Norway spruce (Picea abies L. Karst) clonal trial in southern Sweden, and effects of imposed silvicultural treatments and genetics were investigated in a loblolly pine (Pinus taeda L.) trial in southwestern Georgia, USA at age 15 and 16 years. The loblolly pine trial was designed with different fertilizer and herbicide treatment combinations applied to 25 open-pollinated first- and second-generation families.;In the Norway spruce trial, high broad-sense heritability values were found for wood density (0.48), microfibril angle (0.41), and wood stiffness (0.50). All investigated growth traits had similar heritability values as reported in earlier studies. The Norway spruce material also showed high age-age correlations between different sections of the wood cores sampled at breast height when moving from pith to bark. This indicated that early selection for wood quality traits would be possible. Unfavorable genetic correlations between volume growth and wood stiffness indicated that selection for volume only at age 10 would result in a 0.27% decrease in wood stiffness associated with every 1% increase for volume growth at age 26.;In the loblolly pine trial, the means for individual-tree stem volume were 185 dm³ in the combined fertilization and herbicide treatments, while in the other extreme, the control plots (with no treatments), mean stem volume averaged 91 dm³. Significant differences among treatment combinations for height, volume, sweep, forking defect, squared acoustic velocity, and wood density were also found. Squared acoustic velocity ranged from 14.5 km²/s² in the fertilization only plots to 16.4 km²/s² in the herbicides only plots, while the average core density varied from 465 kg/m³ in the control plots to 450 kg/m³ in the combined fertilization and herbicide plots. The loblolly pine trial had significant family effects for every trait. Individual-tree heritability values were 0.26 for height, 0.33 for volume, 0.10 for sweep, 0.39 for branch angle, 0.29 for forking defect, 0.23 for fusiform rust incidence (caused by the fungus Cronartium quercuum (Berk.) Miyabe ex Shirai f. sp. fusiforme), 0.41 for squared acoustic velocity, 0.32 for whole core weighted density, 0.28, for ring 2-6 core section density, and 0.78 for ring 7-16 core section density. Corresponding values for family-mean heritability values were 0.85 for height, 0.86 for volume, 0.60 for sweep, 0.90 for branch angle, 0.87 for forking defect, 0.84 for rust, 0.90 for squared velocity, 0.88 for whole core weighted density, 0.86 for ring 2-6 core section density, and 0.95 for ring 7-16 core section density. The genetic and phenotypic correlations between the growth and form traits were generally low and non-significant. Genetic and phenotypic correlations were significant for a number of combinations of wood quality traits while correlations were generally low and non-significant between growth and form traits and wood quality traits.;Interactions between silviculture and genetics were not significant for any of the measured traits, and the family rankings were stable across treatment combinations. Based on the results from this trial, the risk of losing value in terms of growth or wood quality due to unfavorable interactions between genetic material and silvicultural prescriptions is low when selected and improved half-sib coastal loblolly pine genetic material is used.