Trade-offs between wood density and radial growth in the Region H white spruce Controlled Parentage Program, Alberta, Canada

• Author / Creator

  Matheson, Robert Thomas

• Trade-offs between wood density and radial growth rate in white spruce were investigated. Decreases in wood density associated with increased radial growth rate have been well documented in several tree species, including white spruce (Picea glauca (Moench) Voss). One of the goals of the Region H white spruce Controlled Parentage Program is to increase stem volume at rotation; however, the Forest Genetic Resource Conservation and Management Standards of Alberta (2016) require program proponents to consider the indirect selection of correlated traits, including wood density, when selecting for increased growth rates. Resistograph drilling resistance (%), Pilodyn penetration depth (mm), wood specific gravity and diameter inside bark (mm) at breast height were measured in 40 different families from three progeny test sites at age 26. Two to eight trees/family/site were selected for drilling resistance and diameter at breast height measurements, two to eight trees/family for two sites were selected for penetration depth and two to seven trees/family across all three sites were selected for wood specific gravity assessment. Analyses included phenotypic and genotypic correlations between the various traits, regression analyses for estimating wood specific gravity using drilling resistance and penetration depth measurements and calculation of narrow sense heritability and breeding values for drilling resistance, penetration depth and diameter inside bark. These breeding values were plotted against the breeding values for height (cm) at age 25, which were provided by the Government of Alberta. A paired t-test showed that significant differences existed between drilling resistance measurements taken from the north and east aspects of individual trees, but a significant difference was not found between penetration depth for the same trees. Significant differences existed between sites for all four traits; however, significant differences existed only for drilling resistance between families. Additionally, coefficients of variation showed that the variation in diameter was two to three times greater compared to any of the wood density measurements. Phenotypic correlations between the various quantitative traits were typically moderate in strength (r ~ 0.5) at both the individual- and family-level and all were significant. The relative standard error was approximately 5-10% of the respective correlation coefficient. Multiple linear regression showed that both drilling resistance and penetration depth were relatively poor predictors (r2 ~ 0.4) of wood specific gravity at both the individual- and family-level. There was no genotype-by-environment interaction detected for drilling resistance or Resistograph, but there was for both penetration depth and diameter inside bark. Narrow sense heritabilities were generally low for diameter at breast height (h2 < 0.15) and higher (h2 > 0.3) for drilling resistance and penetration depth, except for Hay River, which showed the opposite response for drilling resistance (h2 = 0.11) and diameter inside bark (h2 = 0.42). The relative standard error associated with each heritability estimate was generally high (30-150% of the heritability). Genetic correlations for all traits were significant and weak to moderate (0.3 < r > 0.7) at the individual-level and very weak (r < 0.15) and not significant at the family level. At the phenotypic level, there is some evidence that increased radial growth rate is associated with a decrease in wood density; however, the decrease in wood density is very small (< 10%) and the variation in wood density is much lower than that found in diameter. Additionally, the range of wood density and level of variation in the Region H white spruce Controlled Parentage Program was similar to wild stands in Quebec, indicating that there was no loss in wood density through selection for height. Resistograph appears to be a more sensitive measurement for iv assessing wood density compared to Pilodyn, as it was able to delineate significant differences even at the family level and provided the highest estimates of heritability with relatively lower associated standard errors. The genetic correlation between drilling resistance and diameter inside bark was virtually non-existent (rg = -0.08). Forest companies should monitor the wood density of natural and artificially-regenerated stands on an ongoing basis and assess wood density within each tree improvement program and each generation within a respective program to ensure that mean wood density does not decline compared to natural stands over time.

• Subjects / Keywords

  • Tree improvement
  • Pilodyn
  • Phenotypic correlation
  • Wood density
  • Resistograph
  • Heritability
  • Genetic correlation
  • Forest genetics
  • White spruce

• Graduation date

  Fall 2019

• Type of Item

  Thesis

• Degree

  Master of Science

• DOI

  https://doi.org/10.7939/r3-x2pp-zx35

• License

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