Potential improvement of lodgepole pine (Pinus contorta Dougl. ex Loud. var. latifolia Engelm.) solid-wood properties was examined by estimating age trends of inheritance, age–age genetic correlations, and the efficiency of early selection using 823 increment cores sampled from 207 half-sib families at two independent progeny trials, aged 34–35 years, located in northern Sweden. High-resolution radial variation of annual ring width, wood density, microfibril angle (MFA), and modulus of elasticity (clearwood stiffness; MOES) was measured using SilviScan. The dynamic stiffness (MOEtof) of standing trees was also obtained using Hitman ST300. Heritabilities ranged from 0.10 to 0.64 for growth and earlywood, transition-wood, and latewood proportions, from 0.29 to 0.77 for density traits, and from 0.13 to 0.33 for MFA and stiffness traits. Genetic correlations between early age and the reference age (26 years) suggested that early selection is efficient at age 4 years for MFA and between ages 5 to 8 years for density and MOES. Unfavorable diameter–stiffness genetic correlations and correlated responses indicate that breeding for a 1% increase in diameter would confer 5.5% and 2.3% decreases in lodgepole pine MOES and MOEtof, respectively. Index selection with appropriate economical weights for growth and wood stiffness is highly recommended for selective breeding.

We reviewed the genetic parameter estimates carried out from 1992 to 2006 for height increment in genetic tests of Norway spruce and Scots pine, to describe patterns of genetic variation, heritability, and genetic correlations. The material included seedling and clonal tests in Sweden, aged between 5 and 20 years. Multiple regression was used to explore relationships between parameter values and test environments. Results showed moderate narrow-sense heritabilities ( b h 2 : mean =0.29 in Norway spruce; mean =0.23 in Scots pine) that decreased with test site latitude for both species. In Norway spruce, b h 2 increased with better growth and decreased with tree age, while for Scots pine, b h 2 increased with tree age and southward transfer. The additive genetic coefficient of variation ( A V C ; mean 15%), in Norway spruce, decreased with growth as well as site latitude.in Scots pine (mean =8.5%) increased with southward transfer and more southerly test latitude. Additive and genotypic within-site genetic age-age correlations in Norway spruce were high, with mean r A and r G of 0.92 and 0.85, respectively. Corresponding across-sites estimates were on average lower. Genetic parameters were better expressed on favorable sites, at younger ages in Norway spruce and at older ages in Scots pine. The results imply that gain calculations should be based on different parameters in the two species. For maximizing genetic gain in the Swedish breeding program, testing times could be shorter for Norway spruce than for Scots pine. The investigation showed a large variation in parameter estimates from different field experiments, highlighting the importance of testing over multiple sites.

Genetic parameters were estimated for the diameter-height (d-h) relationship and three other tree stem-form characteristics (total height, breast height diameter, and total tree volume) for data from 10 diallel progeny trials of Scots pine (Pinus sylvestris L.), at about 30 years of age in Sweden. Linear mixed models were fit to the data, where adjustments for intertree competition and microsite heterogeneity were made by means of covariates in a nearest-neighbour analysis. The d-h relationship was analyzed with a covariate (tree height) adjusted model of diameter. Average estimates of the additive coefficient of variation and narrow-sense heritability for the d-h relationship were 7.4% and 0.22, respectively. Estimates of dominance were comparatively small (average dominance: phenotypic variance ratio of 0.04). The results indicate that there is scope to modify the d-h relationship by selection and breeding. Additive genetic correlations between the d-h relationship and height were negative, with a mean of -0.62. Selection for height would thus result in stems that are more slender than average, suggesting that tall trees allocate relatively more resources to height growth than to diameter growth. Selection based on height alone will negatively affect volume gain. Résumé :Les auteurs ont estimé les paramètres génétiques de la relation entre le diamètre et la hauteur (d-h) des arbres et de trois autres caractères de forme de la tige (hauteur totale, diamètre à hauteur de poitrine et le volume total de l'arbre) à partir des données de 10 tests de descendances diallèles de pin sylvestre (Pinus sylvestris L.) âgé d'environ 30 ans en Suède. Des modèles linéaires mixtes ont été ajustés aux données, incluant des ajustements pour la compétition entre les arbres et l'hétérogénéité des microsites effectués au moyen de covariables dans une analyse du plus proche voisin. La relation d-h a été analysée à l'aide d'un modèle de diamètre ajusté pour une covariable (la hauteur de l'arbre). Les estimations moyennes du coefficient de variation additive et de l'héritabilité au sens strict pour la relation d-h affichaient des valeurs respectives de 7,4 % et 0,22. Les estimations de dominance étaient comparativement faibles (le rapport moyen de la variance de dominance sur la variance phénotypique était de 0,04). Les résultats indiquent qu'il est possible de modifier la relation d-h par la sélection et les croisements. Les corrélations génétiques additives entre la relation d-h et la hauteur étaient négatives, avec une moyenne de -0,62. La sélection pour la hauteur produirait donc des tiges plus effilées que la moyenne, ce qui porte à croire que les grands arbres allouent relativement plus de ressources à la croissance en hauteur qu'à la croissance en diamètre. La sélection pour la hauteur uniquement aura un effet négatif sur le gain en volume.[Traduit par la Rédaction]

Genetic differences are described between improved and unimproved Scots pine (Pinus sylvestris L.) in 36 northern Swedish field tests, covering wide geographical and climatic gradients (latitude 62.3°–67.8°N). Improved trees were represented by progenies from controlled crosses of first-generation, phenotypically selected plus trees, whereas unimproved trees originated from unselected natural stands. Improved trees were superior in terms of height (9.2%), stem diameter (5.4%), and stem volume (18.9%) at the age of 27.4 years. The height growth of improved trees from ages of 10.5 years to 27.4 years was similar to that of unimproved trees at a site with a higher site index. Improved trees had a 5.5% greater height/diameter ratio (i.e., were more slender) than unimproved trees, whereas differences between the tree categories in terms of survival and frequencies of ramicorns and stem breaks were minor and mostly insignificant. Little or no interaction between tree categories and site conditions for growth characters was found, implying that the results are generally applicable. No difference in response to competition between the improved and unimproved trees was detected. However, differences in their reactions to transfer were found: survival rates increased more and height growth decreased less in improved trees than in unimproved trees when grown at a site south of their geographical origin. The use of competition and height indices based on neighbouring trees to adjust for bias and site variability in single-tree plots significantly improved the estimates.

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Genetic parameters, performance of provenances, and genotype by environment interaction (G × E) for diameter at breast height (DBH), survival, and modulus of elasticity of time-of-flight (MOE tof) (an indirect measure of stiffness), were investigated in six lodgepole pine progeny trials, aged 33-36 years, within three breeding zones in northern Sweden. Provenances of Yukon origin had the highest growth but lowest stiffness at higher latitude, while those of British Columbia (BC) origin grew faster at lower latitudes and had highest stiffness within zone 5. Combined-site heritability estimates ranged from 0.09 to 0.19 for DBH, from 0.19 to 0.27 for MOE tof , and from 0.13 to 0.26 for survival. Type-B genetic correlations (r b) were generally high for all studied traits, except for DBH and survival in zone 4 (r b = 0.74 and 0.40, respectively) and for MOE tof in zone 2 (r b = 0.46). On the basis of the results obtained in this study, G × E for stiffness in northern Sweden and unfavourable growth-stiffness genetic correlation should be considered in selective breeding programmes of lodgepole pine. To achieve the highest stiffness for lodgepole pine, provenances of Yukon origin should be planted at lower latitudes and those of BC origin should be planted at lower elevations within the tested breeding zones.

Possibilities for early selection of clones for future seed cone production were studied in a clonal seed orchard of Scots pine (Pinus sylvestris L.) in northern Sweden over the first 30 years following establishment. The annual data were modelled as series of bivariate analyses. The correlations between cone production of clones in any individual year and that of a previous year, and cumulative cone production over all years were studied. The corresponding multivariate analysis for a full data fit simultaneously was best estimated with a genetic distance-based power model (AR). The genetic (variation among clones) and environmental variation were of the same magnitude. The genetic correlations were larger than the phenotypic correlations and both increased with orchard age. Basing selection of clones on a single observation at an early age to improve future cone production was not effective, but efficiency increased if cumulative cone count over many years was used. Year-to-year genetic correlations indicated that early forecasts by clone of cone production at mature ages are highly uncertain. Reliable predictions (moderate correlations) could be achieved only if based on rather mature grafts, 14 or more years after establishment.