Crown structure, absorbed photosynthetically active radiation (APAR) and growth were analyzed in 300 replicated loblolly (Pinus taeda L.) and slash pine (Pinus elliottii Engelm. var. elliotti) clones to: (1) quantify genetic variation in crown structural traits, growth and APAR at the species, family and clonal levels; and (2) estimate within-family genetic and environmental influences on measured variables. Species and family-within-species differences were found in some growth traits, crown size, leaf area, APAR and branch angle. Loblolly pine developed larger crowns, exposed more leaf area with an acute angle, and intercepted more radiation than slash pine. Significant differences among clones within-family were found for stem volume and crown architecture. Loblolly pine and slash pine within-family, individual-tree broad-sense heritabilities ranged from 0.00 to 0.41 for growth and crown structural traits and most were between 0.10 and 0.25 when estimated from a combined analysis across families. Genetic correlations of crown size, leaf area and APAR with volume increment generally ranged from 0.60 to 0.75. This knowledge of the genetic interactions among growth and crown structural traits improves our understanding of how crown morphology affects light interception and stand development, and ultimately how these attributes can be incorporated in the selection of families or clones for the development of new crop tree ideotypes.

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We quantified basal area increment phenology over a 2-year period in one loblolly pine (Pinus taeda L.) and four slash pine (Pinus elliottii Engelm. var. elliottii) full-sib families propagated as rooting cuttings. In 2002, basal area growth started in March and stopped in October for both species, while in 2003, initiation and cessation occurred 2 weeks earlier for all families. In both years, peaks in basal area increment occurred in short (2–3 week) periods in the early spring for all families, followed by linear basal area growth until cessation. While there were significant size differences among taxa (species and families) at age 6 and 7 years, genetic differences in basal area growth rate were only expressed during short, discrete time periods primarily in the spring and fall. Basal area growth rate increased during periods when water soil availability increased (up to 300 mm), but an excess in water availability in the soil had a negative impact on growth. Within-family individual-tree broad-sense heritabilities ranged from 0.01 to 0.37 for all traits. In general, heritabilities were higher for growth traits than for phenological traits for all families. Both the strength and direction of correlation estimates of phenological traits with growth rate varied across families and years.

Background: Development of a relatively simple growth modelling approach for plantation species that allows derivation of cardinal (base, optimum and ceiling) air temperatures for growth, whilst accounting for changes in organism size, would represent a considerable advance over existing models. Such an approach would provide insight into species phenology and, in an agronomic setting, allow growers to closely match species to sites. Here, a model is described that can be used to predict seasonal variation in growth and cardinal air temperatures from simple seasonal measurements at a single site. Methods: The model was applied to data from an irrigated trial comprising two Eucalyptus species and three Eucalyptus crosses. Using measurements of mean daily air temperature data and stem volume, taken over a two year period, the model was fitted to the data and used to estimate cardinal air temperatures for the five species/crosses. Results: The model predictions corresponded well to the actual data for all five species/crosses, with R 2 ranging from 0.993 to 0.999. The optimum air temperature, T o , for E. camaldulensis x E. globulus of 26.9°C significantly exceeded T o for the other four species/crosses, where T o ranged from 15.4 to 18.7°C. As T o for E. camaldulensis x E. globulus was close to the highest mean daily air temperature recorded at the study site, the air temperature modifier for this species was almost always sub-optimal and consequently this cross was not well matched to the site. In contrast, T o for the other four species/crosses were considerably closer to the mean air temperature of the site with T o for E. nitens most closely approximating the mean air temperature (15.4 vs. 13.0°C).

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Understanding the changes in early growth efficiency (GE, growth/leaf area) may improve forest production through the selection of appropriate genotypes at early stages. We investigated different early growth responses of genotypes of Eucalyptus globulus (7), E. nitens (3), and E. nitens × E globulus (E. gloni) (7) in south-central Chile. To evaluate seasonal growth, plants of each genotype were established in a completely randomized block design in coarse sandy soil (i.e., low water holding capacity), with spring and summer irrigation. The current monthly increment (CMI) in wood volume (cm 3 tree −1 month −1 ), and leaf area index (LAI, m 2 m −2 ) were used to calculate GE at 4.1, 7.5, 10.4, 13.4, and 15.4 months of age, corresponding to five growing seasons (first summer, fall, winter, spring, and second summer). The interaction between genotype and season had a significant effect (p < 0.001) on LAI and GE, but not on CMI. In general, CMI values declined in winter, but increased greatly in the second summer. LAI values were stable during the first three seasons, increased in spring, and peaked in the second summer. During all seasons, a significant (p < 0.001) relationship between growth and LAI was observed, with differences in model coefficients among taxa. The highest GEs were observed mainly for E. globulus, which grew with small changes in the LAI. In general, our findings showed that eucalyptus genotypes with higher annual GEs presented higher seasonal GEs, except for some E. globulus genotypes. Changes in seasonal GEs among genotypes suggest that the same environment drives a significant response in the early growth stage as a consequence of climate influences on carbon allocation among different eucalyptus genotypes.