Rolling Shear Properties of Cross-Laminated Timber Made from Australian Plantation Eucalyptus nitens under Planar Shear Test

With the increasing availability of fast-growing Eucalyptus plantation logs in Australia in recent years, the timber manufacturing sector has become interested in discovering the opportunities of producing value-added timber products from this resource. Cross-laminated timber (CLT) could be a potential sustainable product recovered from this resource and supply material for commercial buildings. Shear of the inner cross-laminates, known as rolling shear, is one of the governing factors in serviceability and limit state design for this product under out-of-plane loading. This study evaluated the rolling shear (RS) properties of CLT with heterogonous layup configurations using different structural grade Eucalyptus nitens (E. nitens) timber under the planar shear test. Based on the results, Gr and τr values were shown to be significantly correlated with the density of the CLT panel. There was also a positive correlation between the RS modulus and MOR of the CLT panel. The specimens with high MOE in the top and bottom layers indicated the highest τr and Fmax values. This indicated that using high-grade boards in the top and bottom lamellae plays an important role in increasing the RS strength, whereas using them in the cross-layer has a positive contribution in increasing shear modulus. The maximum observed RS strength and modulus ranged from 2.8–3.4 MPa and 54.3–67.9 MPa, respectively, exceeding the RS characteristic values of the resource. The results obtained in this study were comparable to those recommended in European standards for softwood CLT, demonstrating the potential use for eucalypt timber boards in CLT production. This paper provides an important insight into supporting the potential engineering applications of CLT panel products fabricated with eucalypt plantation.

Análisis de Germinación de Semillas de Eucalyptus nitens Tratadas con Radiación Gamma: Indicios de Efecto Hormético

Se analiza un ensayo de germinación en laboratorio para evaluar el efecto de cinco dosis de radiación gamma (10, 20, 30, 40 y 50 Gy) más un testigo sin irradiar, sobre los parámetros capacidad de germinación (CG), energía germinativa (EG) y periodo de energía (PE) de semillas de Eucalyptus nitens. Se concluye la existencia de un efecto significativo de radio-hórmesis asociado al tratamiento de 10 Gy, el cual aumenta la capacidad germinativa respecto al testigo sin irradiar. Ninguno de los tratamientos restantes resulta diferente al testigo en capacidad germinativa, energía germinativa ni periodo de energía. Se comparan los resultados con los registrados en la bibliografía y se plantean recomendaciones para estudios posteriores en esta materia.

Analysing the effect of thermal modification on the calorific values of Eucalyptus nitens wood

Gross and net calorific value of 13 samples of Eucalyptus nitens wood were determined at HAWK (Hochschule für Angewandte Wissenschaft und Kunst), Göttingen, Germany. Among 13 samples, 12 were thermally modified and one was unmodified. Calorific values of samples were determined by using a bomb calorimeter, and the wood components (cellulose, hemicellulose, lignin, and extractives) already analysed by Wentzel et al. (2019). After determination of the values, samples were statistically analysed by R studio to find the relations among the calorific value, temperature, and wood components. The gross calorific value and net calorific value of the untreated sample of Eucalyptus nitens were found to be 18.83 MJ/kg and 17.48 MJ/kg, and after thermal modification these increased up to 20.24 MJ/kg and 18.84 MJ/kg. Upon statistical analysis, the results for lignin showed a strong correlation with the temperature of thermal treatment and calorific value.

Genomic studies with pre-selected markers reveal dominance effects influencing growth traits in Eucalyptus nitens

Genomic selection (GS) is being increasingly adopted by the tree breeding community. Most of the GS studies in trees are focused on estimating additive genetic effects. Exploiting the dominance effects offers additional opportunities to improve genetic gain. To detect dominance effects, trait relevant markers may be important compared to non-selected markers. Here we used pre-selected markers to study the dominance effects in a Eucalyptus nitens (E. nitens) breeding population consisting of open-pollinated (OP) and controlled-pollinated (CP) families. We used 8221 trees from six progeny trials in this study. Of these, 868 progeny and 255 parents were genotyped with the E. nitens marker panel. Three traits; diameter at breast height (DBH), wood basic density (DEN) and kraft pulp yield (KPY) were analysed. Two types of genomic relationship matrices based on identity-by-state (IBS) and identity-by-descent (IBD) were tested. Performance of the genomic best linear unbiased prediction (GBLUP) models with IBS and IBD matrices were compared with pedigree-based additive best linear unbiased prediction (ABLUP) models with and without the pedigree reconstruction. Similarly, the performance of the single-step GBLUP (ssGBLUP) with IBS and IBD matrices were compared with ABLUP models using all 8221 trees. Significant dominance effects were observed with the GBLUP-AD model for DBH. The predictive ability of DBH is higher with the GBLUP-AD model compared to other models. Similarly, the prediction accuracy of genotypic values is higher with GBLUP-AD compared to the GBLUP-A model. Among the two GBLUP models (IBS and IBD), no differences were observed in predictive abilities and prediction accuracies. While the estimates of predictive ability with additive effects were similar among all four models, prediction accuracies of ABLUP were lower than the GBLUP models. The prediction accuracy of ssGBLUP-IBD is higher than the other three models while the theoretical accuracy of ssGBLUP-IBS is consistently higher than the other three models across all three groups tested (parents, genotyped, non-genotyped). Significant inbreeding depression was observed for DBH and KPY. While there is a linear relationship between inbreeding and DBH, the relationship between inbreeding and KPY is non-linear and quadratic. These results indicate that the inbreeding depression of DBH is mainly due to directional dominance while in KPY it may be due to epistasis. Inbreeding depression may be the main source of the observed dominance effects in DBH. The significant dominance effect observed for DBH may be used to select complementary parents to improve the genetic merit of the progeny in E. nitens.

Thinning Influences Wood Properties of Plantation-Grown Eucalyptus nitens at Three Sites in Tasmania

Thinning of forestry plantations is a common silviculture practice to increase growth rates and to produce larger dimension logs. The wood properties, basic density and stiffness, are key indicators of the suitability of timber for particular purposes and ultimately determine timber value. The impact of thinning operations on wood properties is, therefore, of considerable interest to forest growers and timber producers. To date, studies examining the impact of thinning on wood properties have produced variable results and understanding of the consistency of the effects of thinning treatments across various sites for important plantation species is limited. Two non-destructive assessment techniques, drilling resistance and acoustic wave velocity, were used to examine the impact of thinning on basic density and stiffness in 19–21-year-old plantation grown Eucalyptus nitens across three sites. Commercial thinning to 300 trees ha−1 decreased the stiffness of standing trees and this effect was consistent across the sites. Reduction in stiffness due to thinning ranged from 3.5% to 11.5%. There was no difference in wood properties between commercially and non-commercially thinned trees to 300 trees ha−1 and no difference in wood properties when thinned to 500 trees ha−1. Basic density was not affected by thinning. The site had significant effects on both basic density and stiffness, which were lowest at the highest precipitation and highest elevation site. The results indicate that wood properties are influenced both by silviculture and site environmental differences. This knowledge can be used for the better management of E. nitens resources for solid wood production.

Flexural characteristics of Eucalyptus nitens timber with high moisture content

The demand for timber resources in the building industry has been increasing. Plantation Eucalyptus nitens is of interest because of its sustainable supply and potential for structural applications. However, few design standards cover strength values of plantation eucalypt timber, especially flexural failure below and above the fibre saturation point, which is an important mechanism of failure in bending members used in the building industry. Static bending tests were undertaken using a universal testing machine to examine nonlinear bending behaviour of 130 fibre managed E. nitens small clear wood samples at low and high moisture contents (MC). The mean bending modulus of rupture (MOR) was 80.7 MPa for low MC and 59.0 MPa for high MC. The high MC samples exhibited larger displacements at low ultimate loads, while the low MC samples showed abrupt failures at relatively small displacements with high ultimate loads. The design characteristic values for low and high MC E. nitens were 68.5 MPa and 39.8 MPa, respectively. This research demonstrates that fibre managed E. nitens timber is a promising timber for structural applications, especially when exposed to water, as the MOR reduction of E. nitens timber above FSP is relatively lower than those of P. radiata, which is a traditional construction material.