Improving Eucalyptus nitens for sawn-board, veneer and paper products

Eucalyptus nitens is widely planted for pulpwood, and increasingly also for solid-wood timber products, in cool-temperate climates. This thesis investigated the potential of tree breeding to improve the properties of E. nitens grown for sawn boards, pulpwood and veneer products. Two studies were undertaken using a 14 -15 year old E. nitens provenanceprogeny trial established in Tasmania and comprising 420 open-pollinated families collected from three native races. In the first study, methods were developed to track the identities of 560 pedigreed trees through harvesting, transportation and sawmill processing. A second study tracked 548 trees from the same trial through a rotary peeled veneer production system. Genetic parameters were estimated for a total of 20 tree, log and wood traits relevant to sawn board, veneer and pulpwood products. Genetic differences among races of E. nitens were significant in wood stiffness, growth, stem form and pulpwood traits, but not significant for log end-splitting and sawn board checking traits. The Southern race had the most favourable mean values. Significant additive genetic variation within races was observed in all traits except log-taper, demonstrating that the quality of plantation-grown E. nitens wood products could be improved through breeding. Strongly positive genetic correlations among diameter at breast height (DBH) at ages 4, 9 and 14 years and between DBH all ages and the traits survival, log volume and stem straightness, demonstrated that early-age selection for DBH would not compromise stem straightness and would improve product volume recovery. Log end-splitting was under moderate genetic control but there was a negative genetic correlation between end-splitting and solidwood product volume.Sawn board and veneer sheet stiffness was highly heritable, and strongly correlated with acoustic wave velocity (AWV), measured in standing trees and logs. Consistent with previous studies in E. nitens, wood basic density, near infra red-(NIR) predicted kraft pulp yield (KPY) and cellulose content (CC) had moderate-to-high heritabilities, although coefficients of additive genetic variation for these traits were small. Estimated genetic correlations between standing tree AWV and each of the traits veneer sheet modulus of elasticity (MOE), sawn-board MOE, KPY, CC and basic density were highly significant and strongly positive, suggesting that standing tree AWV could be adopted as an indirect non-destructive selection criterion for improving solid-wood product stiffness, while simultaneously improving wood chemical traits favoured by the pulpwood industry. Basic density had no significant genetic relationship with KPY and CC, although other studies have reported moderate to strong significant values. Surface and internal checking in sawn boards, which are important defects leading to value downgrade, were shown to be under moderate levels of additive genetic control. Internal checking in wedges cut from log disks and in wafer sections cross-cut from processed boards were strongly and positively genetically correlated. However, the genetic correlation of checking traits with density and AWV were generally not significant. Work presented in this thesis clearly demonstrates the potential for genetic improvement of E. nitens for pulpwood, sawn-boards and veneer production. A new method of tracking trees in processing studies has been established. Methods for assessing checking have been developed, and the utility of nondestructive AWV and NIR techniques has been confirmed for use in E. nitens breeding programs, aiming to simultaneously improve the quality and recovered volume of pulpwood and solid-wood products.