Potential of plantation-grown eucalypts for structural sawn products. II.<i>Eucalyptus nitens</i>(Dean &amp; Maiden) Maiden and<i>E. regnans</i>F. MuelL

Abstract

Summary Plantation-grown 15- to 29-year-old Eucalyptus nitens (Dean & Maiden) Maiden and 15- to 30-year-old E. regnans F. Muell. from Tasmania and Victoria were tested as a resource for structural sawn products. Back-sawn products were dried, dressed, visually stress graded, and subjected to a four-point bending test, and small clear specimens were tested under central point loading. Knots in both species were more frequent and larger than in material from natural forests, and significantly decreased the modulus of rupture in bending (MOR) and modulus of elasticity (MOE) in most cases, determining the structural grades of 2400 mm boards. There was a marked incidence of decay in E. regnans trees. Satisfactory drying of 2400 mm boards was achieved and most internal checking did not significantly affect MOR and MOE. Strength groupings suggested SD6 for E. nitens and SD5 for E. regnans. The in-grade testing allocated F5 for E. nitens and F7 for E. regnans. The stress grades derived from the ingrade testing agreed relatively well with those derived from the strength grouping and visual grading for both species. The difference in strength grouping between plantation and mature forest trees of E. nitens appeared to be due to age. However, the difference for E. regnans is suspected to be a combined consequence of age effects and probable inferior clearwood strength properties of the particular plantation trees tested. This eucalypt plantation material is capable of producing useful structural products, performing in a similar range of applications as most of the plantation-grown softwood resource, and imported species such as Douglas- fir.