Effect of stocking on juvenile wood stiffness for three 'Eucalyptus' species

The effects of stocking on wood stiffness (MoE) for three 'Eucalyptus' species are quantified using a 6-year-old trial established in New South Wales, Australia. An acoustic time-of-flight tool measured the velocity between two probes in the outerwood, from which the stiffness was estimated. Four stocking levels (714, 1,250, 1,667 and 3,333 sph) were examined. Stiffness varied significantly between all species, with 'E. cloeziana' showing the highest stiffness (14.2-15.7 GPa), followed by 'E. pilularis' (12.2-13.5 GPa) and 'E. dunnii' (10.7-12.6 GPa). There was a stiffness increase (around 11%) between 714 and 1,250 stems/ha for all species but thereafter differences between stockings were not always significant. Trees were also assessed for basic density, 'dbh', total height, crown area, green crown height and stem slenderness (height/'dbh'). Only stem slenderness had a significant association (0.41 ± 0.17) with stiffness. These findings suggest that, where stiffness is a priority, forest managers could reduce establishment costs with low stockings (around 1,250 stems/ha).