SELECTED MECHANICAL-PROPERTIES OF FAST-GROWING POPLAR HYBRID CLONES

Twenty-eight nine-year-old trees from ten clones of the hybrid Populus x euramericana from one site in Quebec were sampled to study the vari ation of selected mechanical properties within trees, within clones, a nd among clones. Four small and clear ASTM wood samples were taken fro m each tree at breast height, as well as a 10-mm diameter increment co re. The parallel-to-grain compliance coefficient and ultimate crushing strength were evaluated on the ASTM samples for air-dry and green con ditions. The dynamic compliance coefficient was measured on increment cores using an ultrasonic wave propagation method. Differences in all mechanical properties among clones were highly significant, while vari ation among trees was generally not significant. The dynamic complianc e coefficient tended to be lowest near the pith, increased to a maximu m at one third of the tree diameter, and then decreased outward toward s the bark. There was also a highly significant correlation between me chanical properties of ASTM samples and dynamic compliance coefficient s of increment cores. Mechanical properties were only moderately corre lated to wood density. Finally, there was a significant but weak corre lation showing that wood density and mechanical properties decreased w ith increasing growth rate.