Physical and mechanical properties of plantation-grown tamarack

This study evaluates the physical and mechanical properties of plantation-grown tamarack (Larix Laricina (Du Roi) K. Koch.) in order to assess its potential uses and classify it among other commonly used softwoods. Sampling was done with probability proportional to volume and testing, according to ASTM D 143-52. Density, shrinkage, annual ring width, mechanical strength and stiffness in bending, compression parallel and perpendicular to grain, shear, and hardness were all evaluated and compared to the properties of naturally seeded tamarack and other softwood species. The static bending and compression parallel to grain strength values were significantly lower for plantation tamarack than natural tamarack, while for compression perpendicular to grain and hardness no significant difference was noted. In longitudinal shear, plantation tamarack was stronger than natural. These relationships of the mechanical characteristics are also evident in comparisons with other commercial softwoods; among the species compared, plantation tamarack exhibited the lowest strength values in stiffness and compression parallel to grain and the strongest in compression perpendicular to grain and longitudinal shear. These same relationships between mechanical properties were also noted in comparisons between plantation tamarack inner wood and outer wood. These consistent relationships indicate that, although the density fluctuation may influence some strength characteristics, it is not the only factor. Hypotheses such as microfibril angle (associated with a high proportion of juvenile wood) or high extractive content (usually present in the heartwood of this species) are suggested as influencing factors, but a real understanding of the phenomenon demands a separate investigation, which is beyond the scope of this study. It is evident, however, that in any study of the physico-mechanical properties of a fast-grown plantation wood, the juvenile wood portion is significantly different and should always be treated accordingly.