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Stiffness of wood in fast-grown plantation softwoods: The influence of microfibril angle

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In the literature there are numerous statements to the effect that density is the most important parameter in determining the intrinsic properties of wood. Zobel and van Buijtenen (30) argue, "Specific gravity is of key importance in forest products manufacture because it has a major effect on both yield and quality of fibrous and solid wood products and because it can be changed by silvicultural manipulation and genetic manipulation. Therefore, specific gravity largely determines the value and utility of wood and overshadows the importance of other wood properties."

With regard to fast-grown plantations of Pinus radiata, we note the following propositions. Bunn (4) states, "Basic density is probably the single most important intrinsic wood property for most wood products, particularly if we are contemplating adopting short rotations." While Bamber and Burley (2) point out, "Of all the wood properties density is the most significant in determining end use. It has considerable influence on strength, machinability, conversion, acoustic properties, wearabillty, paper yield and properties and probably many others."

There are qualifications. The most striking is that by Bamber and Burley (2), "In comparing the strength of radiata pine at various ages Kloot (1957) found bending strength to increase with age by a factor of almost three times. However while this increase in strength appears to follow the age-related increase in density, the magnitude of the increase is far in excess of the increase that could be expected from density alone. In the ages he examined, 1 to 40 years, density related strength increases of the order of only 35 percent could be expected so that it is likely that some other factor such as the effect of spiral grain is responsible for this large variation in strength." The ease for spiral grain can be dismissed. A slope of grain of about...