Modelling Pinus radiata lumber characteristics. Part 1: mechanical properties of small clears

Fast-grown plantation wood (particularly the juvenile zone) can have some limiting performance characteristics (stiffness, strength, stability). Improvements in the overall performance of the lumber products will depend on a knowledge of the most important factors which can be influenced by either silviculture or tree breeding. Some wood technologists believe that the traditional view of wood density as the single most-important factor may be flawed, and that other parameters (e.g., microfibril angle, spiral grain, and compression wood) may have an equal or greater effect. During 1996-98, intensive utilisation studies were carried out on Pinus radiata D.Don material from two sites in the central North Island of New Zealand. Sample trees were selected from managed crops (23 and 28 years old respectively) to cover a range of wood properties. They were chosen on the basis that they represented a wide range of tree characteristics (diameter, branch habit), and subsequently the full range of log and stem properties was measured from wood disc samples and sawn lumber. One of the objectives of the research was to document the relative importance of a number of properties known to influence both mechanical properties and product performance. Some of the studies comprised a series of standard "small clears " tests, designed to untangle the impacts of wood density, ring width, spiral grain, compression wood, and microfibril angle on bending strength (MoR) and stiffness (MoE). Altogether 450 "small clears " samples were selected, covering the range of log and lumber properties existing in 51 stems from 15 clones across the two trials. Each wood sample was designated "juvenile " (within 10 rings from the pith — 304 pieces) or "mature " (129 pieces) depending on the location within the tree stem