An increase in the stiffness of lumber with a decrease in initial tree spacing was confirmed forPinus patulaSchiede ex Schltdl. & Cham. The underlying properties of microfibril angle, wood density and knot frequency explained 71% of the variation in lumber stiffness. Tree spacing also influenced wood properties independent of radial growth rate. Rapid growth rates and reduced harvesting ages of South African-grown pine plantations have caused a reduction in the stiffness of structural lumber, which accounts for about 75% of all sawn wood. Microfibril angle and wood density are known to influence wood stiffness, which may be manipulated by the growing space of trees. The objective of this study was to evaluate the effect of slower growth rates, caused by narrow tree spacing, on the suitability of Pinus patula Schiede ex Schltdl. & Cham. wood for structural lumber. An 18- and a 19-year-old spacing experiment with four levels of initial tree spacing (1.83 m × 1.83 m, 2.35 m × 2.35 m, 3.02 m × 3.02 m and 4.98 m × 4.98 m) were sampled. Linear and non-linear mixed-effects models were developed to examine the effect of tree spacing on the quality of wood and lumber as defined by the modulus of elasticity, modulus of rupture and knot frequency of 208 boards and the ring-level microfibril angle and wood density of 86 radial strips. Wood and lumber quality improved with decreasing spacing, and only the narrowest spacing had lumber that conformed to the requirements of the lowest South African structural grade. Microfibril angle, wood density and knot frequency explained 71% of the variation of lumber stiffness. After accounting for ring width differences, there remained a significant effect of initial spacing on the parameters of models predicting microfibril angle and wood density. Wide initial spacing is discouraged if higher strength grades are desired for Pinus patula lumber.

中文翻译：

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Pinus patulaSchiede ex Schltdl 的弯曲木材特性。& 湛。随着初始树间距的减小而改进

Pinus patulaSchiede ex Schltdl 的木材刚度随着初始树间距的减小而增加。& 湛。微纤维角度、木材密度和结节频率的潜在特性解释了木材刚度变化的 71%。树间距也影响木材特性，与径向生长速率无关。南非种植的松树种植园的快速生长速度和缩短的采伐期导致结构木材的刚度降低，结构木材约占所有锯材的 75%。已知微原纤维角度和木材密度会影响木材刚度，这可能受树木生长空间的影响。本研究的目的是评估由狭窄的树间距引起的较慢的生长速度对 Pinus patula Schiede ex Schltdl 适宜性的影响。& 湛。用于结构木材的木材。采样了 18 年和 19 年的树间距试验，初始树间距为 4 个级别（1.83 m × 1.83 m、2.35 m × 2.35 m、3.02 m × 3.02 m 和 4.98 m × 4.98 m）。开发了线性和非线性混合效应模型来检查树木间距对木材和木材质量的影响，这些影响由 208 板的弹性模量、断裂模量和结节频率以及环级微纤维角度和木材密度为 86 条放射状。木材和木材质量随着间距的减小而提高，只有最窄的间距的木材符合南非最低结构等级的要求。微纤维角度、木材密度和结节频率解释了木材刚度变化的 71%。在考虑环宽差异后，初始间距对预测微纤维角度和木材密度的模型参数仍有显着影响。如果希望松木木材具有更高的强度等级，则不鼓励使用较宽的初始间距。