The flexural lumber properties of Pinus patula Schiede ex Schltdl. & Cham. improve with decreasing initial tree spacing

Abstract

& Key message An increase in the stiffness of lumber with a decrease in initial tree spacing was confirmed for Pinus patula Schiede 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. & Context 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. & Aims 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. & Methods 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. & Results 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. & Conclusion Wide initial spacing is discouraged if higher strength grades are desired for Pinus patula lumber.

Physico-Mechanical Properties and Growth Characteristics of Pine Juvenile Wood as a Function of Age and Planting Spacing

“…The literature reports that several species are more sensitive to this variation. In studies with Pinus patula, tree spacing signifi cantly infl uenced the mechanical properties of wood (Erasmus et al 2018;Erasmus et al, 2020). 11-year-old Pinus radiata forests, planted with high planting densities (2500 stems ha -1 ) had positive eff ects on wood stiff ness in relation to the planting of 833 stems ha -1 .…”

Effect of Initial Planting Density on Growth Traits and Wood Properties of Triploid Chinese White Poplar (Populus tometosa) Plantation

“…Liziniewicz et al [7] recorded that the mean height of 23-year-old lodgepole pine increased with increasing initial planting density. The initial planting density also affects wood properties, such as basic wood density (BWD) [8][9][10], fiber traits [10], and wood chemical composition [11]. Ahmed et al [12] reported that the planting density influence on growth traits and wood properties is greater than that of the wood chemical composition.…”

Exploring new frontiers in forecasting forest growth, yield and wood property variation

“…Vaughan et al (2019) showed in Pinus ponderosa that it is not growth rate, per sé, which is closely tied to variation in wood properties (in their case, focussing on wood density as an indicator) but rather annual climate peculiarities which lead to variation in the timing and extent of transitions into latewood production. Erasmus et al (2020), looking at Pinus patula, found a clear effect of tree spacing. This was not just on wood density but also on the less-often measured but critically important, microfibril angle.…”