The effect of stand density management on Pinus patula lumber properties

Abstract

Rapid growth rates and the accompanying reduced rotation ages of forest plantations have resulted in increased proportions of juvenile wood. Growing space markedly influences growth rate and may be manipulated by stand density management. The objective of this study was to evaluate the effect of stand density on the modulus of elasticity (MOE), modulus of rupture (MOR) and other selected properties of young (16–20 years) South African-grown Pinus patula lumber. Thirty-seven trees from two commercial stands were processed into 71 logs, cant sawn into lumber and tested for MOE, MOR, wood density and distortion. The first stand was planted at 1334 stems ha−1 and thinned to 827 stems ha−1 at age 11. The second stand was planted at 1667 stems ha−1 and was unthinned. Lumber from a previous study on 17 different commercial stands from more conventional (lower) stand density management regimes was also analysed using linear mixed-effect models. Only lumber from the 1667 stems ha−1 stand conformed to the requirements for structural use and had a considerably higher mean MOE of 8967 MPa compared to 7134 MPa for the 1334/827 stems ha−1 stand and 5556 MPa for the more conventional stands. MOR values were adequate for all stands. Unlike previous studies on other species, slenderness did not seem to have a profound effect on the MOE of the lumber from these P. patula trees. Stand density management therefore has the potential to increase lumber stiffness of P. patula and should be considered as a forest management intervention for wood quality improvement by saw-log growers in South Africa.