Increased planting density as a means for improving Pinus elliottii lumber stiffness

Faster growth and reduced harvesting ages are causing a reduction in the stiffness of lumber from South African grown pine plantations. The objective of this study was to determine whether increased planting densities of Pinus elliottii would result in improved stiffness of its sawn lumber and whether it would affect other relevant lumber properties. Four planting density treatments (403, 1 097, 1 808, and 2 981 stems ha^?1) of a 12-year-old experimental spacing trial were processed into lumber. The static modulus of elasticity (MOE_stat), modulus of rupture (MOR), warp, knot properties and density of the lumber were measured for 172 boards. Results showed that the planting density had a significant effect on the MOE_stat of the lumber. The higher mean MOE_stat (up to 27% increases) of lumber from densely planted trees seems to be the result of the higher slenderness and the slower diameter growth of these trees. Planting density also had a significant effect on the twist, knot area ratio and the number of knots per board. The magnitude of the effect on each of these properties, however, was relatively low.