EFFECT OF STAND DENSITY ON FLEXURAL PROPERTIES OF LUMBER FROM 2 35-YEAR-OLD LOBLOLLY-PINE PLANTATIONS

This study reports on the effect of stand density on the flexural properties and grade compliance of lumber from two 35-year-old loblolly pine plantations. Grade compliance determination involved performing bending strength tests on the lumber, which was visually graded according to Southern Pine Inspection Bureau (SPIB) rules, to ascertain if the actual strength values were consistent with the requirements of the assigned visual grades. The results indicate that stand density is an important factor influencing the flexural strength and grade compliance of the lumber produced from the plantations studied. Specifically, lumber from the denser 35-year-old stand, which had 70/25 site index, 8- x 8-ft original spacing (thinned only once at age 18) and 230 trees/acre with 141-sq ft basal area at harvest time, has about 92% and 64% compliance to required design flexural strength and stiffness values, respectively. It is now evident from the results of this study and a previous study by the authors that even dense stands must be older than 35 years of age before they can be harvested for lumber production to ensure attainment of at least 95% lumber grade compliance, i.e., strength values are consistent with assigned visual grades. More studies are definitely needed to determine the appropriate harvest age.