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 prop erties and grade compliance of lumber from two 35-year-old loblolly pi ne plantations. Grade compliance determination involved performing ben ding 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 as signed visual grades. The results indicate that stand density is an im portant factor influencing the flexural strength and grade compliance of the lumber produced from the plantations studied. Specifically, lum ber 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/ac re with 141-sq ft basal area at harvest time, has about 92% and 64% co mpliance to required design flexural strength and stiffness values, re spectively. It is now evident from the results of this study and a pre vious study by the authors that even dense stands must be older than 3 5 years of age before they can be harvested for lumber production to e nsure attainment of at least 95% lumber grade compliance, i.e., streng th values are consistent with assigned visual grades. More studies are definitely needed to determine the appropriate harvest age.