Strength Properties of Juvenile and Mature Wood of Twelve Families of Loblolly Pine (Pinus Taeda L.)

The wood mechanical properties of progeny from twelve open-pollinated parent trees were examined. Six families were from parents which had high wood specific gravity and six were from parents which had low wood specific gravity. Thirty-two-year-old trees, that had been planted at Many, Louisiana, were sampled and juvenile and mature wood test specimens were prepared. Maximum crushing strength, modulus of rupture, modulus of elasticity and wood specific gravity were determined from compression parallel to the grain tests and static bending tests. Maximum crushing strength, modulus of rupture, modulus of elasticity, and specific gravity were found to vary significantly between family and between wood-type Uuvenile or mature) specimens. The family by wood-type interaction was found to be not significant for all of the four wood properties measured. The six highest total tree means for modulus of rupture and modulus of elasticity were for the six families that came from parents having high specific gravity_ For both maximum crushing strength and wood specific gravity, only one of the six highest total tree means was from a family having a low specific gravity parent. For all test specimens examined, the mean maximum crushing strength, mean modulus of rupture, mean modulus of elasticity, and mean wood specific gravity were found to be 6,386 pounds per square inch (p.s.i.), 13,546 p.s.i., 1,542,342 p.s.i., and .502 respectively. For the juvenile wood, the means for these four properties were 5,269 p.s.i., 11,462 p.s.i., 1,224,470 p.s.i., and .453 respectively. For the mature wood specimens, the means for these four properties were 7,438 p.s.i., 15,533 p.s.i., 1,845,514 p.s.i., and .548 respectively. A strong, positive relationship was found between the mechanical strength properties and wood specific gravity. A strong, positive relationship was also found between modulus of rupture and modulus of elasticity. The results of this study appear to support the hypothesis that gains made in wood specific gravity, made through parent selection, are then also realized in improved mechanical properties of the wood produced from the progeny.