Growth Rate and Bending Properties of Selected Loblolly Pines
Keywords:Growth rate, static bending properties, loblolly pine, modulus of rupture, modulus of elasticity, specific gravity, juvenile wood
The modulus of rupture and modulus of elasticity in center-point bending were determined for 1/2- X 1/2- X 10-in. specimens cut between pith and bark from twelve trees of loblolly pine of different growth rates. Six of these trees were fast-grown, 15-year-old, genetically selected stock; 3 trees each came from a 25-year-plantation and a 41-year-old forest. The original location of the specimens in the trees was between 11 and 14 ft above the ground. The average diameter of the trees at breast height was approximately 81/4 in. for each population.
The specific gravity, modulus of rupture, and modulus of elasticity of the wood from the three populations showed a marked initial trend of increasing magnitude with distance from the pith. At distances from the pith greater than about 21/2 in., there was little or no change in the properties of wood from the 25- and 41-year-old trees. The properties of the wood from the 15-year-old trees continued to show an increase for at least about 4 in. from the pith. For a given distance from the pith, the properties were, on average, higher in the older trees than in the younger trees. When the properties were related to the number of growth rings from the pith, however, there were no significant differences between the properties of wood from trees of different growth rates. Similarly, rate of growth did not appear to affect the relationships between specific gravity, modulus of rupture, and modulus of elasticity. Consequently, although fast-grown trees contain a larger volume of juvenile wood than more slowly grown trees, the properties of their mature wood should not be significantly reduced by the fast growth rate.
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