Relative resistance to breaking of Pinus taeda and Pinus palustris

Abstract

Patterns from hurricane damage indicate that longleaf pine is more windfirm than loblolly pine. Tree windfirmess has been attributed to many factors including species and material properties like wood strength and stiffness. Because longleaf pine wood is stronger and stiffer than loblolly pine wood, this study used static winching methodology to see if these properties account for differences in wind firmness by measuring bending force required to break stems (MMAX). Stress-strain diagrams were constructed for pulled trees to explore how they behave under increasing loads. Based on these diagrams, living trees appear to act as linear elastic materials as they experience increasing static lateral stress. As expected, longleaf pine stems were stiffer than loblolly pine wood in situ based on Young's modulus of elasticity. Tree basal area was the best predictor of MMAX for both species, however, species had no significant effect on the maximum bending moment required to break tree stems of a given basal area for these trees under these conditions. The stiffness of the stems was higher for longleaf than loblolly as indicated by the modulus of elasticity, but the strength of the stems as indicated by the modulus of rupture was not significantly different between the species. Differences in the volumetric density of foliage, however, were consistent with the observed differences in stem failure between the species. For trees with the same diameter, loblolly pine had higher values of leaf area per unit crown length than longleaf pine.