Mechanical Structure of the Stem of Arborescent Palms

Mechanical properties of the stem tissue were examined for the arborescent rain forest palms Welfia georgii, Iriartea gigantea, Socratea durissima, Euterpe macrospadix, Prestoea decurrens, and Cryosophila albida. Dry density, elastic modulus, and modulus of rupture are greatest toward the base and periphery of palm stems. All of these properties increase markedly with inferred age. The capacity to increase stem stiffness and strength is the major means by which arborescent palms compensate for increased structural demands during height growth. Young palms are overbuilt with respect to diameter and older palms are underbuilt, compared with arborescent dicotyledons and conifers. Yet there is a tendency to maintain a constant margin of safety against mechanical failure by increases in stem tissue stiffness and strength, with initial low values increasing to exceptionally high values. Stiffness and strength of palm stem tissue increase more rapidly with specific gravity than would be expected from existing models that describe mechanical properties of cellular solids. This difference between palm stem tissue and common woods may result from differences in cell structure and cell wall chemical composition.