A Structural Approach to the Function of Buttresses of Quararibea Asterolepis

Abstract

Buttresses of lowland tropical forest trees have long been thought to serve as structural supports. This morphometrical study of the buttresses and other characteristics of Quararibea asterolepis demonstrates and describes the nature of the support role played by buttresses. Buttresses tend to grow on the side of the tree that faces the prevailing winds, thereby functioning as tension members that help prevent the tree from being blown over. The buttresses become proportionately larger as the tree grows, providing the tree with greater support as its crown becomes exposed to the stronger winds of the upper forest canopy. In particular, buttress height increases much faster than tree height. This disproportionate increase reduces by °15% the potential vulnerability of the trunk to snapping or twisting under stress due to winds. On the other hand, no specific relationship independent of tree size can be demonstrated between the length of a buttress and the radius of the crown above or opposite that buttress. There is thus no evidence that buttresses counteract stresses due to crown asymmetries of a particular trees.