Buttress arrangement in Pterocarpus officinalis (Fabaceae): effects of crown asymmetry and wind

Buttresses are distributed independently of compass direction in Pterocarpus officinalis at a site in western Puerto Rico where prevailing winds blow out of the east-northeast. Buttress length is associated with same-side crown radius. These results contradict findings in studies of other species of trees where buttresses point into the wind and are presumed to function as tension members. No simple explanation of buttress asymmetries emerges from the study. External stresses seem not to contribute significantly to the development of buttresses in this species, and the current conduction hypothesis of Petch (1930) and Richards (1966) is weakened by the evidence that grain is not straight. Nevertheless, buttresses probably are important to the survival of the tree. P. officinalis grows in deep mud, and buttresses provide a broad platform that appears to minimize toppling.