Butteressing of Tropical Trees: A Descriptive Model and New Hypotheses

A descriptive model is proposed for buttressed tree bases. Comparing buttressed bases with hypothetical cylindrical bases of the same upper diameter, the model predicts higher surface/volume ratios for buttressed bases but roughly equivalent or lower total wood volume. Improved support might thus be achieved without increased energy expenditure on wood. Hypotheses are proposed to account for decreasing size and frequency of buttresses with increasing latitude and, in the tropics, altitude. Gradients in soil structure, nutrient distribution, and extent of soil flooding may be correlated with buttressing, but the strongest correlation is probably with gradients in net energy input and in seasonality of input. Decreasing temperatures may select for lower surface/volume ratios, thicker bark, and deeper rooting, all of which are incompatible with buttress development. Away from tropical lowlands, increasing population size and increasing adult mortality may reduce selection for iteroparity and hence lower selection for adaptations such as buttressing which favor it. Increased risk of fire and of winter-drought stress may also result in decreased buttressing with increasing latitude.