Allometric variation of shade-tolerant tree species in a Mexican tropical rain forest

In tropical rain forests, shade-tolerant tree species exhibit the typical wide-crown architectural type characteristic of low-light environments. In recent studies, though, some shade-tolerant species have been found not to show this typical architectural type. In the present study, the stem and crown architectural type of three shade-tolerant tree species was analyzed, two from the forest understorey and one from the mid-canopy. Twelve architectural variables were measured in 254 saplings between 50 cm and 300 cm tall in Los Tuxtlas, Mxico. The allometric analysis showed that the three species are not similar in architecture. Instead, they present architectural differences related to their adult canopy position. Both sub-canopy species presented thicker stems and flatter crowns, while the mid-canopy species was taller, presenting a slenderer stem and crown, and a less vertical crown shading. It is concluded that within the group of shade-tolerant tree species there is certainly more than a single architectural crown type depending on the adult canopy position of the particular species. The previous single wide-crown architectural type is not the only or typical architectural type for shade-tolerant species.