Stem architecture of shade tolerant species in a low-stature tropical rain forest in Mexico

The relationship of diameter and height of the stem is an architectural feature that is related to shade tolerance of the trees, as well as mechanical resistance to stem buckling. Theoretically it is postulated a high value of this coefficient for shade-tolerant species. The tropical rain forest of Los Tuxtlas, Mexico is a lowstature forest with higher light levels in the understory, in comparison with other forests in the world. It was estimated the value of the diameter/height coefficient for 275 tree saplings (100-300 cm) of three shadetolerant species and compared with the theoretically proposed values of stem buckling limit in trees. Particularly for this forest and contrary to general assumptions, we expect to find a low coefficient value due to increased height growth in comparison to diameter growth caused by high light levels in the understory. Indeed the three species showed a low coefficient of 0.492 for Guamia sp., 0.745 for Pseudolmedia oxyphyllaira, and 1.15 for Trophis mexicana. This may suggest that the height-diameter coefficient value of the stem for these species is in relation to the high levels of light in this forest in particular.