GAP-DEPENDENCE AND LEAF CHARACTERISTICS OF TREES IN A TROPICAL LOWLAND RAIN-FOREST IN MEXICO

Woody tropical rain forest species were grouped according to their dependence on gaps for regeneration as obligate gap species, gap-dependent and gap-independent species. Differences in leaf size, shape, anatomy, and mineral nutrient concentrations among these species groups were studied. Obligate gap species had larger leaves than both gap-dependent species and gap-independent species. Gap-independent species had more elongated leaves, and had larger stomata but a lower density of stomata. Gap-dependent species had higher specific leaf weight values and more N and P per unit area than the two other species groups. Gap-dependent species also had more K per unit area and thicker leaves than obligate gap species. Gap-dependent species were more often deciduous, and gap-independent species were less often deciduous than expected on the basis of the distribution of deciduous species over the total species sample. No such segregation existed with respect to compound-leaved species. Gap-dependent species had a greater contrast in most of the leaf characteristics in sun vs shade environments than both obligate gap species and gap-independent species. It is argued that the differences in leaf characteristics between species of different groups are probably related to the way the species exploit their characteristic environments.