Causes of high abundance of two species of trees in a rain forest of Mexico
Trees ramon (Brosimum alicastrum) and chicozapote (Manilkara zapota) are abundant in rain forests of Mexico and Central America; reach heights of over 30 m dominate the canopy. Their abundance contrasts with the low density of most species in the rain forests, which is the cause of its high ecological diversity. Ecological studies have preferably explained the low density of species and less frequently searched the reasons for the abundance of species like ramon and chicozapote. These species have valuable edible fruits. Since they are abundant in areas near archaeological sites, it is proposed that the origin of this forest is anthropogenic, and result of silvicultural management. We present the results of a study conducted in a rain forest that is located in the state of Veracruz, Mexico, where ramon and chicozapote are dominant species. The purpose was to identify common features that explain their abundance. For each species abundance and size structure of the population was estimated; an analysis of their patterns of resource allocation to stems, leaves and roots in seedlings and juveniles was conducted; these attributes explain the probability of survival of plants in these stages in their life cycle.
The average density of chicozapote individuals with DBH> 1 cm and height ≥ 2m, was not significantly different from the average density of individuals of ramon. In both species predominated individuals with DAP from 1-10 cm. The DBA maximum for ramon was 30 cm, while the maximum DBA for chicozapote was 55 cm. In seedlings and juveniles the situation was different because ramon had a density 10 times greater than chicozapote. Differences also appeared in the pattern of resource allocation; chicozapote had thicker and heavier leaves, and accumulated more biomass per cm of stem and root. Chicozapote had a survival rate of seedlings and juveniles of ≈ 80% per year, while in ramon was ≈10% per year. To achieve high densities of trees, ramon must maintain high densities of seedlings and juveniles. The reason for the abundance in both species is ecological, but have developed different strategies.