Structure of the high evergreen tropical forest of Naha, Chiapas, Mexico

Background: In the middle of last century, it was considered that tropical rainforest covers around 12.8 % of Mexico, but today this area is mainly occupied by agricultural lands, prairies, and secondary vegetation while just a little portion has mature forested vegetation. One of the more serious troubles in the Lacandon region, is the decrease of its rainforest area, because of a hard colonization process, expansion of communication paths, excessive logging, and incorporation of new rainforest areas to the agricultural and livestock production. This study was conducted in the Lacandon Community Naha, located at the north of the Lacandon rain forest, at the Municipality of Ocosingo, Chiapas, where some areas with mature rain forest are found and the rest is subject to traditional diversified and intensified use. Research question: How are structure and composition in the relicts of mature or well-preserved vegetation in the tropical rainforest of the Lacandon Community Naha? Study site and period of research: This study was conducted in the Lacandon Community Naha, located at the north of the Lacandon rain forest, at the Municipality of Ocosingo, Chiapas, from November 1993 to May 1995. Methods: Inside the lands of this community, we conducted 25 vegetation samplings in plots of 400 m(2) each (a hectare in total) in mature fragments of the rainforest. The evaluated structural traits were: floristic composition, density, frequency, basal area, and height. We calculated the importance value of the species in the community and its relative contribution in the six forest strata recognized with the help of lacandon informants. Results: We found 283 species of vascular plants in the total sampled area, belonging to 199 genera and 84 families. The structural analysis of vegetation corroborated the presence of six recognized forest strata, with distinctive height, floristic composition, and life forms. Density in the studied hectare was 15,632 individuals, and the absolute basal area 136.78 m(2). The importance value allowed to define the relative importance of the species in each stratum, according to the field observations. Terminalia amazonia records the highest importance value in all the strata. Conclusions: It was possible to describe with detail the tropical rain forest in Naha. The assistance of lacandon informants was crucial to recognize the zones with mature rainforest and their strata. There is an inverse relationship between density and basal area. The importance to evaluate in a quantitatively way the relicts of mature or well-preserved vegetation is highlighted as an indispensable reference to rehabilitate degraded areas, or to apply corrective actions for adequate advantage.