Proyecto de Graduación (Licenciatura en Ingeniería Forestal) Instituto Tecnológico de Costa Rica, Escuela de Ingeniería Forestal, 2015.Weather conditions may cause a change in the structure of plants in the altitudinal gradient. The objective of this study was to relate the floristic composition in populations of trees in two altitudinal floors in a primary forest. Four permanent plots were established: two plots on high altitude floor to 710 m and two plots on the ground floor to 570 m, of 2500 m2 each plot, we measured the diameters, total height and tree species were identified within sample plots. We analyze the horizontal and vertical structure of the forest through the basal area, average total height and aboveground biomass, it were compared between each altitudinal floor with a homogeneity test Chi square. 48 families were found, with 110 genera and 145 species, to 579 individuals identified. For basal area and average total height there are not significant differences between the altitudinal floors. While, for above-ground biomass on the ground altitude floor was significantly higher in the high floor, may be due to climatic conditions of the site. By having a low sampling intensity of 0.11, we cannot explain what happens at the ecosystem level, by a high sampling bias.Instituto Tecnológico de Costa Rica. Escuela de Ingeniería Forestal
