Análisis estructural de un bosque mesófilo de montaña en el extremo oriental de la Sierra Madre del Sur (Oaxaca), México

We analyzed vegetation structure in a 1-ha plot of cloud forest at Santo Tomás Teipan (Oaxaca, Mexico). Considering its marginal location near the edge of a region covered by this vegetation type on the Sierra Madre del Sur, we examined to what extent this community differed from other cloud forest communities thriving under better conditions for this plant formation. Each individual with diameter at breast height (DBH) ≥2.5 cm was located in a system of coordinates; besides, its taxonomic identity, crown cover, DBH and total height as well as the height to the first branch and the crown base were recorded. Basal area (46.41 m2 ha-1), cover (44,247.33 m2 ha-1), and density (1,035 ind. ha-1) figures fall within the known range for the lower montane rain forests of tropical America. According to structure and composition, two strata were differentiated: a lower one (2 to 11 m), and an upper one (11 to 30 m). Overall dominance corresponded to Cornus disciflora, an upper stratum species. In the plot two topographic conditions were distinguished, namely lower ravine slope and hilltop, which seem to be associated to contrasting soil characteristics. Although this topographic heterogeneity does not match the structural homogeneity of the forest, we detected some clumped patterns for individual species that were preferentially distributed in one of these conditions. The structure of the forest at Teipan is comparable to that of similar forests, but its diversity is relatively low. This may be explained by the absence of taxa occurring in the adjacent dry tropical communities, unlike other cloud forests whose flora appears to be enriched with some elements typical of tropical moist communities with which they abut.