Structure and composition of the vegetation in four sites of the Sierra Madre Occidental

Abstract

The structure and composition of tree species were evaluated in the Sierra Madre Occidental, in the area of El Salto, Pueblo Nuevo, state of Durango, Mexico. Four study sites (2 500 m²) were established, where 10 plots of 100 m² were randomly located. The registered variables were individual height (m), diameter at breast height (cm), and projected crown area (m²). The dominance of each species was quantitated according to its basal area, and its density, according to the number of individuals. The importance value index (IVI) was then calculated. The diversity and species richness were estimated using the Shannon-Wiener diversity index (H') and the Margalef index (DMg), respectively, and Bray-Curtis ordination was utilized to obtain the similarity between sites. The results show that there were 18 tree species belonging to 9 genera. The Santa Bárbara site exhibited the largest number of species (9), while ejido Adolfo Ruíz Cortines had the smallest (6 species). Quercus sideroxyla is the most ecologically important species in ejido Adolfo Ruíz Cortines and ejido El Brillante, followed by Quercus durifolia in S2, and Pinus cooperi was the most important species in the Santa Bárbara reserve site. Santa Bárbara had the highest Shannon diversity index (1.51), and ejido Banderas had the lowest (0.93). The highest values for the Margalef index (1.79) corresponded to the Santa Bárbara reserve site (S4), and the lowest (0.97), to ejido El Brillante (S2). The Bray–Curtis ordination revealed similarity (25.59 %) between ejido Adolfo Ruíz Cortines and ejido El Brillante, indicating a tendency to heterogeneity.