摘要：
Aims Changes in the structure and composition of forests, whether caused by natural or anthropic events, alter the microenvironment, sometimes irreversibly. Since the local environment has a direct impact on basic ecological processes, this has become a key component of research. Mexican beech forests (Fagus grandifolia subsp. mexicana) in the Sierra Madre Oriental are restricted to sites with specific climate, soils and topography, making them an ideal natural system for ecological research. The objectives of this study were to identify the relationship between the microenvironment and the tree and shrub structure and composition of Mexican beech forests in the state of Hidalgo, and to compare the floristic similarity of these forests on the country scale using data from seven localities.
Methods Specimens were collected for a period of one year at all localities in the state of Hidalgo where beech forests are located. At each locality, five 400 m 2 plots were established, and structural attributes (basal area, coverage, density and species richness) and six environmental variables were measured in the plots. The relationship between structure and microenvironment was estimated by simple correlation and canonic correspondence analysis (CCA). In addition, floristic similarity between different beech forest localities in the Sierra Madre Oriental was estimated by correspondence analysis (CA).
Important findings Twenty tree species and eight shrub species were identified; at all localities studied F. grandifolia subsp. mexicana dominated the canopy. The multivariate analysis indicated that (i) in the four localities in the state of Hidalgo, all microenvironmental variables except pH are related to the variation observed in species composition and structure; (ii) the El Gosco locality had both tree and shrub species and microenvironmental factors different from those observed in the Fagus forests at the other localities in the study and (iii) the localities studied in order to draw country-scale comparisons could be divided into three groups by floristic similarity. The first group consisted of the Hidalgo localities, the second of the Veracruz localities, and the third, more different from the others, of the Tamaulipas locality. The results of this study provide the first reference for the relationship between the range of microenvironments and species structure in Mexican beech forests. Microenvironmental conditions in the larger beech forests could be used as a model for designing management and conservation programs for this plant association. Because of its particular ecological and historical characteristics, this association could serve as an example of biodiversity conservation in Mexico.
