干旱区生态环境知识资源中心

Understanding of the natural factors that lead to complex changes in forest ecosystems is limited. Worldwide, there are only a few forests as pristine and isolated as the Sierra de La Laguna in the southernmost range of the arid Baja California, Mexico. Its outstanding trait as a model system is that anthropogenic stressors are notably absent, which facilitates the study of natural ecological processes of the forest because separating human-induced ecological changes from natural ones is not a simple matter. In this study, we sampled sites and defined vegetation units on the basis of dominance of the canopy by the main tree species. We identified three forest types: the pine and encino forests that occupy the higher areas and the roble forest at lower elevations. For each living tree in the sampling plots, we measured height, canopy coverage per tree, diameter at breast height, as well as the amount of deadwood, leaf litter, and abundance of young trees. A succesional competition occurs between Pinus and Quercus sensu lato; we conclude that the encino forest represents a climax condition, the pine type represents an early succesional stage, and the roble forest type is a simple climax community.