Considerable changes in the vegetation can be observed in the altitudinal and latitudinal gradients in central Chile, from 400 to 3400 m above sea level and from arid to subhumid regions (31°–34° S). The composition of the vegetation, the relative proportions of life forms, and seasonal activities of the species, help to define bioclimatic areas where climatic data are scanty. The presence or absence of certain species is also useful in the evaluation of human impacts on mountain ecosystems.