Abstract

In the Andean desert zone of Chile, three vegetational belts can be distinguished: the subalpine belt (3,200-3,500 m); the low alpine belt (3,500-4,250 m); and the high alpine belt (4,250-4,450 m). In the Cordillera Dona Ana area (29-degrees-45' S, 60-degrees-59' W) soils show a great variation in chemical and drainage characteristics which may explain the patchy distribution of plant species. In the subalpine belt, the shrubby species (> 1 m) are found exclusively on north-facing slopes in rocky sites with shallow soils, and this may be related to thermal refuges. In contrast, many subshrubs and perennial herbs grow mainly on south-facing slopes or on hillsides with deep sediments. Most leguminous species grow on soils rich in calcium, and this may be due to their greater ability to fix atmospheric nitrogen. Large areas with hypothermal anomalies have no vegetation, except when covered by sediments of other origins (such as volcanic or intrusive). At the same altitudinal level, the chemical characteristics, drainage of the substrate, and winter snow accumulation determine which species are present.