Geographical Description of Three Fog Ecosystems in the Atacama Coastal Desert of Chile*

During the past century the precipitation measured at the Atacama coastal desert was less than two millimetres as an annual average, 60 % of the years Iquique did not receive a drop of rain. These are extremely difficult conditions for vegetation to grow and develop. However, some small ecosystems or oases can still be found at the Cordillera de la Costa. They are maintained with fog water. In almost 7 years of measurements at the oasis of Alto Patache, it was found an average of 7,8 L m-2 d-1 of fog water collected by SFC. These fog oases are located in a mega cliff and in mountains close to the sea, also they can be found farther inland along fog corridors. The Alto Patache ecosystem (20°49´S-70°09´W) shows a variety of shrub and herb species, depending on altitude, type and orientation of relief, plateau or cliff. The Pajonales (20°30´S-70°00W) ecosystem is monospecific, being Tillandsia landbeckii (Bromeliaceae) the only species recognized. The Chipana oasis (21°15´S-70°03´W) is composed mainly by cacti Eulychnia iquiquensis in association with shrub and herb species. These oases have been studied from a biogeographical point of view. Several parameters regarding flora (number of species), structure of the vegetation (density, coverage, vitality) and geographical features (form of relief, altitude, micro-topography, slope exposure, substrate and soils) were measured and analysed. The results show that the oases studied lie at altitudes between 400 and 1200 m.a.s.l., being altitude, relief exposure to the predominant winds (SW, S) and substrate significant factors of presence and vitality of vegetation