An Impossible Ecosystem
The Atacama Desert is the driest non-polar desert on Earth. Some areas receive less than a millimeter of rain per year, and certain riverbeds show evidence of being dry for 120,000 years. Yet, on the steep coastal mountainsides near Paposo, isolated pockets of dense vegetation thrive. These are the lomas, or fog oases, ecosystems that survive almost entirely without rain. Their existence depends on a persistent coastal fog, known locally as the camanchaca.
This dense fog is a product of the cold, north-flowing Humboldt ocean current. The cold water cools the air above it, causing moisture to condense into a thick stratocumulus cloud bank that rolls inland. While the water droplets in the fog, measuring just 1 to 40 microns in diameter, are too small to fall as rain, they provide life-giving water through a process of direct condensation. As the fog moves through the vegetation, droplets collect on the surfaces of leaves, stems, and lichens, a phenomenon called horizontal precipitation. This process is most effective at altitudes between 300 and 1,000 meters, creating distinct bands of green on the otherwise barren hills.
Islands of Endemic Life
The fog oases are terrestrial islands, separated from each other by hyper-arid desert. This isolation has led to high levels of endemism, with many species found nowhere else on Earth. The northern coastal Atacama hosts about 550 species of vascular plants, with an endemism rate exceeding 60%. The slopes near Paposo support at least 120 species of flowering plants and ferns.
The flora includes highly adapted species from the cactus genus Copiapoa, which has evolved to survive almost entirely on moisture from the coastal fog. Other characteristic plants include various species of Nolana and bromeliads like Tillandsia landbeckii, an "airplant" that captures moisture directly through filaments on its leaves. These plant communities, in turn, support a surprising variety of animal life. Guanacos and vicuñas graze in these vegetated zones. The South American gray fox can be found here, along with smaller mammals like Darwin's leaf-eared mouse. The lomas also provide an important habitat for birds, insects, and reptiles like the Vallenar toad.