Ecological Relationships of Desert Fog Zone Lichens

Abstract

Abstract. Patterns of environmental conditions prevailing in coastal desert fog zones provide habitats extremely favorable for lichen growth. Phylogenet- ically related groups of lichens occur in geographically isolated desert fog zones, but endemism at both the species and genus levels is relatively high. The ecological importance of lichens in these regions is related to morpholog- ical and physiological adaptations to water uptake in both a liquid and vapor form. Much of this moisture is unavailable to vascular plants, allowing a large biomass of lichens to occur in areas with little or no vascular plant cover. The relative importance of fruticose lichens in such habitats, in comparison to crustose and foliose forms, is determined largely by the physical form of at- mospheric moisture. Coastal deserts share many environmental features common to all deserts. Rainfall is low and vegetation is commonly sparse or lacking. At the same time, coastal deserts have certain distinctive characteristics not shared by inland deserts. Temperature differences between night and day are moderated by the proximity of the sea. More important for lichens, however, is the typical occurrence of high atmospheric humid- ity, fog and/or dew along the coast. Extensive coastal deserts occur in three areas of the world: the Peruvian and Chi- lean Atacama deserts, the coastal Sonoran Desert in Baja California and the Namib Desert in southwestern Africa. Each of these areas shares the same origin of climatic development in the movements of sub-tropical high pressure centers resulting in the transport and upwelling of cold currents adjacent to their coasts. Details of the general climatology of these regions has been described in many publications (e.g. Meigs, 1966; Rumney, 1968). Each of these coastal fog deserts is characterized by lichen floras rich in both diversity and biomass. This review describes the ecological and floristic relationships of lichens in these coastal fog deserts with particular emphasis on the coastal Atacama and Baja California regions. Coastal Atacama Desert.-The Atacama desert along the coasts of Peru and north- ern Chile, perhaps the driest region in the world in terms of measurable precipitation, extends from the region north of Trujillo near the Ecuadorian border of Peru (50?S) south to La Serena (30?S) in Chile, a total distance of more than 3500 km. Along this belt is a narrow strip of coastal desert whose biological characteristics are profoundly influenced by frequent maritime fogs. The cold northward flowing Humboldt current