Included here is the Atacama Desert which extends south from the Peru-Chile border for some 1000 km along the western Andes. It is regarded as the driest place on earth.

Atacamian Cactus Plains

Cacti are usually characteristic of flat areas where soil texture is course and unfavourable for shrub species. The most common species are members of the endemic or near endemic genus Copiapoa (Cactaceae). For example, on some of the flat plains in the Atacama the endemic Copiapoa cinerea var. columna-alba (Cactaceae) can form almost monospecific stands. Small geophytic cactus such as the endemic Neoporteria esmeraldana (Cactaceae) may also be present. These typically grow under a fine layer of quartz sand. In places endemic species such as Copiapoa longistaminea, C. serpentisulcata as well as C. cinerea form large mounds measuring up to 1 m in diameter and about 60 cm high. Apart from cacti scattered shrubs such as Heliotropium pycnophyllum, Tetragonium maritima and the endemic Gypothamnium pinifolium (Asteraceae) may also be present, while other associated species may include the endemic or near endemic Frankenia chilensis (Frankeniaceae) and Polyachyrus fuscus (Asteraceae).

Atacamian Fog Zone (Lomas) Formations

Found in both the Peruvian and Atacama deserts these are best developed on the upper slopes of the coastal escarpments at altitudes between about 200-1500 m. It is here that the combined effects of onshore moisture laden fogs and steep topography create condensation. The fogginess also reduces solar radiation, which in turn reduces levels of evapotranspiration. Consequently, canopy cover can be up to 30% or more. In the Atacama, cacti such as the endemic Echinopsis deserticola and Eulychnia saint-pieana (Cactaceae) and shrubs such as the endemic Euphorbia lactiflua (Euphorbiaceae) can reach heights of 2 m or more. Other charactersitic shrubs include Stachys pannosa and the endemic Balbisia peduncularis (Geraniaceae), Centaurea cachinalensis (Asteraceae), Heliotropium taltalense (Boraginaceae) and Nolana leptophylla (Nolanaceae), while locally common species include Puya boliviensis and the endemic Oxalis gigantea (Oxalidaceae). The high relative humidity also provides conditions suitable for epiphytic species such as fruticose lichens and the endemic vascular plant Tillandsia geissei (Bromeliaceae). However, herbaceous ground layer species are only common during period of relatively high rainfall despite the fog and there are virtually no annual species. This is surprising considering their relative abundance on the dryer slopes at lower elevations. In the lomas of southern Peru on the coastal range of Arequipa about 80 vascular plant species have been recorded between altitudes of 300-1000 m and it is reckoned that about 80% of the flora is endemic. Among these are Chenopodium petiolare (Chenopodiaceae), Cristaria divaricata (Combretaceae), Encelia canescens (Asteraceae), Loasa urens (Loasaceae) and Nolana arenicola (Nolanaceae). The best know lomas formation in Peru is the Lomas de Lachay about 60 km north of Lima. Above about 300 m distinctive formations occur on the hillsides and canyons. These are often dominated by endemic taxa such as Acmella alba (Asteraceae), Croton ruizianus (Euphorbiaceae), Galinsoga caligensis (Asteraceae), Hebecladus umbellatus (Solanaceae), Nicotiana paniculata (Solanaceae), Senecio albadianus (Astereaceae) and Solanum montanum (Solanaceae).

Atacamian Desert Vegetation

The vegetation in the arid interior valleys and above and below the lomas is very sparse. In the south there is slightly more precipitation. In the region between La Serena and Rio Copiapo, for example, there are succulent communities in the interior. These include mound-forming species of Eulychnia and Tephrocactus together with shrubby endemic species such as Adesmia argentea (Fabaceae), Bulnesia chilensis (Zygophyllaceae), Cordia decandra (Boraginaceae) and Heliotropium stenophyllum (Boraginaceae). However, between Vallenar and Copiapo, the interior vegetation is virtually absent. Scattered perennial endemics such as Argylia radiata (Bignoniaceae), Caesalpina angulata (Fabaceae), Nolana pterocarpa (Nolanaceae), Polyachyrus fusco (Asteraceae) and a few other species are the only significant plants for many kilometers. Above and below the fog-zones, vegetation cover also drops sharply. Above the fog-zone between Chanaral and Antofagasta there are stands of Copiapoa together with various endemic Nolana species such as N. peruviana, N. sedifolia, N. stenophyllum and N.villosa (Nolanaceae) and shrubby endemics like Gypothamnium pinifolium (Asteraceae) and Polyachyrus cinereus (Asteraceae). Below the fog-zone there are often dense mounds of the endemic Deuterocohnia chrysantha (Bromeliaceae) and Puya boliviensis in the transition zone to more arid conditions, but in the arid zone proper the vegetation is often reduced to scattered shrubs of species such as the endemic Copiapoa haseltoniana (Cactaceae). Further north in the Sechura Desert of northern Peru there are large areas that support very little vegetation, but Parkinsonia aculeata and the narrow endemic Alternanthera peruviana (Amaranthaceae) can be locally common. Much of the flat sandy terrain, however, is devoid of vegetation but the dunes are often colonized and stabilized by Capparis scabrida together with Cryptocarpus pyriformis and Distichlis spicata.


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