The Atacama Desert is an elongated strip of desert along the northwest coast of Chile, essentially bounded by the Pacific Ocean on the west. It extends nearly 1600 kilometers (km) and reaches a maximum width of 180 km. In many areas rainfall has never been recorded, and the Atacama is considered one of the driest deserts in the world. Consequently, an extremely arid, almost barren, landscape predominates. Despite the aridity of this desert, some cacti (Eulychnia), perennials (Nolana), and mesquite (Prosopis) occur in basins where occasional water accumulation occurs. Relatively few animal species have adapted to this arid environment and therefore, faunal diversity and density is extremely low. Even bacteria are scarce, and in many portions of the desert insects and fungi are absent. The intrinsic value of the Atacama Desert's plant and animal communities lies in the unique nature of their composition, the high levels of endemism and remarkable species adaptations for survival in some of Earth's most demanding conditions.
Location and general description
The Atacama Desert ecoregion occupies a continuous strip for nearly 1600 km along the narrow coast of the northern third of Chile from near Arica (18°24' S) southward to near La Serena (29°55' S). This desert is a sparsely populated virtually rainless plateau, running east from the Pacific Ocean to the Andes Mountains. The average width is less than 100 km. The xeric conditions extend up to 1500 meters (m) above sea level on the drier slopes. The faulted coastal mountains (mostly 500 to 1000 m high) are composed of Cretaceous sediments (limestone and sandstone) over more ancient masses of crystalline rocks.
The Atacama Desert is considered to be one of the driest coastal deserts in the world. Vegetation must contend with an annual rainfall of 0.6 millimeters (mm) in Arica and 2.1 mm in Iquique. The Atacama becomes slightly less arid as it moves southward. The average monthly temperatures in Iquique range from 14.5°C in September to 21°C in March. Further limiting plant growth is the extremely low total organic carbon and nitrogen content of the Atacama soils; for example, total organic carbon levels are lower than those of the Sahara Desert and the Mojave Desert by significant amounts. While bacterial occurrences are even scarce compared to other deserts, there are a number of extremophiles and lithic microbial communities which specialize in exploiting minerals such as dolomite, quartz, gypsum, halite and limestone.
Topography and substrate combine to influence the patterns of moisture availability and areas of suitable habitat. Where isolated mountains or steep coastal slopes intercept the clouds, a fog zone develops with a stratus layer concentrated against the hillsides. The moisture allows the development of fog-zone plant communities termed "lomas" (small hills) near the coast and in lower portions of numerous gorges (quebradas) between sea level and 1100 m. These plant formations also have been called the fertile belt, fog oases, or meadows on the desert. Plant communities of the lomas consist of mixtures of annual and short-lived perennial and woody scrub vegetation.
The northern coastal zone has almost no vegetation. Among some of the plant species found in this zone are cacti growing at elevations over 500 meters. Eulychnia iquiquensis and Copiapoa sp. Near Iquique, there is large community of Tillandsia landbeckii growing at 990 to 1100 meters in elevation. The valleys along streams support plant communities that are composed of trees: including Chilean mesquite (Prosopis chilensis), Tamarugo (P. tamarugo), Humboldt's willow (Salix humboldtiana), Schinus areira, Long-spine acacia (Acacia macrantha) and Tara (Caesalpinia spinosa) and other shrubby and herbaceous plants. On slopes moistened by drizzle during the winter, sparse strands of Tillandsia spp. may exist in association with a few lichens.
Near the town of Antofagastsa, the region is practically devoid of vegetation except for Eulychnia iquiquensis and Copiapoa sp. Only some brush plants occur along the coastal plateaus, dependent for survival on the moisture of persistent fog, they include Heliotropium pycnophyllum, Ephedra breana and Lycium deserti. In places away from the area of fog formation, the desert is almost lifeless. In these areas, even decomposition does not occur. Some of the dead vegetation may be thousands of years old.
The southern Atacama Desert has a fog-zone vegetation, populated with approximately 230 species of vascular plants. Euphorbia lactiflua and Eulychnia iquiquensis are dominant species in the central area of this zone. Other shrubby species in the zone include Echinopsis coquimbana, Oxalis gigantea, Lycium stenophyllum, Proustia cuneifolia, Croton chilensis and Tillandsia geissei. Bromeliads are also present along the coastal flats in this southern part, and include Deuterocohnia chrysantha and Puya boliviensis.
The southernmost area in the ecoregion is near Chañaral. This area has communities of shrubs such as Skytanthus acutus, Encelia canescens, Frankenia chilensis, and Nolana rostrata. Annuals and perennials include Perityle emoryi, Oenothera coquimbensis, Adesmia latistipula, Astragalus coquimbensis, Cruckshanksia verticillata, Fagonia chilensis and Tetragonia angustifolia.
The intrinsic value of the Atacama Desert's plant and animal communities lies in the unique nature of their composition, the high levels of endemism and some species' remarkable adaptations for survival in some of the planet's most demanding conditions. The highly endemic flora is of particular importance. There are some traditional uses of species by the local inhabitants, e.g. food from Oxalis spp., medicinals from Salvia tubiflora and Ephedra spp.
There are approximately 550 species of vascular plants representing 225 genera and 80 families in the lomas formations. The most diverse families are the Asteraceae, Nolanaceae, Cataceae, Boraginaceae, and Apiaceae. Endemism is very high (over 60%). Most of the plant species mentioned earlier are endemic to the Atacama Desert. Three cacti are endemic to the northern part of the Atacama Desert; they are Eulychnia iquiquensis and Copiapoa sp. Endemic shurbs of the ecoregion include Berberis litoralis, Anisomeria littoralis, Atriplex taltalensis, Adesmia viscidissima, Croton chilensis, Nicotiana solanifolia, Teucrium nudicaule, Monttea chilensis, Stevia hyssopifolia, Senecio almeidae and Gutierrezia taltalensis. Endemic plants near Tocopilla are Malesherbia tocopillana, Mathewsia collina and Nolana tocopillensis.
Understandably, few animals have adapted to successfully inhabit this extremely dry habitat. The few scorpions and insects are the prey of lizards (Tropidurus spp.) and of a small passerine of the genus Geositta. An occasional bird of prey or vulture can be found scavenging on the carrion of domestic animals. Mammalian species are also few in number, with Darwin's leaf-eared mouse (Phyllotis darwini) and the South American gray fox (Pseudalopex griseus) encountered infrequently. The growth of a few scattered shrubs and herbaceous plants such as lichens enables certain specialized insects and poisonous spiders to colonize these deserts.
Near-endemic amphibians are represented by the Vallenar toad (Rhinella atacamensis), which occurs in and near oases and streams year-around. Breeding occurs in permanent pools (including livestock water tanks), streams and rivers.Eggs are laid in long strings, and the larvae develop where these were laid. R. atacamensis achieves is highest altitude occurrence at 2574 meters near Mostazal.
A greater diversity of flora and fauna can be found on the lomas. Several birds, such as the Peruvian song-sparrow (Zonotrichia capensis) and the Pacific blue-black grassquit (Volatinia jacarina) visit the lomas at the beginning of the winter when many insect pupae hatch. The lomas in bloom are also visited by several species of hummingbirds (e.g., Rhodopis spp., Myrtis spp., and Thaumastura spp.). There are six restricted species of birds found in the north of this ecoregion and the Sechura desert ecoregion; these birds include the Chilean woodstar (Eulidia yarrellii), thick-billed miner (Geositta crassirostris), white-throated earthcreeper (Upucerthia albigula), cactus canastero (Asthenes cactorum), slender-billed finch (Xenospingus concolor, and tamarugo conebill (Conirostrum tamarugense). The chilean woodstar, slender-billed finch, and tamarugo conebill are threatened species.
The region has been moderately affected by roads and mining operations. The northern area of the ecoregion has been especially affected by overgrazing of domestic livestock, collection of firewood, and commercial gathering of rare plants, including the Chilean wine palm, various cacti and bulbs.
Some nearby areas have archaeological importance. The beauty and rarity of the lomas formations provide opportunities for tourism combined with scientific studies. If the impact on the delicate communities is controlled through supervision, lomas formations can be enjoyed by the public and preserved. Environmental education on the importance, rarity, and the unusual characteristics of these natural resources is desperately needed. For example, Quebrada El León needs some recuperation from overuse and could become a lasting and informative oasis as a nature reserve for residents of Caldera and Copiapó.
Three protected areas exist within the extreme desert region. Pan de Azúcar National Park (established in 1986, IUCN category II) covers 438 square kilometers (km2). It has been recommended that this park be expanded northward to include Quebrada Esmeralda (25°50' S) and Quebrada de Las Lozas (25°41' S), which would protect areas very rich in cacti diversity. La Chimba National Reserve (IUCN category IV) of 30 km2 was recently established and lies approximately 15 km north of Antofagasta. Pampa del Tamarugal National Reserve, 1023 km2 in size, is one of the key areas for the conservation of the threatened tamarugo conebill (Conirostrum tamarugense).
Types and severity of threats
A few port towns exist in this desert. Iquique, Caldera, and Antofagasta are located on precarious sea-eroded terraces at the base of coastal cliffs. These towns are the outlet for the numerous mining centers in the interior tectonic basins. The wealth of the region lies in its mineral resources (copper, sodium chloride, sodium nitrate, iodine salts), not in its spare biotic resources.
Most threats to this ecoregion are closely associated with the few human population centers. Specifically, these include increased urbanization, pollution, road construction, intensive livestock grazing (numerous goats), fuelwood gathering, commercial plant collecting, and erosion.
Since many sites have become accessible by road only recently (i.e., within the past 12 years), Atacama's specialized ecosystems remained well preserved until recent times. Road construction in association with mining operations is increasing human occupation in the region. With the rise in copper prices during the 1980s, reactivation of mining activities utilizing large quantities of sulphuric acid has had an essentially undocumented impact on terrestrial and marine life.
Justification of ecoregion delineation
The Atacama Desert is distinguished as being one of the driest places in the Americas and said to resemble a lunar landscape. Inititial delineation’s followed Di Castri, however for the linework we followed Simmonetti and Montenegro to draw the northern and southern boundaries. Eastern delineations follow the United Nations Educational, Scientific and Cultural Organization (UNESCO) boundary for the neighboring puna ecoregion in the high Andes, and the western delineation is the Pacific Ocean.
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