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 Arroyo (stream system) Scrublands
Open but fairly rich assemblages of shrubs are associated with arroyo systems in the Atacama. Permanent scrub communities occur, for example, in the drainage areas associated with the Quebrada Pan de Azúcar. Here there are open stands of the endemic Nolana divaricata and N. leptophylla (Nolanaceae) which in places are accompanied by Eremocharis fruticosa, Tetragonia maritima and the endemic Loasa chilensis (Loasaceae) and Nolana mollis (Solanaceae). The latter species becomes dominant in certain areas. Where growing conditions are favourable other species such as Heliotropium linarifolium, Loasa elongata, Ophryosporus triangularis and the endemic Oxyphyllum ulicinum (Asteraceae) may be present. Semi-woody perennials like the endemic Frankenia chilensis (Frankeniaceae) and Nolana salsoloides (Nolanaceae) may also be encountered but these are low growing. Ground layer herbaceous species are limited but can be plentiful in years with significant rainfall. For example, dense populations of the endemic annuals Astragalus coquimbensis (Fabaceae) and Nolana aplocaryoides (Nolanaceae) can occur. However, these communities tend to be extremely dynamic and community structure can vary from year to year depending on levels of rainfall.
Atacamian Bajada Scrub Formations
On bajada (descent) slopes near the coast where runoff water accumulates there are distinctive scrub formations. The dominant species include the endemic Gypothamnium pinifolium (Asteraceae) and Nolana mollis (Nolanaceae). Other important shrubs are Eremocharis fruticosa, Heliotropium pyncnophyllum, Ophryosporus triangularis, Tetragonium maritima and the endemic Polyachyrus fuscus (Asteraceae). Some of the above species can also be found in the arroyo formations, but endemic species such as Deuterocohnia chrysantha (Bromeliaceae), Encelia canescens (Asteraceae) and Euphorbia lactiflua (Euphorbiaceae) are rocky slope specialists. Herbaceous plants are virtually non-existent during dry years, but in wet years there can be impressive displays of both annual and perennial species. Abundant species include the endemic Argylia radiata (Bignoniaceae), Cistanthe grandiflora (Portulaceae) and Cruckshanksia pumila (Rubiaceae). However, like the arroyo formations, these plant communities are highly dynamic and may vary from year to year. Certain species such as Gypothamnium pinifolium require two years of good rainfall before they can become successfully established.
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