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In geography, an oasis (//; plural: oases //) is the combination of a human settlement and a cultivated area (often a date palm grove) in a desert or semi-desert environment. Oases also provide habitat for animals and spontaneous plants.
The word oasis came into English via Latin: oasis from Ancient Greek: ὄασις óasis, which in turn is a direct borrowing from Demotic Egyptian. The word for oasis in the later attested Coptic language (the descendant of Demotic Egyptian) is wahe or ouahe which means a "dwelling place".
Oases are made fertile when sources of freshwater, such as underground rivers or aquifers, irrigate the surface naturally or via man-made wells. The presence of water on the surface or underground is necessary and the local or regional management of this essential resource is strategic, but not sufficient to create such areas: continuous human work and know-how (a technical and social culture) are essential to maintain such ecosystems..
Rain showers provide subterranean water to sustain natural oases, such as the Tuat. Substrata of impermeable rock and stone can trap water and retain it in pockets, or on long faulting subsurface ridges or volcanic dikes water can collect and percolate to the surface. Any incidence of water is then used by migrating birds, which also pass seeds with their droppings which will grow at the water's edge forming an oasis. It can also be used to plant crops.
The location of oases has been of critical importance for trade and transportation routes in desert areas; caravans must travel via oases so that supplies of water and food can be replenished. Thus, political or military control of an oasis has in many cases meant control of trade on a particular route. For example, the oases of Awjila, Ghadames, and Kufra, situated in modern-day Libya, have at various times been vital to both North-South and East-West trade in the Sahara Desert. The Silk Road across Central Asia also incorporated several oases.
In North American history, oases have been less prominent since the desert regions are smaller, but in the USA they have allowed colonisation of the western desert regions around the Rockies. Las Vegas is an example of such a settlement.
People who live in an oasis must manage land and water use carefully; fields must be irrigated to grow plants like apricots, dates, figs, and olives. The most important plant in an oasis is the date palm, which forms the upper layer. These palm trees provide shade for smaller trees like peach trees, which form the middle layer. By growing plants in different layers, the farmers make best use of the soil and water. Many vegetables are also grown and some cereals, such as barley, millet, and wheat, are grown where there is more moisture. In summary, an oasis palm grove is a highly anthropized and irrigated area that supports a traditionally intensive and polyculture-based agriculture. The oasis is integrated into its desert environment through an often close association with nomadic transhumant livestock farming (very often pastoral and sedentary populations are clearly distinguished). However, the oasis is emancipated from the desert by a very particular social and ecosystem structure. Responding to environmental constraints, it is an integrated agriculture that is conducted with the superposition (in its typical form) of two or three strata creating what is called the "oasis effect " :
- the first and highest stratum is made up of date palms (Phoenix dactylifera L.) and maintains freshness;
- an intermediate stratum includes fruit trees (orange, banana, pomegranate, apple, etc.);
- the third stratum, in the shade, of herbaceous plants (market gardening, fodder, cereals).
- Great Man-Made River – the world's largest irrigation project; developed in Libya to connect cities with fossil water.
- Qanat – Water management system using underground channels
- Wadi – River valley, especially a dry (ephemeral) riverbed that contains water only during times of heavy rain
- Water supply – Provision of water by public utilities, commercial organisations or others
- (in French) Battesti, Vincent (2005) Jardins au désert: Évolution des pratiques et savoirs oasiens: Jérid tunisien. Paris: IRD éditions. ISBN 978-2-7177-2584-1.
- Douglas Harper. "Etymonline - Origin of 'Oasis'". Online Etymology Dictionary. Retrieved 2011-07-30.
- Society, National Geographic (2011-06-10). "oasis". National Geographic Society. Retrieved 2018-04-30.
- Vincent Battesti, The Power of a Disappearance: Water in the Jerid region of Tunisia in B. R. Johnston et al. (eds), Water, Cultural Diversity & Global Environmental Change: Emerging Trends, Sustainable Futures?, 2012, UNESCO/Springer, p. 77-96. ISBN 978-9400717732.
- Vincent Battesti, Resources and Appropriations: Back to the Jerid Oases (Tunisia) after the Revolution, Études rurales 2015, vol. 2013/2 (192): 153-175 ISSN 0014-2182 ISBN 978-2-7132-2398-3
- "Oasis | geological feature". Encyclopedia Britannica. Retrieved 2018-04-30.
- Battesti, Vincent (2005). Jardins au désert, Évolution des pratiques et savoirs oasiens, Jérid tunisien. Paris: IRD Éditions. p. 440. ISBN 9782709915649.