Ecoregions of the sahara

Mali and Algeria.

Tibesti-Jebel Uweinat montane xeric woodlands: The Tibesti and Jebel Uweinat highlands foster higher, more regular rainfall and cooler temperatures, which support woodlands and shrublands of palms, acacias, myrtle, oleander, Tamarix, and several rare and endemic plants. The ecoregion covers 82,200 km² (31,700 mi²) in the Tibesti of Chad and Libya, and Jebel Uweinat on the border of Egypt, Libya, and Sudan.

Saharan halophytics: Seasonally flooded saline depressions in the Sahara are home to halophytic, or salt-adapted, plant communities. The Saharan halophytics cover 54,000 km² (20,800 mi²), including the Qattara and Siwa depressions in northern Egypt, the Tunisian salt lakes of central Tunisia, Chott Melghir in Algeria, and smaller areas of Algeria, Mauritania, and Western Sahara.

Tanezrouft: One of the harshest regions on Earth and the driest in the Sahara, contains no vegetation and very little life. The Sahara comprises several distinct ecoregions, whose variations in temperature, rainfall, elevation, and soils harbor distinct communities of plants and animals. According to the World Wide Fund for Nature (WWF), the ecoregions of the Sahara include:

• Atlantic coastal desert: The coastal desert occupies a narrow strip along the Atlantic coast, where fog generated offshore by the cool Canary Current provides sufficient moisture to sustain a variety of lichens, succulents, and shrubs. It covers 39,900 square kilometers (15,400 square miles) in Western Sahara and Mauritania.^[25]
• North Saharan steppe and woodlands: This ecoregion lies along the northern desert, next to the Mediterranean forests, woodlands, and scrub ecoregions of the northern Maghreb and Cyrenaica. Winter rains sustain shrublands and dry woodlands that form a transition between the Mediterranean climate regions to the north and the hyper-arid Sahara proper to the south. It covers 1,675,300 square kilometers (646,800 square miles) in Algeria, Egypt, Libya, Mauritania, Morocco, Tunisia, and Western Sahara.
• Sahara desert: This ecoregion covers the hyper-arid central portion of the Sahara where rainfall is minimal and sporadic. Vegetation is rare, and this ecoregion consists mostly of sand dunes (erg, chech, raoui), stone plateaus (hamadas), gravel plains (reg), dry valleys (wadis), and salt flats. It covers 4,639,900 square km (1,791,500 square miles) of Algeria, Chad, Egypt, Libya, Mali, Mauritania, Niger, and Sudan.
• South Saharan steppe and woodlands: The South Saharan steppe and woodlands occupy a narrow band running east and west between the hyper-arid Sahara and the Sahel savannas to the south. Movements of the equatorial Intertropical Convergence Zone (ITCZ) bring summer rains during July and August which average 100 to 200 mm (3.9 to 7.9 in), but vary greatly from year to year. These rains sustain summer pastures of grasses and herbs, with dry woodlands and shrublands along seasonal watercourses. The ecoregion covers 1,101,700 km² (425,400 mi²) in Algeria, Chad, Mali, Mauritania, and Sudan.
• West Saharan montane xeric woodlands: Several volcanic highlands in the western portion of the Sahara provide a cooler, moister environment that supports Saharo-Mediterranean woodlands and shrublands. The ecoregion covers 258,100 km² (99,700 mi²), mostly in the Tassili n'Ajjer of Algeria, with smaller enclaves in the Aïr of Niger, the Dhar Adrar of Mauritania, and the Adrar des Iforas of

Location and General Description

From the Atlantic Ocean in the west, the greater Sahara stretches across Africa to the Red Sea and down to the highlands of Ethiopia, encompassing an area 9,100,000 square kilometers (km²). This ecoregion covers the central Sahara Desert, between 18° and 30° N, and has an area of 4,619,260 km². The northern and southern margins of the Sahara, which receive more rainfall and have greater vegetation cover, are described separately.

The surface of the desert ranges from large areas of sand dunes (erg Chech, Raoui), to stone plateaus (hamadas), gravel plains (reg), dry valleys (wadis), and salt flats. Several deeply dissected mountain massifs (Ahaggar, Tassili N'Ajjer, Tibesti, and Aïr) rise from the desert areas, and are delineated as separate ecoregions. Vast underground aquifers that underlie much of the region sometimes penetrate the surface, resulting in oases.
The Sahara is located in a climatic divide. The Intercontinental Convergence Zone moves up from the south, but stops before the center of the Sahara, and consequently hardly carries any rain. Similarly, the winter rainfall of North Africa does not reach far south enough to regularly bring rain to the central Sahara. Consequently, the rainfall, albeit extremely rare, can fall in any season. The annual rainfall is below 25 millimeters (mm), and in the eastern part of the desert it is less than 5 mm per annum. The scarcity of rainfall in this ecoregion is aggravated by its irregularity, as no rain may fall for many years in some areas, followed by a single intense thunderstorm.
The Sahara is one of the hottest regions in the world, with mean annual temperatures exceeding 30°C. In the hottest months, temperatures can rise over 50°C, and temperatures can fall below freezing in the winter. A single daily variation of -0.5°C to 37.5°C has been recorded. The Sahara is also extremely windy. Hot, dust-filled winds create dust devils which can make the temperatures seem even hotter.
The extreme aridity of this area is a relatively recent feature. Much larger areas of the Sahara had adequate water only 5000 to 6000 years ago. It is not clear how much of this ecoregion was covered with vegetation, but in other parts of the Sahara the vegetation was closer to the savanna woodlands of eastern and southern Africa. Currently the ecoregion is in a "hyper arid" phase, with high summer temperatures, lower winter temperatures and rainfall between 0 and 25 mm per annum.
Precambrian rocks are exposed in few places across the Sahara. During the Mesozoic much of North Africa was under water and marine deposits were deposited. The area was uplifted in the Middle Tertiary and has been eroding ever since. Shifting sands and bare rocks cover only about one-fifth of the greater Sahara. More than half of the area comprises soils known as yermosols, with shallow profiles over gravel or pebble beds. These soils have been developing over the past 50 million years.
In terms of the phytogeographical classification of White, the ecoregion is classified as the Sahara regional transition zone. Throughout most of the ecoregion there is very little perennial vegetation. Where it occurs, it is confined to areas where ground water reaches the surface or to areas with runoff. The plants that are present tend to be much more diversified in western Sahara than eastern Sahara, due to the lack of rain to the east. They have strictly Sahara-Arabian affinities, with exceptional adaptations to aridity. Large expanses of ergs and regs will be devoid of any visible plant life for years, but following rainfall, vegetation cover may reach more than 50 percent on sand dunes and 20 percent on the gravel plains.

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Sahara intro

The Sahara is the world's largest hot desert. At over 9,400,000 square kilometres (3,630,000 sq mi), it covers most of Northern Africa, making it almost as large as Europe or the United States. The only larger desert in the world is Antarctica, classified as such due to very low precipitation rates. The Sahara stretches from the Red Sea, including parts of the Mediterranean coasts, to the outskirts of the Atlantic Ocean. To the south, it is delimited by the Sahel: a belt of semi-arid tropical savanna that comprises the northern region of central and western Sub-Saharan Africa.