<P> The North Saharan steppe and woodlands is 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 (646,840 sq mi) in Algeria, Egypt, Libya, Mauritania, Morocco, and Tunisia . </P> <P> The Sahara Desert 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 kilometres (1,791,500 sq mi) of: Algeria, Chad, Egypt, Libya, Mali, Mauritania, Niger, and Sudan . </P> <P> The South Saharan steppe and woodlands ecoregion is 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 (4 to 8 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 . This ecoregion covers 1,101,700 square kilometres (425,400 sq mi) in Algeria, Chad, Mali, Mauritania, and Sudan . </P> <P> In the West Saharan montane xeric woodlands, several volcanic highlands provide a cooler, moister environment that supports Saharo - Mediterranean woodlands and shrublands . The ecoregion covers 258,100 square kilometres (99,650 sq mi), 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 Mali and Algeria . </P>

What is one feature of the sahara desert