Belts of natural vegetation, corresponding to the rainfall pattern, extend from east to west and range from traces of tropical forest along the Sénégal River to brush and savanna in the southeast. Only sandy desert is found in the centre and north of the country. Mauritania is home to seven terrestrial ecoregions: Sahelian Acacia savanna, West Sudanian savanna, Saharan halophytics, Atlantic coastal desert, North Saharan steppe and woodlands, South Saharan steppe and woodlands, and West Saharan montane xeric woodlands.