The Southwestern Arabian foothills savanna, also known as the Southwestern Arabian Escarpment shrublands and woodlands, is a desert and xeric shrubland ecoregion of the southern Arabian Peninsula, covering portions of Saudi Arabia, Yemen, and Oman.
Geography The ecoregion occupies moderate elevations in the peninsula's mountainous southwest, which include regions such as the Hejaz. The foothills savanna is bounded on the west and south by the Arabian Peninsula coastal fog desert, which extend along the coastal strip between the foothills and the Red Sea and Gulf of Aden. At about 2000 meters elevation, the foothills savanna transitions to the Southwestern Arabian montane woodlands. The drier Red Sea Nubo-Sindian tropical desert and semi-desert lies to the northwest along the Red Sea coast, and wraps around the north and east between the foothill savanna and the hyper-arid Arabian Desert ecoregion of Central Arabia. The mountains rise from the Red Sea and Gulf of Aden in a series of escarpments. The highest peaks are the Southwest Yemen mountains, which generally diminish in height to the north (towards Hejaz (in modern-day Saudi Arabia)) and east (towards Dhofar in modern-day Oman)). The rocks are generally Precambrian, and include granite, gneiss, and schist. In places they are overlain by areas of younger volcanic rock, known as harrats. In Hadhramaut and Dhofar, the terrain is mostly sedimentary, including limestones, sandstones, bauxite and conglomerates over a base of older Precambrian igneous and metamorphic rocks.
Climate The climate is tropical to subtropical and semi-arid. Average annual rainfall is generally 250 mm or less, and with areas of higher rainfall in the southeastern mountains. Marine upwelling along the Arabian Sea coast chills the air above sea's surface, creating fog during the summer months that cools and provides moisture to southeastward-facing mountain slopes in Dhofar and southern Yemen.
Flora The principal plant communities include drought-deciduous open thorn woodlands, drought-deciduous woodlands, evergreen woodlands, shrublands, and dry grasslands. The vegetation varies with elevation, rainfall, and soils, and has been extensively altered by livestock grazing and human use. Acacia-Commiphora woodlands predominate up to 1000 meters elevation. They consist of drought-deciduous open woodlands and thorn scrub, with species of the genera Acacia and Commiphora predominant. On east-facing slopes, Commiphora is often absent, and species of Acacia predominate. Characteristic trees of these lower-elevation woodlands include Vachellia flava, Vachellia abyssinica, Vachellia etbaica, Senegalia hamulosa, Senegalia mellifera, Vachellia tortilis, Commiphora kataf, Commiphora myrrha, Commiphora kua, and Commiphora gileadensis. Other trees and shrubs include Euphorbia cuneata, Euphorbia triaculeata, Grewia tenax, Hibiscus micranthus, Maytenus senegalensis, Melhania denhami, Dobera glabra, Aloe spp., Cadaba farinosa, Boscia arabica, Adenium obesum, Barleria spp., Boswellia carteri, Maerua crassifolia, and Sterculia africana. On certain seaward-facing slopes facing the Arabian Sea, moisture-bearing winds from the Arabian Sea create orographic precipitation and frequent fog. The higher humidity sustains semi-deciduous woodlands between 500 and 900 meters elevation, dominated by the endemic tree Terminalia dhofarica, together with Carissa edulis, Dodonaea viscosa, Euclea racemosa subsp. schimperi, Olea europaea subsp. cuspidata, and Searsia somalensis. These subhumid woodlands, shrublands, and coastal dunes are found in the Ureys (or Areys) range in southwestern Yemen, the Hadramaut mountains in southeastern Yemen, and the Dhofar Mountains in southwestern Oman. Some authors classify these distinctive subhumid woodlands and shrublands as a separate ecoregion, the South Arabian fog woodlands, shrublands, and dune. Acacia-Commiphora woodlands continue up to 1800 meters elevation, and these higher-elevation woodlands are characterized by Senegalia asak, S. etbaica, Vachellia tortilis, Commiphora gileadensis, C. myrrha, Moringa peregrina, Searsia tripartita, Dobera glabra, Euphorbia cuneata, Grewia villosa, Cadia purpurea, Carissa edulis, Cordia abyssinica, and Terminalia brownii. Seasonal watercourses, or wadis, are lined with Breonadia salicina, Cordia abyssinica, Ficus vasta, and Mimusops laurifolia. In a few sheltered wadis with year-round moisture on the western slopes of the escarpment, including Jabal Fayfa, Mimusops laurifolia, an evergreen tree, has grown to great age and large size, and these trees are the largest in Saudi Arabia. Semi-evergreen woodlands of Barbeya oleoides and Olea europaea are found between 1800 and 2200 meters elevation, and form the transition between the Acacia-Commiphora woodlands at lower elevations and the high-elevation Juniper woodlands of Southwestern Arabian montane woodlands ecoregion. The flora of the ecoregion has many affinities to that of tropical East Africa. Acacia-Commiphora woodlands are characteristic of the dry East African lowlands and foothills, and the Southwestern Arabian woodlands and savannas share many species. Southwestern Arabia's high-elevation forests and humid forests at lower elevations share many Afromontane species with the high mountains of Eastern Africa.
… excerpt ends here. Continue reading the full article.
