Eastern Region

Topography, geography and vegetation.

Eastern Saudi Arabia is bounded on the north by Northern Province, south by Sultanate of Oman, east by countries such as United Arab Emirates, Qatar and Kuwait and on the west by Dahna desert. Geologically, the whole territory is characterized by Tertiary sediments with significant areas covered by eolian sands and late Tertiary to Quaternary gravel sheets. Floristically, the entire region is divided into 8 sub regions. They are Northern plains, the central coastal lowlands, the south coastal lowlands, northern summan, southern summan, northern Dahna, southern Dahna and the Rub al-Khali.

The Northern plain is a linear depression bordering Hafar Al-Batin. It is a large dead, flat plain rising very gradually from sea level in the east to about 400 meters elevation in the west. The Central Coastal lowlands extend from Ras as-Saffaniyah on the northern coast to Dhahran in the southeast and bounded on the west by the escarpment of Summan. It is a coastal plain, rising slowly to the inland. The terrain is generally a sabkhah with some incursions of sea. The south coastal lowlands is more or less similar to Central coastal Lowlands; most of which are covered by fairly deep sand. This sub region is bounded on the west by some of the world’s largest oil fields and on the southwest by the escarpment of Summan while on the south it borders with Rub Al-Khali. The Northern Summan is bounded on north and east by the Northern Plains and the Central coastal lowlands, and on the west by the Northern Dahna. The topography of this sub region is generally of rocky uplands which provide poor conditions for vegetation. Topographically, Southern Summan is similar to Northern Summan and is characterized by arid climate and  low species diversity. The Northern Dahna is a major topographic feature of the Arabian Peninsula. It provides a natural boundary between central and eastern Arabia and links the Peninsula’s two major sandy deserts, the Great Nafud in the north and the Rub-Al-Khali in the south. The Dahna consists of a significant number of parallel longitudinal ridges, which may be separated from each other by bands of rocky or gravel ground. Vegetation in these sand dunes are dominated by Artemisia monosperma and Calligonum comosum. The Southern Summan subregion is divided from the Northern Summan subregion by an old Riyadh-Dammam road. Vegetation in this subregion is more or less similar to the northern counterpart. The Rub-al-Khali, the largest of all subregions is about 500,000 sq km. Among this, 80% of the land area falls within the Eastern Saudi Arabia. The region is magnificent in many respects being the largest continuous sand sheet of the world. Some of the sand dunes in this part of the desert is as high as 250 m.  

Climate of the Eastern Saudi Arabia is generally arid with temperature rising from 15 ⁰C in January to a maximum of about 42 ⁰C in August-September period. Annual rainfall means range from around 100 mm in the north and northeast during winter to less than 10 mm in the Rub al-Khali.  

Haloxylon salicornicum and other saltbush communities indicate that soils of northern plains are generally saline. This species is the most dominant plant in the northeastern Saudi Arabia. It ranges from Iraq in the northeast down into the northern edge of the Rub al-Khali. Vegetation in these areas is also mixed with other saltbush dominants such as Anabasis lachnantha, Agathophora alopecuroides, Seidlitzia rosmarinus and Suaeda spp.  In the southwest of the northern plains, relatively well drained loamy sands prevail, leading to the growth of Rhanterium epapposum. It favors better drained soil on higher ground. Along with this species, annuals such as Plantago boissieri, Ifloga spicata, Lotus halophilus, etc. also grow luxuriantly in these habitats. Vegetation of the Central coastal lowlands is dominated by Panicum turgidum associated with Lycium shawii, Leptadenia pyrotechnica and Calligonum comosum. Other species in this community includes Heliotropium bacciferum, Moltkiopsis ciliata, Polycarpaea repens, Monsonia nivea, Stipagrostis plumosa, Convolvulus cephalopodus and Centropodia forsskalii. Sand dunes of Dahna desert and in the inland sands, the most characteristic community is Calligonum comosum and Artemisia monosperma along with tussocks of perennial grasses Stipagrostis drarii and a sedge, Cyperus conglomerates. A wide variety of annuals may also be found in this sand such as Plantago boissieri, P. psammophila, Eromobium aegyptium, Cutandia memphitica, Linaria tenuis, Anthemis scrobicularis, etc. The density of this community diminishes as we approach to the south. In the Rub Al-Khali desert, the dominant vegetation is represented by the endemic plant, Cornulaca arabica, supported by Calligonum crinitum, Tribulus macropterus var. arabicus, Limeum arabicum and Cyperus conglomerates. Although this community is limited on the north of Rub al-Khali, it appears to be extended towards south. 

In and around the coastal and inland sabkhas, vegetation is dominated by halophytic associations, chiefly represented by Binertia cycloptera, Halocnemum stobilaceum, Suaeda vermiculata and Seidlitzia rosmarinus. Presence of a mangrove species, Avicennia marina is one significant vegetation component found in the coastal regions. Although the population of Avicennia is in a highly degraded state, patches of dense populations could be found in inlets and creeks.