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Ethiopian xeric grasslands and shrublands

An arid, semi-desert ecoregion bordering the Red Sea and the Gulf of Oman, the Ethiopian xeric grassland and shrubland lies mainly between sea level and 800 m elevation. There are, however, many hills and massifs, which range up to 1,300 m as well as outstanding fault-induced depressions, such as the Danakil, lying as low as 160 m below sea level. This region is extremely active tectonically, experiencing many earthquakes and intermittently active volcanoes. Rainfall is very low and yearly averages range from 100 to 200 mm, with less rain falling closer to the coast. There are many species of interest, including the endemic Archer's lark (Heteromirafra archeri), a species of dragon tree (Dracaena ombet), and a large suite of desert ungulates, including the last viable population of African wild ass (Equus africanus somalicus).

  • Scientific Code
    (AT1305)
  • Ecoregion Category
    Afrotropical
  • Size
    58,800 square miles
  • Status
    Vulnerable
  • Habitats

Description
Location and General Description
This ecoregion extends inland from the Red Sea and the Gulf of Oman, including the Dahlak Archipelago and other islands, stretching from the Sudanese-Eritrean border, south through Ethiopia to Djibouti and eastwards into Somalia, in the Somaliland region of the country. While it mainly lies between sea level and 800 m, there are many arid hills and massifs up to 1,300 m. Higher massifs such as the Goda and Mabla in Djibouti are considered to be outliers of the Ethiopian Montane Forest ecoregion. There are also fault-induced depressions, such as the Danakil Depression and Lac Assal, lying as much as 160 m below sea level. Elevation generally increases westward towards the Ethiopian and Eritrean highlands. The region is extremely active tectonically, and it experiences many earthquakes associated with the continuing enlargement of the Rift Valley. Volcanoes in the ecoregion are also intermittently active. Basement rocks are composed mainly of Tertiary lava flows, although there are also Quaternary basinal deposits at the northern end and pre-Cretaceous basinal deposits on the northern coast of Somalia. Soils developed over the lava deposits are mainly lithosols, while regosols are predominant on the Quaternary and pre-Cretaceous basinal deposits. There are very few permanent watercourses. The most notable is the Awash River of Ethiopia that terminates in a series of lakes near the border with Djibouti.

The climate is very hot and dry. Mean annual rainfall varies from less than 100 mm close to the coast to around 200 mm further inland. Mean minimum temperatures range from 21° to 24°C, and mean maximum temperature is around 30°C .

Phytogeographically, White (1983) regarded this ecoregion as part of the Somali-Masai regional center of endemism and mapped the vegetation as ‘Somalia-Masai semi-desert grassland and shrubland’. Along the coast, mangroves occur in muddy areas, primarily around wadi "outwashes" and inlets, while further inland, vegetation changes to grass shrub steppe. Acacia mellifera and Rhigozum somalense dominate the basaltic lava fields while scattered Acacia tortilis, A. nubica, and Balanites aegyptiaca can be found in the sandy plains. Stands of Hyphaene thebaica occur in depressions and along wadis (Audru et al. 1987).

Biodiversity Features
Due largely to political instability in the region over the last 30 years, many elements of the fauna and flora remain poorly known. As a suggestion of floral richness, an estimated 825 to 950 species have been observed in Djibouti, although many of these have been found only in the small outlying patches of the Ethiopian montane forest (Magin 1999). These outliers are part of the Day Forests and Mabla Massifs above 1,100 m in Djibouti.

Among mammals, desert ungulates are well represented. African wild ass (Equus africanus somalicus, CR) survives in the Buri Peninsula area of central Eritrea, possibly the last viable population of this critically endangered species. Beira antelope (Dorcatragus megalotis, VU) occur in the region where Djibouti, Ethiopia, and Somalia meet. Dorcas gazelles (Gazella dorcas,VU), Soemmerring's gazelles (Gazella soemmerringii, VU), Salt’s dikdik (Madoqua saltiana), and gerenuks (Litocranius walleri) all still occur (East 1999, Magin 1999). Beisa oryx (Oryx beisa) persist, but have been greatly reduced by hunting pressure.

The reptilian fauna is relatively rich, but there are very few amphibians. Levels of endemism are generally low, with strict endemics limited to only one bird, Archer’s lark (Heteromirafra archeri, VU), a gerbil Gerbillus acticola, and two geckos, Arnold’s leaf-toed gecko (Hemidactylus arnoldi) and a subspecies of the northern sand gecko (Tropiocolotes tripolitanus somalicus). Among the plants, dragon ombet (Dracaena ombet, EN) and Bankoualé palm (Livistona carinensis,VU) are notable (Magin 1999).

Current Status
Human population density is typically less than 10 persons per km2. In some areas, there is less than 1 person per km2. The dominant ethnic groups are the nomadic pastoralist Afars and a Somali clan, the Issas. Human density, however, does not account for grazing animals. The conservation status of this ecoregion is not good with few protected areas and lack of enforcement in existing ones.

Although large blocks of "natural" habitat remain, much has been degraded through over-exploitation. There is only one protected area, the Mille-Serdo Wildlife Reserve (8,766 km2) in Ethiopia, but there are two proposed Eritrean protected areas on the Buri Peninsula in the coastal lowlands, and the Danakil Depression. The Eritrean government has also enacted a system of closures for the last remaining patches of natural vegetation throughout the country that will greatly assist the conservation of vegetation and species of the ecoregion.

Types and Severity of Threats
The major threats are widespread overgrazing and tree cutting for fuel and timber, particularly around the increasingly permanent settlements. Clearance for agriculture along the few permanent watercourses is also a major problem. Populations of most large mammal species have been severely reduced through hunting by local people and by the government and resistance armies during 30 years of war. Some species, such as giraffes (Giraffa camelopardis), are believed to be locally extinct. Other large mammals have been reduced to very small populations.

Justification of Ecoregion Delineation
The boundaries of this ecoregion follow the ‘Somalia-Masai semi-desert grassland and shrubland’ vegetation unit of White (1983), from just north of the Sudan/Eritrea border to the extremely narrow coastal strip along the northern coast of Somalia (Somaliland). This eastern border follows the range limit of some species like the Dorcas gazelle (Gazella dorcas), and encompasses the range of others, such as the African wild ass (Equus africanus). White’s (1983) larger ‘Somalia-Masai semi-desert grassland and shrubland’ unit that extends further east along the Horn of Africa was separated into distinct ecoregions based on their unique plant and vertebrate compositions.

References
Audru, J., G. Cesar, G. Forgiarini, and J. Lebrun. 1987. La Végétation et les Potentialités Pastorales de la République de Djibouti. Institut d’Elevage et de Médecine Vétérinaire des Pays Tropicaux, Maisons-Alforts, France. 384 pages.

East, R., editor. 1999. African Antelope Database 1998. IUCN/SSC Antelope Specialist Group. ICN, Gland, Switzerland and Cambridge, UK.

Hilton-Taylor, C. 2000. 2000 IUCN Red List of Threatened Species. IUCN, Gland, Switzerland and Cambridge, United Kingdom.

Magin, C. editor. 1999. Monographie Nationale de la Diversité Biologique de Djibouti. Direction de l’Environnement, Ministère de l’Habitat, de l’Urbanisme, l’Environnement et de l’Aménagement du Territoire, Djibouti et l’UICN, Neirobi, Kenya. 263 pages.

White, F. 1983. The vegetation of Africa, a descriptive memoir to accompany the UNESCO/AETFAT/UNSO Vegetation Map of Africa (3 Plates, Northwestern Africa, Northeastern Africa, and Southern Africa, 1:5,000,000). UNESCO, Paris.

WWF. 1998. A conservation assessment of terrestrial ecoregions of Africa: Draft proceedings of a workshop, Cape Town, South Africa, August 1998. World Wildlife Fund, Washington, DC, USA.

Prepared by: Chris Magin, Christine Burdette
Reviewed by: In progress

 

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