Location and General Description
This ecoregion is situated in the southwestern Arabian highlands above 2,000 m and includes part of the Asir Mountains of Saudi Arabia and most of the western highlands of Yemen. In the west, a steep escarpment drops to the Tihamah plain on the Red Sea coast. To the east is a high plateau, with the mountains then sloping more gently to the inner desert regions and sands of the Rub’al-Khali (Empty Quarter).
The escarpment mountains are the principal topographic feature here; they run in a north-south direction, parallel to and overlooking the Red Sea. The rugged mountainous landscape contains several peaks over 3,000m, including Jebal Nabi Shu’ayb which, at 3,760m, is the highest mountain in Yemen and all of the Arabian Peninsula.
The Asir Mountain chain is the highest land in the Arabian Peninsula, which tilts from west to east. East of the mountains the land slopes gradually to the Arabian Gulf. The mountains are composed mainly of sedimentary rocks (limestones, sandstones and shales) of Jurassic, Cretaceous and lower Tertiary periods. These overlie a basement complex of Pre-Cambrian granitic igneous rocks. The climate of the region varies considerably depending on altitude, aspect and season. The highlands receive variable rainfall caused by the southwestern monsoon, which brings damp oceanic winds. These winds are uplifted by the mountains and trigger thunderstorms, particularly during the summer, with most rain falling in April/May and July/August. Annual average rainfall in the escarpment mountains is 600-800 mm, rising to over 1,000 mm in the wettest areas. The high plateau receives 300-500 mm, dropping rapidly to below 100 mm in the east. Temperatures in the highlands are highest in the summer, reaching 20-250C, and lowest in winter with a mean temperature of 100C, although frosts can occur above 2,000 m and snow occasionally falls on the highest peaks (Miller 1994).
In Yemen, a tradition of high-mountain agriculture spanning two thousand years has produced a spectacular terraced landscape on the steep mountain slopes. However, this has eliminated much of the forest and woodland cover and only scattered patches of woodland now survive. Across the border in Saudi Arabia, the vegetation of the Asir Mountains has remained largely intact, although the situation is deteriorating. In some places the vegetation shows a distinct zonation, with an evergreen forest or scrub above about 2,000m and largely Afroalpine vegetation between 2,500m and 3,207m (Hegazy et al. 1998). At these higher altitudes a lush cloud forest exists, including Juniperus procera, usually festooned with the lichen Usnea articulata, the woody shrub Euryops arabicus and Lavandular on the north facing slopes. On the more barren south facing slopes, Aloe sabae and Euphorbia are common. Species forming a dwarf-shrub forest in this zone above 2,500m are Rubus petitianus, Rosa abyssinica, Alchemilla crytantha, Senecio spp. and Helichrysum abyssinicum. In the evergreen forest and scrub a few hundred meters down, the vegetation is dominated by species such as Olea chrysophylla and Tarchonanthus camphoratus. Below 2,000m, an Acacia-Commiphora deciduous bushland and thicket, with Grewia spp. and various succulents, is the most widespread vegetation type (Zohary 1973; Miller 1994).
The flora of southwestern Arabia has strong affinities with parts of Africa, particularly East Africa. Juniperus procera, found above 2,500m in the Asir Mountains, is also very abundant in and characteristic of the East African highlands. There, it is a dominant plant in some montane or subalpine vegetation units. According to Zohary (1973), this forest type is well known in Eritrea, Somalia, Ethiopia, Kenya and Tanzania at almost the same altitudes.
The ecoregion supports about 2000 vascular plant species, of which c. 170 are endemic, including 2 endemic genera (Saltia and Centaurothamnus) (Miller 1994). Miller (1994) describes several areas noteworthy for their vegetation and floristic richness. Of special note are the Juniperus woodlands in the Asir Mountains and remnant escarpment woodlands on Jebel Bura and Jebel Melhan in Yemen. Also in Yemen, near Ibb above 2,800m, Kniphofia sumarae is the only extra-African species of this largely South African genus. Helichrysum arwae, whose closest relatives occur in South Africa’s Drakensburg Mountains, also occurs here. In the extreme south of the ecoregion, near Taiz in Yemen, the Hujariyah is floristically perhaps the richest in Arabia. In the 100 km square grid on which it is centred, 99 of the 357 endemics of mainland Arabia can be found. Restricted to the Hujariyah itself are 8 endemics, including Crotalaria squamigera, Kickxia woodii, Blepharispermum yemenense and Centaurea yemense.
For several thousand years, agriculture has been an important human activity in the western highlands of Yemen. Land races of several crop plants, such as wheat, barley and sorghum, are still cultivated and represent an important genetic resource (Miller 1994). In the past this region was also an important centre for myrrh, a gum resin obtained from some Commiphora species.
This ecoregion, together with the Tihamah plain, is home to the majority of southwest Arabian endemic bird species. The montane juniper woodlands are vital habitat for these birds, such as the Yemen linet (Carduelis yemenensis), Yemen thrush (Turdus menachensis) and Yemen warbler (Parisoma buryi). These species are dependent on juniper berries as a food source and also use the juniper trees for nesting (Newton & Newton 1996). The dramatic cliff faces on the escarpment rim are home to large raptors such as the Griffon vulture (Gyps fulvus) and the Verreaux eagle (Aquila verreauxii) and the small Barbary falcon (Falco pelegrinoides). As the Arabian Peninsula forms a bridge between the African and Eurasian continents, the Asir Mountains and the western highlands of Yemen provide an important resting spot for migrating birds. The high escarpment and cliffs are especially important to migrating raptors in autumn. For example, in excess of 3,000 birds per season pass through Al Hudayah (Evans 1994). Gyps fulvus, bearded vulture (Gypaetus barbatus), Yemen linnet (Carduelis yemenensis), Yemen thrush (Turdus menachensis), and African paradise flycatcher (Terpsiphone viridis) are all resident in the high escarpments of the Asir Mountains. Wadi Turabah in Saudi Arabia is the last place in the Arabian Peninsula where the hammerkop (Scopus umbretta) can be found nesting, and the isolated and distinctive endemic race Pica pica ssp. asirensis is pressent on Shalla ad-Dhana.
Large mammals inhabit these highlands. The Asir escarpment is known to be one of the last strongholds in Saudi Arabia of the Arabian leopard (Panthera pardus ssp. nimr), thought to number around 50 individuals (Nader 1996). This species is listed on the IUCN Red List as critically endangered (Baillie & Groombridge 1996). Panthera pardus ssp. nimr also exists in the western highlands of Yemen but is heavily persecuted. In some areas of Yemen the Hamadryas baboon (Papio hamadryas) is still widespread but said to be declining, while the population of Saudi Arabia is expanding and has become common around cities such as Abha and Taif. The caracal (Caracal caracal ssp. schmitzi) is still relatively widespread, if rarely seen except for when local farmers kill it and hang it on trees or road signs. The Arabian wolf (Canis lupus ssp. arabs) is now extremely rare and in danger of extinction through persecution and hybridization with feral dogs. The rock hyrax (Procavia capensis ssp. jayakari) is still fairly common in areas around Taif, but its distribution range is fast decreasing. The striped hyaena (Hyaena hyaena) is also a resident of this area.
In Yemen, the main responsibility for wildlife conservation and environmental protection lies with the Environment Protection Council. As of 1994, there were no protected areas and little information exists on the current situation, although Miller (1994) indicates that UNEP and IUCN have recommended that a network of reserves be created. In Saudi Arabia the Ministry of Agriculture and Water created the Asir National Park (4,150 km2) in 1981. In this park and its surrounding areas, there are 34 mammal species, 245 bird species, 41 reptile species and 7 amphibian species recorded (Al Khalili & Nader 1984).
The Saudi National Commission for Wildlife Conservation and Development (NCWCD), established in 1986, is the main body responsible for nature conservation and protected area management. The NCWCD has a comprehensive system plan for protected areas (Child & Grainger 1990) that lists 56 terrestrial and 42 marine sites as priority areas for protection and nature conservation. One existing protected area, the Raydah Reserve (approximately 9 km2), is one of the prime areas of intact juniper forest in this ecoregion.
Types and Severity of Threats
The main threats to biodiversity are soil erosion, uncontrolled cutting of fuelwood and timber, and overgrazing by cattle, goats, sheep and camels. In Yemen, Miller (1994) describes how out-migration to oil rich Gulf countries and the general movement of rural people to towns has led to poor maintenance of the agricultural terrace systems, resulting in soil erosion during times of heavy rainfall. Deforestation for timber, fuelwood and charcoal has put remaining areas of woodland on the lower slopes of the escarpment mountains under severe pressure. Miller (1994) makes reference to a World Bank study that shows a daily consumption rate of 16 million kilograms of wood for firewood and timber and 5 million kilograms of wood for charcoal in northern Yemen. This demand for fuelwood has doubled in the last 20 years as a result of population growth and increasing income, despite the use of butane gas for cooking in the main towns.
Hunting with firearms and large numbers of domesticated and feral dogs have created increased pressures on wildlife. In Yemen in recent years, use of stone traps to capture leopards for sale to zoos, display in local villages and for use in traditional medicine is common, earning the trapper large sums of money. This has no doubt been fueled by the interest shown by conservation organizations concerned with the rarity of this predator. In the Asir Mountains, new roads are fragmenting the escarpment into isolated patches and the encroachment of human settlements is introducing more livestock herds to the area. In areas of remaining leopard habitat, human-predator conflicts result from leopard attacks on goats. The rock hyrax is extensively hunted, reducing the population of this favourite prey of the leopard (Lagrot & Lagrot 1999).
Poor regeneration among the juniper forests is causing concern among environmentalists. Once cause may be infestation of cones by a tortricide moth (Hajar et al. 1991); another possible cause is lack of seedling survival caused by human disturbance, grazing pressure or climatic change (Gardner & Fisher 1994).
Justification of Ecoregion Delineation
The boundaries were delineated using Zohary’s (1973) geobotanical map of the Middle East. They are based on Zohary’s vegetation classes of tropical mountain forest mainly of Oleeta africanae and Podocarpeta in lower elevations, and of Junipereta procerae in higher elevations. This corresponds to the Afromontane phytogeographic region of endemism according to Davis et al. (1995).
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Baillie, J., and B. Groombridge. 1996. 1996 IUCN red list of threatened animals. IUCN Gland, Switzerland.
Child, G., and J. Grainger. 1990. A system plan for protected areas for wildlife conservation and sustainable rural development in Saudi Arabia. National Commission for Wildlife Conservation and Development, Riyadh, Saudi Arabia.
Davis, S.D., V.H. Heywood, and A.C. Hamilton, editors. 1995. Centres of plant diversity: a guide and strategy for their conservation. Vol. 1: Europe, Africa, SW Asia, Middle East. WWF and IUCN, Cambridge, UK.
Evans, M.I. 1994. Important bird areas in the Middle East. Birdlife International, Cambridge, England.
Gardner, A.S., and M. Fisher. 1994. How the forest lost its trees: Just so storytelling about Juniperus excelsa in Arabia. Journal of Arid Environments 24:299-301.
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diversity and floristic relations along an altitudinal gradient in south-west Saudi Arabia. Journal of Arid Environments 38:3-13.
Lagrot, I., and J. F. Lagrot. 1999. Report on the status of the Arabian leopard in the Arabian Peninsula. Unpublished report to the Arabian Leopard Trust, United Arab Emirates.
Miller, A. G. 1994. Highlands of south-western Arabia: Saudi Arabia and Yemen. Pages 317-319 in S. D. Davis, V. H. Heywood and A. C. Hamilton, editors. Centres of Plant Diversity, Vol.1. WWF, IUCN, Gland, Switzerland.
Nader, I. A. 1996. Distribution and status of five species of predators in Saudi Arabia. Journal of Wildlife Research 1(2):210-214.
Newton, S. F., and A. V. Newton. 1996. Seasonal changes in the abundance and diversity of birds in threatened juniper forest in the southern Asir mountains, Saudi Arabia. Bird Conservation International 6:371-392.
Zohary, M. 1973. Geobotanical foundations of the Middle East. Vols. 1 and II. Gustav Fisher Verlag, Stuttgart.
Prepared by: Robert Llewellyn-Smith
Reviewed by: Fred Launay