Mediterranean dry woodlands and steppe
Steppe scene in eastern Morocco toward the Algerian border. @ C.Michael Hogan
The Mediterranean dry woodlands and steppe ecoregion forms a buffer between the Mediterranean forest ecoregions and the Sahara Desert farther south. The ecoregion is thought to have been partially forested in prehistory, but today scrub vegetation predominates. For example the written history of the Roman Colony of Volubilis at a similar latitude in Morocco shows numerous olive trees and other forest species present circa AD 200. One knows that settlement became less forested and more desicated as the climate warmed slightly from the settlement date through the Medieval Warming Period. A number of narrowly endemic species of plants are found here, although there are few endemic vertebrates. The ecoregion is currently highly threatened by the change from nomadic pastoralism to settled agriculture and grazing. The overgrazing widely practised here is considered to be leading to increased desertification in the area.
Location and General Description
WWF
The Mediterranean dry woodland and steppe ecoregion is distributed across a wide band of North Africa, inland of the moister Mediterranean Woodland and Forest ecoregion. In the west, it extends from eastern Morocco, across northern Algeria and into Tunisia, where it reaches the Mediterranean Sea. To the east in Libya lie two discrete outliers situated on opposite sides of the Gulf of Sidra. The first occurs to the north of the Jabal Nafusaand and the second lies in the Jabal al Akhdar. There is another outlier in northeast Egypt to the west of the Nile Delta. In Algeria, this ecoregion extends from the south side of the Tellien Atlas, the middle altitude of the Atlas Saharien, Hauts plateaus, and the presaharian zone.
With respect to topography, the Hauts plateaus zone between the two Atlas (Tellien and Saharien) mountain blocks is generally flat and occurs as a network of higher altitude plains. The ecoregion is particularly characterized by the presence of calcareous slabs called "dalles."
The climate is chiefly arid, with annual rainfall between 100 and 300 millimeters (mm). The rainfall regime is stormy, occurring mostly during the winter months. The temperature can fall close to 0°C during the winter and reach over 40° C in the summer months, with the annual mean temperature around 18° C.
In terms of the phytogeographical classification of White (1983), this ecoregion is considered part of the Mediterranean/Sahara regional transition zone. The main vegetation types are forests, matorrals, "steppes arborées", Chamaephytic and graminean steppes. A large area is also occupied by sand and halophile landscapes.
Jbel Aberdouz, High Atlas National Park, Morocco. (Photograph by Jeffrey England) On the south side of the two Atlas (Tellien and Saharien) mountain blocks, vegetation contains a mixture of Pinus halepensis and Juniperus phoenicea at average latitude, replaced by "steppe arborée" of Juniperus phoenicea and Stipa tenacissima further inland. Other species typical of the "steppe arborée" are Globularia alypum, Salsola vermiculata, Thymus ciliatus, Helianthemum virgatum, Cistus libanotis, Rosmarinus tournefortii and Asparagus stipularis.
On the higher plateau, the vegetation comprises different steppe types depending on edaphic factors, such as steppe of Stipa tenacissima in the sides of the Atlas and glacis with argilo-sandy soils; steppe of Artemisia "Herba alba"in the glacis and depressions that are silty; steppe of Lygeum spartum which follows sandy accumulations. In the more sandy accumulations, there are mosaic vegetation types including patches of Thymeleae muicrophila, of Aristida pungens, of Retama retama, and of Tamarix sp.
In the Dayas, vegetation includes betoum (Pistacia atlantica), Ziziphus lotus, Anvillea radiata, Bubonium graveolens and Malva aegyptiaca.
The human population of the ecoregion is low, with settled agriculture occurring only in valleys near a supply of water. Traditional agriculture is possible in favorable areas, including Dayas (depressions with good quality soil) and Wadis beds. Here, people cultivate fodder for animals and crops for their own food. Agriculture is episodic and varies according to the annual rainfall patterns. Population densities of one to five persons square kilometer (km2) are typical, and most people are not permanently settled. However, there are some permanent settlements in coastal towns in the ecoregion that are mainly involved with fishing activities.
Biodiversity Features
The flora of the ecoregion is mainly comprised of widespread species, although there is some ecoregion-wide endemism, and some important local centers of endemism within the ecoregion. Much of this region is thought to have been formerly forest. Patches of forest consisting principally of Pinus halepensis, Juniperus phoenicea and Quercus ilex remain, especially in the mountains. Currently much of the landscape is dominated by a mosaic of grassland consisting almost entirely of Stipa tenacissima or Lygeum spartum, alternating with patches of dwarf Artemisia "herba alba" shrubland. Around the Jabal al Akhdar in the Libya]n Arab Jamahiriya, there is an important enclave of nearly 100 endemic plant species, including Arbutus pavarii, Crocus boulosii, and Cyclamen rohlfsianum.
The fauna of the ecoregion is composed mainly of widespread species, with no strict endemic species in any vertebrate group. There are a number of nearly endemic small mammal species including, Gerbillus andersoni, Gerbillus latastei, G. syrticus (CR), Gerbillus grobbeni (CR), Allataga tetradactyla (EN) and Microtus guentheri. There are extant populations of the Barbary sheep (Ammotragus lervia, VU), which is threatened by habitat destruction and poaching. Some populations of gazelles also occur. For example, 400 individuals of Mountain gazelle (Gazella cuvieri, EN) are found in the Mergub nature reserve in Algeria. The local subspecies of striped hyena (Hyaena hyaena barbara, DD) may also occur in the ecoregion. Near-endemics are few and notable species are uncommon among reptiles, amphibians, and birds in the ecoregion.
The ecoregion supports a number of species that have more strictly Palearctic affinities, such as wild boar (Sus scrofa), European otter (Lutra lutra), and red fox (Vulpes vulpes). Palearctic reptiles and amphibians are also found in the ecoregion, for example Natrix natrix and the amphibians Bufo regularis, Rana ridibunda and Bufo viridis.
Many of the species surviving are reduced in population and some species have been extirpated through the activities of man. The ostrich (Struthio camelus) was fairly common in the northern Sahara at the end of the 19th century, but was extirpated from the area by the early 20th century.
Current Status
There is some debate on whether this ecoregion was originally forested. If that is the case, then the original forest has been almost completely replaced by species typical of drier areas. Even in this drier vegetation there has been loss of habitat. For example, in both the Libya]n Arab Jamahiriya and in Egypt, the original vegetation has been severely degraded through grazing pressure and collection of woody plants for fuel. In the High Atlas, the vegetation has also been damaged by removal of the Argania scrub, which has allowed replacement in the west by species within genus Euphorbia.
There are a limited number of protected areas in this ecoregion, including the Karabolli National Park (150 km2), Bier Ayyad Nature Reserve (20 km2), and Nefhusa (200 km2) in Libya. In Algeria, protected areas include Mergueb Nature Rreserve (1,200 km2) which is not yet legally recognized, Mergueb Nature Reserve (1,200 km2) and Djelfa Hunting Reserve (320 km2). In Tunisia, two national parks, Bouhedma (164,88 km2) and Chaambi (67,23 km2), occur in the ecoregion and in Morocco there is a permanent hunting reserve (Bouarfa, 2,200 km2).
Types and Severity of Threats
The threats to this ecoregion include removal of the remaining woody vegetation and overgrazing, which removes further elements of the vegetation and contributes to soil erosion. The few remaining stands of trees within the ecoregion are particularly at risk.
Most of the people in this ecoregion are involved in pastoralism (extensive breeding of sheep and goats). During the dry season pastorialists move to the wetter Mediterranean Woodland and Forest ecoregion which has better grazing, and move back to the Mediterranean Dry Woodland and Steppe ecoregion during the rainy season. The recent trend in these areas has been the combination of agriculture and pastoralism (agropastoralism). This has resulted from the permanent settlement of nomads, and is now leading to desertification. The Mediterranean Dry Woodland and Steppe is the area most affected by desertification in northern Africa.
Justification of Ecoregion Delineation
This ecoregion is largely based on White’s ‘Sub-Mediterranean semi-desert grassland and shrubland’ vegetation unit. The extension west of 30°N and 8°W is included with the Acacia-Argania Dry Woodland due to the area’s distinctive flora. Argania spinosa is the only member of the tropical family Sapotaceae to occur on mainland Africa north of the Sahara. The ecoregion also forms a part the Mediterranean sclerophyll and Atlas steppe biogeographic provinces of Udvardy (1975).
References
- de Smet, K.J.M. 1989. Distribution and habitat choice of larger mammals in Algeria, with special reference to nature protection. Ph.D. thesis, Gent State Univ.,Belgium. World Conservation Monitoring Centre, Cambridge.
- Le Houérou, H.N. 1991. Outline of a Biological History of the Sahara. Pages 146-174 in J.A. McNeely and V.M. Neronov, editors. Mammals in the Palaearctic Desert: status and trends in the Sahara-Gobian region. The Russian Acedemy of Sciences, and the Russian Committee for the UNESCO programme on Man and the Biosphere (MAB).
- Udvardy, M.D.F. A classification of the biogeographical provinces of the world. IUCN Occasional Paper No. 18. International Union of Conservation of Nature and Natural Resources, Morges, Switzerland, 1975.
- White, F. 1983. The vegetation of Africa: a descriptive memoir to accompany the UNESCO/AETFAT/UNSO vegetation map of Africa. UNESCO, Paris, France. ISBN: 9231019554
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