Saharan Oases
Today most oases have been used to cultivate date palm (Phoenix dactylifera) but from the remaining undisturbed remnants it seems likely that the natural vegetation of many of them would have been dominated by Hyphaene thebaica (doum palms) together with Calotrophis procera, Citrullus colocynthis (Colocynthis vulgare) and species of Acacia, Capparis, Maerua and Tamarix. For example, in small wild oases extending southeast and east from Bir Tarfawi in Egypt there are stands dominated by Hyphaene thebaica (in Bir El-Shab, for example) growing in association with Phoenix dactylifera and Tamarix nilotica with an under story of Imperata cylindrica and Juncus rigidus. These areas also include stands dominated by Acacia ehrenbergiana and the endemic Cornulaca monacantha (Chenopodiaceae). The northern edge of the Qattara Depression is also considered to be a natural oasis in a narrow zone adjacent to the escarpment. Here, however, the oasis woodland is dominated by Phoenix dactylifera but also includes Tamarix nilotica and has a similar under story to Bir El-Shab Hyphaene thebaica stand. This wild oasis also includes stands of Nitraria retusa growing in depressions and on surrounding dunes Zygophyllum nudum growing on the drier slopes. Other areas of wild oases can be found in the in the northernmost parts of the Farafra Oasis in Egypt particularly around Wadi Hennis. Here the vegetation is characterized by stands of Alhagi mannifera, Imperata cylindrica, Phoenix dactylifera, Tamaria amplexicaulis, T. aphylla and T. nilotica.
Saharan Wadis
Apart from oases, these are the only desert habitats where trees and large shrubs grow, and can be broadly divided into Acacia, Hyphaene and Tamarix communities. In fact, most of the woody species found in the Sahara belong to one of these genera. The Acacia formations usually occur on rocky beds and typically include the near endemic Acacia tortilis subsp. raddiana, A. gummifera, Balanites aegyptiaca, Maerua crassifolia and Ziziphus mauritiana as the main woody species, while the common herbs and subshrubs are Cassa italica, Caylusea hexagyna, Lavendula stricta, the near endemic Cleome Arabica (Cleomaceae), and the grass Panicum turgidum. Tamarix communities, often dominated by T. ‘articulata’, occur in large sandy wadis. The ground between the trees is often occupied by Calligonum comosa, Leptadenia pyrotechnica and Stipagrostis pungens. Hyphaene communities are characteristic of the large wadis radiating from the slopes of Tibesti. In addition to Hyphaene thebaica, these fringing forests normally include Acacia albida, A. nilotica subsp. adstringens and Salvadora persica.
Saharan Sandy Desert (Erg) Vegetation
Shifting sand is usually barren of vegetation but even where there is a degree of stability plants can only get established when their roots can penetrate into damper layers. The species composition of this demanding habitat varies. In the Western Sahara the main species are Stipagrostis pungens and endemic scrub Cornulacea monacantha (Chenopodiaceae). In the north several other scrub species can be found including Ephedra alata and the endemic Genista saharae (Fabaceae) and Retama retam (Fabaceae), while in central and southern areas Leptadenia pyrotechnica is one of the main scrub species. Apart from the near endemic Malcolmia aegytiaca (Brassicaceae) annual species are rarely found because the constantly moving sand hampers their establishment.
Saharan Pituranthos tortuosus-Gymnocarpus decandrum Desert Vegetation
Vegetation dominated by the two herbaceous species Pituranthos tortuosus and Gymnocarpus decandrum can be found, for example, on the Miocene and Quaternary plateaus of northern Marmarica. Other herbaceous species include the near endemic Zygophyllum album (Zygophyllaceae), but many of the associates are dwarf shrubs. Several other endemic or near endemic species commonly associated with this community include Anabasis articulata (Amaranthaceae), Erodium hirtum (Geraniaceae), Salsola tetrandra (Chenopodiaceae) and Trigonella stellata (Fabaceae). This vegetation also appears to spread in to the Mediterranean or sub-Mediterranean zones and has been recorded, for example, around Sidi Barrani in Egypt.
Saharan Artemisia inculta-Carduncellus mareoticus Desert Scrub
Vegetation dominated by dwarf shrubs of Artemisia incluta and the herbaceous composite Carduncellus mareoticus can be found, for example, just south of the Mediterranean vegetation known as Thymelaea hirsuta – Plantago albicans coastal shrubland and in some cases appears to straddle the border between the Southern Mediterranean and Saharan bioprovinces. Thymelaea hirsuta can also be an important component of this desert scrub especially in non-saline depressions. In saline depressions the main associate is Atriplex halimus, while other common associates may include Haloxylon scoparium. Among the associated endemic or near endemic species are Anabasis articulata (Amaranthaceae), Asparagus stipularis (Asparagaceae), Erodium hirtum (Geraniaceae), Salsola tetrandra (Chenopodiaceae), Trigonella stellata (Fabaceae) and Zilla spinosa (Brassicaceae).
Saharan Anastatica hierochuntica-Anabasis articulata Desert Scrub
Species poor islands of this vegetation are widely distributed and can be found, for example, north and northwest of the Qattara Depression. Its average height is no more than about 5 dm and average species number is usually less than five per square metre. Anastatica hierochuntica and Anabasis articulata often grow together but in the most extreme areas the vegetation can be reduced to almost pure stands of Anabasis articulata. In less hostile areas the few other species may include Astragalus trigonus, Atriplex leucoclada, Cotula cinerea, Ephedra alata, Fagonia arabica, Helianthemum lippii, Mesembryanthemum teretifolia, Salsola baryosma, Zygophyllum coccineum and the endemic or near endemic Pituranthos tortuosus (Apiaceae), Salsola tetrandra (Chenopodiaceae), Trigonella stellata (Fabaceae) and Zygophyllum album (Zygophyllaceae). However, this vegetation tends to be of a transitional nature with certain resident species reaching their northern limit and others reaching their southern limit. The remoteness of the vegetation around the Qattara Depression means that it normally escapes from grazing by sheep or goats but is occasionally grazed by camels.
Saharan Stipagrostis plumosa Desert Grassland
Grassland dominated by tussocks of Stipagrostis plumosa can be found, for example, on the Eocene limestone in the Bahariyah, Sitra abd Farafra regions of Egypt. In the northern part of the Farfra oasis the vegetation typically grows in deep karstic holes filled with sand and known locally as flowerpot vegetation. Associated species mainly comprise herbaceous perennials and dwarf shrubs and may include Astragalus trigonus, A. vogelii, Calligonum comosum, Convolvulus pilosellifolius, Cotula cinerea, Fagonia arabica, Farsetia aegyptiaca, Launaea nudicaulis, Salsola baryosma, Stipagrostis zittelii, Tamarix passerinoides and the endemic or near endemic Anabasis articulata (Amaranthaceae), Cornulaca monacantha (Chenopodiaceae), Pituranthos tortuosus (Apiaceae), Suaeda vermiculata (Chenopodiaceae) and Zygophyllum album (Zygophyllaceae).
Saharan Cornulaca monacantha-Fagonia arabica Desert Scrub
Scrublands dominated by the endemic or near endemic Cornulaca monacantha (Chenopodiaceae) are widely distributed but the association with Fagonia arabica appears to be less extensive and in Egypt is mainly distributed around the Farafra Oasis. Cornulaca monacantha is the only host of the parasitic flowering plant Cistanche phelypaea and so this species also becomes a characteristic component of this formation. Other common associates depending on location include the endemic or near endemic Pituranthos tortuosus (Apiaceae) and Zygophyllum album (Zygophyllaceae), while other less common species include the near endemic Anabasis articulata (Amaranthaceae) and Tragonum nudatum (Fabaceae).
Saharan Zygophyllum coccineum-Salsola baryosma Desert Scrub
This vegetation is one of the most important precipitation-dependent communities found outside oases. It can exist in areas with precipitation less than 5 mm per annum but only where there are reliable supplies of run-off. Such conditions can be found, for example, in the piediment zones of the Abu Tartur Hills and the hills around Dakhla and Kharga oases in Egypt. Depending on location other common associates may include Astragalus vogelii, Trichodesma africanum and the near endemic Zilla spinosa (Brassicaceae). Schouwia thebaica (Brassicaceae) is also characteristic of some sub-associations. The genus of the species appears to be endemic to parts of the Sahara and Arabian Peninsula. Other associates may include Francoeuria crispa, Fagonia indica, Farsetia ramosissima, the rare Psoralea plicata, and the endemic or near endemic Anabasis articulata (Amaranthaceae) and Cornulaca monacantha (Chenopodiaceae). Some of this vegetation is known to be extremely ancient. Age determinations have shown that some of the Salsola baryosma is up to five centuries old.
Saharan Gravel Desert (Reg) Vegetation
This type of habitat is fairly extensive especially in the hyper-arid zones, but unlike the more sandy areas, it is much less prone to wind erosion. Also in contrast to the sandy areas, the vegetation is almost entirely dominated by therophytes such as Asthenatherum (Danthonia) forskalii, Ifloga spicata, Neurada procumbens, Plantago ciliata, Polycarpaea repens (fragilis), the near endemic Fagonia glutinosa (Zygophyllaceae) and Monsonia nivea (Geraniaceae), and species of the endemic genus Ammodaucus (Apiaceae). The few perennial species include the endemic Haloxylon scoparium (Chenopodiaceae), which forms diffuse communities in northern Sahara. Where deeper sand occurs communities characterized by Lasiurus hirsuta and the near endemic Zilla spinosa (Brassicaceae) can be found.
Saharan Stone Desert (Hamada) Vegetation
Stone pavements or hamadas are characteristic of plateaus where all products of weathering are removed by wind. Much of these areas are devoid of vegetation and plants can only grow in rock crevices and depressions where soils and moisture can accumulate. Despite this, species richness is comparatively high in these areas, and there is considerable variation in species composition. Among some of the more characteristic species are Astericus graveolens, Cymopogon schoenanthus, Enneapogon desvauxii, E. scaber, Fagonia latifolia, Farsetia aegyptiaca, Forsskalea tenacissima, Moricandia arvensis, Reseda villosa, and Salvia aegyptiaca. In the northwestern Sahara the endemic Fredolia (Anabasis) aretioides (Chenopodiaceae) is often the only perennial to occur over extensive plateau surfaces. This remarkable plant forms dense cushions up to 50 cm in diameter. Associated species include Limoniastrum feei and the almost leafless umbellifer Pitvranthos battandiferi. In central Sahara hamada is almost absent except on the rocky flanks of high mountains where characteristic species include the near endemic perennials Aerva persica and Anabasis articulata (Amaranthaceae). These rocky habitats also provide habitat for various chasmophytic species such as Erodium glaucophyllum, Fagonia mollis and the near endemic Helianthemum kahiricum (Cistaceae) and Reaumuria hirtella (Tamaricaceae).
Saharomontane Vegetation
Distinctive montane vegetation is mainly confined to the higher mountains such as Ahaggar, Tassil’ n’ Ajjer and Tibesti, which receive more rain than the surrounding lowlands. The main types of vegetation are montane wadis communities, montane grassland and dwarf shrubland. On Ahaggar the most characteristic tree of the wadis is Olea laperrinei, often found in association with the two shrubs Pictacia atlantica and the near endemic Rhus tripartite (Anacardiaceae). However, this type of vegetation is completely absent from Tibesti, but in the moister wadis of both Ahaggar and Tibesti, communities characterized by Nerium oleander and the endemic Myrtus nivellei (Myrtaceae) occur. Tibesti, on the other hand, has a much richer woody flora than Ahaggar, especially on its wetter south and southwest slopes. The most characteristic species here is the near endemic Acacia seyal (Fabaceae), while associated species include Acacia albida, Boscia salicifolia, Cordia sinensis, Ficus ingens, Grewia tenax, Securinega virosa, the near endemic Balanites aegyptiaca (Zygophyllaceae) and Maytenus senegalensis (Celastraceae) and the endemic Ficus teloukat (Moraceae). Not present though is the remarkable endemic tree Cupressus dupreziana (Cupressaceae), which reaches heights of 20 m and may have a bole measuring 3 m in diameter. This species is now confined to a few rocky valleys in Tassili n’ Ajjer. The montane grasslands are generally dominated by Stipagrostis obtusa and the near endemic Aristida caerulescens (Poaceae). More locally Eragrostis papposa is dominant while in the closely grazed grasslands found in sheltered places on the summit of Emi Koussi in Tibesti the endemic Eragrostis kohorica (Poaceae) is the main grass species. Other endemic grasses found on Tibesti include Agrostis tibestica, Avena tibestica and Festuca tibestica (Poaceae). These grasslands may also include several low scrub species such as Fagonia flamandii and the near endemic Anabasis articulata (Amaranthaceae) and Zilla spinosa (Brassicaceae). In other areas dwarf scrub becomes more prominent particularly on summits above 2600m. On Ahaggar these include Pentzia monodiana and Artemisia herba-Alba, whereas on Tibesti Pentzia monodiana is usually associated with Artemisia tilhoana and Ephedra tilhoana.
Saharan Halogypsophilous Vegetation
This salt tolerant vegetation is mostly confined to depressions devoid of any drainage and as a result subjected to high levels of evaporation. Salt from sub-surface strata is brought to the surface by capillary action. In hypersaline situations the extreme halophyte Halocnemum strobilaceum may be the only species present, but in less demanding situations species such as Limonium pruinosum, Nitraria glaucum, Salsola sieberi, Suaeda mollis, Zygophyllum cornutum, the endemic Arthrocnemum glaucum (Chenopodiaceae) and Limoniastrum guyonianum (Lamiaceae) and near endemic Salsola tetragona (Chenopodiaceae), Traganum nudatum (Chenopodiaceae) and Zygophyllum album (Zygophyllaceae) be can be found but there is some regional variation. Where gypsaceous loamy sands occur a new suite of species are encountered often dominated by Salsola baryosma and the near endemic Suaeda vermiculata (Chenopodiaceae). Other associated species include the endemic Lycium inticatum (Solanaceae) and Nucularia perrinnii (Chenopodiaceae) and the near endemic Atriplex halimus (Chenopodaceae).
Saharan Zygophyllum coccineum-Schouwia thebaica ‘Saline’ Desert Scrub
Vegetation characterized by these two species covers large parts of the Western Desert and is well represented in and around the Qattara Depression, which is up to 135 m below sea level. However, runoff from the surrounding escarpments increases the level of water available. Zygophyllum coccineum is the main pioneer species sometimes forming almost pure stands but in distinctly saline areas the endemic or near endemic Zygophyllum album (Zygophyllaceae) may also be present usually growing on the margins. Schouwia thebaica is a desert annual of the Brassicaceae family. The genus Schouwia appears to be endemic to the Sahara and parts of the Arabia Peninsula. Other common associates depending on locality include Capparis leucophylla, Pergularia tomentosa and Zygophyllum simplex, while in the inner margins of large depressions the endemic or near endemic Acacia raddiana (Fabaceae) may become established. Other endemic or near endemic taxa associated with this vegetation include Cleome droserifolia (Cleomaceae), Monsonia nivea (Geraniaceae) and Trigonella stellata (Fabaceae). Grazing in the Qattara Depression is mainly restricted to the camels of Bedouins since the nearby Qara population is mainly based on crop cultivation.
Further information required.
References
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