South Arabian Mountain Vegetation (General)
The mountains of Fayfa harbor a rich flora that is more or less similar to that of Yemen and nearby countries in Africa such as Ethiopia and Eritrea. The west facing slopes, which benefit from constant moisture-laden breezes from the Red Sea hold several micro hotspots and sustain a number of endemics and several endangered species; these include a few remaining stands of vulnerable species such as Dracaena ombet (Ruscaceae), Dorstenia foetida (Moraceae), and species of Ceropegia. Jabal Fayfa is differentiated into a spectrum of climatic zones, each with a distinct vegetation cover. The vegetation of the foothills is rather sparse and highly degraded due to heavy grazing and flash floods. Further east, the area is thrown into a set of mountains with altitudes ranging from 800 to 1200 m. The flora in these areas is not strikingly rich, but dense vegetation is not uncommon on open and eroded slopes of the escarpments. Dominant members of the vegetation between altitudes of 1500-2000 m include Juniperus procera, Ficus sycomorus, Acacia mellifera, A. seyal, Euclea schimperi and Carissa edulis. The entire Fayfa Mountains can be divided into three regions: low-lying mountains (up to 1000 m), high altitude wadis, and escarpments. The vegetation of the low-lying areas is often dominated by Acacia etbaica along with occasional trees of A. mellifera and A. asak. Species of Commiphora and Acacia ehrenbergiana are the main components of the hills below 500-900 m. Other trees such as Acacia abyssinica, Combretum molle, Tichellia emetica, Tamarindus indica, Ziziphus spina-christi, Dobera glabra, Mimusops laurifolia and Delonix elata form local dominants but mainly on west facing slopes. Vegetation of high altitude (above 2000 m) is often in a highly degraded state due to urbanization. However, patches of vegetation dominated by trees such as Juniperus procera, Olea europaea, Ficus sycomorus, Dracaena ombet, etc can be found in certain localities. Shrubs and woody herbs typically include Dodonaea angustifolia, Otostegia fruticosa, Plectranthus asirensis, Pluchea dioscoridis, Psiadia punctulata, Pulicaria schimperi, Tagetus minuta, Teucrium yemense, and grasses such as Themeda triandra, Hyparrhenia hirta, Tetrapogon villosus, Sporobolus nervosus and Rhynchelytrum repens. Dense vegetation is virtually absent on east facing slopes. However, succulent shrubs including species of Aloe and Euphorbia can be found in most areas along with Acacia asak and occasionally Moringa peregrina trees
South Arabian Acacia-Commiphora Bushland
These bushlands often dominate at low altitudes. Several associated shrubs, such as Adenium arabicum, Anisotes trisulcus, Grewia tembensis, Maerua oblongifolia and Acalypha fruticosa, can also be found in abundance. Other important plants include Carissa edulis, Clutia lanceolata, Otostegia fruticosa, Ricinus communis, Rumex nervosus, Solanum incanum, Solanum schimperianum and species of Commiphora. The herbaceous flora includes Anagallis arvensis, Conyza stricta, Evolvulus alsinoides, Pennisetum setaceum, Themeda triandra and species of Chenopodium.
South Arabian Upland Acacia-Commiphora Woodland
On the Yemen escarpment these woodlands are dominated by species of Acacia such as Acacia asak and A. mellifera and several Commiphora species like the endemic Commiphora kataf and C. myrrha (Burseraceae). Associated trees include Adina microcephala, Cordia abyssinica and Terminalia brownii, while the many shrubs include Ziziphus spina-christi and the endemic or near endemic taxa Euphorbia balsamifera subsp. adenensis (Euphorbiaceae), Dracaena serrulata (Dracaenaceae) and Psiadia arabica (Asteraceae).
South Arabian Montane Juniper Woodland
Outside Africa, these Juniperus procera dominated woodlands, are confined to the Asir Mountains. They form a belt usually between about altitudes of 1400 m and 2500 m, and the trees are typically festooned with the lichen Usnea articulata. The understory, which is usually fairly open, is characterised by species such as Asparagus africanus, Clutia myricoides, Conyza incana, Lavendula dentata and the endemic or near endemic Euryops arabicus (Asteraceae). Other associated species include Alkanna orientalis, Anthemis tigrensis, and the endemic or near endemic Nepeta defersiana (Lamiaceae).
South Arabian Wadi Riparian Forest
Wadi ecosystems are based on periodic runoff following heavy rains, and although there are no permanent rivers in this BioProvince, the larger wadis such as Wadi Rhima, Wadi Siham, Wadi Surdud, Wadi Mawr and Wadi Zabid, which originate in the mountains of southwestern Arabia, have permanent water along parts of their lengths. These often deeply incised river valleys provide habitat for some of the best riparian forests in Arabia. The characteristic trees include Breonadia salicina, Celtis toka, Combretum molle, Cordia africana, Mimusops laurifolia, Phyllogeiton discolor, Tamarindus indica, Terminalia brownii, Trichilia emetica, Ziziphus mucronata, Z. spina-christi and various species of Ficus. Among the lower growing trees and shrubs are Maesa lanceolata, Myrica salicifolia, Nuxia congesta and Phoenix reclinata. Wadis are also characterized by the genus Tamarix, and in fact, the Arabian Peninsula is the centre of diversity for this genus with many species showing circum-Arabian distributions. Typical species include Tamarix aucheriana, T. mascatensis and the endemic or near endemic T. arabica (Tamaricaceae). They have an interesting adaption to desert conditions. In addition to salt, the salt glands of these plants also excrete an alkaline solution that can absorb moisture hygroscopically. The few endemic or near endemic taxa found in wadis include Acacia johnwoodii (Fabaceae), the fan palm Livistonia carinensis (Arecaceae) and Tarenna graveolens subsp. arabica (Rubiaceae).
South Arabian Mountain Grassland
The only remaining primary grasslands in Arabia are now restricted to the Arabo-Alpine islands of southern Arabia. They are dominated by low growing, tufted, perennial, endemic species such as Andropogon crossotes, Festuca crypantha and Tripogon oliganthes (Poaceae) while other grasses include various cold resistant Stipa species. Often associated with these grass clumps is the endemic parasite Striga yemenica (Scrophulariaceae). Various cushion-forming plants, such as Cichorium bottae, Dianthus uniflorus and the endemic Anthemis yemenensis (Asteraceae) also feature in these grasslands. They harbour a number of endemic Apiaceae elements of Holarctic origin including Oreoschimperella arabiae-felicis, Peucedanum inaccessum and Pimpinella woodii, and several interesting endemic geophytes such as Crinum yemenense (Amaryllidaceae) and Kniphofia sumarae (Asphodelaceae). The latter is the only extra-African species of this largely South African genus.
South Arabian Succulent Euphorbia Scrubland
These xeromorphic succulent scrublands often interspersed with xeromorphic, open grasslands, occur in a well developed belt extending from the southern Asir and Yemen highlands eastward into the uplands of the Habramawt. The vegetation is typically dominated by various succulent Euphorbias, although their species composition varies according factors such as altitude and degree of exposure. The main species include several endemics or near endemics such as Euphorbia ammak, E. balsamifera subsp. adenensis, E. fruticosa, E. hadramautica, E. inarticulata and E. parciramulosa (Euphorbiaceae). Associated characteristic succulents include Kleinia odora and Sarcostemma viminale (Asteraceae), and various endemic species like Aloe yemenica (Liliaceae), Caralluma cicatricosa and Ceropegia rupicola (Asclepiadaceae). A number of succulent climbers of the genus Cissus (Vitaceae) may be present, and strange pachycaulous trees like Adenium obesum (Apocynaceae) and Adenia venenata (Passifloraceae). Other associated endemic or near endemic species includes Caralluma plicatiloba (Asclepiadaceae), Dracaena serrulata (Dracaenaceae) and Endostemmon tereticaulis (Lamiaceae).
South Arabian Upper Montane Aloe-Crassula Community
Above an altitude of about 2000 m the succulent Asclepiadaceae and Euphorbiaceae are more or less replaced by succulent Crassulaceae and frost resistant species of Aloe (Liliaceae). These have close floristic affinity to succulent belts in the Afromontane zones of East Africa. The near endemic Aeonium leucoblepharum (Crassulaceae) is always present together Cotylodon bargeyi and various species of Crassula and Kalanchoe. The main Aloe species at these altitudes are A. menchensis and the endemic A. rubroviolaceae (Liliaceae). Other associated endemic species include Caralluma hexagona (Asclepiadaceae), Centaurothamnus maximus (Asteraceae), Delosperma harazianum (Aizoaceae) and several species of Phagnalon including Phagnalon harazianum, P. stenolepis and P. woodii (Asteraceae).
South Arabian Dwarf Shrub Vegetation of Exposed Cliffs
The rocky cliffs and escarpments of the Haraz Mountains of the Yemeni escarpment provide a great diversity of microhabitats varying according to degree of exposure, drainage and rock type. On windward, humid cliffs, an association dominated by the endemic Aloe menachensis (Liliaceae) often predominates. Other plants include various endemic or near endemic species such as the shrubs Thymus laevigatus (Lamiaceae), Maytenus parviflora (Celastraceae), and tall herbs such as Acanthus arboreus (Acanthaceae) and Rumex limoniastrum (Polygonaceae). In more humid situations, such as dripping caves, ferns become more conspicuous, and also provide habitat for the endemic or near endemic Primula verticillata (Primulaceae). In less precipitous places, such as lava plateaus, Elionurus muticus and Macowania ericifolia usually become more abundant. These are usually confined to rock fissures where the endemic or near endemic Scutellaria rubicunda subsp. arabica (Lamiaceae) may also be encountered.
Further information required.
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