|Plant Diversity of Saudi Arabia
Flora and Vegetation of Tabuk Province
The Tabuk Province, located at the northern side of Saudi Arabia, is significant both in terms of its unique topography and plant diversity. The flora of Tabuk Province reflects a combination of plants belonging to three or four phytogeographical regions, such as Saharo-Arabian, Mediterranean, Somalia-Masai and Irano-Turanian. The topography of Tabuk region comprised of northern Tihama on its wesstern side and part of the northern Hijza Mountains (Madyan Mountain) and a high plateau (Hismah Plateau) on its eastern side. Topographically, the area is divided into coastal salt marsh, coastal plains, foothills, Mountains and plateau. Coastal salt marsh, an area extends from 5 meters to about 500 m, is characterized by brackish and loose sands and dominated by salt bushes comprised of Zygophylllum album, Z. decumbens, Z. coccineum, Limonium axillare, Suaeda vermiculata, Aeluropus lagopoides and occasionally with isolated stands of Nitraria retusa and Tamarix senegalensis. These communities are associating with small and big populations of Juncus rigidus, Sedlieitzia rosmarinus, Halocnemum strobilaceum, Halopeplis perfoliata along with shrubby Suaeda monoica, and and occasionally with grasses such as Panicum turgidum, Pennisetum divisum, etc. Estuaries are devoid of mangroves. However, patches of fragmented populations of Avicennia marina can be seen at some locations, bordering with Madina Province and in a few islands away from coast.
Unlike the coastal sabkhas dominated by halophytic communities, coastal plains are dominated by glycophytes on vast open plains covered by non-saline wind-blown sand and on wadis covered by accumulating sand and gravels eroded from crystalline rocks through the action of flash floods. Undulating wadis generally cut this area. Vegetation on this terrain mainly concentrated along the edges of these wadis, is dominated by Hyphaene thebaica, Maerua crassifolia, Moringa peregrina, Vachellia flava, V. tortilis, etc. In areas where the soil contains excess moisture, large trees such as V. raddiana could be found as occasional plant along with Capparis decidua and Maerua crassifolia. Vegetation of the nearby hillocks is restricted to runnels, gullies and rocky crevices where sand and propagules accumulate during run off. Dominating natives of these areas are Aerva javanica, Capparis cartilaginea, Crotalaria aegyptia, Convolvulus hystrix, Fagonia mollis, Iphiona scabra, Ochradenus baccatus, Pulicaria undulata, etc. Significant number of perennial plants and annuals appear in these areas after a showers which makes entire slopes green during spring. Open plains are mainly covered by dwarf shrublands, dominated by Leptadenia pyrotecynica, Vachellia tortilis, Haloxylon salicornicum, Senna italica, etc. Nebkhas are common along these open plains, where moving sand accumulate at the base of species such as Calligonum comosum, Haloxylon salicornicum, Panicum turgidum and Rhazya stricta to form a convex mound of sand or a dune hummock. Vegetation of the open plain is generally sparse, except during spring where an array of ephemerals appears immediately after a scanty shower.
Foothills and low altitude mountains are composed of different forms metamorphosed sediments, granites and volcanic rocks. Foothills are generally barren looking and devoid of any perennial plant cover during summer months. However, in some parts, dwarf shrub-land consists of Haloxylon salicornicum with occasional stands of Lycium shawii dominates the foot-hills while Vachellia woodlands dominate the wadi summit. In spring, the entire area changes to green due to the presence of ephemerals and new growth on dwarf perennials. The ravines and gullies along the lower part of the hilly areas are dominated by Fagonia mollis, Echinops glaberrimus, Iphiona mucronata, Lavandula coronopifolia, Ochradenus baccatus, Otostegia fruticosa, Pulicaria undulata, Stachys aegyptiaca., etc.. Majority of rocky slopes are covered by large populations of grasses such as Stipagrostis plumosa, the spikes of which often give an off-white appearance to the hillocks.
On the eastern side of the low altitude hillocks and mountains lies the high altitude mountain many of them are as high as 2500 m, such as Jabal Ad Dubbagh, Jabal Lawz and Jabal Al Shaiti. During winter or early spring, these mountains are covered by snow of various depths because of the influence of northern Mediterranean climate. Though the density of vegetation on these mountains is generally poor and several populations are highly fragmented, many of these mountains are a treasure house and plant diversity hot spots holding several Mediterranean and Irano-Turanian elements. Species such as Astragalus echinus ssp. arabica, Atraphaxis spinosa, Launaea spinosa, Nepeta sheilae, Origanum syriacum, Astragalus echinus, Launaea spinosa, Prunus korshinskyi, Thymus decussates, Tulipia biflora are so far recorded from the runnels of these high altitude slopes. The status of the population of the flagship species, Juniperus phoenicea is in a highly impoverished state due to poor regeneration, a phenomenon attributed to prolonged drought or due to unsustainable use of these mountains’ natural resources such as wood cutting . This population is highly fragmented with isolated individual plants with very old trunks, reminding of luxurious woodland of the past. North facing slopes of Jabal Lauz are dominated by Prunus korshinskyi along with Atraphaxis spinosa, Astragalus echinus ssp. arabica, Allyssum subspinosum, origanum syriacum. On the southern sides, particularly Jabal Dubbagh, high altitude of the mountains support the growth of relic Juniperus phoenicea populations along with dwarf shrub land communities such as Artemisia seiberi, Tanacetum santolinoides, Pulicaria glutinosa, Atraphaxis spinosa, Dodonaea angustifolia, Varthemia Montana, Phlomis brachyodon, Teucrium leucocladum, etc.
The eastern part of Tabuk Province, a high altitude plateau, contains wadis and high raise buttes and sandy plains. Among the wadis, Wadi Dessah is a prominent one in terms of species diversity. . The wadi is long with sand covered wadi beds and protected on both sides by red and yellow sand stone pinnacles and butts of various altitudes. It holds significant number of rare/endangered species found refuge along the runnels and gullies of butts. Part of the plateau is a UNESCO world heritage site of sandstone butts surrounded by mobile sand sheets or deep sands. Occasional trees such as Vachellia gerrardii along with shrubs such as Haloxylon persicum, H. salicornicum, Retama raetam, Artemisia monosprema, etc. dominate the sandy habitats. Representative species of deep sands include, Artemisia monosperma, Centropodia forsskalii, Haloxylon persicum, Heliotropium digynum, Moltkiopsis ciliata, Stipagrostis drarii. Overall, perennial plant cover on large tracts of rangeland is sparse except during spring, where several annuals and shallow rooted bulbous plants appear over large tracts of thin sand covered areas.
Approximately 450 species belonging to 73 families are represented in the area.
Flora of Tabuk Province
Written and managed by Dr. Jacob Thomas