The Socotra Island xeric shrublands is a terrestrial ecoregion that covers the large island of Socotra and several smaller islands that constitute the Socotra Archipelago. The archipelago is in the western Indian Ocean, east of the Horn of Africa and south of the Arabian Peninsula. Politically the archipelago is part of Yemen, and lies south of the Yemeni mainland.
Socotra has a uniquely diverse ecosystem. The islands are home to a high number of endemic species; up to a third of its plant life is endemic. It has been described as "the most alien-looking place on Earth."[2]
The ecoregion is at increasing risk from human activities. The WWF describes the Socotra Archipelago's conservation status as "Critical/Endangered".[7][8][9]
Geography
Socotra is the easternmost island in the Socotra Archipelago, and constitutes around 95% of the archipelago's landmass. The island has an area of approximately 3,600 km2,[10] and measures 132 kilometres (82mi) in length and 49.7 kilometres (30.9mi) in width.[11] Socotra lies some 240 kilometres (150mi) east of the coast of Somalia and 380 kilometres (240mi) south of the Arabian Peninsula.[12]
A coastal plain, up to 5 km wide, extends around most of Socotra. The coastal plain's soils are mostly alluvial deposits of stone and coarse sand. The Noged Plain along the island's south shore has areas of sand dunes. The center of the island is a plateau, 300 to 700 meters in elevation, composed mostly of Cretaceous limestone. The Hajhir Mountains in northwestern Socotra are composed of precambrian granites and metamorphic rock, and include Mashanig, the island's highest point (1,519 m).[7]
The other islands in the archipelago are Samhah and Darsah, known as The Brothers, and Abd al Kuri. Abd al Kuri is the westernmost island and lies closest to the African mainland, only 90 km away. Abd al Kuri has an area of 133 km2 and is dominated by a limestone plateau reaching up to 740 metres elevation. Samhah is 50 km southwest of Socotra with an area of 41 km2 and also comprises a limestone plateau reaching 680 metres elevation. Darsah lies east of Samhah and is the smallest at 17 km2 and 350 metres elevation. Abd al Kuri and Samhah are inhabited, but largely deserted during the winter monsoon season.[10]
Politically, Socotra and most of the other islands are part of Yemen, and constitute Socotra Governorate. Geographically, Socotra and the rest of its archipelago are part of Africa – a geologic and biogeographic extension of the Horn of Africa.[7]
The archipelago is an ancient continental fragment. The opening of the East African Rift created the Gulf of Aden and separated the islands from the Arabian Peninsula starting 18 million years ago. Lower sea levels during the ice ages connected Socotra to Samhah and Darsah, but deeper sea trenches kept Abd al Kuri separated from the African mainland and the other islands.[10]
Climate
The climate of the ecoregion is tropical and mostly arid. It is influenced by the Indian Ocean's monsoon winds. The April-to-October southwest monsoon brings hot dry winds from the Horn of Africa. The Northeast monsoon arrives during the winter months, from November to March, and brings lower temperatures and more moisture.[7]
Average annual rainfall ranges from 150 mm on the coastal plain to more than 1,000 mm in the mountains. Rainfall is sporadic and unpredictable. Tropical cyclones are rare. Nighttime dew is an important water source for the islands' plants.[7]
The mountains intercept moisture-bearing winds, which creates more clouds, fog, and orographic precipitation. The mountains are also cooler than the lowlands. Small mountain streams sustain aquatic habitats, and can flow down through the lowlands during the cooler and wetter winter months and during high rainfall events.[7] Sea-facing slopes and cliffs also receive more moisture from sea fogs and orographic precipitation than other lowland areas.[10]
Abd al Kuri, Samhah, and Darsah have desertic climates and no year-round surface streams.[10]
Flora
The long geological isolation of the Socotra archipelago and its fierce heat and drought have combined to create a unique and spectacular endemic flora. Botanical field surveys led by the Centre for Middle Eastern Plants, part of the Royal Botanic Garden Edinburgh, indicate that 307 out of the 825 (37%) plant species on Socotra are endemic, i.e., they are found nowhere else on Earth.[13] Genera endemic to the Socotra archipelago include Angkalanthus, Ballochia, Cephalocrotonopsis, Cyanixia, Duvaliandra, Haya, Lachnocapsa, Paraerva, Socotrella, and Tamridaea. The entire flora of the Socotra Archipelago has been assessed for the IUCN Red List, with 3 Critically Endangered and 27 Endangered plant species recognised in 2004.[13]
Dragon's blood tree is one of the most striking of Socotra's plants. Its red sap was thought to be the dragon's blood of the ancients, sought after as a dye, and today used as paint and varnish.[13] Socotra's various endemic aloes were also important historically for medicine and cosmetics. Other endemic plants include the giant succulent tree Dorstenia gigas, the cucumber tree Dendrosicyos socotranus, the rare Socotran pomegranate (Punica protopunica), Aloe perryi, and Boswellia socotrana.[15]
About 15 species of mammals live on Socotra. There are four species of bats, the Egyptian mouse-tailed bat (Rhinopoma cystops), Geoffroy's horseshoe bat (Rhinolophus clivosus), Somalian trident bat (Asellia italosomalica), and the endemic Socotran pipistrelle (Hypsugo lanzai). The Egyptian mouse-tailed bat has been recorded on all the islands, and the other three species only on Socotra.[16] The other mammals were introduced by humans. The Socotran wild ass is a feral population of African wild ass (Equus africanus) that lives in the lowlands of Socotra. Introduced livestock include dromedary camels, cattle, and goats, which include both domestic and feral populations. Other introduced mammals include the domestic cat (Felis catus), lesser Indian civet (Viverricula indica), black rat (Rattus rattus), house mouse (Mus musculus), Etruscan shrew (Suncus etruscus), and Madagascan pygmy shrew (Suncus madagascariensis).[17]
Reptiles constitute a diverse Socotran vertebrate fauna with 31 species. If one excludes the two recently introduced species, Hemidactylus robustus and Hemidactylus flaviviridis, all native species are endemic. There is a very high level of endemism at both species (29 of 31, 94%) and genus levels (5 of 12, 42%). At the species level, endemicity may be even higher, as phylogenetic studies have uncovered substantial hidden diversity.[18] The reptile species include skinks, legless lizards, and one species of chameleon, Chamaeleo monachus.
Over the two thousand years of human settlement on the islands the environment has slowly but continuously changed, and, according to Jonathan Kingdon, "the animals and plants that remain represent a degraded fraction of what once existed."[15] The Periplus of the Erythraean Sea says the island had crocodiles and large lizards, and the present reptilian fauna appears to be greatly reduced. Until a few centuries ago, there were rivers and wetlands on the island, greater stocks of the endemic trees, and abundant pasture. The Portuguese recorded the presence of water buffaloes in the early 17th century. Now there are only sand gullies, and many native plants only survive where there is greater moisture or protection from livestock.[15] The remaining Socotra fauna is greatly threatened by goats and other introduced species.
Conservation and threats
The United Nations Environment Programme named unplanned urbanisation and tourism development, overgrazing, resource exploitation, invasive species, and climate change as threats to Socotra's biodiversity. Socotra has become economically isolated from mainland Yemen since 2014 by the Yemen civil war. As a result the price of cooking gas and other fuels has increased, causing residents to turn to wood for heat and cooking.[22]
World Heritage Site
The island was recognised by the United Nations Educational, Scientific and Cultural Organization (UNESCO) as a world natural heritage site in July 2008. The European Union has supported such a move, calling on both UNESCO and International Organisation of Protecting Environment to classify the island archipelago among the environmental heritages.[6]
Socotra or Saqatri is an island of Yemen in the Indian Ocean. Lying between the Guardafui Channel and the Arabian Sea and near major shipping routes, Socotra is the largest of the six islands in the Socotra archipelago. Since 2013, the island has been part of the Socotra Archipelago Governorate.
Abd al Kuri is a rocky island in the Guardafui Channel. As a part of the Socotra Archipelago Governorate of Yemen, it lies about 65 miles (105 km) southwest of the main island of Socotra. Its terrain primarily consists of granite and diorite covered with limestone.
Pulicaria stephanocarpa is a species of flowering plant in the family Asteraceae. It is endemic to Yemen's Socotra archipelago, where it is native to the islands of Socotra, Samhah, and Abd al Kuri. Its natural habitats are subtropical or tropical dry shrubland and rocky areas.
Paraerva microphylla is a species of flowering plant in the family Amaranthaceae. It is a subshrub or shrub endemic to the islands of Socotra and Abd al Kuri in the Socotra archipelago off the coast of East Africa, which are politically part of Yemen.
Heliotropium wagneri is a species of plant in the family Boraginaceae. It is endemic to the islands of Abd al Kuri and Samhah in Yemen's Socotra archipelago. Its natural habitats are subtropical or tropical dry shrubland and subtropical or tropical dry lowland grassland.
Limonium paulayanum is a species of plant in the family Plumbaginaceae. It is a subshrub or shrub endemic to Yemen's Socotra Archipelago, where it is native to the islands of Socotra, Samhah, and Abd al Kuri. Its grows in coastal dwarf shrubland and on inland cliffs and rocky areas, from sea level to 550 metres elevation.
Limonium sokotranum is a species of plant in the family Plumbaginaceae. It is a subshrub or shrub endemic to Yemen's Socotra Archipelago, where it is native to the islands of Socotra, Samhah, and Abd al Kuri. Its grows in coastal dwarf shrubland and inland cliffs and rocky areas from sea-level to 550 metres elevation.
Ochradenus socotranus is a species of plant in the Resedaceae family. It is a shrub endemic to the islands of Socotra and Samhah in Yemen's Socotra Archipelago. Its natural habitat is dry rocky slopes from 10 to 700 metres elevation.
Oldenlandia pulvinata is a species of plant in the family Rubiaceae. It is a cushion-forming subshrub endemic to the islands of Socotra, Abd al Kuri, and Samhah in Yemen's Socotra Archipelago. It is widespread in shrubland and in rocky areas on plains and limestone plateaus from sea level to 800 metres elevation.
Polycarpaea kuriensis is a species of plant in the family Caryophyllaceae. It is endemic to the islands of Socotra, Samhah, and Abd al Kuri in Yemen's Socotra Archipelago. Its natural habitats are subtropical or tropical dry shrubland and rocky areas.
Priva socotrana is a species of plant in the family Verbenaceae. It is a subshrub endemic to the islands of Socotra and Samhah in Yemen's Socotra Archipelago. It is common and widespread in dry shrublands and woodlands on limestone escarpments and plateaus from 50 to 950 metres elevation.
Dendrosicyos is a monotypic genus in the plant family Cucurbitaceae. The only species is Dendrosicyos socotranus, the cucumber tree. The species is endemic to the island of Socotra in Yemen, and is the only species in the Cucurbitaceae to grow in a tree form. The species name was originally spelled D. socotrana, but this is corrected to masculine grammatical gender according to the International Code of Nomenclature for algae, fungi, and plants.
The Djibouti xeric shrublands is an ecoregion defined by One Earth, consisting of a semi-desert strip on or near the Red Sea and the Gulf of Aden coasts in Eritrea, Ethiopia, Djibouti and Somalia. This ecoregion lies mainly between sea level and 800 meters (m) elevation. There are, however, many hills and massifs, which range up to 1300 m as well as outstanding fault-induced depressions, such as the Danakil, lying as low as 155 m below sea level. This region is extremely active tectonically, experiencing many earthquakes and intermittently active volcanoes. Rainfall is very low and yearly averages range from 100 to 200 millimeters (mm), with less rain falling closer to the coast. There are many species of interest, including the endemic Archer's lark, a species of dragon tree, and a large suite of desert ungulates, including the last viable population of African wild ass.
Cissus subaphylla is a low shrub in the grape family Vitaceae. It is endemic to the Yemeni islands of Socotra and Samhah. The plant grows mainly in dry, low-lying areas on alluvial fans or on limestone slopes, and is rarely found above elevations of 300 metres (980 ft), where it is replaced by C. hamaderohensis. It does not have the climbing habit of other Cissus species, and its stems are flattened and gray-green in colour, with relatively small leaves and flowers. The tangled mats of C. subaphylla stems act as a protective covering for plants regularly eaten by goats and other browsing animals; the plant is thus important in the rehabilitation of species such as Dendrosicyos, Maerua and Commiphora.
The Socotra Archipelago, officially the Socotra Archipelago Governorate, abbreviated to Socotra Governorate, is one of the governorates of Yemen. It includes a number of islands in the Indian Ocean south of mainland Yemen, the largest of which is Socotra.
The wildlife of Yemen is substantial and varied. Yemen is a large country in the southern half of the Arabian Peninsula with several geographic regions, each with a diversity of plants and animals adapted to their own particular habitats. As well as high mountains and deserts, there is a coastal plain and long coastline. The country has links with Europe and Asia, and the continent of Africa is close at hand. The flora and fauna have influences from all these regions and the country also serves as a staging post for migratory birds.
Haemodracon riebeckii, known as the dragon-tree gecko or blood dragon gecko, is a species of lizard in the family Phyllodactylidae. The species is endemic to the Socotra archipelago, Yemen.
The Southwestern Arabian foothills savanna, also known as the Southwestern Arabian Escarpment shrublands and woodlands, is a desert and xeric shrubland ecoregion of the southern Arabian Peninsula, covering portions of Saudi Arabia, Yemen, and Oman.
The Red Sea Nubo–Sindian tropical desert and semi-desert ecoregion covers extremely arid land along the northeastern Red Sea, the southern Sinai Peninsula, and on a thin strip along the Israel-Jordan border. Most of the coastal land is flat, but there are high mountains in southern Sinai. Biodiversity is limited by the low moisture levels – some areas go for years without significant rain. Portions of the area support a thin savannah-like cover of widely scattered trees and scrub, surrounded by grasses that briefly flourish after a rainfall. Biodiversity is highest in the mountains of Sinai, and in the wadis and gullies that retain moisture.
References
↑ Eric Dinerstein, David Olson, et al. (2017). An Ecoregion-Based Approach to Protecting Half the Terrestrial Realm, BioScience, Volume 67, Issue 6, June 2017, Pages 534–545; Supplemental material 2 table S1b.
↑ Huntingford, George Wynn Brereton (1980). The Periplus of the Erythraean Sea. Hakluyt Society. p.103. ISBN978-0-904180-05-3.
1 2 3 4 5 6 Banfield LM, Van Damme K, Miller AG. Evolution and biogeography of the flora of the Socotra archipelago (Yemen). In: Bramwell D, Caujapé-Castells J, eds. The Biology of Island Floras. Cambridge University Press; 2011:197-225.
↑ Benda, Petr & Nasher, Abdul Karim & Van Damme, Kay & Vallo, Peter & Reiter, Antonín. (2017). Bats (Mammalia: Chiroptera) of the Eastern Mediterranean and Middle East. Part 14. Bat fauna of the Socotra Archipelago, Yemen. 10.13140/RG.2.2.14724.63360.
↑ Josef Suchomel, Josef (2012). "Mammals of Socotra". Friends of Soqotra. Accessed 15 August 2020.
↑ Vasconcelos R, Montero-Mendieta S, Simó-Riudalbas M, Sindaco R, Santos X, et al. (2016) Unexpectedly High Levels of Cryptic Diversity Uncovered by a Complete DNA Barcoding of Reptiles of the Socotra Archipelago. PLOS ONE 11(3): e0149985. https://doi.org/10.1371/journal.pone.0149985
↑ Apel, M. and Brandis, D. 2000. A new species of freshwater crab (Crustacea: Brachyura: Potamidae) from Socotra Island and description of Socotrapotamon n. gen. Fauna of Arabia 18: 133-144.
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