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 measures 132 kilometres (82mi) in length and 49.7 kilometres (30.9mi) in width.[10] Socotra lies some 240 kilometres (150mi) east of the coast of Somalia and 380 kilometres (240mi) south of the Arabian Peninsula.[11]
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 closest to the African mainland, only 90 km away.
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]
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.[7]
Nighttime dew is an important water source for the islands' plants. 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]
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.[12] 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.[12]
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.[12] 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.[14]
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.[15] 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).[16]
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.[17] The reptile species include skinks, legless lizards, and one species of chameleon, Chamaeleo monachus.
The coral reefs of Socotra are diverse, with many endemic species.[14]
Human impacts
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."[14] 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.[14] The remaining Socotra fauna is greatly threatened by goats and other introduced species.
Conservation and threats
As a result of the 2014 Yemen civil war in mainland Yemen, Socotra became isolated and the gas prices became high, causing residents to turn to wood for heat.
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 four islands in the Socotra archipelago. Since 2013, the archipelago has constituted the Socotra Governorate.
The Galápagos Islands xeric scrub, also known as the Galápagos Islands scrubland mosaic, is a terrestrial deserts and xeric shrublands ecoregion that covers the Galápagos Islands. The Galápagos Islands are volcanic in origin, and remote from continents and other islands. The ecoregion is well known for its unique endemic species, including giant tortoises, birds, and marine iguanas, which evolved in isolation to adapt to islands' environments.
The wildlife of Djibouti, consisting of its flora and fauna, is in a harsh landscape with forest accounting for less than one percent of its area. Most species are found in the northern part of the country in the Day Forest National Park at an average elevation of 1,500 metres (4,900 ft), including the massif Goda, with a peak of 1,783 metres (5,850 ft). It covers an area of 3.5 square kilometres (1.4 sq mi) of Juniperus procera forest, with many of the trees rising to 20 metres (66 ft) height. This forest area is the main habitat of the critically endangered and endemic Djibouti spurfowl, and another recently noted vertebrate, Platyceps afarensis. The area also contains many species of woody and herbaceous plants, including boxwood and olive trees, which account for sixty percent of the identified species in the country.
Acridocarpus socotranus is a species of plant in the family Malpighiaceae. It is endemic to Socotra, an archipelago which is part of Yemen. It occurs in woodlands, thickets, and succulent shrubland habitat, where it is a common species.
The Gulf of California xeric scrub is a xeric shrubland ecoregion of Mexico's Baja California Peninsula.
The Mediterranean woodlands and forests is an ecoregion in the coastal plains, hills, and mountains bordering the Mediterranean Sea and Atlantic Ocean in North Africa. It has a Mediterranean climate, and is in the Mediterranean forests, woodlands, and scrub biome.
The Socotra golden-winged grosbeak or Socotra grosbeak is a finch endemic to Socotra, an island in the Indian Ocean off the coast of Yemen. R. socotranus is by some authorities held to be the only species of the then-monotypic genus Rhynchostruthus, including all other golden-winged grosbeaks therein as subspecies. But in recent times the three populations are usually considered a distinct species, with R. socotranus being limited to the Socotra population, the Arabian golden-winged grosbeak becoming R. percivali, and the Somali golden-winged grosbeak R. louisae.
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 Arabian Peninsula coastal fog desert, also known as the Southwestern Arabian coastal xeric scrub, is desert ecoregion on the southern coasts of the Arabian Peninsula, which experiences thick fogs where visibility may be reduced to 10 metres (33 ft). It is classed as an Afrotropical fog desert
The Djibouti Xeric Shrublands ecoregion is 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 island of Socotra. 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 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.
The Madagascar succulent woodlands are a xeric shrublands ecoregion in southwestern and central western Madagascar. Native plants survive in the arid climate and long dry season with adaptations like succulent leaves, water storing trunks, photosynthetic stems, and dropping leaves during the dry season. The ecoregion is threatened by various human activities.
The La Costa xeric shrublands (NT1309) is an ecoregion in Venezuela that stretches along the Caribbean coast. The dry scrub and savanna has been subject to modification since the 16th century by European colonists who replaced it by a patchwork of farm fields and pasturage. Little of the original habitat remains.
The Pilbara shrublands is a deserts and xeric shrublands ecoregion in Western Australia. It is coterminous with the Pilbara IBRA region. For other definitions and uses of "Pilbara region" see Pilbara.
The Somali montane xeric shrublands is a desert and xeric scrubland ecoregion in Somalia. The ecoregion lies in the rugged Karkaar Mountains, which run parallel and close to Somalia's northern coast on the Gulf of Aden, and follows coast from Cape Guardafui south to Eyl on the Arabian Sea.
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 Namibian savanna woodlands, also known as the Namib escarpment woodlands, are the deserts and xeric shrublands ecoregion of Namibia and Angola.
The Socotran pipistrelle or Lanza's pipistrelle is an endangered species of vesper bat in the family Vespertilionidae. It is endemic to Socotra Island in Yemen, and is the only mammal thought to be endemic to the island.
The Diksam Plateau or Dixam Plateau is a limestone plateau in Socotra, Yemen. The Firmihin forest, located east of the Dirhur canyon within the plateau, has the highest concentration of Dragon's Blood Trees on the entire island.
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.
↑ 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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