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." Socotra is considered the jewel of biodiversity in the Arabian Sea. In the 1990s, a team of United Nations biologists conducted a survey of the archipelago's flora and fauna. They counted nearly 700 endemic species, found nowhere else on earth; only New Zealand, Hawaii, New Caledonia, and the Galápagos Islands have more impressive numbers. In 2008 Socotra was recognised as a UNESCO World Heritage Site. The ecoregion is at increasing risk from human activities. The WWF describes the Socotra Archipelago's conservation status as "Critical/Endangered".
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, and measures 132 kilometres (82 mi) in length and 49.7 kilometres (30.9 mi) in width. Socotra lies some 240 kilometres (150 mi) east of the coast of Somalia and 380 kilometres (240 mi) south of the Arabian Peninsula. 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). 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. 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. 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.
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. 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. 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. Sea-facing slopes and cliffs also receive more moisture from sea fogs and orographic precipitation than other lowland areas. Abd al Kuri, Samhah, and Darsah have desertic climates and no year-round surface streams.
Flora
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