Granitic Seychelles
Granitic Seychelles forests
The small granitic island of Chauve Souris (Praslin)
Map of the Granitic Seychelles
Ecology
RealmAfrotropical
BiomeTropical and subtropical moist broadleaf forests
Geography
Area166 km2 (64 sq mi)
CountriesSeychelles
Coordinates4°30′58″S 55°34′37″E / 4.516°S 55.577°E / -4.516; 55.577
Conservation
Conservation statusCritical/endangered
Protected38 km2 (23%)[1]

The Granitic Seychelles are the islands in Seychelles which lie in central position on the Seychelles Bank and are composed of granite rock. They make up the majority of the Inner Islands, which in addition include the coral islands along of the rim of the Seychelles Bank, namely Bird Island and Denis Island. The Granitic Seychelles contrast with the Coralline Seychelles or the Outer Islands, several island groups made up of low coral islands with dry, infertile soils. [2] [3] [4]

The Granitic Seychelles are home to tropical moist forests, with several endemic species, including the coco de mer (Lodoicea maldivica), and the jellyfish tree (Medusagyne oppositifolia).[5]

Geography

Mahé is the largest and tallest island in Seychelles, at 145 square km and up to 905 m elevation. There are 42 granitic islands, in descending order of size: Mahé, Praslin, Silhouette, La Digue, Curieuse, Félicité, Frégate, Ste. Anne, North, Cerf, Marianne, Grand Sœur, Thérèse, Aride, Conception, Petite Sœur, Cousin, Cousine, Long, Récif, Round (Praslin), Anonyme, Mamelles, Moyenne, Ile aux Vaches Marines, L'Islette, Beacon (Ile Sèche), Cachée, Cocos, Round (Mahé), L'Ilot Frégate, Booby, Chauve Souris (Mahé), Chauve Souris (Praslin), Ile La Fouche, Hodoul, L'Ilot, Rat, Souris, St. Pierre (Praslin), Zavé, Harrison Rocks (Grand Rocher).

The Granitic Seychelles are fragments of the ancient supercontinent of Gondwana, and have been separated from other continents for 75 million years. The Granitic Seychelles form the northernmost part of the submarine Mascarene Plateau.[5] There are mafic xenolith intrusions in the granite in some areas.

Climate

The archipelago is about 5 degrees south of the equator, and has a humid tropical climate with little seasonal variation in temperature. Average annual rainfall varies with elevation, and exposure, ranging from 2,300 to 5,000 mm. There are heavy monsoon rains in the summer (November to February). Trade winds blow steadily from the southeast during the cooler months.[5]

Flora

The native vegetation of these islands consisted of palm, pandanus screw pines, and hardwood forest with mossy, ferny, cloud forest at higher elevations. The flora shows links with both Madagascar to the south and the African mainland to the west. Having been so isolated the islands are rich in endemic plant life including palm trees such as the coco de mer.[5]

The Granitic Seychelles have a relatively low number of flowering plant species, but a high rate of endemism. Approximately 268 flowering plant species are native to the island, in 216 genera. 28% of the species are endemic, with at least 13 endemic genera, of which most are monospecific.[6] Endemic genera include Deckenia, Glionnetia, Lodoicea, Medusagyne, Nephrosperma, Northia, Paragenipa, Phoenicophorium, Protarum, Roscheria, Seychellea, Vateriopsis, and Xyroschoenus.[7] 35% of flowering plant species are endangered.[6]

Fauna

The unique lizard and reptile populations of the Seychelles include seven species of caecilian and the iconic giant tortoises, Aldabrachelys gigantea arnoldi on the Granitic Seychelles, and Dipsochelys dussumieri on Aldabra. There have been some extinctions but the remaining endemic birds of these islands include the Seychelles scops owl (Otus insularis) and the Seychelles paradise flycatcher (Terpsiphone corvina).[5]

Threats and preservation

200 years of human settlement has seen the removal of much of the ancient habitat (including planting of coconut, vanilla and cinnamon), and the introduction of damaging invasive species. The Vallée de Mai on Praslin is the largest example of natural palm forest and is a World Heritage Site.[8]

References

  1. ↑ 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.
  2. ↑ "Map of Ecoregions 2017". Resolve. Retrieved August 20, 2021.
  3. ↑ "Granitic Seychelles forests". Digital Observatory for Protected Areas. Retrieved August 20, 2021.
  4. ↑ "Granitic Seychelles forests". The Encyclopedia of Earth. Retrieved August 20, 2021.
  5. 1 2 3 4 5 "Granitic Seychelles forests". Terrestrial Ecoregions. World Wildlife Fund.
  6. 1 2 Sylvain G. Razafimandimbison, Kent Kainulainen, Bruno Senterre, Charles Morel, and Catarina Rydin (2020). Phylogenetic affinity of an enigmatic Rubiaceae from the Seychelles revealing a recent biogeographic link with Central Africa: gen. nov. Seychellea and trib. nov. Seychelleeae. Molecular Phylogenetics and Evolution, Volume 143, 2020, 106685. ISSN 1055-7903, https://doi.org/10.1016/j.ympev.2019.106685.
  7. ↑ World Checklist of Vascular Plants (WCVP). Checklist of endemic plants of Seychelles. Retrieved 11 November 2023.
  8. ↑ Martin, Emma and Burgess, Neil. Granitic Seychelles Forests. One Earth. Retrieved 11 November 2023.
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