woensdag 29 februari 2012

Mexico, Sian Ka'an

In the language of the Mayan peoples who once inhabited this region, Sian Ka'an means 'Origin of the Sky'. Located on the east coast of the Yucatán peninsula, this biosphere reserve contains tropical forests, mangroves and marshes, as well as a large marine section intersected by a barrier reef. It provides a habitat for a remarkably rich flora and a fauna comprising more than 300 species of birds, as well as a large number of the region's characteristic terrestrial vertebrates, which cohabit in the diverse environment formed by its complex hydrological system.

Sian Ka'an is situated on the eastern side of the Yucatán Peninsula in the state of Quintana Roo. Where possible, boundaries were defined to coincide with natural features: the site is bounded by the Caribbean Sea and the barrier reef to a depth of 50 m in the east; by the junction between the marshes and semi-evergreen forests in the south-east; and by the junction of Chetumal and Espiritu Santo bays catchment basin in the south. The northern and north-eastern boundaries are defined by the limits of farming cooperatives. The northern sites can be reached by a dirt track from Tulum, whereas Punta Pajaros is only accessible by boat or aircraft.
Sian Ka'an lies on a partially emerged coastal limestone plain which forms part of the extensive barrier reef system along the eastern coast of Central America. Much of the reserve lies in a zone of recent Pleistocene origin which still appears to be in a transitional stage. A large series of sinkholes (cenotes) exist in the area and are characteristic features of the Yucatán and Florida peninsulas. The hydrological cycle is complex and the water table is permanently close to the surface. There is little surface running water within the reserve as it usually filters fairly rapidly through the shallow rendzina and saskab (granular whitish and brittle limestone) soils, and the limestone rock to subterranean channels. Owing to their hardness the waters in the reserve are generally very clear. A geological fault crosses the reserve from south-west to north-east, influencing its topography and hydrology. In general, soils are unsuitable for agriculture.
Medium altitude semi-evergreen forest represents the climax vegetation in non-flooded areas, although it is scarce in accessible parts due to disturbance. Some 120 trees and shrubs have been recorded, including larger trees. Some 100 tree and shrub species have been identified in medium and low semi-deciduous forest. The abundance of palm is a characteristic feature of this forest type. Flood forest is subdivided into low forest with closed and open canopy tree communities, the latter being found in lower, wetter areas. It can form monospecific 'islands' on patches of dark soil. Grass communities cover large areas to the south and north and occur among mangroves and inland forests (although not in areas of high salinity). This vegetation type occurs as a mosaic with three intermingled associations. Low islands known as hammocks or petenes emerge from the flooded marshes. Larger petenes may have a central waterbody. There are extensive areas covered by scattered dwarf mangroves to the east of the freshwater marshes.
Coastal dunes stretch along 64 km of the coast, from the northern limit of the reserve to Punta Allen and from Punta Hualastoc to Punta Tupac. As Sian Ka'an lies so close to the Caribbean islands, there is a strong affinity between their flora. The introduction and cultivation of coconut has replaced about 60% of the natural vegetation on the coastal dunes. Selective felling has affected mahogany, red cedar and white cedar. There are an estimated 1,200 plant species.
As regards the Sian Ka'an fauna, a total of 103 species of mammal has been recorded including five species of cat - jaguar, puma, ocelot, margay and jaguarondi. Other mammals include Central American tapir, Caribbean manatee, spider monkey, howler monkey, kinkajou, white-tailed deer, red brocket, white-lipped peccary, paca, tayra and collared anteater. Some 339 bird species have also been recorded, with about two-thirds breeding inside the reserve. Due to the great diversity of aquatic habitats, marine and wading birds are well represented. There are 16 raptor species, as well as frigate bird, cormorant, roseate spoonbill, greater flamingo and jabirus; and 42 species of amphibian and reptile have been recorded. These include four of the six turtle species found along the Mexican coast; green, hawksbill, loggerhead and leatherback. Morelet's crocodile and American crocodile also occur. Fish are abundant, and over 52 species have been recorded. A total of 550 terrestrial and 843 aquatic invertebrate species have been observed.
There are 23 Mayan sites in the reserve, while the Chunyaxché ruins, Vigia Del Lago and Xamach, are just to the north. Recently, a 24 km Mayan artificial canal was discovered. The reserve is located in the least-developed part of Quintana Roo, and the population is predominantly of Mayan origin, in whose language Sian Ka'an means 'Origin of the Sky'.

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