Location and General Description
The islands of San Andrés (the southernmost, at 12º36’N-81º42’W, with a surface area of 24 km2), Santa Catalina and Providencia (the northernmost, at 13º23’N-81º22’W, with a surface area of approximately 17 km2) and a group of keys and small islands, are located 150 km east of the Nicaraguan coast (Bluefields) and 620 km northwest of Cartagena (Colombia). The Miskitos Keys, with more than 85 islands, are located 40 km east of Awas Tara (northeastern Nicaraguan coast on the Caribbean) at 14º26’N-82º50’W and cover a total area of 500 km2, i.e., each key has an average area of some 6 km2 (Ledec et al. 1995).
The climate in this ecoregion is humid tropical lowlands, with average precipitation of 2000 mm per year based on annual rainfall of about 1900 mm, at San Andrés and 1532 mm at Providencia and relatively constant and high temperatures (average 27 ºC) throughout the year. Rainfall generally follows a pattern defined by a dry season (3-4 months) and a rainy season (generally with two peaks of maximum rainfall, one in June and the other from September to November). The ecoregion is highly influenced by the climate of the tropical Caribbean islands, not really wet but humid during half of the year while the other half is dry and hot. The ecoregion’s favorable location however does mean that hurricanes are rare and/or very weak (Barriga et al. 1985).
San Andrés Island is formed over a volcanic cone that presumably appeared during the Miocene epoch. There is no indication that the island was connected to the continent by a land bridge. Limestone deposited at the top of the volcanic cone created the so-called San Andrés calcareous formation, consisting of compact and hard white coral-engendered limestone from the Miocene epoch, overlaid by calcareous deposits or saltpeter, irregularly consolidated with a great variety of marine fossils in which coral is not predominant. This formation constitutes the axis of the island’s hills (Barriga et al. 1985). The topography of the island is formed by a chain of hills extending the length of the island from north to south, skirted by a coastal plain. The maximum elevation is 100 m. Providencia, the second largest island, also has a central mountain chain with peaks of 350 m. of elevation, with geomorphology similar to those of San Andrés (Barriga et al., 1985). The topography of the larger Miskitos keys is characterized by some hills no higher than 10 meters ASL. (Ledec et al. 1995)
The predominant potential vegetation of the ecoregion has been almost totally destroyed. It would cover most of the larger islands (except for coastal areas) and would be a lowland tropical rainforest with oceanic influence. The original vegetation of San Andrés was a lush forest with numerous species that lose their leaves during the dry months. By the 17th century, lumber operations had already begun to harvest the most sought-after woods including mahogany (probably Swietenia mahogani), cedar (Cedrela sp.), "palo brasil" (Haematoxylon sp.) and fustic (Chlorophora tinctoria). Subsequent settlement of the island led to the forest’s being eradicated and replaced primarily by cotton crops and later by coconut crops. The degraded stages of these primary forests are low and dense thickets made up of Lantana spinosa, Croton sp., Randia sp. and Xylosma sp., which are relatively frequent on the island (Barriga et al. 1985).
A certain number of both animal and plant species and subspecies are confined to only one island in the ecoregion, these species are endemisms due to the phenomenon of insularity. Some of these species are found on San Andrés Island including two land birds the San Andrés mockingbird (Mimus magnirostris) and Sam Andrés vireo (Vireo caribaeus) and two reptiles a lizard (Anolis concolor) and a snake (Coniophanes andresensis) (UNEP 1998). They could easily become extinct in the near future if adequate protection is not provided for the few natural areas where these species remain. Due to the relatively long duration of the dry season, numerous plant species temporarily lose their leaves. It should be noted that of the timber-yielding species cited in the previous section we can confirm the existence of only some Chlorophora tinctoria trees and cedars (various species of Meliaceae). The rest became extinct some time ago (Barriga et al. 1985, Marquez 1987).
There are only two species of native bats on San Andrés Island, Artibeus jamaicensis and Molossus molossus. There are three species of doves, and Leptotila jamaicensis neoxena (ground dove) is an endemic subspecies of the island. Two endemic species of passeriforms on the island are Mimus magnirostris (nightingale) and Vireo caribaeus, and other subspecies are Icterus leucopteryx lawrencii, Vireo altiloquus canescens, Coereba flaveola oblita and Dendroica petechia flavida. As endemic birds of the Archipelago (San Andrés and Providencia) we have: Coccyzus minor abbotti (species of cuckoo), Anthracothorax prevostii hendersoni (the only hummingbird on the archipelago), and two passeriforms, Tiaris bicolor grandior (grass bird) and Elaenia martinica cinerascens. There are three snake species on San Andrés Island and of these Coriophanes andresensis is endemic. Of the seven species of saurians present, one gecko subspecies (Sphaerodactylus argus andresensis) is endemic (Barriga et al., 1985). The Caribbean monk seal (Monachus tropicalis) is today considered extinct.
One outstanding feature of this ecoregion is the presence of coral reefs, one of the largest and best preserved in the western Caribbean Sea, considered a part or an extension of the great belicean reef, very outstanding in terms of marine biodiversity. Even if the ecoregion category is applied to land areas, the reefs are an outstanding feature, obviously related to the island.
This ecoregion is endangered due to the critical decrease of its area. In the Miskitos Keys, mangroves of Avicennia germinans and Rhizophora mangle are predominant and act as an ecological niche for birds and other animals. On these keys, there is a Marine Reserve with IUCN category Ia protection (Ledec et al. 1995). The original vegetation that covered most of the islands of San Andrés and Providencia is destroyed and almost completely altered by deforestation, tilling and intensive cattle raising. Established areas of pasture and agriculture or settlement and migratory farming represent 40 km2 according to data from the Ministry of Finance in 1983, the entire islands. In San Andrés isolated trees and small localized groups of trees survive, apart from secondary bushy vegetation in uncultivated areas or forming an irregular undergrowth among the crops of coconut palm, while there are some remnants of the forest in the central massif of Providencia. It is very important to preserve the remaining patches of original vegetation that currently have no protection of any kind, in order to prevent their complete destruction and to create forest areas as recreational areas.
Types and Severity of Threats
The massive uses of insecticides for crops must be avoided since they directly and seriously affect endemic insect life and threaten the entire tropical food chain indirectly and directly (Barriga et al. 1985). It is a recommendation, but something of very severe impact on the island has been tourist infrastructure and overuse including too many big hotels are covering important land area, overusing water supplies, generating garbage and contaminating waters that are thrown directly into the seas.
There´s an official Reserve in Providencia, Old Providence National Park, a part of the National Park System, which protects island forests, mangroves and some reefs.
On San Andrés Island, brown rats are a veritable plague for coconut plantations and what little is left of the natural vegetation because they are so numerous. There is only one predator of rats among the wild animals on the island, the boa (Boa constrictor); unfortunately, farmers hunt down this native reptile species. It is likely that some North American birds of prey reach the island during period of migration, but the island has no resident species among this group.
Justification of Ecoregion Delineation
These islands were separated from the mainland ecoregions because of their inclusion as a secondary endemic bird area (Providence Island s012 & San Andrés Island s013) by Stattersfield et al. (1998). We felt these islands were sufficiently different from the mainland ecoregions, coupled with a unique history and prolonged isolation, to warrant their own ecoregion.
Barriga T., C. Hernández, and T. Jaramillo, et al. 1985. La Isla de San Andrés. Contribuciones al conocimiento de su ecología, flora, fauna y pesca. Universidad Nacional de Colombia. Bogotá, Colombia.
Márquez, G. 1987. La islas de Providencia y Santa Catalina: Ecologia . Fondo Fen Colombia – Universidad Vacional de Colombia. Colombia.
Ministerio de Hacienda y Crédito Público. 1983. Mapa de la República de Colombia, 1:500.000. Departamentos de Atlántico, Bolívar, César, Guajira, Magdalena. Instituto geográfico "Agustín Codazzi". Bogotá, Colombia.
Ledec, G., M. Pellegrini, and J. Beltran, 1995. The World Bank operational manual: Operational Policies. Critical Natural Habitats in Latin America and the Caribbean. Washington, DC.
UNEP Islands Web Site. 1998. United Nations System-Wide Earthwatch: A window on United Nations work to observe and assess the global environment. http://www.unep.ch/islands/IXF.htm#1480
Stattersfield, A.J., et al. 1998. Endemic bird areas of the world: priorities for biodiversity conservation. Birdlife Conservation Series No. 7, BirdLife International, Cambridge, U.K.
Prepared by: Ugo D’ambrosio
Reviewed by: Emilio Constantino, Christine Burdette