Science Fair Project Encyclopedia
The Juan Fernández archipelago is located 670 km off the coast of Chile, and is composed of the volcanic islands Robinson Crusoe, located closest to the mainland at 33º 13' S, 78º 50' W; the islet Santa Clara, 1 km southwest of Isla Robinson Crusoe; and Alexander Selkirk (Alejandro Selkirk) at 33º 45'S, 80º 46'W, 181 km further west. The islands are mainly known for having been the home to the sailor Alexander Selkirk for four years, which fact inspired the novel Robinson Crusoe. The islands have an area of 126 km2, of which 93 km2 are taken up by Robinson Crusoe Island (together with Santa Clara), and 33 km2 by Alexander Selkirk. The population is 633 (all on Robinson Crusoe Island), of those 598 reside in the capital, San Juan Bautista, on Cumberland Bay on the North coast of the island (census of 2002).
The archipelago administratively belongs to V Region of Valparaíso, and more specifically forms one of the nine "comunas" of the province of Valparaíso.
The archipelago was discovered by chance on 22nd November 1574, by the Spanish sailor Juan Fernández, who was sailing between Peru and Valparaíso and deviated from his planned course. He called the islands Más afuera, Más a Tierra, and Islote de Santa Clara.
In the 17th and 18th century it was used as an hide-out for pirates.
In 1966 the Chilean government renamed Isla Más Afuera to Alejandro Selkirk and Isla Más a Tierra to Robinson Crusoe, in order to promote tourism. Incidentally, Selkirk never set foot on Más Afuera, only on Más a Tierra.
The islands are volcanic in origin, and were created by a hot spot in the earth's mantle that broke through the Nazca Plate to form the islands, which were then carried eastward off the hot spot as the Nazca Plate subducts under the South American continent. Radiometric dating indicates that Santa Clara is the oldest of the islands, 5.8 million years old, followed by Robinson Crusoe, 3.8-4.2 million years old, and Alexander Selkirk, 1.0-2.4 million years old. Alexander Selkirk is the largest of the islands, at 50 sq km; its highest peak is Los Innocentes at 1319 meters. Robinson Crusoe is 48 sq km, and the highest peak, El Yunque, is 916 meters. Santa Clara is 2.2 sq km, and reaches 350 meters.
The islands have a subtropical climate, influenced by the cold Humboldt Current which flows northward along the South American coast east of the islands, and the southeast trade winds. The temperature ranges from 3-34ºC, with an annual mean of 15.4ºC. Higher elevations are generally cooler, with occasional frosts on Robinson Crusoe. Rainfall is higher in the winter months, and varies with elevation and exposure; elevations above 500 meters experience almost daily rainfall, while the western, leeward side of Robinson Crusoe and Santa Clara are quite dry. Average annual rainfall is 1081 mm, varying from 318 to 1698 mm year to year. Much of the variability in rainfall depends on the El Niño-Southern Oscillation.
The Juan Fernández islands are home to a high percentage of rare and endemic plants and animals, and are recognized as a distinct ecoregion. The volcanic origin and remote location of the islands meant that the lslands' flora and fauna had to reach the archipelago from far across the sea; as a result, the island has relatively few plants and very few animals. The closest relatives of the archipelago's plants and animals are found in the Temperate broadleaf and mixed forests ecoregions of southern South America, including the Valdivian temperate rain forests, Magellanic subpolar forests, and Desventuradas Islands.
There are 209 native species of vascular plants in the Juan Fernandez Islands, approximately 150 of which are flowering plants, and 50 are ferns. 126 species, or 62 percent, are endemic, with 12 endemic genera and one endemic family, Lactoridaceae . Many plants are characteristic of the Antarctic flora, and are related to plants found in southern South America, New Zealand and Australia.
Vegetation zones generally correspond to elevation, with grasslands and shrublands at lower elevations, tall and montane forests at middle elevations, and shrublands at the highest elevations. The two main islands have somewhat distinct plant communities.
Alexander Selkirk is mostly covered with grassland from 0-400 meters, interspersed with wooded ravines (quebradas), home to dry forests of Myrceugenia and Fagara . From 400 to 600 meters are lower montane forests, with upper montane forest from 600 to 950 meters. The treeline is at approximately 950 meters, above which is alpine shrubland and grassland, dominated by temperate Magellanic vegetation such as Acaena , Dicksonia, Drimys, Empetrum , Gunnera, Myrteola , Pernettya, and Ugni .
On Robinson Crusoe, grasslands predominate from 0-100 meters; introduced shrubs from 100-300 meters; tall forests from 300-500 meters; montane forests from 500-700 meters, with dense tree cover of Cuminia , Fagara , and Rhaphithamnus ; tree fern forests from 700-750 meters, and brushwood forests above 750 meters. Santa Clara is covered with grassland.
Three endemic species dominate the tall and lower montane forests of the archipelago, Drimys confertifolia on both main islands, Myrceugenia fernandeziana on Robinson Crusoe, and M. schulzei on Alexander Selkirk. Endemic tree fern species of southern hemisphere genus Dicksonia (D. berteriana on Robinson Crusoe and D. externa on Alexander Selkirk) and the endemic genus Thyrsopteris (T. elegans) are the predominant species in the tree-fern forests. An endemic species of sandalwood, Santalum fernandezianum, was overexploited for its fragrant wood, has not been seen since 1908, and is believed extinct.
The Juan Fernández Islands have a very limited fauna, with no native mammals, reptiles, or amphibians. Seventeen land and sea-bird species breed on the islands. The island has three endemic bird species, and two endemic subspecies. Robinson Crusoe Island is home to an endemic and endangered hummingbird, the Juan Fernández Firecrown (Sephanoides fernandensis). This large hummingbird, about 11 cm (5 in) long, is thought to number only about 500 individuals. The other endemic bird species are the rayadito (Aphrastura masafuerae) of Robinson Crusoe and the Juan Fernández tit-tyrant (Anairetes fernandezianus).
The Juan Fernandez Fur Seal (Arctocephalus philippii) lives on the islands. This species was nearly exterminated in the sixteenth to nineteenth century, but it was rediscovered in 1965. A census in 1970 indicated about 750 fur seals present in the Archipelago. Only two were sighted on the Desventuradas Islands. The actual population of the Desventuradas may be higher, because the species tends to hide in sea caves. There seems to be a yearly population increase of 16-17%.
2002, 633; 2004, 340
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