Archipelago Juan Fernández
Located in the eastern South Pacific, 667 km west from the Chilean coast of South America, lie the three isolated
islands that comprise the Archipelago Juan Fernández (Juan Fernández Islands). The archipelago consists
of Isla Robinson Crusoe (93 km²), Isla Alejandro Selkirk
(85 km²) and Isla Santa Clara (5 km²). Isla
Alejandro Selkirk lies 181 km west from Isla Robinson Crusoe and Isla Santa Clara lies 1.5 km off the southwestern
peninsula of Isla Robinson Crusoe. In addition to the main islands there a numerous smaller islets and offshore
rocks. The islands unique flora and fauna are protected as the Juan Fernández Archipelago National Park (1935)
and as an IUCN Biosphere Reserve (1977). The
archipelago forms a remote part of the Chilean province of Valparaiso.
The islands are volcanic in origin, having formed over a hot-spot between 1 and 5 million years ago on the 850 km long Juan Fernández Ridge. Santa Clara is the oldest at 5.8 million years old, Robinson Crusoe around 4 million years, and Alejandro Selkirk between 1 and 2 million years. Today the islands are inactive and have become heavily eroded into deeply dissected and rugged landscapes of ridges, valleys and narrow ravines. All are mountainous — Isla Alejandro Selkirk (1,319 m, Cerro de Los Inocentes), Isla Robinson Crusoe (916 m, El Yunque) and Sant Clara (375 m) — with very few areas of level ground. Coastlines are equally rugged and convoluted, consisting of tall cliffs, steep slopes and narrow rocky beaches.
The islands experience a subtropical climate that is influenced by the cold waters of the subantarctic Humboldt current and by the south east trade winds. The mean annual temperature is 15.4 °C, with an annual rainfall of around 1,080 mm. Precipitation falls mainly in a rainy season from March to December and can be highly variable — due the effects of the El Niño Southern Oscillation. At higher elevations, where temperatures are lower, rain falls on most days of the year.
Due to their extreme isolation the islands have low numbers of plant and animal species — but those present constitute a flora and fauna that displays high levels of endemicity, with an endemism rate among vascular plants of over 60 per cent. There are 209 native species of vascular plants, 150 of which are flowering plants, and 50 are ferns. 126 species are endemic, with 12 endemic genera and one endemic family — the Lactoridaceae. Many of the islands plants have affinities with those of southern South America, New Zealand and Australia — reflecting their wind, ocean and animal delivery to the islands. Many areas are devoid of vegetation cover due to over-logging, over-grazing and the resulting soil erosion.
Vegetation cover is dependant upon elevation. Grasses and shrublands dominate at lower elevations (grasses are the main flora of Santa Clara) as well as numerous introduced species. At slightly higher elevations vegetation consists of tall lowland forest dominated by the islands largest tree species: the endemic Canelo (Drimys confertifolia), the endemic Luma (Myrceugenia fernandeziana) found on Isla Robinson Crusoe, and a second Luma species (M. schulzei) found on Isla Alejandro Selkirk, and Nothomyrica fernandeziana. Lower montane forest contains Canelo and Luma, together with the Manzano (Boehmeria excelsa) and two species of the large endemic tree, the Naranjillo — Fagara mayu on Isla Robinson Crusoe and F. externa on Isla Alejandro Selkirk. Higher yet, is the tree-fern zone consisting of large dense stands of tree ferns, with the endemic species of the genus Dicksonia and Thyrsopteris being the most common. At heights of over 850 m vegetation takes on a brushwood character.
The islands have a limited number of animal species, with no native species of mammal, amphibian or reptile. Seventeen land and sea-bird species breed on the islands including the endemic Juan Fernández Firecrown (Sephanoides fernandensis) a critically endangered hummingbird — which pollinates around 9% of the islands flora. Other highly endangered species of bird include the Juan Fernández Petrel (Pterodroma externa), Stejneger’s Petrel (P. longirostris) and the Masafeura Rayadito (Aphrastura masafuerae). The islands are also home to the rare Juan Fernández Fur Seal (Arctocephalus philippii) — once thought to be extinct, but rediscovered on the islands in 1965.
