Juan Fernández Islands temperate forests
The Juan Fernández Islands temperate forests ecoregion is exclusive to the Juan Fernández archipelago. As in most oceanic islands, its biota has a different combination of species than equivalent mainland areas. Because islands are difficult to reach, and each continental species has different dispersal capability, it is inevitable that islands will possess a non-representative sample of the species from the near continents. These forests contain a high percentage of endemism among vascular plants and possess the only endemic hummingbird known for oceanic islands. These unique taxa have evolved after the emergence of the islands, estimated in 1-5.8 millions of years, from the first colonizers.
These islands were discovered in 1574 by the Spanish navigator Juan Fernández and are also known as Robinson Crusoe Islands, so named because the Scottish sailor, Alexander Selkirk, was self-marooned there for over 4 years, and his experiences served as the inspiration for Daniel Defoe’s famous novel.
Location and General Description
The Juan Fernández archipelago is located 667 kilometers (km) off the coast of continental Chile in the south-eastern part of the Pacific Ocean and is of the few regions of the world where there was no permanent human settlements before 16th century. It comprises three main islands: Isla Robinson Crusoe (= Masatierra) at 33º 13' S, 78º 50' W, the closest to the mainland, Santa Clara, 1 km to the SW of Isla R. Crusoe, and Isla Alejandro Selkirk (= Masafuera) at 33º 45'S, 80º 46'W, 181 km further west.
These islands are of volcanic origin and are supposed to have formed over a "hot spot" in the Earth's crust and then subsequently moved eastwards as the Nazca Plate has been subducted beneath the South American continent. Radiometric dating indicated the following ages for the islands: Santa Clara, 5.8 million years old, R. Crusoe, 3.8-4.2 million years old, and A. Selkirk, 1.0-2.4 million years old. The area of each island is: A. Selkirk (50 km2), R. Crusoe (48 km2), and Santa Clara (2.2 km2). The highest point (1319 meters (m), Los Inocentes) is on Isla A. Selkirk. Isla R. Crusoe reaches 916 m (El Yunque), while Santa Clara attains only 350 m. The topography includes spectacular vertical cliffs and deeply cut ravines.
The climate is subtropical and strongly influenced by fluctuations in the general northward flow of the cold subantarctic Humboldt ocean current and the south east trade winds, that creates a high-winter and low-summer rainfall pattern and a stable-temperature environment. The temperatures range throughout the year from 3-34 ºC, with an annual mean of 15.4 ºC. Frost occasionally occurs on Isla A. Selkirk. The rainy season lasts from March to December. Average annual rainfall is 1081 millimeters (mm), ranging yearly from 318 to 1698 mm, though there is high spatial variability with higher rainfall and lower temperatures as altitude increases. The lower, western side of Isla R. Crusoe, and that of Isla Santa Clara, are very dry, receiving rain only during tropical storms. In the regions over 500 m high of both major islands, rainfall is often daily, but of short duration. Some areas are wet enough to support forests of tree ferns. Occasionally the oceanic and atmospheric currents are disrupted bringing anomalous climatic conditions to the islands, as in 1973 when warm ocean waters contributed to a prolonged wet season, probably as part of the general Pacific-wide El Niño-Southern Oscillation anomalies.
As most oceanic islands, this ecoregion has an extraordinary biota with unique assemblages of species and high levels of endemism. Nevertheless, the richness of its flora contrasts the paucity of its fauna.
Although the flora of the archipelago is small in number (ca. 150 flowering plant species and 50 fern species), the archipelago contains a high level of endemic vascular plants (about 62.5%) including 12 genera and one family: Lactoridaceae. In addition, the species density and the density of endemics is higher than any other oceanic island: 2.08 species/km2 and 0.98 endemics/km2, respectively. Moreover, these species are of considerable importance, not only because they may be a key to early angiosperm radiation, but also because several species may provide basic elements in understanding evolution in certain groups. The most speciose family is Asteraceae, that underwent a broad diversification of the first colonizers on these islands; it includes the four endemic genera: Centaurodendron (2 subspecies (spp.)), Dendroseris (11 spp.), Robinsonia (7 spp.), and Yunquea (1 sp.). Other endemic genera are: Cuminia (Lamiaceae, 1 sp.), Juania (Arecaceae, 1 sp.), Lactoris (Lactoridaceae, 1 sp.), Megalachne (Poaceae, 2 spp.), Ochagavia (Bromeliaceae, 1 sp.), Podophorus (Poaceae, 1 sp.), Selkirkia (Boraginaceae, 1 sp.), and Thyrsopteris (Dicksoniaceae, 1 sp.).
The majority of the angiosperm species have very small or small flowers. Most species are hermaphroditic, 9% are dioecious, and 9% are monoecious. Studies of compatibility of about 14% of the flora indicate that 85% of these species are self-compatible, but their level of autogamy is low. Nevertheless, selfing mediated via geitonogamy is the most frequent mechanism of pollen transfer. Outcrossing is mainly achieved through dioecy and self-incompatibility, or promoted by dichogamy in the hermaphroditic flowers, and facilitated by wind pollination.
The terrestrial fauna of the islands is far less impressive than the flora. There are no native mammals, amphibians or reptiles; a native frog (Pleuroderma sp.) from continental Chile was presumably introduced by humans. The Fernandezian insect fauna is small as well, and is notably lacking species usually dedicated to floral visits.
From the 296 breeding bird species of Chile, only eleven are endemic, and five of these are restricted to the Juan Fernández Islands. Thus, this ecoregion is of major importance to the fauna of Chile. Seventeen land- and seabird species breed regularly on the Juan Fernández Archipelago. Amongst these, eight species and subspecies are endemic, and four additional species breed outside of the archipelago only on Mocha or Desventuradas Islands. The birds endemic at the species level are: the Juan Fernández firecrown, Sephanoides fernandensis (the only endemic hummingbird known on oceanic islands), the "rayadito" from Masafuera, Aphrastura masafuerae, the Juan Fernández tit-tyrant, Arlairetes fernandezianus, and the endemic at the subspecies level: the Juan Fernández red-backed hawk, Buteo polyosoma exsul, and the Juan Fernández sparrow hawk, Falco sparverius fernandensis. The short-eared owl, Asio flammeus, the green-backed firecrown, Sephanoides sephaniodes, the austral thrush, Turdus falcklandii, and the austral blackbird, Guracus curaeus, are shared with continental Chile.
On these island forests, floral visitors are absent or rare, other than the two mentioned hummingbird species. About 9% of the extant flora is hummingbird pollinated and it is estimated that around 47% are wind pollinated. The diet of the hummingbirds includes nectar from 14 autochthonous plant species.
Each island has its own somewhat distinct vegetation types. On Isla R. Crusoe the zones are: grasslands (0-100 m altitude), introduced shrubs (100-300 m), tall forests (300-500 m), lower montane forests (500-700 m), tree fern forests (700-750 m), and high brushwood on exposed cliffs (500-850 m). Isla Santa Clara has been denuded of shrubby vegetation and consists largely of grassy slopes throughout. On Isla A. Selkirk the zones are: grassland slopes (0-400 m) and deep ravines ("quebradas", 0-500 m), lower montane forests (400-600 m), upper montane forests (600-950 m), high brushwood (950-1100 m), and an "alpine zone" (1100-1300 m).
Grassy slopes with native and introduced species of grasses and other herbaceous weeds, cover much of the lower altitudes of both major islands, as well as nearly all of Santa Clara. Abundant here are Danthonia collina, Stipa laevissima and Piptochaetium bicolor. On Isla A. Selkirk, Anthoxanthum odoratum is the most common grass species. Acaena ovalifolia has become a widespread weed on Isla R. Crusoe, together with the two most noxious pests in the islands, namely Aristotelia chilensis ("maqui") and Rubus ulmifolius ("zarzamora").
Tall lowland forest is dominated by the largest trees in the archipelago: Drimys confertifolia (on both main islands), Myrceugenia fernandeziana (on Isla R. Crusoe) and M. schulzei (on Isla A. Selkirk). Lower montane forest contains Drimys confertifolia and Myrceugenia fernandeziana, together with Boehmeria excelsa, Coprosma oliveri, C. pyrifolia, and two species of Fagara (F. mayu on Isla R. Crusoe and F. externa on Isla A. Selkirk). The tree fern forest zone consists of dense stands of Thyrsopteris elegans and Dicksonia berteriana, with a dark, moist forest floor. On Isla A. Selkirk, D. berteriana is replaced by D. externa. Upper montane forest contains Azara serrata var. fernandeziana, Blechnum cycadifolium, Cuminia eriantha, Lactoris fernandeziana, and Rhaphithamnus venustus.
Brushwood forest occurs on the highest slopes at about 850 meters (m) altitude, or on exposed escarpments and ridges (to 550 m). Species in this zone include Berberis corymbosa, Colletia spartioides, Dendroseris marginata, Eryngium bupleuroides, Ochagavia elegans, Pernettya rigida, and Robinsonia gayana.
The importance of the flora of the Juan Fernández and its level of endangerment, as well as of its endemic fauna, are manifest by the Chilean government designation of this archipelago as a National Park in 1935 (administrated by the CONAF) and by the International Union for the Conservation of Nature (IUCN) designation of it as a World Biosphere Reserve in 1977, listed in their "most threatened" category. In addition, Bird Life International's identifies them as a critical conservation priority and they also appear in the WWF/IUCN's global study of Centers of Plant Diversity and Endemism. CONAF is actively working to save the endemic plants with support from the Chilean Government and several international organizations. However, the incipient restoration work seems insufficient to stall the effects of many aggressive introduced species.
Types and Severity of Threats
The native flora is characterized by low fire tolerance and poor adaptation to herbivore resistance. Many of the unique plant species of these forests have very few populations and, in several cases, even few individuals, surviving. This has a detrimental effect on plant reproduction: a) the density of conspecifics is fundamental to favor higher levels of inter-plant pollen transfer, and b) reproductive success depends on the quantity and quality of effective pollination visits, and both of these are likely to depend on local abundance. It is estimated that more than 50% of the endemics are threatened. Feral animals are the greatest threat because they exert devastating effects on the island’s habitats, especially on Isla A. Selkirk where there are several thousand goats. Rabbits are the main threat on the other two islands, where several thousand occur in the drier zones. Wild dogs and pigs have been eradicated from the islands. Domesticated grazing animals used to roam the entire Isla R. Crusoe, but they are now restricted near the only village of San Juan Bautista, surrounding Cumberland Bay. Introduced mammals also have a great impact on the autochthonous birds, because some animals eat the eggs and/or the birds.
Earlier, the effect of introduced animals was exacerbated by logging. Native species were cut to provide timber for sailing ships, as well as for local construction material and firewood. As a consequence of the opening of lower-elevation forests, a number of colonizing shrubs native to the mainland and introduced onto the islands have invaded large tracts of disturbed forest, competing with endemic sister species. Rubus ulmifolius and Aristotelia chilensis cover large areas where no other native species can compete. Both species regenerate from cut stumps making control difficult. On upper ridges, the introduced Ugni molinae dominates some areas. These three weeds have fleshy fruits that are bird-dispersed by the thrush. Amazingly, there are 227 introduced and naturalized species registered so far, many more than the native and endemic species, and in addition to the cited weeds, Lantana camara and Lonicera japonica have the potential to be serious pests.
Invasives also pose secondary effects. If they produce nectar and are hummingbird visited (as many do), their prosperity may also lead to both a reduced visitation rate and reduced effective pollination of the endemics. For instance, the highly invasive Rubus ulmifolius is heavily visited as a nectar source by the native hummingbird and it seems to be better suited than the endemic hummingbird to feed on this plant species. This fact, among others, is postulated to have differentially favored the native hummingbird at the expense of the endemic one, whose populations are declining.
Last but not least, human disturbance of the fragile island habitats is to be mentioned. Anthropogenic alterations of oceanic islands have taken place on a greater scale than on most continental systems.
As a result of those factors, at least one plant species has gone extinct during historical times (the native sandal, Santalum fernandezianum, cut to extinction by the beginning of the 20th century for its aromatic wood), and several others, with very few individuals or even not collected from the beginning of the century, are on the verge of disappearing.
Justification of Ecoregion Delineation
The very impressive levels of plant endemism – at the specific, generic, and familial levels – in a very small land area, together with some endemic birds – including the only endemic hummingbird known from oceanic islands – clearly make the Juan Fernández Islands temperate forests worthy of international attention and qualify them as a center of biodiversity in their own right.
The Juan Fernandez islands were distinguished from other ecoregions by the great distance of the islands from the mainland and from other islands, and by the number of endemic species present, including 3 species of bird.
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