Magellanic subpolar forests
The Magellanic subpolar forests is an ecoregion dominated by trees of the genus Nothofagus; this geographic zone covers the western part of the southern end of South America as well as the extreme southern parts of Argentina and Chile, known as the region Tierra del Fuego; this ecoregion is the southernmost forest biome on Earth. The Magellanic subpolar forests ecoregion is colder and in parts drier than the Valdivian temperate forests, and in general is floristically poorer.
Faunal species richness and endemism is low; for example, a total of only 168 vertebrates has been recorded here. The fauna is related to that of the bordering ecoregions, especially to that of the Valdivian temperate forests and the Patagonian steppe. Nevertheless, its varied and majestic landscapes that include high mountain peaks, enormous icefields, and innumerable fjords are inhabited by unique and endemic animal and plant species that are sometimes locally abundant within this ecoregion.
Location and general description
The subpolar Nothofagus forests extend along the southern Andes Mountains and the Chilean archipelago from 47 ºS to the Cape Horn, including the regions of southern Aisen and Magallanes in Chile. In Argentina it only covers small surfaces of the western side of the province of Santa Cruz and the south of Tierra del Fuego from lake Buenos Aires to Staten Island. At this latitude three parallel regions, the Cordillera Patagónica Insular, the Cordillera Patagónica Occidental, and the Cordillera Patagónica Oriental form the Andes.
The northern end of the subpolar Nothofagus forests matches the limit of the Valdivian temperate forests and the eastern part of the Nothofagus forests borders the Patagonian steppe and the Patagonian grasslands. Towards the west the region is in contact with the cold southern Pacific Ocean, and on the high Andes vegetation floristically related to the south Andean steppe appears in parts as interrupted islands.
The relief of the northern portion has mountains of about 1500 metres (m), but several high peaks mark the limit between Chile and Argentina such as Mt. San Lorenzo (3706 m), Mt. Fitz Roy (3406 m) and Mt. Murallón (3600 m). Towards the west other very high mountains appear such as Mt. San Valentín (3910 m). Large lakes of glacial origin are also found in the limit of Argentina and Chile such as Lago Gral Carrera-Buenos Aires (the deepest and second largest lake in South America), L. Cochrane-Pueyrredón, L. O’Higgins-San Martín, L. Viedma and L. Argentino. The relief of the southern portion generally decreases to less than 1000 m, and in Tierra del Fuego the sizeable L. Fagnano is found.
Permanent snow, ice caps and glaciers are present in the summits of many of the higher elevations. The effect of the cold temperatures, strong and permanent west winds and high precipitation on the windward side of the mountains of about 5000 millimetres (mm) per year has resulted in three enormous icefields. These are the Northern Patagonian Ice Field (approx. 46º30’S to 47º30’S, 4200 square kilometres), the Southern Patagonian Ice Field (48º30’S to 51º30’S, 13000 km2), and the icefield of Cordillera Darwin in the southwest of Tierra del Fuego (54º30’S to 55ºS, 2300 km2). Some glaciers have receded in recent times, with others advancing; however, during the ice ages of the Quaternary, significant expansions of the glaciers in this ecoregion took place. At the end of the last glaciation, one of the more extensive areas in Patagonia had at least five glacial advances lasting between 70,000 and 11,000 years. At this time a continuous ice-sheet formed south of 42ºS from western Patagonia to the Pacific coast, but the north of the Southern Patagonian ice field rose only a differential height of 300 to 700 m, suggesting that the ice cap left part of the topographic relief uncovered.
Soils of the ecoregion are varied, mostly depending on climate, but are generally acid due to high precipitation, low drainage, and slow decomposition of organic matter in relation to low temperatures. Towards the south and west podsols and acid brown forest soils develop in places with better drainage, and peat accumulates in less drained areas with bogs and tundra vegetation.
The climate of this area is generally wet and temperate-cold, with very cold regimes at high elevations. The effect of the cold northward Humboldt and Antarctica currents on the western and southern coasts makes the area colder than others at similar latitudes, with mean January (austral summer) temperatures lower than 10º C. The strong westerly winds blow all year round, producing high rainfall in the windward west side of the mountains and lower precipitation to the east, and no dry season. In general mean annual temperatures are between 6ºC in the north and 3ºC in the south, and mean annual precipitation varies, decreasing from west to east from approximately 4000 mm to 700 mm respectively. For example, mean annual precipitation in Bahía Félix at 53ºS 70ºW is 4845 mm, while in Ushuaia, Argentina at 54ºS 68ºW it is 545 mm. Precipitation as snow can be abundant all the year round.
The vegetation shows principally two types of forest: chiefly evergreen Guindo Beech (Nothofagus betuloides) forests to the west and deciduous Lenga (Nothofagus pumilio) and Antarctic Beech (Nothofagus antarctica) forests towards the east that extend into Argentina. In Tierra del Fuego the evergreen forests are found to the south and the deciduous forests towards the interior. The deciduous forest is formed by almost pure stands of Nothofagus pumilio at lower elevations, in different combinations with the more ecologically tolerant Nothofagus antarctica, which prevails in more arid situations or less drained soils. In frost pockets a heath dominated by Empetrum and Bolax is found. In humid or wet places of these forests especially rich raised bog-communities grow dominated by Sphagnum, and grasses in the families Juncaceae and Cyperaceae.
The deciduous forest shows a transition to the evergreen forest to the west with mixed Nothofagus pumilio-Nothofagus betuloides forests. With approx. 1000 to 4000 mm precipitation N. betuloides becomes dominant, forming pure forests or mixed with Drymis winteri, Maytenus magellanica and Pilgerodendron uvifera. Inland shrubs of the genera Fuchsia, Ribes, Veronica, Gaultheria and Empetrum accompany, while in coastal situations Veronica elliptica forms a dense scrub. In the northern part of the ecoregion, Coigue (Nothofagus dombeyi) and Chiloe's Coigue (N. nitida) occur up to latitude 48ºS, and Chilean Podocarp (Podocarpus nubigena) up to latitude 51ºS.
In the colder areas with high rainfall of the southwestern parts of the ecoregion, a characteristic vegetation usually termed Magellanic moorland or Magellanic tundra extends through the Chilean archipielago to 48ºS. This tundra is characterized by prostrate dwarf shrubs, cushion plants, grass-like plants and bryophytes on water-logged terrain, that in different combinations form vegetation of scrub or bogs. In sheltered areas, even on the outermost islands, only fragments of the evergreen forest develop. The bogs comprise characteristic species, many with austral affinities such as Astelia, Bolax, Caltha, Donatia, Drapetes, Gaimardia, Lepidothamnus and Phyllachne.
Over the highest mountains, usually limited by a belt of low ‘krumholz’ of prostrate specimens of Nothofagus species, alpine vegetation is found above the forests. The timberline descends from north to south from approximately 1000 m to 500 m. Over it diverse plant communities of dwarf shrubs, cushion heaths, alpine meadows and subnival desert are found. These communities generally increase in richness towards the Patagonian steppe. Similar communities are also found in the vicinity of the glaciers.
The flora of the ecoregion is diverse. The ecoregion is part of the Subantarctic province and shows close relationships to that of the Valdivian temperate forests to the north. This biogeographical province belongs to the Austral realm, and several genera of the ecoregion have representatives or close relatives in Australia, New Zealand and Tasmania, such as Nothofagus trees and Blechnum ferns in the forests, and many cushion and shrub genera of bogs and scrub such as Lepidothamnus, Veronica, Donatia, Gaultheria, Gaimardia, Luzuriaga, Oreobolus, Schoenus and Astelia.
The human populations found in the ecoregion, when Europeans established in the area in the 19th century, were aboriginous groups of maritime cultures that navigated the fjords and canals of the archipielago in bark canoes (e.g., Yamana and Alacaluf), and groups of terrestrial culture that hunted and gathered in the mainland and in the island of Tierra del Fuego (e.g., Aush and Shelknam). Contact of these groups with the European colonists produced reductions in their populations due to violence or lethal, contagious diseases from the Europeans and the relatively few native survivors gradually lost their ancestral customs. Currently this ecoregion is relatively uninhabited in the west as the climate is too harsh, but a few towns are found more to the east such as Cochrane, Puerto Natales, Punta Arenas and Puerto Williams in Chile, and Ushuaia in Argentina. A few roads have been constructed in the latter twentieth century to communicate different parts of the region.
This ecoregion is not as biologically rich as the Valdivian forests to the north, which exhibit a large number of woody plant genera that are not found in the subpolar Nothofagus forests. Conspicuous genera of the underforest such as the Chusquea Bamboos (Chusquea), with Neotropical origin, only reach 48ºS. Most of the epiphytes, and all the viny climbers are also absent from this ecoregion. This has sometimes been related to the effect of the glacial extension during the ice ages that so affected the subpolar Nothofagus forests. Nevertheless, important levels of endemism are found among plants, with several mostly herbaceous species being confined to the ecoregion.
A few examples of conspicuous endemic or nearly endemic plant species found in this ecoregion are grasses such as Deschamsia kingii, Festuca cirrosa, Poa darwiniana, P. yaganica, and herbs or subshrubs such as Onuris alismatifolia, Ourisia fuegiana, O. ruelloides, Senecio eightsii, S. humifusus, S. websteri, Nassauvia latissima, Acaena lucida, Perezia lactucoides, Viola commersonii, V. tridentata, Phyllachne uliginosa, Lebetanthus myrsinites, Nardophyllum bryoides, Caltha dioneifolia, Hamadryas magellanica, Ranunculus sericocephalus, Gavilea australis, Olsynium obscura, Valeriana sedifolia, Abrotanella submarginata, A. trilobata and A. emarginata. Many of these species are found in the mountains, in alpine regions above the forests where many endemic species of this ecoregion also occur.
Although plant endemism at the generic level is low, a few endemic, monospecific genera are found, such as Drapetes, Saxifragella and Saxifragodes. Some monospecific genera such as Pilgerodendron (Cupressaceae family), the world’s southern-most conifer, are especially well represented in the ecoregion. A few Austral genera are especially relevant, because they are most diversified in the ecoregion, such as Abrotanella and Ourisia; both have several endemic species. Some genera do not have endemics but are well represented in diversity, frequency or abundance such as the Austral parasitic fungus Cyttaria associated to Nothofagus species. Cryptogms in general, i.e., fungi, lichens, mosses and liverworts, are important in the ecoregion.
Endemism in the ecoregion flora, however, is not mirrored in the fauna, where there are few endemics. Among the avifauna, most birds of the subpolar Nothofagus forests extend their ranges to the north into the Valdivian forests such as the conspicuous Green-backed Firecrown hummingbird (Sephanoides sephanoides), Magellanic Woodpecker (Campephilus magellanicus), Thorn-tailed Rayadito (Aphrastura spinicauda), Austral Parakeet (Enicognathus ferrugineus), and Black-throated Huet-huet (Pteroptochos tarnii). Some bird species also extend their ranges into the southern Andean or Patagonian steppe. However, there are a few near-endemics avian taxa, such as the Kelp Goose (Chloephaga hybrida); the Ruddy-headed Goose (C. rubidiceps); Blackish Cinclodes (Cinclodes antarcticus); Canary-winged Finch (Melanodera melanodera); and Striated Caracara (Phalcoboenus australis).
Mammals also tend to have geographic distributions that extend north to other Andean ecoregions or east into the Patagonian steppes. The Puma (Puma concolor); two foxes: Argentine Grey Fox (Dusicyon griseus) and Culpeo Fox (Lycalopex culpaeus); Guanaco (Lama guanicoe); Huemul (Hippocamelus bisulcus); Pudu Pudú (Pudu pudu), and Southern River Otter (Lontra provocax) are the largest native terrestrial mammals in the ecoregion, and are locally abundant in some parts of the ecoregion. Historically some of these animals, especially Huemul, have reduced their ranges since the arrival of the Europeans, due to hunting, predation by dogs, susceptibility to cattle diseases, competition with cattle, and competitive conflicts with introduced red deer. The most important populations of huemul are found in the area.
The only endemic and near-endemic mammals are thought to be small ground dwelling mice such as Hershkovitz's Grass Mouse (Akodon hershokovitzi), known to occur only on Isla Capitan Aracena and possibly on the outer islands of the Chilean Archipelago; Woolly Grass Mouse (A. lanosus), occurring in southernmost Chile and Argentina, as far north as northwestern Santa Cruz Province, Argentina; and Markham's Grass Mouse (A. markhami), found only on Isla Wellington in southern Chile.
Thirteen amphibians are found in the ecoregion, all of whom are anuran taxa. Some species of amphibians are characteristic of the ecoregion including the Patagonian Toad (Nannophryne variegata); Marbled Wood Frog (Batrachyla antartandica), found from Mehuin to the Virtudes Islands; Island Spiny-chest Frog (Alsodes monticola), known only from Inchy, in coastal southern Chile; Gray Wood Frog (Batrachyla leptopus), found from Neuquén to lower Río Negro in Argentina, and Concepción to the Aysén Region in Chile.; Gray Four-eyed Frog (Pleurodema bufoninum), occurring in the Patagonian steppe and subpolar forests; Emerald Forest Frog (Hylorina sylvatica), ranging in Chile from the western versant of the Cordillera de Nahuelbuta to Laguna San Rafael, and in Argentina, found in several locations at Nahuel Huapi National Park (southern Neuquén Province and northwestern Río Negro Province) and at Los Alerces National Park (northern Chubut Province); Banded Wood Frog (Batrachyla taeniata), found from Neuquen Province to the lower Rio Negro Province; Chiloe Island Ground Frog (Eupsophus calcaratus), found from Valdivia to Wellington Island in Puerto Eden, Chile to Tromen Lake and Puelo Lake in Argentina; Darwin's Frog (Rhinoderma darwinii VU), occurring in Chile from the province of Maule south to the province of Aisen, and in the Argentine provinces of Neuquen and Rio Negro.
Several amphibians are strictly endemic such as the Puerto Eden Frog (Atelognathus grandisonae), known only from the type locality at Puerto Eden, Wellington Island; Alsodes kaweshkari, found in only two localities: Puerto Edén at Wellington Island and Seno Huemules, both in southern Chile; and Nibaldo's Wood Frog (Batrachyla nibaldoi). No amphibians have been reported in the Isla Grande de Tierra del Fuego, presumably due to the harsh cold climate.
Only six repilian taxa occur in the ecoregion. Two endemic reptiles are found in the eastern limit of the ecoregion, in the ecotone with the steppe: Liolaemus hatcheri and Magellan's Tree Iguana (Liolaemus magellanicus). Other non-endemic reptiles found here are: Bibron's Iguana (Diplolaemus bibronii); and three further tree iguanas: Phrynosaura audituvelata, Liolaemus exploratorum and Liolaemus maldonadae.
Little is known regarding the terrestrial arthropods of this ecoregion, but many taxa are fundamentally important important in the food chain; moreover, several taxa are involved in damaging Nothofagus forest species.
Historical habitation and exploration
Earliest habitation by humans was by the Yaghan people approximately 11,000 years before present. It is somewhat of a mystery how soon Native Americans found their way to the southernmost part of the Americas not long after original crossing of the Bering ice bridge. Nevertheless, the Yaghans had a very hardy lifestyle that not only made use of the forest resources in building their teepee style homes, but included extensive harvesting of marine resources and swimming in the icy waters of this region.
The first detailed scientific European exploration of the region occurred with Charles Darwin's arrival on the HMS Beagle. Darwin spent considerable effort in cataloguing flora and fauna of this ecoregion before journeying further north to explore the more noted Galapogos leg of his trip.
This ecoregion has several more or less protected areas through all its length. The most important from north to south are Chilean National Parks: Laguna San Rafael, Lago Jeinimeni, Bernardo O’Higgins, Torres del Paine, Alberto De Agostini and Cabo de Hornos, and Argentinean National Parks: Perito Moreno, Los Glaciares and Tierra del Fuego. In Chile there are also several National Reserves: Lago General Carrera, Tamango, Katalalixar, Alacalufes, two Forestal Reserves: Magallanes and Laguna Parrillar, and two Natural Monuments: Laguna de Los Cisnes and Los Pingüinos.
Types and severity of threats
The subpolar Nothofagus forests are seriously threatened by habitat conversion at the present time. The region has been affected by extensive burning and logging, especially around the principal urban areas and in the more populated areas of the region. A marked increase in the population and tourism in the northern part of the region has been produced by the recent construction of the Chilean Carretera Austral that currently unites Coihaique to Cochrane and Villa O’Higgins. This could produce problems related to the increment of fires, logging and overgrazing by cattle and sheep. Although the vegetation is probably adapted to grazing by native animals such as huemul and guanaco, the introduction of exotic cattle can have an harmful impact on the ecosystems.
The increase in tourism can have far reaching affects such as the introduction of non-native species. Threats from established alien species continue to cause threats to this ecoregion. Some exotic animals have been introduced purposely for hunting or for fur or meat, such as European Rabbit (Oryctolagus cuniculus) and North American Beaver (Castor canadensis) have already invaded large areas in the southern portion of this ecoregion. Beavers build dams affecting the regeneration of the forest and the hydrology of the region. Alien plants are a major percentage of the flora, especially in open, disturbed places such as in logged or burnt forest. About 25% of exotic species were likely introduced with the European colonization and many have been found on the island of Tierra del Fuego. Although sustainable forestry projects are being attempted in this ecoregion, most forestry management is poor and entire stands are turned into chips of low added value.
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