Location and General Description
The subpolar Nothofagus forests extend along the southern Andes Mountains and the Chilean archipelago from 47ºS 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 (Matus 1998) form the Andes.
The northern end of the subpolar Nothofagus forests limit with the Valdivian temperate forests and the eastern part with 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 (Cabrera 1976).
The relief of the northern portion has mountains of about 1500 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 L. 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 large L. Fagnano is found (Matus 1998).
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 mm per year has resulted in three enormous ice fields. These are the Northern Patagonian Ice Field (approx. 46º30’S-47º30’S, 4200 km2), the Southern Patagonian Ice Field (48º30’S-51º30’S, 13000 km2), and the icefield of Cordillera Darwin in the southwest of Tierra del Fuego (54º30’S-55ºS, 2300 km2). Most glaciers have receded in recent times, but 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 70000 and 11000 years. At this time a continuous ice-sheet formed south of 42ºS from western Patagonia to the Pacific coast (Villagrán et al. 1996), but the north of the Southern Patagonian ice field rose only 300-700 m, suggesting that the ice cap left part of the relief uncovered (Lliboutry 1998).
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 (Correa 1969-1999; Moore 1983a).
The climate of this area is wet and temperate-cold and very cold 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 (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 (Hoffmann 1975). For example, mean annual precipitation in Bahía Félix at 53ºS 70ºW is 4845 mm, while in Ushuaia at 54ºS 68ºW it is 545 mm (Correa 1969-1999; Moore 1973). Precipitation as snow can be abundant all the year round (Correa 1969-1999).
The vegetation shows principally two types of forest, mainly evergreen Nothofagus betuloides forests to the west and deciduous Nothofagus pumilio and Nothofagus antarctica forests towards the east that extend into Argentina (Pisano & Dimitri 1973, Hueck 1978, Moore, 1983, Gajardo 1994, Veblen et al. 1996). 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 pure 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, Juncaceae, Cyperaceae and grasses (Moore 1983a; Gajardo 1994).
The deciduous forest shows a transition to the evergreen forest to the west with mixed Nothofagus pumilio-Nothofagus betuloides forests. With approx. 1000-4000 mm precipitation N. betuloides becomes dominant, forming pure forests or mixed with Drymis winteri, Maytenus magellanica and Pilgerodendron uvifera. Inland shrubs of Fuchsia, Ribes, Hebe, Gaultheria and Empetrum accompany, while in coastal situations Hebe elliptica forms a dense scrub (Moore 1983a; Gajardo 1994). In the north Nothofagus dombeyi and N. nitida are found up to 48ºS, and Podocarpus nubigena to 51ºS (Veblen 1996).
In the colder areas with high rainfall of the south western most parts of the ecoregion a characteristic vegetation specially termed Magellanic moorland (Moore 1983a) or Magellanic tundra (Pisano & Dimitri 1973) 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 approx. 1000 m to 500 m. Over it diverse plant communities of dwarf shrubs, cushion heaths, alpine meadows and subnival desert are found. (Moore 1983a; Gajardo 1994;, Pisano & Dimitri 1973; Arroyo et al. 1992). These communities generally increase in richness towards the Patagonian steppes (Moore 1983b, Arroyo et al. 1989). Similar communities are also found around the glaciers (Pisano & Dimitri 1973).
The flora of the ecoregion is diverse (Correa 1969-1999; Moore 1983a; Henriquez et al. 1995). In terms of the phytogeoghraphical classification of Cabrera (1976), 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, Hebe, Donatia, Gaultheria, Gaimardia, Luzuriaga, Oreobolus, Schoenus and Astelia (Cabrera 1976; Correa 1969-1999; Wardle et al. 2001).
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) (Moore 1983; Martinic 1997). Contact of these groups with the European colonists produced extinction or dramatic reductions in their populations due to violence or lethal, contagious diseases from the Europeans and the few survivors rapidly lost their ancestral customs (Martinic 1997). Currently this ecoregion is relatively uninhabited in the west as the climate is too harsh, but a few cities are found more to the east such as Cochrane, Puerto Natales, Punta Arenas and Puerto Williams in Chile, and Ushuaia in Argentina. Many roads have been constructed recently to communicate different parts of the region.
This ecoregion is not as rich as the Valdivian forests to the north that contain a large number of woody plant genera that are not found in the subpolar Nothofagus forests (Donoso-Zegers 1994). Conspicuous genera of the underforest such as the bamboo Chusquea, with Neotropical origin, only reach 48ºS (Veblen et al. 1996). Most of the epiphytes, and all the climbers are also missing. This has sometimes been related to the effect of the glacial extension during the ice ages that so affected the subpolar Nothofagus forests (Arroyo et al. 1996; Villagrán et al. 1996). Nevertheless, important levels of endemism are found among plants, with several mostly herbaceous species being confined to the ecoregion (Correa 1969-1999; Moore 1983a; Zuloaga & Morrone 1996, 1999; Zuloaga et al. 1994).
A few examples of conspicuous endemic or nearly endemic 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 (Arroyo et al. 1992, 1995).
Although endemism at the generic level is low, a few endemic, monospecific genera are found, such as Drapetes, Saxifragella and Saxifragodes (Moore 1983a; Zuloaga & Morrone 1996, 1999). Some monospecific genera such as Pilgerodendron (Cupressaceae), 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 (Moore 1983; Zuloaga & Morrone 1996). 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 (Boelcke et al. 1985; Gamundí & Horak 1993).
Endemism in the 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 firecrown hummingbird (Sephanoides sephanoides), Magellanic woodpecker (Campephilus magellanicus), rayadito (Aphractura spinicauda), Austral parakeet (Enicognathus ferrrugineus), and black throated huet-huet (Pteroptochos tarnii)(Rozzi et al. 1996). Some also extend their ranges into the southern Andean or Patagonian steppes. There seem to be, however, a few near endemics such as two geese (Chloephaga hybrida and C. rubiceps), blackish cinclodes (Cinclodes antarcticus), black throated finch (Melanodera melanodera) and striated caracara (Phalcoboenus australis) (Peña & Rumboll 1998; Amico pres. comm.).
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 (Dusicyon griseus and D. culpaeus), guanaco (Lama guanicoe), huemul (Hippocamelus bisulcus), pudu pudú (Pudu pudu), and huillín (Lutra provocax) are the largest native animals in the area and are relatively abundant in some parts of the ecoregion (Redford & Eisenberg 1992; Murúa 1996). Historically some of these animals, especially huemul, have reduced ranges since the arrival of the Europeans due to hunting, predation by dogs, susceptibility to cattle diseases and competition with cattle and introduced red deer (Redford & Eisenberg 1992). The most important populations of huemul are found in the area. The only endemic and near-endemic mammals appear to be small ground dwelling mice such as Akodon hershokovitzi, A. lanosus and A. markhami (Redford & Eisenberg 1992).
Some species of amphibians are characteristic of the ecoregion including Bufo variegatus, and a few are endemic such as Atelognathus grandisonae and Batrachyla nibaldoi. No amphibians have been reported in the Isla Grande de Tierra del Fuego (Ubeda pers. comm.). A few endemic reptiles are found in the eastern limit of the ecoregion, in the ecotone with the steppe, such as Vilcunia periglacialis and Liolaemus magellanicus (Cei 1986; Ibargüengoytía pers. comm.). Arthropods are relatively little known but are important in many areas (Arroyo et al. 1995), and several damage Nothofagus forest species (Veblen 1996).
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 main cities 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 grazing 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 exotic 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 (Arroyo et al. 1995). 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 most likely introduced with the European colonization and many have been found on the island of Tierra del Fuego (Moore & Goodall 1977; Brion et al. 1988). 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 (Pickett 1996).
Justification of Ecoregion Delineation
This ecoregion of the southern Andes corresponds to the Magellanic district of the Subantarctic phytogeographical province of Cabrera (1976), which is separated from the related Valdivian district to the north on the basis of differing floral composition, cooler climate, and endemic plants (Cabrera 1976). This province forms part of the Austral (= Antarctic) center of biogeographic endemism of Cabrera (1976) and Cabrera & Willink (1980).
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Prepared by: Cecilia Brion and Cecilia Ezcurra
Reviewed by: In progress