The Patagonian steppe ecoregion extends approximately from the mid-Andean Precordillera southward, terminating immediately north of the Strait of Magellan near the Rio Gallegos. This steppe is bordered on the west by the cold temperate forest slopes of the Andes Range, and on the east by the Atlantic Ocean. It extends northwest as shrubland steppe and to the north as thorn thicket, gradually making the transition to Argentine Monte. This area is a cold desert scrub steppe, with very high wind velocities throughout the year as well as year around frosts likely. This ecoregion has high levels of endemism in both plants and animals.
Location and general description
The Patagonian steppe ecoregion mainly covers the Patagonia region of Argentina from the Atlantic Ocean shore to barely across the border into Chile. The Peninsula Valdés is and outlier of this ecoregion, lying slightly north of the main body. The topography of this ecoregion includes low-lying mountains, plateaus, and plains. Soils are variable but generally rocky-sandy and poor in fine materials and organic matter. The climate is very dry and cold with snow during the winter and frosts nearly year-round however annual precipitation does not normally average more than 200 millimeters (mm). A characteristic of the Patagonian climate is the constant drying wind that blows with great force from the west, particularly in the summer months. Winter generally lasts for five months from about June to September with averages of the coldest month between one tot three °C below freezing. Elevations range greatly in this expansive ecoregion from sea level nearer the shores of the Atlantic up to 2,000 meters (m) in the north and about 700 m in the southern extent of the ecoregion due to the Andean areas on the western side.
In general, the vegetation of this steppe ecoregion is xerophytic and highly adapted for protection against drought, wind, and herbivores. The vegetation is considered strongly related to Andean flora however the average numbers of endemic species for dominant families is very high with as much as 60 percent endemism in Leguminosae and 33 percent in Compositae. There are three main types of vegetative communities. The most densely covered is semi-desert (45%), shrub-steppe (30%), and grass-steppe (20%). Desert like areas also exist with little to no vegetative cover as well as wet meadow areas which have close to 100% cover.
Semi-desert vegetation has highly adapted features; these dwarf and cushion shrubs are the most widely occuring vegetation type in the ecoregion. Shrubs species of Acantholippia, Benthamiella, Nassauvia and Verbena genera grow in these areas as well as cushion plants of Mulinum spinosum and Brachyclados caespitosus and tuft grasses; the most common being species of Poa and Stipa. Also abundant are species with heteroblastic growth and small limited-growth branches covered with tight leaves. Junellia tridens and Nassauvia glomerulosa are good examples of this type of plant. Taller woody shrubs indicate a change to shrub steppe communities within the ecoregion. These species of Anarthrophyllum, Berberis, Schinus, and Verbena can grow up to three meters tall. Valleys and lowlands with higher amounts of water available to vegetation host species of sedges (Eleocharis), rushes (Juncus), grasses (Agrostis, Hordeum, Polypogon) and in saline areas species of halphytic species (Distichlis, Nitrophila, Puccinellina).
In this ecoregion one finds two endemic species of the genus Prosopis, one species of Larrea and species of the genera Lycium and Schinus. Genera and species endemisms are very frequent in this ecoregion, among them Philipiella, Neobaclea, Xerodraba, Benthamiella, Pantacantha, Saccardophyton, Duseniella, Eriachaenium, and Llepidophylum. There are also numerous endemic species of mammals, birds, and amphibians. The National Council for Bird Preservation points to this region as one of the most important in terms of the presence of endemic bird species, and according to the council there are probably ten of such species.
The fauna is very varied in this region. Among birds, one notes the lesser rhea (Pterocnemia pennata), Patagonian tinamou (Tinamotis ingoufi), grey eagle-buzzard (Geranoaetus melanoleucus), peregrine falcon (Falco peregrinus), band-winged nightjar (Caprimulgus longirostris), sharp-billed canastero (Asthenes pyrrholeuca), Patagonian mockingbird (Mimus patagónicus), Patagonian yellow-finch (Sicalis lebruni) just to recite several species. Among mammals one observes the mara (Dolichotis patagonum), Southern viscacha (Lagidium viscacia), Wolffsohn's mountain viscacha (Lagidium wolffsohni), Patagonian weasel (Lyncodon patagonicus), Pategonian opossum (Lestodelphis halli), Humboldt's hog-nosed skunk (Conepatus humboldti), puma (Felis concolor), zorro gris chico (Dusicyon griseus), guanaco (Lama guanicoe), etc. Among the reptiles, one can note lagartijas (Liolaemus fitzingerii), King's tree iguana (L. kingi), Darwin's marked gecko (Homonata Darwinii) and Darwin's gecko (Diplolaemus Darwinii), among others.
Species in danger of becoming extinct or which are classified as Vulnerable include the Ruddy-headed goosd (Chloephaga rubidiceps), South Andean huemul (Hippocamelus bisulcus), Lesser rhea (Pterocnemia pennata), Hooded grebe (Podiceps gallardoi), Patagonian mara (Dolichotis patagonum), Wolffsohn's mountain viscacha (Lagidium wolffsohni), guanaco (Lama guanicoe), zorro gris chico (Dusicyon griseus) and Southern right whale (Eubalaena australis).
Despite the low density of the human population, this ecoregion has been seriously affected due to the fragility of the environment. This ecoregion has many natural reserves. These include the Laguna Blanca National Park (Ramsar), Nahuel Huapi National Park, Perito Moreno National Park, Los Glaciares National Park, Bosques Petrificados Natural Monument, El Payén Provincial Reserve, El Tromen Provincial Reserve, Domuyo Provincial Reserve, Somuncurá Provincial Reserve, Laguna Aleusco Provincial Reserve, Bosques Petrificados José Ormachea Provincial Reserve, Bahía San Julián Provincial Reserve, and Península de Valdés Provincial.
Types and severity of threats
The major problem is desertification due to overgrazing primarily by domesticated sheep, damaging the limited plant coverage and exposing the soil to erosion. In addition to the topsoil loss, native fauna are being displaced by enormous numbers of domesticated livestock, who are competing for the same biomass of grass stocks. Many species of fauna are also now in regression due to the tempting prices paid for the skins of chulengos (baby guanacos) and choique rhea feathers. There is also pressure on foxes and pumas from hunting and/or poisoning because they are persecuted for being considered by some ranchers as a potential threat to flocks.
Justification of ecoregion delineation
Within Argentina the delineations for the Patagonian Steppe were derived from Daniele and Natenzon, and linework follows their "Estepa Arbustiva Patagónica Arida (arid Patagonian woodland steppe)" region. Other resources consulted include Cabrera and Morello. The linework for the western portion and within Chile was modified according to UNESCO and expert opinion at ecoregional priority setting workshops: Valdivia, Chile, Bariloche, Argentina, and Concepción, Chile.
- For a terser summary of this entry, see the WWF WildWorld profile of the Patagonian Steppe
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- UNESCO. 1980. Vegetation map of South America. Map 1:5,000,000. Institut de la Carte Internationale de Tapis Vegetal. Toulouse, France.
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