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The phytogeographic region of Patagonia (the south-eastern portion of the geopolitical region of Patagonia) extends over 500,000 km² in extreme south-eastern South America (Ragonese 1967; Vila and Bertonatti 1993). A narrow strip in the north between the Andean Cordillera and the monte region widens to the south into a vast tableland from the Andes to the Atlantic Ocean (Map 80) (Cabrera and Willink 1973). The border to the west is with the temperate rain forest (Dimitri 1972) and the Altoandina region (Cabrera 1976), and to the north and east with the monte region (Ruiz Leal 1972). Most of Patagonia lies within the Argentine Republic, with a small portion penetrating Chilean territory in the far south on both sides of the Strait of Magellan.
The region is formed by a Precambrian nucleus - the Patagonian massif, with deposits of eruptive rock (basalt) and terrestrial and marine sediments from the Early Permian to Tertiary. The terrain is a sequence of mesa plains stepping down eastward to the sea, from varied Andean piedmont elevations (2000 m in the north to 700 m in the south). In Chubut Province east of the Andes and longitude 71°W, the precordillera Patagónica (Sierra de Tecka and extensions) rises to 1300-1500 m or more (e.g. Cerro Putrachoique, 1700 m); farther east between longitudes 70°-69°W and the Chubut and Senguerr rivers occur the Patagonian Central Ranges (Sierras Centrales Patagónicas), with elevations to 1690 m (Cerro Boquete) and 1651 m (Cerro Negro) (Volkheimer in Soriano 1983).
The predominant soils are sandy and stony, and poor in organic matter. Along a narrow strip near the Patagonian cordillera down to the Atlantic Coast in the far south are soils richer in organic matter. In restricted moist areas such as bogs, the soils are acidic or neutral. Rivers descend from the cordillera and traverse the region from west to east with scarce flow (being unnavigable); they have little influence on the vegetation.
The climate is characterized by severe dryness, with average annual precipitation below 200 mm, and by low temperatures (annual mean 9°-5°C) and constant drying high winds from the west. The precipitation can vary greatly from year to year (e.g. 157-519 mm at Pilcaniyeu east of San Carlos de Bariloche). Winter lasts 4-5 months (about June-September), with the daily minimum of the coldest month averaging 1°-3°C below freezing, and with no month assuredly frost-free (Walter and Box in Soriano 1983).
The vegetation is xerophytic, with ample predominance of adaptations to the low temperatures and the desiccating effect of the strong winds constantly blowing. Plant cover generally varies from 20-40%, with extremes near 0% in desert areas ("huayquerías" or badlands) and 100% in wet meadows ("vegas" and "mallines"). The dominant types of vegetation are semi-desert (45%), shrub-steppe (30%) and grass-steppe (20%) (Movia, Soriano and León 1987; Soriano 1982, 1983). Up to 28 different communities have been described, distributed among five phytogeographic districts (Soriano 1956; Cabrera 1976). Numerous physiographic units have been recognized (Ambrosetti and Méndez 1983; Beeskow, del Valle and Rostagno 1987; Movia, Soriano and León 1987; Speck et al. 1982).
In deserts the plant cover is c. 5-15%, with halophytes of Chenopodiaceae predominant (Atriplex, Nitrophila, Suaeda, Chenopodium), sometimes accompanied by Halophyton ameghinoi (Halophytaceae).
Semi-desert, with c. 40% of the soil surface covered, is the most widely occurring vegetation type (Soriano, Sala and León 1980; Soriano 1983). Dwarf and cushion shrubs are dominant (e.g. Acantholippia, Benthamiella, Brachyclados, Chuquiraga, Nassauvia, Nardophyllum, Verbena) and tuft grasses common (Stipa, Poa) (Paruelo et al. 1992).
Shrub-steppe is characterized by the presence of taller woody shrubs, which in restricted areas can reach 3 m (Soriano 1982). Among the most conspicuous elements are species of Adesmia, Anarthrophyllum, Berberis, Chuquiraga, Lycium, Mulinum, Schinus and Verbena. In the east around San Jorge Gulf grow thick shrub communities (Trevoa, Colliguaja), covering up to 60% or more of the soil surface.
In the west bordering the temperate rain forest, where soils are richer, extends grass-steppe dominated by Festuca pallescens, which accounts for up to 90% of the vegetation, often accompanied by other grass species (e.g. Agrostis, Bromus, Deschampsia, Poa, Trisetum). The grass-steppe may reach 80% cover in non-degraded areas.
Moist meadows occupy valleys and lowlands scattered through the region where water availability is higher. Sedges (Eleocharis, Scirpus) and rushes (Juncus) are abundant, as are numerous species of grasses of various genera (Agrostis, Deschampsia, Hordeum, Polypogon), which grow intermingled with diverse dicotyledons (Acaena, Caltha, Geranium, Plantago, Ranunculus). In saline lowlands grow turfs of predominantly halophytic species in genera such as Distichlis, Frankenia, Nitrophila, Puccinellia and Suaeda.
In some areas intrusions of species characteristic of the monte region are abundant - Acantholippia seriphioides, Prosopidastrum globosum, Schinus polygamus and Stipa tenuis (Ruiz Leal 1972).
In modified areas numerous adventitious species have established, especially near highways and populated areas. The presence of weeds introduced from the Mediterranean region is not uncommon, and at times very conspicuous (Bromus, Erodium, Galium, Stellaria, Vulpia, various crucifers).
In the northern part of Tierra del Fuego two main vegetation types can be recognized: the grass-steppe, dominated by Festuca gracillima accompanied by other grasses (e.g. Agropyron, Hordeum, Festuca, Poa); and Fuegian meadows. The grass species dominant in the steppe are sometimes replaced by other plants (Chiliotrichum diffusum, Empetrum rubrum) that give a distinct physiognomy to the community. The Fuegian meadows occupy low flooded areas; their most important components are grasses (e.g. Alopecurus, Deschampsia, Hordeum, Phleum), accompanied by diverse dicotyledons (Moore 1983).
The flora of the Patagonian region shows clear affinities with the Andean flora (Cabrera 1976; Cabrera and Willink 1973), and is the product of a unique set of extreme climatic conditions of low temperature and aridity. It has an estimated 1200 species of vascular plants (Correa 1969-1988-), almost exclusively angiosperms, with c. 30% endemics. Ephedra is the only genus of gymnosperms and very important in some areas. Compositae is the best-represented family (200 spp., 33% endemic), followed by Gramineae (190 spp., 13% endemic) and Leguminosae (120 spp., 60% endemic). Other well-represented families are Cruciferae (80 spp., 30% endemic), Cyperaceae (40 spp., 7% endemic) and Umbelliferae (40 spp., 33% endemic). There is one quasi-endemic family in the region, Halophytaceae; and there are six endemic genera, usually represented by few species: Philippiella (Caryophyllaceae), Neobaclea (Malvaceae), Xerodraba (Cruciferae), Benthamiella (Solanaceae), and Eriachaenium and Duseniella (Compositae) (Soriano 1956).
The absence of deep differences in relief poorly defines the northern boundary of the region, which has a vague delimitation with the Alto-Andean region, and with the "monte" scrubland following approximately the 13°C annual isotherm (Roig 1972; Ruiz Leal 1972). The western limit and the southern limit, with the temperate rain forest (CPD Site SA45), are well defined with clear physiognomic and floristic characteristics (Dimitri 1972).
The knowledge of useful Patagonian plants is very fragmentary. According to information collected by travellers, numerous native species are (or have been) used for food or medicinals. Recent efforts to collect data are far from sufficient to cover the folkloric cultural wealth, which is being lost rapidly. Some species (Festuca pallescens, F. gracillima) are important forage in naturally vegetated areas that are grazed, whereas others are toxic to cattle (Astragalus spp., Festuca argentina, Poa huecu). Recently programmes have been implemented to collect germplasm of native species (Oliva, Montes and Mascó 1993).
Social and environmental values
The Tehuelche, who originally occupied the region, have dwindled to c. 50 persons. The Araucano (from Chile) penetrated the region especially in the 19th century (having begun to immigrate in the 16th century); the 50,000 who live in Argentina are being acculturated and losing their language. Many species were grown, such as maize, "quinoa" (Chenopodium), Amaranthus, "mango" (Bromus mango), potatoes, "oca" (Oxalis), "madi" (Madia sativa) and "frutilla" or "fresa" (Frageria chiloensis) (Parodi 1966). Except for maize, their local cultivation has ceased.
The predominant economic activity in Patagonia since the end of the 19th century has been sheep-farming (INTA 1993; Soriano 1983). The whole region is dependent in its development on the fluctuations in the price of wool. Extensive exploitation is based on heavy grazing of the natural vegetation, which takes place by c. 10,000 ranches of up to several thousand hectares with flock sizes that may reach 10,000 sheep or more (20-60 per km²).
The regional palaeoflora is very rich; some fossils from the Carboniferous have been found. However the most striking specimens, which draw some tourists, are the huge petrified trees of Araucaria mirabilis (100 m tall and 3.5 m dbh) in the conifer forests of the Jurassic (Menéndez 1972) - before the rise of the Andes.
The density of people is low (1 inhabitant per km²), but over-grazing from the sheep is very intense, which (made worse by wood-cutting) has led to serious desertification that threatens all of the region (INTA 1993; Soriano and Movia 1986). For example in 1972, 26% of Chubut Province and 38% of Santa Cruz Province showed eroded areas (Soriano 1983). Within National Parks, the principal problem is persistence of populated areas, although their overall impact is not great.
Most important are considerations related to control of the overgrazing (León and Aguiar 1985; Soriano and Movia 1986; Soriano, Sala and León 1980). There is now an official plan to reverse the process of desertification in Patagonia (INTA 1993).
Few protected areas strictly correspond to this phytogeographic unit, but many cordillera National Parks include a representative part of adjacent Patagonian steppe (Erize 1993; WCMC 1992). Three of the protected areas bordering Chile include important sectors of Patagonia in their eastern portions: (1) down to 720 m, Nahuel Huapi National Park (4281 km²) and National Nature Reserve (3300 km²) - the first National Park in South America, begun in 1903; (2.1) down to 400 m, Los Alerces NP (1875 km²) and NNR (755 km²), and (2.2) particularly Perito Francisco P. Moreno NP (851 km²) and NNR (299 km²) down to 900 m - both parks/reserves were established in 1937.
Entirely within this phytogeographic unit in north-western Patagonia (39°30'S, 70°20'W) in the Province Neuquén, is Laguna Blanca NP (82 km²) and adjoining NNR (30 km²), which was created in 1940 (Roquero 1968; Correa-Luna 1977). Bosques Petrificados Natural National Monument (100 km²), created in 1954, is in south-eastern Patagonia (47°40'S, 68°00'W) in the Province Santa Cruz. It protects impressive remnants of the Jurassic petrified forest. There is a proposal to create a park in the east in the Valdés Peninsula Multiple Use Reserve (3600 km²).
Map 80. Patagonia, Argentina and Chile(CPD Site SA46
Ambrosetti, J.A. and Méndez, E. (1983). Los tipos biológicos de Raunkier en las comunidades vegetales de Río Turbio, Provincia de Santa Cruz, Argentina. Deserta 7: 12-39.
Beeskow, A.M., del Valle, H.F. and Rostagno, C.M. (1987). Los sistemas fisiográficos de la región árida y semiárida de la Provincia de Chubut. Centro Nacional Patagónico, Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET). Puerto Madryn, Argentina. 173 pp.
Cabrera, A.L. (1976). Regiones fitogeográficas argentinas. In Parodi, L.R. (ed.), Enciclopedia argentina de agricultura y jardinería, 2nd edition. Vol. 2(1). Editorial Acmé, Buenos Aires. Pp. 1-85.
Cabrera, A.L. and Willink, A. (1973). Biogeografía de América Latina. Organización de los Estados Americanos (OEA), Serie de Biología, Monogr. No. 13, Washington, D.C. 117 pp.
Correa, M.N. (1969-1988-). Flora patagónica. Instituto Nacional de Tecnología Agropecuaria (INTA), Col. Científ. 8. Buenos Aires.
Correa-Luna, H. (1977). La conservación de la naturaleza: parques nacionales argentinos. Servicio Nacional de Parques Nacionales, Buenos Aires. 169 pp.
Dimitri, M.J.L. (ed.) (1972). La región de los bosques andino-patagónicos: sinópsis general. INTA, Col. Científ. 10. Buenos Aires. 381 pp.
Erize, F. (1993). Los parques nacionales de la Argentina y otras de sus áreas naturales, 2nd edition. El Ateneo, Buenos Aires. 238 pp.
INTA (1993). Proyecto de prevención y control de la desertificación en la Patagonia/Project for prevention and control of desertification in Patagonia. INTA, Buenos Aires. 19 pp.
León, R.J.C. and Aguiar, M.R. (1985). El deterioro por uso pasturil en estepas herbáceas patagónicas. Phytocoenology 13: 181-196.
Menéndez, C.A. (1972). Paleofloras de la Patagonia. In Dimitri, M.J.L. (ed.), La región de los bosques andino-patagónicos. INTA, Col. Científ. 10: 129-165.
Moore, D.M. (1983). Flora of Tierra del Fuego. A. Nelson, Oswestry, Shropshire, U.K. and Missouri Botanical Garden, St. Louis, Missouri, U.S.A. 396 pp.
Movia, C.P., Soriano, A. and León, R.J.C. (1987). La vegetación de la cuenca del Río Santa Cruz (Provincia de Santa Cruz, Argentina). Darwiniana 28: 9-78.
Oliva, G.E., Montes, L. and Mascó, E.M. (1993). Collecting native forage germplasm in Patagonia. FAO/IBPGR, Plant Genetic Resources Newsletter 93: 34-37.
Parodi, L.R. (1966). La agricultura aborigen argentina. Editorial Universidad de Buenos Aires (EUDEBA), Buenos Aires. 48 pp.
Paruelo, J.M., Aguiar, M.R., Golluscio, R.A. and León, R.J.C. (1992). La Patagonia extrandina: análisis de la estructura y funcionamiento de la vegetación a distintos niveles. Ecología Austral 2: 123-136.
Ragonese, A.R. (1967). Vegetación y ganadería en la República Argentina. INTA, Col. Científ. 5. Buenos Aires. 218 pp.
Roig, F.A. (1972). Bosquejo fisionómico de la vegetación de la Provincia de Mendoza. Bol. Soc. Argent. Bot. 13 (Supl.): 49-80.
Roquero, M.J. (1968). La vegetación del Parque Nacional Laguna Blanca (estudio fitosociológico preliminar). An. Parques Nac. 11: 209-223.
Ruiz Leal, A. (1972). Los confines boreal y austral de las provincias patagónica y central respectivamente. Bol. Soc. Argent. Bot. 13 (Supl.): 89-118.
Soriano, A. (1956). Los distritos florísticos de la provincia patagónica. Rev. Invest. Agríc. 10: 323-347.
Soriano, A. (1982). Patagonia. In Vervoorst, F. (ed.), Conservación de la vegetación natural en la República Argentina. Soc. Argent. Bot. - Fundación Miguel Lillo, Serie Conserv. Naturaleza No. 2. Tucumán.
Soriano, A. (1983). Deserts and semi-deserts of Patagonia. In West, N.E. (ed.), Temperate deserts and semi- deserts. Ecosystems of the World Vol. 5. Elsevier, Amsterdam. Pp. 423-460.
Soriano, A. and Movia, C.P. (1986). Erosión y desertización en la Patagonia. Interciencia 11(2): 77-83.
Soriano, A., Sala, O.E. and León, R.J.C. (1980). Vegetación actual y vegetación potencial en el pastizal de coirón amargo (Stipa spp.) del sudoeste del Chubut. Bol. Soc. Argent. Bot. 19: 309-314.
Speck, N.H., Sourrouille, E.A., Wijnhoud, S., Munist, E., Monteith, N.H., Volkheimer, W. and Menéndez, J.A. (1982). Sistemas fisiográficos de la zona Ingeniero Jacobacci-Maquinchao (Provincia de Río Negro). INTA, Col. Científ. 19. Buenos Aires. 215 pp.
Vila, A.R. and Bertonatti, C. (1993). Situación ambiental de la Argentina. Bol. Técn., Fundación Vida Silvestre Argentina, Buenos Aires. 74 pp.
WCMC (1992). Protected areas of the world. A review of national systems. Vol. 4. Nearctic and Neotropical. IUCN, Gland, Switzerland and Cambridge, U.K. 459 pp.
This Data Sheet was written by Dr Carlos B. Villamil (Universidad Nacional del Sur,
Departamento de Biología, Perú 670, 8000 Bahía Blanca, Argentina).
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