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CENTRES OF PLANT DIVERSITY AND ENDEMISM
VIII. Southern Cone
The biogeographic Southern Cone includes most of extratropical South America from roughly south of 30°S latitude to Tierra del Fuego at 55°S. The Andes reach their highest altitude (Cerro Aconcagua, 6959 m) on the Argentina/Chile border, and the region also includes vast lowland areas (the pampas) and tablelands (Patagonia). In accord with the ample latitudinal and altitudinal ranges, the climate covers a whole spectrum of variants from generally dry and warm, dry and cold, and moist and cold. The annual precipitation varies from c. 100 mm (Patagonian steppe) to c. 5000 mm (Valdivian forest). The region has been treated phytogeographically with diverse criteria by different authors, but the subdivisions proposed by Cabrera and Willink (1973) are widely accepted.
Three phytogeographic units (provinces) are included in the north-eastern half of the Southern Cone: pampas, espinal and monte, all having strong floristic affinities with the chaco farther north, but clearly delimited on floristic-physiognomic criteria.
Mediterranean Chile but particularly Altoandina and Patagonia share numerous floristic and physiognomic characteristics; with the puna, the latter two regions constitute an independent Andino-Patagonian Dominion (Cabrera and Willink 1973). The Altoandina comprises the highest elevations of the southern Andes along the Chile/Argentina border, extending upwards from 4400 m in the north to 500 m in Tierra del Fuego. The vegetational limit is 5600 m in the north-east, at Famatina. The southernmost portion appears as islands interspersed among the subantarctic forest.
The temperate rain forest of Chile and Argentina comprises perhaps the most distinct floristic unit in South America, and the only one in which a considerably high number of elements alien to the neotropics can be found. It has been assigned conveniently to the Antarctic Region (Cabrera and Willink 1973; M.T.K. Arroyo 1994, pers. comm.).
Almost all of the main vegetation formations (except tropical forest) are represented in the Southern Cone: prairie, grass-steppe, shrub-steppe, scrub, desert, tundra, sclerophyllous forest, deciduous temperate forest and evergreen forest. A number of physiognomically well-characterized phytogeographic units are generally recognized.
The "pampas" cover c. 900,000 kmē between latitudes 28°-39°S and longitudes 50°-65°W in the southernmost part of Brazil, the whole of Uruguay and the central-eastern part of Argentina. These vast plains are only interrupted by a few low mountain ranges; the highest mountains reach 1300 m, in Argentina's Sierra de la Ventana north of Bahía Blanca. The climate is mild with precipitation of 600-1200 mm more or less evenly distributed through the year. The soils are very rich. The dominant vegetation types are grassy prairie and grass-steppe in which numerous species of the Gramineae tribe Stipeae (Stipa and Piptochaetium) are particularly conspicuous. There is an almost absolute lack of native trees, except along main watercourses.
The "espinal" is a winter-deciduous dry-forest band that embraces the pampas on the west. Both this phytogeographic province and the pampas province are clearly defined on physiognomic terms due to the presence in the espinal of occasional trees, mainly species of Prosopis. There are palm communities dominated by Syagrus yatay. This region is also clearly separate from the neighbouring chaco due to the espinal's absence of large Schinopsis trees.
The "monte" occupies a great portion (c. 600,000 kmē) of central-western Argentina between 28°-44°S, from sea-level in the south-east to 3400 m in the north-west (Hunziker 1952). The climate presents wide daily and yearly temperature fluctuations, with the precipitation below 200 mm per year - conditions of semi-aridity and aridity. The dominant vegetation is shrub-steppe in which several species of Zygophyllaceae (Larrea, Bulnesia, Plectrocarpa) are conspicuous. Succulents are abundant, mainly Cactaceae which become dominant in the north-west on the eastern slopes of the mountains. That area, the "prepuna", has sometimes been recognized as an independent phytogeographic unit (Cabrera 1976).
Mediterranean Chile extends between 29°-38°S from the lower western Andean slopes to the Pacific Ocean. The climate is dry in summer and cool and damp in winter. The Coastal Cordillera (with highest elevation c. 2200 m) parallels the Andes through the entire region. Various vegetation types are present: shrubby xerophytic communities, evergreen matorral, palm forest of Jubaea chilensis, bamboo-dominated (Chusquea) thickets, sclerophyllous forest, hygrophilous forest, relict deciduous Nothofagus forest at the northern limit of its distribution, and alpine-like steppe.
The Altoandina province has been divided into three districts: Quichua, Cuyano and Austral (Cabrera 1976). The climate is cold and dry (with more humidity southward), averaging annually e.g. c. 3°C in Mina Aguilar (Jujuy) and c. -2°C in Cristo Redentor (Mendoza); the scarce precipitation may come as snow, and winds are strong. The most important vegetation types are grass-steppe, chamaephyte-steppe (having low woody and herbaceous species with buds on aerial branches close to the ground), and shrub-steppe; there are also bogs, and semi-deserts with lichens.
Grass-steppe is composed of isolated plants, sometimes also including chamaephytes and hemi-cryptophytes in rosettes. Among the important elements are Festuca, Poa, Stipa and Calamagrostis (Deyeuxia) with dwarf dicots in mats (e.g. Adesmia, Mulinum, Senecio, Azorella, Junellia, Verbena) (Hunziker 1952; Ward and Dimitri 1966); there are also cacti in cushions (Opuntia subgenus Tephrocactus). Lichen semi-desert occurs on the most humid slopes and can reach 5900 m (Nevado de Chaņi). Chamaephyte-steppe generally occupies high elevations with loose soil; dwarf plants are common, e.g. Senecio spp., and cushions of Oxalis compacta, Valeriana spp., Pycnophyllum molle and Werneria spp. In wet locales there are bogs of Cyperaceae, Juncaceae and Gramineae.
The Patagonian steppe is a vast semi-desert region from below 2000 m on the eastern slopes of the Andes to the Atlantic Ocean and northward to the monte. The vegetation is primarily xeric shrubland, large scrub areas of cushion-like and dwarf shrubs, and grassy steppe.
Temperate rain forest occupies the southernmost portion of the continent and Tierra del Fuego, along a narrow fringe east of the cordillera in Argentina and south of 40°S latitude and in Chile between the Andes and the Pacific Ocean.
The pampas, espinal and monte can be treated jointly with the chaco, which shares almost all the genera, as a single floristic unit. These four regions have been considered to constitute the Chaco Dominion (Cabrera and Willink 1973; Cabrera 1976). They are also related, although to a lesser degree, to the Patagonian and the Alto-Andean regions. No data are available on the number of species in this floristic region as a whole.
In the Argentinian portion of the pampas, the number of species of vascular plants probably reaches 1800 (Cabrera 1963-1970), among which there are very few ferns and fern allies, and only one genus of gymnosperms (Ephedra). The families with the largest number of species are Gramineae and Compositae, with other well-represented families being Amaranthaceae, Caryophyllaceae, Chenopodiaceae, Cyperaceae, Cruciferae, Leguminosae, Malvaceae, Solanaceae and Umbelliferae. Recent floristic surveys in the southern portion of the pampas have found c. 500-600 species in areas of 5000-10,000 kmē (Villamil, unpublished). Endemism is low (5-15%).
In the monte Bulnesia, Larrea and Plectocarpa of the family Zygophyllaceae are dominant, accompanied by Monttea aphylla, Bougainvillea spinosa, Cercidium australe, etc. Xerophilous species of Bromeliaceae (Deuterocohnia, Abromeitiella, Tillandsia, Puya) and Cactaceae are also well represented. The number of endemic species is c. 30, some of which dominate certain areas. In spite of its great floristic uniformity, this region has phytogeographical interest due to its affinities with North American semi-deserts and as well the Chilean Mediterranean region (Morello 1958).
Mediterranean Chile includes c. 1800-2400 species, and its endemism may be one of the highest in South America.
Although there are no comprehensive data about the whole Alto-Andean region, species richness and diversity are surely high. Among the best represented families are Gramineae [with many species of Calamagrostis (Deyeuxia), Festuca, Poa, Stipa, etc.], Leguminosae (Astragalus, Adesmia, etc.) and Compositae (Senecio, Chuquiraga, Mutisia, etc.). Most of the genera are of neotropical origin, but there is a good representation of holarctic elements, and in its southern sector the Altoandina has an increasing proportion of antarctic elements (Cabrera 1976). There are no endemic families, and various endemic genera - Barneoudia, Pycnophyllum, Hexaptera, Nototriche and Werneria.
The temperate rain forest includes numerous floristic elements of both the antarctic and the Andean floras. Several woody gymnosperm species constitute conspicuous elements of the local vegetation, among them the second longest-lived tree in the world (Fitz-roya cupressoides), which attains over 3600 years (Lara and Villalba 1993).
Extra-tropical South America has not been a centre of radiation of cultivated plants of comparable importance to the Peruvian area. Only recently are breeding programmes being carried on. Numerous species have been used traditionally as medicinal plants and others have attained relevance as ornamentals. The floristic richness of grasslands assures a most important genetic reservoir especially for forage species.
The pods of several species of Prosopis ("algarrobo") are important forage resources, and also are used as human food and to prepare fermented beverages, although their use is limited to local communities. "Madi" (Madia sativa) is an oilseed species from the southern Andean region. "Mango" (Bromus mango) is a cereal that had been considered extinct, but recently was rediscovered. Fragaria chiloensis is a wild ancestor of cultivated strawberries. The seeds of the endemic Araucaria araucana have been staple food for indigenous populations until present times. The endemic Chilean palm tree (Jubaea chilensis), with edible fruits, was threatened with extinction due to over-exploitation to obtain the sugar from its sap. Fruits of a variety of native species are edible or locally used to prepare confections, such as several species of Cereus and related genera, Berberis ("calafates"), Zizyphus mistol ("mistol") and Geoffroea decorticans ("chaņar"). Other species are highly reputed for honey production, such as Eucryphia cordifolia ("ulmo"), which is endemic to the temperate rain forest. Numerous species are used for furniture-making (Prosopis), construction (Araucaria, Nothofagus, Fitz-roya), fuelwood or charcoal and as natural dyes. Textile fibres are obtained from various bromeliads (Puya, Deuterocohnia). Numerous species from the Alto-Andean region are used as forage, fuel or medicinals (Ruthsatz 1974).
Although awareness about the importance of conservation from ethical as well as social and economic perspectives is progressing, the negative impact of human activities is still considerable upon most of the ecosystems in the Southern Cone. Deforestation by farming and overgrazing, often followed by soil erosion and desertification, are the most important factors of ecosystem degradation and destruction of the original vegetation (IUCN 1993). Erosion by wind and water are the main problems in large portions of the pampas, espinal and monte regions. The Patagonian steppes are profoundly affected by overgrazing of sheep, whereas goats have a more noticeable impact on the mountainous areas and in the monte, where the best forage species are being replaced by less valuable plants. In the forested areas the most valuable timber species are selectively cut and replaced by farming, or planting of more rapidly growing exotic trees such as Eucalyptus spp. and Pinus spp.
In some regions such as the pampas and Mediterranean Chile, the impact of human activity has drastically transformed the original landscape, of which there remains only relicts. The once abundant megafauna (felids, canids, camelids, cervids) has virtually disappeared from these regions. In the espinal large areas have been or are being deforested for farming and fuelwood.
Argentina was the first country in Latin America to create a National Park (Nahuel Huapi, in 1903), and has a centralized administration. There are a total of 190 protected areas which cover 4.35% of the national territory (Barzetti 1993). Many of the National Parks have been created for geopolitical rather than ecological or biogeographical reasons, and consequently some natural regions are proportionately over represented, such as the subantarctic forest, whereas others, such as the pampas, are not represented at all in the national system of protected areas. A series of large protected areas and Biosphere Reserves has been created recently; effective measures for their protection still have to be implemented.
In Uruguay 0.17% of the national territory is in eight protected areas under IMPARQUES administration (Barzetti 1993). In developing a country-wide national system of protected areas, priority in investigation and management plans has been given to 16 of 36 potentially important or protected areas. Efforts are concentrated in the south-eastern region (Atlantic plains), which is richest in biodiversity. The proposed national system would bring protection to 0.70% of the country. There is no integrated and definitive legislation for the management of protected areas (WCMC 1992).
In Chile the main conservational concern is related to over-exploitation of the native forests for timber, woodchips and fuel. The national system of protected areas is centralized, and 18.18% of the national territory is under some kind of conservation management, with 79 protected areas (Barzetti 1993). However the development of protective policies is too recent to have prevented the degradation inflicted upon a substantial portion of the Chilean forests.
In order to effectively accomplish conservation objectives, the systems of protected areas throughout the Southern Cone must be increased both in quality and quantity. Care should be taken to assign protective status to representative samples of all the ecosystems, including those with no obvious touristic or scenic appeal.
Centres of Plant Diversity and Endemism
SA44. Mediterranean region and La Campana National Park
SA45. Temperate rain forest of Chile
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