South America

Topics: Andes, South America, Tropical and subtropical moist broadleaf forests Pages: 18 (6939 words) Published: March 20, 2013
The continent of South America has about one-eighth of the Earth's land surface, situated between latitudes 12°N-55°S and longitudes 80°-35°W; no other continent has a greater latitudinal span. Eighty percent of its land mass is within the tropical zone, yet it extends into the subantarctic. The extensive zones of temperate and cold climates in the vicinity of the Equator, in the Andes, are unique. The land area of about 17,519,900-17,529,250 km² is under the jurisdiction of 13 countries (Table 49); French Guiana is governed as an overseas department of France. The region's 1995 population of c. 320 million people is estimated to reach 452 million people in 2025. Three of the world's 21 megacities are in South America: São Paulo, Buenos Aires and Rio de Janeiro (WRI, UNEP and UNDP 1994). Geological setting

Although the neotropics may be conveniently considered as a single phytogeographic unit, the region is geologically complex. The neotropics include not only the South American continental plate but the southern portion of the North American plate, as well as the independent Caribbean plate (Clapperton 1993). The complicated geological history of the region, for example as these plates intermittently separated and collided through the Cretaceous and the Tertiary, provides the milieu within which plant evolution has been superimposed. South America has been an island continent during most of the period of angiosperm evolution, whereas Central America constitutes one of the two tropical parts of the Laurasian "world continent". Both South America and North America have been moving westward, roughly in tandem, since the breakup of Pangaea in the Mesozoic. In contrast, the Antillean plate with its flotsam of Antillean islands formed only during the Cenozoic and has moved in a retrograde eastern direction, at least with respect to its larger neighbours. Whereas South America and North America have been widely separated through most of their geological histories, there has been generally increasing contact between them through most of the Cenozoic, culminating in their coalescence with formation of the Isthmus of Panama c. 3.1 million years ago (Keigwin 1978). The date of this epochal event in neotropical geological history has been gradually estimated to be younger, with estimates of 5.7 million years ago giving way to as recently as 1.8 million years ago (Keller, Zenker and Stone 1989). In addition to their Pleistocene connection via the Isthmus of Panama, South America and North America apparently were more or less directly interconnected via the protoAntilles for a short time near the end of the Cretaceous, prior to formation of the Caribbean plate (Buskirk 1992). The outstanding geological feature of South America is the Andes, the longest mountain range in the world, which extends in a nearly straight line of over 7000 km from the north to the southern tip of the continent. The Andes have the highest mountain in the Western Hemisphere, the highest mountain in the world's tropics, and as measured from the centre of the Earth (rather than metres above sea-level), the highest mountain in the world. The most important break in the north-south sweep of the "cordillera" is the Huancabamba Depression in northern Peru, where the eastern chain of the cordillera is entirely ruptured (by the Marañón River) and even the western chain dips to 2145 m (at the Abra de Porculla). The existence of this massive mountain range has had profound effects on plant and animal evolution in South America, and consequently has profound effects on essential conservation priorities. In essence, the Andes represent a classical plate tectonic upthrust of continental rock, as the leading edge of the westward-moving South American plate collides with the oceanic Pacific plates. The Southern Andes are the oldest, with significant uplift already present in early Cenozoic times, prior to the Oligocene. Most of the uplift of the Central Andes...
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