Ecosystem of South America

The subregions of South America, the fourth-largest continent in the world, contain the most extensive diversity of flora and fauna on the planet. South America is known for its massive mountain ranges and very long rivers, especially the Amazon, and for its rain forests, which are threatened by pressures toward clearance of the land for agriculture.

The major geographical and geological features of the South American continent determine in large measure the differences in regional environmental conditions. Geologically the most spectacular feature of the continent is the mountain range of the Andes, which stretches some 7,000 kilometers (4,350 miles) from Venezuela in the north to Argentina in the south. The mountains pass through Colombia, Ecuador, Peru, and Chile and reach average heights of 4,000 meters (about 13,000 feet). The highest peak (7,000 meters, or nearly 23,000 feet) is Aconcagua in western Argentina near the Chilean border. The Andes, which form two main ranges in South America (the Western and Eastern Cordilleras), are essentially the continuation of the tectonic uplifting that formed the North American Rocky Mountains, with the accompanying phenomenon of major volcanic activity in Mexico and Central America.

After the Andes, much of the continental interior is the Altiplano, a high plateau (more than 3,500 meters, or almost 11,500 feet) running from the Peru-Bolivia border into northern Argentina. The Altiplano is the highest permanently inhabited subregion of any of the world’s five continents. Perhaps its most famous geographical site is Lake Titicaca, South America’s second-largest lake (8,300 square kilometers, or 3,200 square miles, compared to Venezuela’s Lake Maracaibo, which covers about 12,950 square kilometers, or 5,000 square miles). Titicaca’s elevation of 3,800 meters (12,500 feet) makes it the highest navigable lake in the world. The environmental harshness of the Altiplano is rivaled, if not surpassed, by the striking phenomenon of the Atacama Desert, which runs some 966 kilometers (600 miles) along the northern portion of Chile’s Pacific Ocean coast. Its Peruvian counterpart, the Sechura Desert, is nearly as dry. A few desert oases are found in the Sechura, the most famous being the small village of Huacachina in southwestern Peru, with its unexpected clear-water lagoon. Rainfall levels in this region are very low (an average of 1 millimeter, or 0.04 inch, in the Antofagasta midcoastal region). This lack of appreciable rainfall is largely the result of an atmospheric inversion effect caused by the cold Humboldt Current that follows Chile’s coast.

and Vegetation

Although the Altiplano forms a transitional between the Andes and the Amazon basin, the vast majority of the plant and animal species of South America are found in the latter two zones. Plant species in the Andes generally correspond to levels of altitude. A broad layered zone referred to as the montane forest is found between about 600 meters (1,970 feet) and 3,500 meters (11,500 feet). Here the dominant (lower montane) tree species share ecological space with a wide variety of liverworts, mosses, ferns, and some flowering plants, including orchids. Many of these are epiphytes (plants that grow without roots in the soil). Other species found in the lower montane zone are Lauraceae (the laurel family), Melastomataceae (a family of perennial flowering herbs and shrubs), Rubiaceae (the family including madder, bedstraw, and coffee varieties), and some Moraceae (the fig family).

Higher montane vegetation depends more on misty conditions than on direct rain. Typical plants up to elevations of 4,000 meters are ferns and lichens, with fewer species of, and more widely scattered, trees. Specialists have identified several other strata of Andean vegetation at elevations above the tree line, often called the tropical alpine zone. One important stratum, typical of the central Andes from northern Peru extending into northern Argentina, is the puna (which is itself divided into substrata ranging from 3,000 to 5,000 meters, or 9,800 to 16,400 feet, called humid, dry, and desert puna). Here the main forms of vegetation are grasses, with scattered flowering plants.

The contrast between the high mountains and Altiplano and the tropical areas of South America is almost total. The massive network of waterways that eventually form the main channel (the Solimões) of the Amazon River flow from two continental shields: the Guiana Shield to the north and the Brazilian (or Amazonian) Shield to the south. Because of major fluctuations in the volume of water carried by the Amazon (the result of seasonal rainfall in the Amazon basin—which averages upward of 230 centimeters, or about 90 inches, per year), the Solimões expands and recedes in known as the varzea. The average width of this floodplain is about 24 kilometers (15 miles). The total area of the Amazon basin (the largest in the world) is almost 7.8 million square kilometers (3 million square miles), but vegetation within the basin, although considered tropical, varies considerably.

Despite a popular association of tropical rain-forest environments with dense jungle, problems linked with poor soil quality and irregular drainage patterns in the Amazon basin have produced different patterns of vegetation. Where there are very high annual rainfall levels and high average annual temperatures (around 26.7 degrees Celsius, or 80 degrees Fahrenheit), Amazon basin plant species are categorized as lowland tropical vegetation. In some areas, mostly in the varzea but also in poorly drained areas of Amazonia, vegetation has to survive long periods underwater. As one progresses toward and onto terra firma, actual bands of different plant species emerge, beginning with what are called tropical dry forests, which eventually blend into grassy savanna zones. Brazil’s cerrado (Portuguese for “closed”—that is, interior), for example, covers about one-fifth of the country, with a characteristic vegetation of grass and short twisted trees. In Brazil, Colombia, and Venezuela alone, savannas occupy some 2.6 million square kilometers (about 1 million square miles), an area about one-quarter the size of Canada.

Beyond the world-renowned Amazon, a second major tropical forest zone is noteworthy, that associated with the Orinoco River, which is 2,100 kilometers (1,300 miles) long and receives waters from eleven tributaries in mountainous Colombia and Venezuela. Among these are the Apure, the Arauca and Guaviare (from Colombia), and the Caroní (from sources in the Guiana highlands) The Orinoco is the second-largest river in South America. Its enormous delta (covering almost 23,300 square kilometers, or 9,000 square miles) on the Atlantic coast of Venezuela is a maze of different waterways surrounded by marshy tropical lowlands. Given the variety of major tributaries coming from many different directions into the main channel of the Orinoco, the total waterway system served, until recent times, as the principal route of access to otherwise inaccessible inland areas, and even as far as the llanos (plains) of Colombia.

Two major environmental subregions of South America are Patagonia and the Pampas. The latter, flat and grassy plains mainly in Argentina and Uruguay, are well known as a natural for cattle raising. Patagonia, in contrast, is the spectacular mountainous region of southern Chile that ends at Cape Horn and the Tierra del Fuego (land of fire) island archipelago shared with southern Argentina. Patagonia’s inland terrain is marked by very high craggy and glacier-clad mountains. The southern mountain zone (the Magellanes) contains Torres del Paine National Park, where peaks rise to more than 2,700 meters (9,000 feet). Another major mountainous preserve, Laguna San Rafael National Park, is located in the northern Patagonian region of Aisén.

Environmental Concerns

The widespread building of dams to produce electricity has seriously affected the Amazon and other South American river environments. The natural habitats of flora and fauna have been altered, and isolated indigenous populations have been displaced, their traditional lifestyles threatened.

Moreover, the economies of the more developed areas in South America depend on intensive exploitation of either resources or agriculture. In the latter case, overdependence on single crops (monoculture) has had negative effects. The continual expansion of the land area under cultivation—typical of large plantations, especially coffee plantations and corn/ethanol plantations in Brazil, for example—has contributed to deforestation, and repeated planting of the same crops has depleted soil fertility.

A major environmental issue facing tropical South America, one that is global in its implications, involves the repercussions that start with deforestation. As the surfaces of tropical forests recede, corresponding reductions occur in the level of oxygen (given off by all plants in the carbon dioxide-oxygen exchange process) released to the atmosphere. Of more immediate local environmental importance is the destruction of the natural ecosystem that sustains regionally typical vegetation. Concurrently, local animals, including rare species, are menaced with extinction, either because of the destruction of their natural or because increased “commercial” access to their habitat encourages the illegal exportation of the animals to “exotic” pet markets abroad. A particularly alarming example of forest depletion involves South America’s world-renowned big-leaf mahogany (Swietenia macrophylla), which was listed as endangered by the Convention on International Trade in Endangered Species in 2002. The total original virgin mahogany surface has been estimated to be nearly 300 million hectares (741 million acres); this amount has been reduced by more than 175 million hectares (432 million acres) through logging and intentional “forest conversions” (clearing for agriculture). By 2023, its conservation status had been upgraded to vulnerable. Groups such as the Rainforest Alliance were helping communities harvest mahoghany sustainably.

Programs aimed at promoting the conservation of Amazonian forests and animal species are quite numerous. Some private conservation groups in South America even seek individual contributions from abroad, presumably to purchase small plots of virgin forest to save them from irresponsible logging. In a different, clearly official arena, the Brazilian government has worked toward clarifying landownership titles (many falsified through the intimidation of small-scale landowners by large-scale investors), with the aim of implementing stricter regulations regarding the conditions that must be met before forest vegetation can be removed.

South American regions as far apart as the Amazon basin and the Andean highlands are experiencing equally alarming ecological threats, although of different types, as a result of large-scale economic development schemes. Environmentalists from around the globe have registered opposition to oil drilling in pre-Amazonian areas of Peru and in the Brazilian Amazon. Indigenous populations in these areas depend on the maintenance of ecosystems (water networks, vegetation, and fauna) that have long been the bases of their traditional local economies. A prototypical example of this problem appeared in 2004, when exploitation by foreign companies of the Camisea natural gas field in Amazonian Peru drew international attention from environmentalists who criticized what they considered to be irresponsible actions leading to deforestation, declining medicinal plant resources, and degradation of local water supplies stemming from oil and gas in surrounding soils.

Bibliography

Borma, L.S. et al. "Beyond Carbon: The Contributions of South American Tropical Humid and Subtropical Forests to Ecosystem Services." Reviews of Geophysics, vol. 60, no. 4, Dec. 2022, doi.org/10.1029/2021RG000766. Accessed 23 July 2024.

Daly, Douglas C., and John D. Mitchell. “Lowland Vegetation of Tropical South America.” In Imperfect Balance: Landscape Transformations in the Pre-Columbian Americas, edited by David L. Lentz. New York: Columbia University Press, 2000.

Luteyn, James L., and Steven P. Churchill. “Vegetation of the Tropical Andes.” In Imperfect Balance: Landscape Transformations in the Pre-Columbian Americas, edited by David L. Lentz. New York: Columbia University Press, 2000.

Meggers, Betty J. Amazonia: Man and Culture in a Counterfeit Paradise. Rev. ed. Washington, D.C.: Smithsonian Institution Press, 1996.

Wirth, Christian, Gerd Gleixner, and Martin Heimann, eds. Old-Growth Forests: Function, Fate, and Value. New York: Springer, 2009.