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| Amazon rainforest |
South America is the most diverse continent in terms of flora, primarily because of its location and geography.
South America’s floristic diversity is increased by its high mountains, especially the Andes Mountains, which extend from north to south along the western part of the continent for much of its length.
South America has such diverse biomes as tropical rain forests, tropical savannas, extremely dry deserts, temperate forests, and alpine tundra.
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The largest of these biomes are deserts, savanna, and tropical forest. With the rapid rate of deforestation in places like the Amazon basin, some plants may become extinct before being cataloged, let alone studied.
The subtropical desert biome is the driest biome in South America and is considered the driest desert in the world, with an average annual precipitation of less than 0.25 inch (4 millimeters).
The desert biome is restricted primarily to the west coast of South America from less than 10 degrees south of the equator to approximately 30 degrees south.
Dry conditions prevail from the coast to relatively high elevations in the Andes. The Atacama Desert, in northern Chile, and the Patagonian desert, in central Chile, are the most notable South American deserts. Smaller desert regions also occur in the rain shadow portions of the Andes.
Next on the moisture scale are the savanna biomes. Savanna occurs in two distinctly different areas of South America.
The largest savanna region includes three distinctive regions: the cerrado; the Pantanal; and farther south, in southern Brazil, Uruguay, and northern Argentina, the grassland called the Pampas. The other savanna region, the llanos, is found in lower-elevation areas of Venezuela and Colombia.
Although a few of the forests in South America are dry, most are rain forests, receiving annual precipitation from 79 inches to 118 inches (2,000-3,000 millimeters). The Amazon rain forest, the world’s largest, accounts for more than three-fourths of the rain-forest area in South America.
One of the most species-rich areas of the world, it is being rapidly destroyed by logging, ranching, and other human activities. Smaller rain forests are located along the southeastern coast of Brazil and in the northern part of Venezuela.
Covering much smaller areas are a small mediterranean region in central Chile characterized by cool, wet winters and warm, dry summers.
In the far south of Chile and Argentina is a small area of temperate forest, becoming alpine tundra in the far south. Temperatures are relatively cool and mild year-round (except in the far south, where it can be extremely cold in the winter.
Plants of the Subtropical Desert
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| Oxalis flower (Oxalis carnosae) growing in the Atacama at extremely dry locations |
In the Atacama Desert, one of the world’s driest, some moisture is available, but it is limited to certain zones. Coastal regions below 3,280 feet (1,000 meters) receive regular fog (called camanchacas).
Rainfall is so low in the Atacama Desert that even cacti (which normally store water) can hardly acquire enough water from rainfall alone, so many plants, including bromeliads, receive a portion of their water from the fog. At midelevation areas there is no regular fog; thus, there is almost no plant cover.
At higher elevations, the rising air has cooled sufficiently to produce moderate amounts of rainfall, although the vegetation is still desert like. Shrubs typically grow near stream beds, where their roots can reach a permanent source of water.
The Atacama Desert often appears barren, but when a good dose of moisture becomes available ephemerals change its appearance, seemingly over night.
Ephemerals are typically annuals that remain dormant in the dry soil as seeds. When moisture increases, they quickly germinate, grow, flower, and set seed before dry conditions prevail again.
In the days and weeks following a good rain, many grasses appear and provide a backdrop for endless varieties of showy flowers, many endemic to (found only in the region of) the Atacama Desert.
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| showier flowers in Atacama desert |
Among the showier flowers are species of Alstroemeria (commonly called irises, although they are actually in the lily family) and Nolana (called pansies, although they are members of a family found only in Chile and Peru).
Conditions in the Patagonian desert are less harsh. The vegetation ranges from tussock grasslands near the Andes to more of a shrub-steppe community farther east.
Needlegrass is especially abundant throughout Patagonia, and cacti are a common sight. In the shrub-steppe community in the eastern Patagonian desert, the shrubs quilembai and the cushion like colapiche are common. Where the soil is salty, salt bush and other salt-tolerant shrubs grow.
Plants of the Tropical Savanna Biome The cerrado region of east central Brazil and southward is not only the largest savanna biome of South America but also one of the most romanticized of theworld’s savannas.
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As in the Old West of North America, the grasslands of Brazil have cowboys who traditionally have used the cerrado for farming and cattle ranching. With ever increasing pressure from agriculture, the cerrado is now under attack in various ways.
Extensive fertilization, associated with modern agriculture, planting of trees for timber production, and the introduction of foreign species, especially African grasses, have all begun to change the cerrado. Frequent fires also have taken their toll.
The cerrado contains more than ten thousand species of plants, with 44 percent of them endemic. As much as 75 percent of the cerrado has been lost since 1965, and what remains is fragmented. A number of conservation groups are trying to save as much as possible of what remains.
Two other savanna regions farther south are the Pantanal and the Pampas. Although the Pantanal is a savanna, during the rainy season it becomes a wetland and is a haven for aquatic plants.
Later, the Pantanal dries out and grasslands appear in place of the water. This unique area is under attack by a variety of human activities, including navigation and artificial drainage projects, mining, agriculture, and urban waste.
The Pampas, like the great prairies that once covered central North America, is composed almost solely of grass. Trees and shrubs grow near bodies of water, but everywhere else grass predominates.
Cattle ranching and wheat and corn farming are the primary occupations of the area and are thus the primary threat. Because the area is farther south than the Pantanal, it has a more temperate climate. Pampas grass from this area has been exported as an ornamental plant.
The last major savanna region is the llanos, located at lower elevations in the drainage area of the Orinoco River in Venezuela and Colombia. This area has pronounced wet and dry seasons.
At the lowest elevations, treeless grasslands persist after the water from the rainy season subsides. On the higher plains is a scattering of smaller trees. The mauritia palm can also be found here in poorly drained areas.
Plants of the Tropical Forest Biome
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| Plants of the Tropical Forest Biome |
The Amazon rain forest is the largest contiguous rain forest in the world. It is so large and so lush with tree growth that its transpiration is actually responsible, in part, for the wet climate of the region.
Plant diversity is so great here that no comprehensive plant guide currently exists for many parts of the Amazon rain forest. Of tens of thousands of plant species, a large number have never been described.
This one-of-a-kind botanical treasure is being destroyed at a rapid pace of between 5,000 and 10,000 square miles (13,000-26,000 square kilometers) per year. The causes for this destruction are primarily logging, agriculture, and cattle ranching.
A common practice for preparing an area for cattle ranching or farming has been to simply burn the forest, not even necessarily logging it first, and then to allow the grass and other vegetation or crops grow in its place.
The soils of the rain forest are so poor, however, that this practice usually depletes the soil within a few years, and the land becomes a useless wasteland. Mining and oil drilling have also taken their toll.
The Amazon rain forest is an extremely complex biome. The main plant biomass is composed of trees, which form a closed canopy that prevents much of the sunlight from reaching the forest floor.
Consequently, the forest floor has little herbaceous growth, and most smaller plants tend to grow as epiphytes on the branches and trunks of trees. Common epiphytes in the Amazon rain forest include orchids, bromeliads, and even some cacti.
There is a large diversity of bromeliads, ranging from small, inconspicuous species to larger species, such as tank bromeliads that can collect significant amounts of water in their central whorl of leaves. The water in these plants can contain a whole miniature ecosystem, complete with mosquito larvae, aquatic insects, and frogs.
Ferns are another significant member of the epiphyte community. Some larger species of ferns, often called tree ferns, also grow in the understory. Lianas, or vines, are a prominent component as well.
The trees that formthe canopy are stratified into three fairly discrete levels. The lowest two levels are the most crowded, and the highest level comprises extremely tall trees, often referred to as emergent trees because they stand out randomly above the fairly continuous lower two layers.
Many of the tallest trees are buttressed at the base, an adaptation that seems to give them greater stability. Beneath the canopy, there are some smaller palms, shrubs, and ferns, but they only occur densely where there is a break in the canopy that allows in greater light.
Some rain-forest species of trees are well known, primarily because of their economic value. A favorite tree for use in furniture is the mahogany. Because its wood is highly prized, many species of mahogany are becoming rare or extinct.
The South American rain forests are also the original source of rubber. Brazil had a monopoly on rubber until seeds were smuggled out and planted in Malaysia. Synthetic rubber has now replaced natural rubber for many applications.
Another popular tree is the Brazil nut tree, an abundant food source that has been exploited by suppliers of mixed nuts. The native cacao tree produces fruits from which cacao beans are extracted, then processed tomake chocolate.
Every year during the rainy season, the lowest elevation areas of the Amazon rain forest are flooded with several feet of water, which recedes after a few months. The trees flourish in this flooding cycle.
A few even have unique adaptations, such as producing fruits that are eaten by fish, thus assuring the spread of their seeds. The flooding can be so extensive in some areas that the water reaches the lower parts of the canopy.
Coastal tropical rain forests also occur in north-western and southeastern South America. There are a high number of endemic species in each of these forests.
Some tree species are so rare that they may be found in an area of only a few square miles and nowhere else. Where the tropical rain forest meets the ocean, mangrove trees have become adapted to the tidal environment.
Mangroves have prop roots, which make the trees look like they are growing on stilts. They also frequently have special root structures that extend above the water at high tide and allowthe roots to breathe. Mangrove trees are also extremely salt-tolerant.
Plants of the Mediterranean and Temperate Forest Biomes
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| Plants of Temperate Forest Biomes |
One of the world’s five mediterranean climate regions is found in central Chile. This climate is characterized bywarm, dry summers and cool, wet winters. The vegetation, called matorral, is composed primarily of leathery-leaved, evergreen shrubs that are well adapted to the long summer drought.
The matorral is the only mediterranean area that has bromeliads. At lower elevation areas, somewhat inland,many of the shrubs are drought deciduous; that is, they drop their leaves in the summer. In more inland parts of this biome, the espino tree is common.
Because South America extends so far south, it actually has a small region containing temperate forests. These forests range from temperate rain forest to drier temperate forest, and in all cases are typically dominated by southern beeches.
The under growth is dominated by small evergreen trees and shrubs. Fuchsias, which are valued the world over for their showy flowers, are common in the undergrowth. Although not rich in species, the temperate rain forests of southern South America can be lush.
In the far south, before the extreme climate restricts the vegetation to alpine tundra, a region of elfin wood lands predominates. These wood lands can be nearly impenetrable,with the densest growth often associated with patches of tall bamboo.