The South American continent hosts a range of biomes that influence global climate and harbor extraordinary levels of life. Stretching from the equatorial tropics to the sub-Antarctic south, this landmass encompasses all of the world’s major climate zones, giving rise to an unparalleled diversity of habitats. Its geography, dominated by a mountain range along its western edge and a large river basin to the east, drives the distribution of its unique flora and fauna. Ecological processes originating here, such as the regulation of atmospheric moisture, have consequences that extend far beyond the continent’s borders. Understanding South American ecology requires examining the distinct biomes and the atmospheric and oceanic forces that shape them.
The Amazon: Engine of the Continent
The Amazon basin covers approximately seven million square kilometers, forming the largest lowland in Latin America and encompassing the world’s largest tropical rainforest. This ecosystem sustains high biodiversity and plays a considerable role in regulating global atmospheric composition. The rainforest is estimated to contain about 16,000 different tree species, with nearly 390 billion individual trees. A small subset of about 227 “hyperdominant species” accounts for half of all the individual trees in the region.
The Amazon’s influence extends deeply into the continent’s hydrology through the “flying rivers,” a system of atmospheric moisture recycling driven by the forest itself. Trees absorb water through their roots and release it into the atmosphere via evapotranspiration, a process that can recycle up to 75% of the regional rainfall. This atmospheric flow is estimated to carry approximately 20 billion tons of water vapor daily, comparable to the Amazon River’s own flow.
This moisture is transported westward by prevailing winds, acting as a freshwater supply for regions hundreds of kilometers away. When this aerial moisture meets the Andes, it is forced southward, providing rainfall to southern Brazil, Paraguay, and northern Argentina. The Amazon River is the largest in the world by discharge volume, releasing an average of 215,000 to 230,000 cubic meters of water per second into the Atlantic Ocean, representing about 20% of the total riverine discharge into the world’s oceans.
Vertical Ecology of the Andes Mountains
Stretching over 7,000 kilometers along the continent’s western margin, the Andes mountain chain creates a pronounced ecological layering known as vertical zonation. This arrangement of distinct biomes is determined primarily by the rapid decrease in temperature and change in moisture as altitude increases.
The zonation includes:
- The Tierra caliente (hot land) up to approximately 1,200 meters.
- The Tierra templada (temperate land), where tropical mountain forests thrive up to 2,500 meters.
- The Tierra fria (cold land), extending to about 4,000 meters, characterized by cloud forests and high-altitude cultivation.
- The Tierra helada (frozen land), which includes the páramo and puna grasslands, extending up to 5,200 meters.
This highest zone presents challenges including low oxygen levels, intense ultraviolet (UV) radiation, and extreme daily temperature swings.
Plants in these high-altitude environments have developed specialized morphological and biochemical traits to persist, such as small, thick leaves and a compact growth habit to minimize wind and water loss. They also synthesize UV-absorbing compounds to protect their cellular DNA. Andean animals also exhibit physiological adaptations to the thin air. Native camelids like the vicuña and alpaca possess a unique form of hemoglobin with a high oxygen affinity and thin-walled pulmonary arteries that resist the high blood pressure common in lowlanders exposed to altitude.
Extreme Environments: Deserts and Grasslands
Beyond the Amazonian forest and the Andean slopes, vast areas of South America are dominated by environments characterized by water scarcity or extreme seasonal variation. Along the Pacific coast, the Atacama Desert is one of the world’s driest non-polar regions, yet life persists through a unique mechanism of moisture capture. This moisture arrives as dense, coastal fog, locally known as camanchaca or garúa, which is trapped by the coastal hills.
These areas, called lomas formations, are islands of vegetation that rely almost entirely on the fog for water, creating highly endemic ecosystems. In the far south, the Patagonian Steppe presents a cold, semi-arid environment, with vegetation dominated by xerophytic shrubs and tussock grasses. The native grazing ecology was historically shaped by the guanaco, a wild South American camelid, whose migratory patterns promoted grassland health.
The Pampas, in contrast, are temperate grasslands in Argentina, Uruguay, and Brazil, originally characterized by fertile soil and tall grasses. However, the introduction of large-scale domestic grazing, particularly sheep, altered the ecology of both the Pampas and the Patagonian Steppe. Continuous, selective grazing of palatable species led to the degradation of the native tussock structure and often resulted in the encroachment of less palatable shrubs, decreasing the overall carrying capacity of the land.
Shaping Forces: Climate and Ocean Currents
The distribution of these diverse South American biomes is determined by the interplay of atmospheric circulation and ocean currents. The continent’s western climate is influenced by the cold, northward-flowing Humboldt Current, also known as the Peru Current. This current drives coastal upwelling, bringing cold, nutrient-rich deep water to the surface, supporting highly productive marine fisheries.
The cold ocean surface water cools the air mass above it, which then moves over the adjacent land. This cool air suppresses evaporation and creates a stable atmospheric inversion layer, preventing the formation of rain clouds. This mechanism is the primary reason for the hyper-aridity of the Atacama and Peruvian coastal deserts.
The Andes mountains further define the continent’s climate through the rain shadow effect, which varies by latitude. In the tropical north, trade winds carry Atlantic moisture westward, dropping rain on the Amazonian slopes and leaving the Pacific side dry. In the far south of Patagonia, the prevailing wind direction shifts to the westerlies, releasing moisture over the Chilean side and leaving the Argentine Patagonian Steppe in a pronounced rain shadow.
This balance of currents and wind patterns is periodically disrupted by the El Niño-Southern Oscillation (ENSO) cycle. During an El Niño event, warm water spreads eastward across the Pacific, suppressing the cold water upwelling of the Humboldt Current. This causes a temporary crash in marine productivity and leads to uncharacteristic, heavy rainfall along the normally arid coastal deserts.