The Amazon: The World's Largest Rainforest
By Rhett Butler
The Amazon River Basin is home to the largest rainforest on Earth. The basin -- roughly the size of the forty-eight contiguous United States -- covers some 40% of the South American continent and includes parts of eight South American countries: Brazil, Bolivia, Peru, Ecuador, Colombia, Venezuela, Guyana, and Suriname, as well as French Guiana, a department of France.
Reflecting environmental conditions as well as past human influence, the Amazon is made up of a mosaic of ecosystems and vegetation types including rainforests, seasonal forests, deciduous forests, flooded forests, and savannas. The basin is drained by the Amazon River, the world's largest river in terms of discharge, and the second longest river in the world after the Nile. The river is made up of over 1,100 tributaries, 17 of which are longer than 1000 miles, and two of which (the Negro and the Madeira) are larger, in terms of volume, than the Congo (formerly the Zaire) river. The river system is the lifeline of the forest and its history plays an important part in the development of its rainforests.
At one time Amazon River flowed westward, perhaps as part of a proto-Congo (Zaire) river system from the interior of present day Africa when the continents were joined as part of Gondwana. Fifteen million years ago, the Andes were formed by the collision of the South American plate with the Nazca plate. The rise of the Andes and the linkage of the Brazilian and Guyana bedrock shields, blocked the river and caused the Amazon to become a vast inland sea. Gradually this inland sea became a massive swampy, freshwater lake and the marine inhabitants adapted to life in freshwater. For example, over 20 species of stingray, most closely related to those found in the Pacific Ocean, can be found today in the freshwaters of the Amazon.
The World's Largest Rainforests [more]
1. Amazon Basin, South America
2. Congo Basin, Africa
3. Indonesian Archipelago, Southeast Asia
How large is the Amazon rainforest?
The extent of the Amazon depends on the definition. The the Amazon River drains about 6.915 million sq km (2.722 sq mi), or roughly 40 percent of South America, but generally areas outside the basin are included when people speak about "the Amazon." The biogeographic Amazon ranges from 7.76-8.24 million sq km (3-3.2 million sq km), of which just over 80 percent is forested. For comparison, the land area of the United States (including Alaska and Hawaii) is 9,629,091 square kilometers (3,717,811).
Nearly two-thirds of the Amazon lies in Brazil.
About ten million years ago, waters worked through the sandstone to the west and the Amazon began to flow eastward. At this time the Amazon rainforest was born. During the Ice Age, sea levels dropped and the great Amazon lake rapidly drained and became a river. Three million years later, the ocean level receded enough to expose the Central American isthmus and allow mass migration of mammal species between the Americas.
The Ice Ages caused tropical rainforest around the world to retreat. Although debated, it is believed that much of the Amazon reverted to savanna and montane forest (see chapter 3-Ice Ages and Glaciation). Savanna divided patches of rainforest into "islands" and separated existing species for periods long enough to allow genetic differentiation (a similar rainforest retreat took place in Africa. Delta core samples suggest that even the mighty Congo watershed was void of rainforest at this time). When the ice ages ended, the forest was again joined and the species that were once one had diverged significantly enough to be constitute designation as separate species, adding to the tremendous diversity of the region. About 6000 years ago, sea levels rose about 130 meters, once again causing the river to be inundated like a long, giant freshwater lake.
THE AMAZON RIVER TODAY
Today the Amazon River is the most voluminous river on Earth, eleven times the volume of the Mississippi, and drains an area equivalent in size to the United States. During the high water season, the river's mouth may be 300 miles wide and every day up to 500 billion cubic feet of water (5,787,037 cubic feet/sec) flow into the Atlantic. For reference, the Amazon's daily freshwater discharge into the Atlantic is enough to supply New York City's freshwater needs for nine years. The force of the current -- from sheer water volume alone -- causes Amazon River water to continue flowing 125 miles out to sea before mixing with Atlantic salt water. Early sailors could drink freshwater out of the ocean before sighting the South American continent.
The river current carries tons of suspended sediment all the way from the Andes and gives the river a characteristic muddy whitewater appearance. It is calculated that 106 million cubic feet of suspended sediment are swept into the ocean each day. The result from the silt deposited at the mouth of the Amazon is Majaro island, a river island about the size of Switzerland.
THE AMAZON RAINFOREST
While the Amazon Basin is home to the world's largest tropical rainforest, the region consists of a number of ecosystems ranging from natural savanna to swamps. Even the rainforest itself is highly variable, tree diversity and structure varying depending on soil type, history, drainage, elevation, and other factors. This is discussed at greater length in the rainforest ecology section.
THE CHANGING AMAZON RAINFOREST
The Amazon has a long history of human settlement, but in recent decades the pace of change has accelerated due to an increase in human population, the introduction of mechanized agriculture, and integration of the Amazon region into the global economy. Vast quantities of commodities produced in the Amazon — cattle beef and leather, timber, soy, oil and gas, and minerals, to name a few — are exported today to China, Europe, the U.S., and other countries. This shift has had substantial impacts on the Amazon.
This transition from a remote backwater to a cog in the global economy has resulted in large-scale deforestation and forest degradation in the Amazon — more than 1.4 million hectares of forest have been cleared since the 1970s. An even larger area has been affected by selective logging and forest fires.
Conversion for cattle grazing is the biggest single direct driver of deforestation. In Brazil, more than 60 percent of cleared land ends up as pasture, most of which has low productivity, supporting less than one head per hectare. Across much of the Amazon, the primary objective for cattle ranching is to establish land claims, rather than produce beef or leather. But market-oriented cattle production has nonetheless expanded rapidly during the past decade.
Industrial agricultural production, especially soy farms, has also been an important driver of deforestation since the early 1990s. However since 2006 the Brazil soy industry has had a moratorium on new forest clearing for soy. The moratorium was a direct result of a Greenpeace campaign.
Mining, subsistence agriculture, dams, urban expansion, agricultural fires, and timber plantations also result in significant forest loss in the Amazon. Logging is the primary driver of forest disturbance and studies have shown that logged-over forests — even when selectively harvested — have a much higher likelihood of eventual deforestation. Logging roads grant access to farmers and ranchers to previous inaccessible forest areas.
Deforestation isn't the only reason the Amazon is changing. Global climate change is having major impacts on the Amazon rainforest. Higher temperatures in the tropical Atlantic reduce rainfall across large extents of the Amazon, causing drought and increasing the susceptibility of the rainforest to fire. Computer models suggest that if current rates of warming continue, much of the Amazon could transition from rainforest to savanna, especially in the southern parts of the region. Such a shift could have dramatic economic and ecological impacts, including affecting rainfall that currently feeds regions that generate 70 percent of South America's GDP and triggering enormous carbon emissions from forest die-off. These emissions could further worsen climate change.
PROTECTING THE AMAZON RAINFOREST
While destruction of the Amazon rainforest is ongoing, the overall rate of deforestation rate in the region is slowing, mostly due to to the sharp drop in forest clearing in Brazil since 2004.
Brazil's declining deforestation rate has been attributed to several factors, some of which it controls, some of which it doesn't. Since 2000 Brazil has established the world's largest network of protected areas, the majority of which are located in the Amazon region. Since 2004 the government has also had a deforestation reduction program in place. This includes improved law enforcement, satellite monitoring, and financial incentives for respecting environmental laws. Furthermore, the private sector — especially the soy, logging, and cattle industries — are increasingly responsive to consumer demand for less-damaging commodities. Finally the Brazilian Amazon has been the site of a number of innovative and ambitious conservation experiments, ranging from jurisdictional commodity certification to indigenous led Reducing Emissions from Deforestation and Degradation (REDD+) projects to Norway's billion dollar performance-based payment for cutting deforestation.
RECENT NEWS ON THE AMAZON
Amazon deforestation moratorium extended 18 months
The Brazilian soy industry has extended its deforestation moratorium for another 18 months. The moratorium, which was established in 2006 after a high-profile Greenpeace campaign, bars conversion of forests in Brazilian Amazon for soy production. Independent analysis has shown it to be highly effective — just prior to the moratorium, soy accounted for roughly a fifth of recent deforestation, while today its share is less than one percent.
Rising deforestation, fossil fuels use drive Brazil's emissions 8% higher
Brazil's carbon emissions jumped 7.8 percent in 2013 due to rising deforestation and fossil fuels use, according to data released by Observatório do Clima (Climate Observatory), an alliance of mostly Brazilian non-profits.
Field plots offer biased view of the Amazon
Field plots in the Amazon are often not representative of the habitats surrounding them, potentially biasing extrapolations made across the region, argues a new paper published in the Proceedings of the National Academy of Sciences (PNAS). The research is based on advanced three-dimensional mapping of forest structure within field plots and in surrounding areas using sensors aboard the Carnegie Airborne Observatory, an airplane-based system.
Brazilian government silent as deforestation rises in the Amazon
Deforestation in the Brazilian Amazon continues to outpace last year's rate by a significant margin, reveals data released today by Imazon, a Brazilian non-profit. Imazon's analysis of satellite data shows that for the 3-month period ended October 31, 2014, deforestation is running 226 percent of last year's rate. Forest degradation, which often precedes outright clearing, is pacing 691 percent ahead of last year.
Greenpeace investigation prompts Belgian authorities to seize timber shipment
Authorities in Belgium seized two containers of Brazilian timber in Antwerp following a demonstration by Greenpeace, which alleged that the Ipe timber had been cut illegally and therefore violated the EU's trade laws.
New tapir? Scientists dispute biological discovery of the century
Nearly a year ago, scientists announced an incredible discovery: a new tapir species from the western Amazon in Brazil and Colombia. The announcement was remarkable for a number of reasons: this was the biggest new land mammal discovered in more than 20 years and was only the fifth tapir known to the world. But within months other researchers expressed doubt over the veracity of the new species.
New birds arise due to emigration not separation
A bird's eye view of speciation in the Neotropics. How long does it take for a new species to develop? Not long, it turns out. In fact, only a few thousand years — an evolutionary blink of an eye. A recent article published in Nature tracked neotropical bird speciation, or the process by which new species emerge.
New laws may turn Brazil's forests into mines
With the world’s largest system of protected areas and a 70 percent drop in the deforestation rate of the Amazon over the past decade, Brazil has made huge strides in safeguarding what’s left of its wilderness. However, this progress now hangs in the balance, with new laws threatening to turn many of the country’s protected areas into mines and dams.
Reducing tax evasion could help save the Amazon
Taxing underutilized land in the Amazon could conserve forests, boost productivity, and alleviate poverty, argues study.
Amazon rainforest is getting drier, confirms another study
Parts of the Amazon rainforest are getting considerably less rain, leading trees to absorb less carbon, finds a study published this week in the journal Proceedings of the National Academy of Sciences.
Daring activists use high-tech to track illegal logging trucks in the Brazilian Amazon
Every night empty trucks disappear into the Brazilian Amazon, they return laden with timber. This timber —illegally cut —makes its way to a sawmills that sell it abroad using fraudulent paperwork to export the ill-gotten gains as legit. These findings are the result of a daring and dangerous investigation by Greenpeace-Brazil.
As Amazon deforestation falls, small farmers play bigger role in forest clearing
Smallholder properties account for a rising proportion of overall deforestation in Brazilian Amazon, suggesting that Brazil’s progress in cutting forest loss through stricter law enforcement may be nearing the limits of its effectiveness, finds a new study published in the Proceedings of the National Academy of Sciences.
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AMAZON RAINFOREST PICTURE HIGHLIGHTS
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