Until relatively recently, it was widely believed that the Amazon Rainforest was incapable of sustaining large scale human development. New findings have challenged this view, and evidence of ancient agriculture suggests that humans once developed this fragile region in ways so subtle that – in the form of carefully managed soils and prehistoric orchards – they have been hiding in plain sight all this time, challenging the basic tenants of “agriculture” as western eyes tend to recognize it.
|The Amazon||Create your own rainforest in a jar|
|What makes the Amazon a rainforest?||Experiment with indigenous agriculture|
|Diverse but Fragile||Plan for the future using tools of the past|
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- What makes the Amazon such an extraordinary place?
- Why is the Amazon Rainforest important to the Earth’s environment on a global scale?
- Identify and describe some of the wildlife found in the Amazon Rainforest.
The Amazon River is the largest river by discharge of water in the world, greater than the next seven largest independent rivers combined — the Amazon accounts for roughly one-fifth of the world’s total river flow. The river flows through the Amazon Rainforest. The Amazon represents over half of the planet’s remaining rainforests, and comprises the largest and most biodiverse tract of tropical rainforest in the world, with an estimated 390 billion individual trees divided into 16,000 species.
Wet tropical forests are the most species-rich biome, and tropical forests in the Americas are consistently more species rich than the wet forests in Africa and Asia. As the largest tract of tropical rainforest in the Americas, the Amazonian rainforests have unparalleled biodiversity. One in ten known species in the world lives in the Amazon Rainforest. This constitutes the largest collection of living plants and animal species in the world.
The region is home to about 2.5 million insect species, at least 40,000 plant species, 2,200 fishes, 1,294 birds, 427 mammals, 428 amphibians, and 378 reptiles have been scientifically classified in the region. One in five of all the bird species in the world live in the rainforests of the Amazon, and one in five of the fish species live in Amazonian rivers and streams.
Additionally, more than 20 percent of the world’s oxygen is produced in the Amazon Rainforest. It is also a tremendous store of carbon dioxide, absorbing nearly three quarters of a billion metric tons of the gas each year. Since carbon dioxide is a large contributor to global warming, the Amazon’s role as a carbon sink cannot be undervalued. For these reasons, the Amazon Rainforest is sometimes called “the lungs of the planet.”
Some of the more remarkable species found in the Amazon include:
What makes the Amazon a rainforest?
- How do global weather patterns interact with the geography of South America to create the Amazon?
So why does the Amazon Rainforest exist? After all, at a similar latitude in Africa, the Sahara is the world’s largest desert. Why such a difference?
The most simple answer as to why the Amazon exists lies in the interactions between the Andes mountains and larger global weather patterns.
In the western part of the continent, plate tectonics causes the Nazca Plate to slide beneath the South American Plate. This process is called subduction, which creates the Andes, the second tallest mountain range in the world. As the South American Plate moves west, it crumples, rising to form jagged peaks, something like the way a carpet pushed across a floor folds up on itself when it hits a piece of furniture and has nowhere else to go.
These tall mountains create what scientists call a rain shadow – they are so tall that rain clouds literally crash into them. At this latitude, near the equator, the prevailing winds move from east to west – from Africa, across the warm Atlantic Ocean, and into the Amazon Basin. These are the same trade winds that brought European sailors like Columbus to the Americas starting in the late 1400s. Then, as now, they carry in warm, wet air from the equatorial Atlantic Ocean.
This wet air is coupled with convection from the massive forest. Just like you, trees breath. And just like you, as they breath, they release moisture back into the air. Since the Amazon Rainforest is so huge, this means it releases an incredible amount of moisture into the tropical air every day, which is in turn picked up by these westward-moving winds.
Unable to pass, the moisture carried by these winds drops as rain, leaving one side of the mountains – the narrow band along the west coast, which hugs the Pacific Ocean, incredibly dry – meanwhile dropping incredible amounts of rain on the eastern side, which then drain some 6,000 miles all the way back to the Atlantic Ocean. That is the Amazon River and its many tributaries, which feed the wet forests of the Amazon Basin.
What that means, in part, is that any rain that falls on the eastern side of the Andes is going to drain back to the east. Think of this as a kind of giant feedback loop… The very presence of the forest causes even more rain.
Compare all of this to Africa, which lacks any such mountains at this latitude. Also, the Sahara is fed by westward blowing winds – which have just traveled across the width of the world’s widest continent, Asia, and therefore carry little moisture for rain. But even the absence of a rainforest in Africa this plays into why the Amazon is wet. Through satellite observation, NASA has demonstrated that an incredible volume of sand in the Sahara is picked up by these winds and carried west, only to fall as a kind of nutrient-rich fertilizer on the Amazon Rainforest some three thousand miles away.
Diverse but Fragile
- Why is the soil of the Amazon so fragile?
- Identify some of the economic threats to the modern Amazon.
Scientists originally thought that the heavy vegetation of tropical rainforests would provide rich nutrients, but for all of its ecological wealth, the heat, the sun, and the constant rain, mean that the Amazon Basin is home to some of the world’s most fragile soil, easily stripped of its nutrients by this constant bombardment.
As rainfall passes through the litter on the forest floor the rain is acidified and leaches minerals from the above soil layers. That sounds very complicated, but basically what it means is that plants to get their nutrition from decaying litter in a very thin band of topsoil. Under normal conditions, the forest replenishes this topsoil itself. The thick canopy diffuses the sunlight, and. when a tree or some other living thing falls, consumers – bacteria, insects, and other creatures – break down the detritus, hungrily reabsorbing its nutrients back into the ecosystem.
The problem comes in when humans clear cut the forest, burning away or cutting down all vegetation. Humans do this for many reasons, including farming, ranching, logging, or drilling for oil, which is abundant in the Amazon. When the rainforest is cut away and the normal cycles of decomposition and replenishment are disrupted, the soil can be destroyed – essentially barren of life for generations to come.
In 1491: New Revelations of the Americas Before Columbus, Charles C. Mann describes the problem this way:
The ecological constraints on tropical soils are in large part due to the gravitational energy of raindrops. Rainfall, drumming down day in and day out, pounds the top few inches of earth into slurry from which nutrients are easily leached and which itself easily washes away. In uncut forest, the canopy intercepts precipitation, absorbing the physical impact of its fall from the clouds. The water eventually spills from the leaves, but it hits the ground less violently. When farmers or loggers clear the tree cover, droplets shoot at the ground with more than twice as much force. Slash-and-burn minimizes the time in which the ground is unprotected. Intensive agriculture is much more productive but maximizes the land’s exposure. This painful trade-off is why ecologists argue that any attempt by tropical forest societies to grow beyond small villages has always been doomed to fail.
- Describe the Yanomami way of life. Why can’t Yanomami communities in the Amazon Rainforest grow larger than those described here?
- What is an uncontacted tribe? Is there life better or worse than yours – or is such a comparison even possible? In your opinion, should they ever be approached by outsiders?
The Yanomami live in tiny villages, usually consisting of their children and extended families. Village sizes vary, but usually contain between 50 and 400 native people. In this largely communal system, the entire village lives under a common roof called the shabono. Shabonos have a characteristic oval shape, with open grounds in the center measuring an average of 100 yards – about the length of a football field. The shabono shelter constitutes the perimeter of the village.
Under the roof, divisions exist marked only by support posts, partitioning individual houses and spaces. Shabonos are built from raw materials from the surrounding rainforest, such as leaves, vines, and tree trunks. They are susceptible to heavy damage from rains, winds, and insect infestation. As a result, new shabonos are constructed every 4 to 6 years.
The Yanomami can be classified as foraging horticulturalists, depending heavily on rainforest resources; they use slash-and-burn horticulture, grow bananas, gather fruit, and hunt animals and fish. Yanomami frequently move to avoid areas that become overused, a practice known as shifting cultivation when the soil becomes exhausted.
The Yanomami are known as hunters, fishers, and horticulturists. The women cultivate plantains and cassava in gardens as their main crops. Men do the heavy work of clearing areas of forest for the gardens, typically using slash and burn methods mentioned earlier. A small area of land is cleared and the vegetation burned, providing a source of nutrients from the ash. For a few years the soil remains sufficiently fertile for the tribe to grow crops. When the soil’s fertility is exhausted, the tribe moves on and clears another small area of forest. The original area is regenerated, as it receives nutrients and seeds from surrounding vegetation. As no lasting damage occurs, when practiced on a small scale by a small population, this method of agriculture is sustainable.
The Yanomami have often been held up by historians and anthropologists as classical examples of rainforest dwellers – living in small groups, subsisting on meager resources, and practicing small scale agriculture in conjunction with hunting and gathering. Indeed, the Yanomami are regarded by some as admirable for the low impact they have had on their surrounding environment, with many observers assuming that their “primitive” lifestyle has represented life in the Amazon has it has been for millennia. For advocates of this point of view, the current large-scale transformation of the Amazon is a byproduct of European colonialism – an unprecedented event in the history of the world.
While it is true that the massive deforestation of the Amazon – for cattle ranching, industrial-scale soy bean farming, oil drilling, and logging – is new, recent discoveries suggest that the Yanomami, along with many other subsistence level tribes living a similar lifestyle throughout the Amazon Basin, are relatively recent arrivals to the region.
In this understanding, the Yanomami – with origins far to the north, along the Caribbean Sea – fled from that homeland into the depths of the forests, escaping the advancing wave of European slave raids, disease, and encroachment between the 1500 and 1800s.
When we look at the peoples of Amazon Rainforest, we may actually be looking at something that is messy and dislocated, rearranged recently and often beyond the full view of the Europeans who unleashed the destabilizing forces of disease, war, capitalism, and slavery in the first place. This way of life – in this environment – are unfamiliar and represent a relative low point in the history Yanamami and many others, who are not rainforest natives, but, in effect, refugees.
Imagine arriving in a city that has just been struck by an earthquake or a hurricane – and judging the survivors for being so disorganized. Imagine that you and your family had relocated to the rainforest, perhaps against your will, perhaps with the goal of avoiding any contact with the outside world. How well would you survive in so alien a place – whose learning curve is so steep?
Indeed, while the Yanomami have had extensive contact with the outside world at this point, the Amazon is home to the largest number of “uncontacted peoples” anywhere in the world.
Uncontacted people, also referred to as isolated people or lost tribes, are communities who live, or have lived, either by choice (peoples living in voluntary isolation) or by circumstance, without significant contact with global civilization. Few peoples have remained totally uncontacted by global civilization. Indigenous rights activists call for such groups to be left alone, stating that it will interfere with their right to self-determination.
In 2013 it was estimated that there were more than 100 uncontacted tribes around the world, mostly in the densely forested areas of South America, Central Africa, and New Guinea. Knowledge of the existence of these groups comes mostly from infrequent and sometimes violent encounters with neighboring tribes, and from aerial footage. Isolated tribes may lack immunity to common diseases, which can kill a large percentage of their people after contact.
The fact of the matter is, though, that most of these groups seem to be aware of the outside world. Historically, they have been victims of slave raids – either during the colonial Spanish period, or during the 1800s, when European and American businessmen sought to tap natural rubber trees, forcibly enslaving natives do to the arduous work of hiking the rainforest and collecting the rubber. We know this happened, because we have the European colonial and imperial records, but we don’t know the full story of many indigenous groups – who were coerced or who resisted, but who often lacked a written language with which to record their experiences. Given this history, it is not hard to imagine Amazonian tribes taking a defensive view toward the outside world. Among uncontacted tribes, memories of the atrocities against their ancestors may still be strong.
Too frequently, when loggers or other outsiders enter the territory of such uncontacted tribes today, violence ensues, with members of the tribe responding aggressively to any visitors. Very little is known about these peoples. What we do know is that they wish to remain uncontacted: they have shot arrows at outsiders and airplanes, or they simply avoid contact by hiding deep in the forest.
So these “primitive peoples” on some level chose their way of life, isolated and subsisting deep in the rainforest. But in another real way, it was forced upon them as a matter of survival in defiance of colonizers, imperialists, and businessmen – who threatened these peoples on the margins of recorded history.
- Why didn’t historians believe that the Amazon could support a society like the Marajó? What evidence began to change their minds?
- What is terra preta? Why do scientists believe it is a man-made creation rather than naturally occurring?
For a long time, it was thought that the Amazon Rainforest was only ever sparsely populated, as it was impossible to sustain a large population through agriculture given the poor soil. Archaeologist Betty Meggers was a prominent proponent of this idea, as described in her book Amazonia: Man and Culture in a Counterfeit Paradise. She claimed that a population density of 0.2 inhabitants per square kilometer (0.52/sq mi) is the maximum that can be sustained in the rainforest through hunting, with agriculture needed to host a larger population. However, recent anthropological findings have suggested that the region was actually densely populated. Some 5 million people may have lived in the Amazon region in AD 1500, divided between dense coastal settlements, such as that at Marajó, and inland dwellers.
The Spanish explorer Francisco de Orellana, the 16th century explorer who was the first European to traverse the Amazon River, reported densely populated regions running hundreds of kilometers along the river, suggesting population levels exceeding even those of today. These populations left no lasting monuments, possibly because they used local wood as their construction material, which would have rotted in the humid climate (stone was unavailable). While it is possible Orellana may have exaggerated the level of development among the Amazonians, their semi-nomadic descendants have the odd distinction among tribal indigenous societies of a hereditary, yet landless, aristocracy, a historical anomaly for a society without a sedentary, agrarian culture. This suggests they once were more settled and agrarian but became nomadic after the demographic collapse of the 16th and 17th century, due to European-introduced diseases, while still maintaining certain traditions. Moreover, many indigenous peoples adapted to a more mobile lifestyle in order to escape colonialism.
The BBC’s Unnatural Histories presents evidence that Orellana, rather than exaggerating his claims as previously thought, was correct in his observations that an advanced civilization was flourishing along the Amazon in the 1540s. It is believed that the civilization was later devastated by the spread of diseases from Europe, such as smallpox. The evidence to support this claim comes from the discovery of numerous geoglyphs dating between 0–1250 CE.
For 350 years after the European arrival by Vicente Yáñez Pinzón, the Portuguese portion of the basin remained an untended former food gathering and planned agricultural landscape occupied by those who survived the epidemics. There is ample evidence for complex large-scale, pre-Columbian social formations, including chiefdoms, in many areas of Amazonia (particularly the inter-fluvial regions) and even large towns and cities. For instance the pre-Columbian culture on the island of Marajó may have developed social stratification and supported a population of 100,000 people.
How is all of this possible, when today the peoples of the Amazon struggle to farm any given plot of land for more than a few years?
While most of the soil of the Amazon Basin is quite infertile when the natural processes of the forest are disrupted for human agriculture, there is one notable exception. More than 2,000 years ago, early Amazonians may have developed a distinctive and truly incredible innovation – an ultra-rich man-made soil called terra preta – to make the land suitable for the large scale agriculture. Terra preta is a unique mixture of charcoal; of ceramic pot sherds, deliberately smashed and mixed throughout the soil, which facilitate drainage and aeration; of organic matter such as plant residues, animal feces, fish and animal bones and other material; and of nutrients such as nitrogen (N), phosphorus (P), calcium (Ca), zinc (Zn), manganese (Mn). This organic matter stays in the terra preta when it is leached out of regular Amazonian soil because of the charcoal – organic matter “sticks” to charcoal, rather than being washed away or attaching to other, nonavailable compounds.
Author Charles C. Mann describes the importance of this innovation quite eloquently in his book, 1491:
Despite the charcoal, terra preta is not a by-product of slash-and-burn agriculture. To begin with, slash-and-burn simply does not produce enough charcoal to make terra preta—the carbon mostly goes into the air in the form of carbon dioxide. Instead, Indians apparently made terra preta by a process that Christoph Steiner, a University of Bayreuth soil scientist, has dubbed ‘slash-and-char.’ Instead of completely burning organic matter to ash, ancient farmers burned it incompletely to make charcoal, then stirred the charcoal into the soil.
If its secrets could be unraveled, he said, it might improve the expanses of bad soil that cripple agriculture in Africa—a final gift from the peoples who brought us tomatoes, maize, manioc, and a thousand different ways of being human.
Terra preta shows high levels of microorganic activities – which actually allows itself to regenerate itself at the rate of 1 centimeter (0.39 in) per year, even thousands of years after its original creation. It is truly one of the most incredible achievements of prehistoric man, anywhere in the world – effectively a living, growing soil that allows human beings to colonize on a massive scale an otherwise inhospitable corner of the world. Surely, this should rank alongside the domestication of livestock or the discovery of agriculture itself – it is the domestication of the very Earth itself.
- What evidence suggests that some trees – such as the peach palm – were cultivated by ancient humans?
- Think about what farming looks like in your part of the world. Why might early European explorers – as well as many modern researchers – miss evidence of this widespread agriculture in the Amazon Rainforest?
Even before the creation of terra preta, Amazonian peoples were shaping their environment, laying the foundation for large-scale rainforest civilizations that are possible now only with extensive trading and supply from the outside world.
In 1491, Charles C. Mann visited the Brazilian Amazon to understand how ancient societies there might have supplied themselves with adequate food, despite the challenges posed by traditional clear cut agriculture in this hot, wet environment:
According to Charles R. Clement, an anthropological botanist at the Brazilian National Institute for Amazon Research (INPA) in Manaus, though, the first Amazonians did avoid the Dilemma of Rainfall Physics. Speaking broadly, their solution was not to clear the forest but to replace it with one adapted to human use. They set up shop on the bluffs that mark the edge of high water—close enough to the river to fish, far enough to avoid the flood. And then, rather than centering their agriculture on annual crops, they focused on the Amazon’s wildly diverse assortment of trees. In his view, the Amazon’s first inhabitants laboriously cleared small plots with their stone axes. But rather than simply planting manioc and other annual crops in their gardens until the forest took them over, they planted selected tree crops along with the manioc and managed the transition. Of the 138 known domesticated plant species in the Amazon, more than half are trees. (Depending on the definition of “domesticated,” the figure could be as high as 80 percent.) Sapodilla, calabash, and tucumá; babaçu, açai, and wild pineapple; coco-palm, American-oil palm, and Panama-hat palm—the Amazon’s wealth of fruits, nuts, and palms is justly celebrated. “Visitors are always amazed that you can walk in the forest here and constantly pick fruit from trees,” Clement said. “That’s because people planted them. They’re walking through old orchards.”
Unlike maize or manioc, peach palm can thrive with no human attention. Tragically, this quality has proven to be enormously useful. In the seventeenth and eighteenth centuries many Amazonian Indians, the Yanomami among them, abandoned their farm villages, which had made them sitting ducks for European diseases and slave trading. They hid out in the forest, preserving their freedom by moving from place to place; in what Balée calls “agricultural regression,” these hunted peoples necessarily gave up farming and kept body and soul together by foraging. The “Stone Age tribespeople in the Amazon wilderness” that captured so many European imaginations were in large part a European creation and a historical novelty; they survived because the “wilderness” was largely composed of their ancestors’ orchards. “These old forests, called fallows, have traditionally been classified as high forest (pristine forest on well-drained ground) by Western researchers,” Balée wrote in 2003. But they “would not exist” without “human agricultural activities.” Indeed, Amazonians typically do not make the distinction between “cultivated” and “wild” landscapes common in the West; instead they simply classify landscapes into scores of varieties, depending on the types of species in each.
Planting their orchards for millennia, the first Amazonians slowly transformed large swaths of the river basin into something more pleasing to human beings. In the country inhabited by the Ka’apor (an Amazonian tribe), on the mainland southeast of Marajó, centuries of tinkering have profoundly changed the forest community. In Ka’apor-managed forests […] almost half of the ecologically important species are those used by humans for food. In similar forests that have not recently been managed, the figure is only 20 percent. Balée cautiously estimated, in a widely cited article published in 1989, that at least 11.8 percent, about an eighth, of the nonflooded Amazon forest was “anthropogenic”—directly or indirectly created by humans.
Our growing understanding has challenged the notion that the Amazon Rainforest is an entirely natural environment, characterized for its entire history by small-scale settlement like that of the Yanomami, relatively unshaped by man until recently. This blended soil supported large populations in the pre-Columbian Amazon, which in turn allowed for the development of complex societies and governments, as well as art and monumental architecture like the tremendous geoglyphs of Marajo – something that until recently, modern scholars thought impossible.
What else haven’t we noticed yet, because we haven’t learned how to look?
- Create and observe a rainforest water cycle in a jar. Supplies needed: 1 large empty jar; 1 rubber band; clear plastic wrap; potting soil or soil from your yard; water; moss or grass with the roots intact. Put the soil into the jar, about two inches deep. Add enough water so that it is standing about an inch above the soil. Put the fresh moss on top of the soil and cover the jar with the plastic wrap. Lock the wrap in place over the mouth of the jar with the rubber band. Place the jar in a sunny place and observe what happens when the sun is low, when it is high, when it is setting, and when it is dark. Log these observations over the period of several days. How is this similar to way water behaves in the rainforest?
- Terra preta has changed what modern researchers thought was possible in the harsh environment of the Amazon. In fact, you can make your own terra preta. Research and experiment with this and other agricultural techniques common in different parts of Native America such as the chinampa, the terrace, and waru waru. Compare two or more of these techniques when used in your schoolyard or backyard to grow a stalk of corn. Measure, chart, and compare the results – which of these techniques gave you the best results? In the midst of calls and trends for more organic, natural methods of farming, what might we learn from Native American techniques?
- Research, explore, and present on the following questions, creating a land-use proposal for the Amazon Basin: If the Amazon is an environment that has been shaped by humans since their arrival thousands of years ago, what does this mean for our modern behavior in the Amazon? Should it be protected as a natural space, or should it be developed for purposes such as ranching, farming, oil production, and logging? Could modern humans take lessons from the ancients and develop the Amazon in a more sustainable way? How?
1491: New Revelations of the Americas Before Columbus by Charles C. Mann.
Tree of Rivers: The Story of the Amazon by John Hemming.
THIS LESSON WAS MADE POSSIBLE THROUGH A GENEROUS GRANT FROM FUND FOR TEACHERS.
You can actually visit the parts of the world featured in this lesson:
- Adventure Blog.
- A Guided Tour of Bolivia, 2016 – Explore the streets of La Paz and El Alto, scramble through the 500 year-old silver mines of Potosi, or race across the barren salt flats of Uyuni. Supplementary photos and information on Bolivia, past and present.
- A Guided Tour of Peru, 2016 – Explore the streets of Cusco and Lima, scramble through Inca ruins from Machu Picchu on down, take a slow boat up the Amazon River from Iquitos, and an even slower boat across Lake Titicaca to the floating man-made islands of the Uros. Supplementary photos and information on Peru, past and present.