Indigenous peoples were stewards of the Western Amazon
Study points to a history of indigenous sustainable use of the Western Amazon stretching back 5,000 years
IMAGE: AN AERIAL PHOTO OF THE ALGODÓN RIVER FLOWING THROUGH A FOREST OF THE AMAZON BASIN IN THE REMOTE NORTHEASTERN CORNER OF PERU. TO EXPLORE THE EXTENT AND SCALE OF INDIGENOUS... view more
CREDIT: ÁLVARO DEL CAMPO
Smithsonian scientists and their collaborators have found new evidence that prehistoric Indigenous peoples did not significantly alter large swaths of forest ecosystems in the western Amazon, effectively preserving large areas of rainforests to be unmodified or used in sustainable ways that did not reshape their composition. The new findings are the latest in a long scientific debate about how people in the Amazon have historically shaped the rich biodiversity of the region and global climate systems, presenting new implications for how the Amazon's biodiversity and ecosystems can be best conserved and preserved today.
In recent years, scientists' understanding of the Amazon rainforest has been increasingly informed by a body of research that suggests the landscape was actively, intensively shaped by Indigenous peoples before the arrival of Europeans. Some studies ascribe the tree species that now dominate the forest to prehistoric human management and landscape engineering. Other work posits that when colonizers from Europe caused massive losses to Indigenous Amazonians with disease, slavery and warfare, the sudden interruption in landscape-scale manipulation resulted in so much forest regrowth that it caused a global drop in atmospheric carbon dioxide that brought about a climactic shift that is known as the "Little Ice Age."
Now a new study led by Smithsonian researchers, published June 7 in the journal Proceedings of the National Academy of Sciences, suggests that for at least the past 5,000 years, large areas of the rainforest in western Amazonia located away from the fertile soils near rivers were not periodically cleared with fire or subject to intensive land use by the Indigenous population before the arrival of Europeans.
The study, led by Smithsonian senior scientist emerita Dolores Piperno of the National Museum of Natural History and the Smithsonian Tropical Research Institute in Panama, is the latest entry in a nearly decade-long scientific debate over prehistoric human influence in the world's largest rainforest.
"Far from implying that complex, permanent human settlements in Amazonia had no influence over the landscape in some regions, our study adds substantially more evidence indicating the bulk of the Indigenous population's serious impact on the forested environment was concentrated in the nutrient-rich soils near rivers, and that their use of the surrounding rainforest was sustainable, causing no detectable species losses or disturbances, over millennia," Piperno said.
To explore the extent and scale of Indigenous modification of the Amazon, Piperno and her co-authors collected and analyzed a series of 10 roughly 3-foot-long soil cores from three sites in the remote northeastern corner of Peru.
The three sites were located at least a half-mile (about 1 kilometer) away from river courses and floodplains, known to researchers as interfluvial zones. Interfluvial forest comprises more than 90% of the Amazon's land area and is therefore crucial to determining the extent of Indigenous influence on the landscape, precisely because most major settlements identified by archaeologists thus far are near rivers.
Piperno and her co-authors used the soil cores to create timelines of plant life and fire history at each location going back some 5,000 years. To do this, the team extracted long-lasting microfossil particles of dead plants called phytoliths and looked for traces of fire such as charcoal or soot. Fire, in a landscape that receives nearly 10 feet of rain annually, is nearly always human in origin and would have been instrumental in clearing large areas of land for human uses, such as agriculture and settlement.
The team identified which plant type each phytolith belonged to by comparing them with a comparative reference library of modern plants and used radiocarbon dating to reveal how long ago the plants lived. The dating of both phytoliths and charcoal determined the age of the plant fossils and any remnants of fire found in a core.
Finally, the researchers also conducted surveys of the modern forests found around each core. These forest inventories evinced the dizzying diversity of the region, yielding 550 tree species and 1,300 other species of plants.
Piperno said all the analyses pointed in the same direction: "We found no evidence for crop plants or slash and burn agriculture; no evidence for forest clearing; no evidence for the establishment of forest gardens. These are very similar to results from other regions of Amazonia. We now have a substantial amount of evidence that extensive, wholesale alterations of forest across the interfluvial areas of Amazonia did not occur in prehistory."
Instead, the researchers saw a rainforest ecosystem that remained relatively stable for thousands of years and is much like the ones still standing in similarly undisturbed regions today.
"This means that ecologists, soil scientists and climatologists looking to understand this region's ecological dynamics and capacity for storing carbon can be confident that they're studying forests that haven't been heavily modified by people," Piperno said.
But she says it also means we "should not assume the forests were once resilient in the face of significant past disturbance," and added that this has important implications for "good sustainable land use and conservation policies" because such policies "require adequate knowledge of past anthropogenic and natural impacts on the Amazonian ecosystem together with its responses."
In light of these results, Piperno and the research team also find the idea that reforestation following the arrival of Europeans triggered the Little Ice Age implausible.
"Without significant forest clearing in these and other regions studied by our team and others it appears unlikely that there was sufficient forest regeneration to have affected global carbon dioxide after European contact," Piperno said.
As for why there does not appear to have been any large-scale modification of the interfluvial Amazon, the simplest explanation for the pattern may be in the soil, which has so few nutrients that it would not have been desirable for crops and other plant manipulations compared to areas on riverbanks and floodplains.
Piperno said that more work still needs to be done in other yet unstudied regions away from riverbanks and floodplains to obtain a wider view of the vast Amazon and that the team's results do not imply that no form of Indigenous forest management occurred in the region, just that it was not intensive enough to show up in the soil cores.
"To me, these findings don't say that the Indigenous population wasn't using the forest, just that they used it sustainably and didn't modify its species composition very much," Piperno said. "We saw no decreases in plant diversity over the time period we studied. This is a place where humans appear to have been a positive force on this landscape and its biodiversity over thousands of years."
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Funding and support for this research were provided by the Smithsonian, the National Science Foundation, the Wenner-Gren Foundation for Anthropological Research, the European Research Council and the Gordon and Betty Moore Foundation.
CAPTION
An interior view of the Amazon Basin forests where scientists sampled soil cores for their study, with each site located at least a half-mile (about 1 kilometer) away from river courses and floodplains--regions known to scientists as interfluvial forests. The researchers also conducted surveys of the modern forests found around each core. These forest inventories evinced the dizzying diversity of the region, yielding 550 tree species and 1,300 other species of plants. Interfluvial forest comprises more than 90% of the Amazon's land area and is therefore crucial to determining the extent of Indigenous influence on the landscape. Smithsonian scientists and their collaborators have found new evidence that prehistoric Indigenous peoples did not significantly alter large swaths of forest ecosystems in the western Amazon, effectively preserving large areas of rainforests to be unmodified or used in sustainable ways that did not reshape their composition. The new findings are the latest in a long scientific debate about how people in the Amazon have historically shaped the rich biodiversity of the region and global climate systems, presenting new implications for how the Amazon's biodiversity and ecosystems can be best conserved and preserved today. The new study led by Smithsonian researchers, published June 7 in the journal Proceedings of the National Academy of Sciences, suggests that for at least the past 5,000 years, large areas of the rainforest in western Amazonia located away from the fertile soils near rivers were not periodically cleared with fire or subject to intensive land use by the Indigenous population before the arrival of Europeans.
CREDIT
Corine Vriesendorp
CAPTION
Long-lasting microfossil particles of dead plants called phytoliths seen under a microscope, sampled from soil cores taken by scientists from the Amazon Basin. Most phytoliths studied by the team were smaller than the width of a human hair. Scientists used the soil cores to create timelines of plant life and fire history at each location going back some 5,000 years. To do this, the team extracted phytoliths and looked for traces of fire such as charcoal or soot. Fire, in a landscape that receives nearly 10 feet of rain annually, is nearly always human in origin and would have been instrumental in clearing large areas of land for human uses, such as agriculture and settlement. Smithsonian scientists and their collaborators have found new evidence that prehistoric Indigenous peoples did not significantly alter large swaths of forest ecosystems in the western Amazon, effectively preserving large areas of rainforests to be unmodified or used in sustainable ways that did not reshape their composition. The new findings are the latest in a long scientific debate about how people in the Amazon have historically shaped the rich biodiversity of the region and global climate systems, presenting new implications for how the Amazon's biodiversity and ecosystems can be best conserved and preserved today. The new study led by Smithsonian researchers, published June 7 in the journal Proceedings of the National Academy of Sciences, suggests that for at least the past 5,000 years, large areas of the rainforest in western Amazonia located away from the fertile soils near rivers were not periodically cleared with fire or subject to intensive land use by the Indigenous population before the arrival of Europeans.?
CREDIT
Dolores Piperno, Smithsonian.
This forest has stayed wild for 5,000 years -- we can tell because of the soil
IMAGE: AERIAL VIEW OF THE PUTUMAYO REGION OF THE AMAZON RAINFOREST IN PERU. view more
CREDIT: ALVARO DEL CAMPO, FIELD MUSEUM
We sometimes think of the Amazon rainforest as unaltered by humans, a peek into the planet's past. In recent years, scientists have learned that many parts of the Amazon aren't untouched at all--they've been cultivated by Indigenous peoples for thousands of years, and mere centuries ago were the sites of cities and farmland. But that's not the case everywhere. In a new study in PNAS, researchers determined that a rainforest in the Putumayo region of Peru has been home to relatively unaltered forest for 5,000 years, meaning that the people who have lived there found a long-term way to coexist with nature--and the evidence is in microscopic bits of silica and charcoal in the soil.
"It's very hard even for experienced ecologists to tell the difference between a 2,000-year-old forest and a 200-year-old forest," says Nigel Pitman, an ecologist at Chicago's Field Museum and a co-author of the PNAS paper. "There's more and more research showing that many Amazonian forests we think of as wilderness are actually only 500 years old, because that's when the people who were living there died from the pandemics brought by Europeans, and the forest has regrown."
"Far from implying that complex, permanent human settlements in Amazonia had no influence over the landscape in some regions, our study adds substantially more evidence indicating the bulk of the Indigenous population's serious impact on the forested environment was concentrated in the nutrient-rich soils near rivers, and that their use of the surrounding rainforest was sustainable, causing no detectable species losses or disturbances, over millennia," says Dolores Piperno, a researcher at the Smithsonian Tropical Research Institute and the study's first author.
Many plants take up silica from the soil and use it to produce microscopic mineral particles called phytoliths that provide structural support. After a plant dies, these phytoliths linger in the soil for thousands of years. Different kinds of plants produce differently-shaped phytoliths, meaning that phytoliths in the soil can be used to determine what kinds of plants lived there in the past.
For this study, Piperno and her colleague Crystal McMichael at the University of Amsterdam needed soil samples from the Putumayo region of the Amazon rainforest in northeastern Peru. That's where Pitman came in. In his work with the Field's Keller Science Action Center, Pitman takes part in "rapid inventories" of the Amazon, intensive information-gathering trips to document the plants and animals of a region and build relationships with the people who live there, in order to help build a case for protecting the area. Piperno and McMichael reached out to Pitman, a botanist, and asked if he'd be able to collect soil samples as he inventoried the Putumayo region's trees.
"The three or four days that we're at one of these sites feel like running a marathon. We have to get a lot done in a really short amount of time, and so we're up really early, we stay up really late, and somehow these soil cores had to be taken at the same time," says Pitman. "Sometimes we collected the soil at midnight, or during rainstorms, when we couldn't survey trees."
To collect the soil, Pitman and his colleagues, including Field Museum associates Juan Ernesto Guevara Andino, Marcos Ríos Paredes, and Luis A. Torres Montenegro, used a tool called an auger. "It's a long metal pole with blades at the bottom, and when you stick it in the ground and rotate it, it carves out a column of soil about 2 to 3 feet long." The team took samples of the soil at different heights on the column, placed them in plastic bags, and transported them back to the US for analysis.
The soil's age roughly correlates to its depth, with newer soil at the top and older soil deeper within the earth. Back in the lab, the researchers used carbon dating to determine the soil's age and then painstakingly sorted through samples under a microscope, searching for phytoliths that would tell them what kinds of plants were living in the area at a given time.
They found that the types of trees growing in the region today have been growing there over the past 5,000 years--an indicator that unlike in other parts of the Amazon, the Putumayo wasn't home to cities and farmland prior to European colonization.
In addition to phytoliths, the researchers also looked for microscopic bits of charcoal. "In the western Amazon where it's wet year-round, finding charcoal tells you that people were there," says Pitman. "There aren't natural forest fires from lightning strikes, so if something burns, it's because a person set it on fire."
The low levels of charcoal in the soil show that while the forest remained unaltered by humans for 5,000 years, people did live in the area--they just coexisted with the forest in a way that didn't change it.
"One of the scary things for conservationists about research showing that so much of the Amazon used to be towns and cropland, is that it's allowed people who aren't conservationists to say, 'If that was the case, then you conservationists are getting upset for no reason--500 years ago, half the Amazon was cut down and all grew back, it's no big deal. We don't have to worry so much about cutting down the Amazon, we've already done it and it turned out fine,'" says Pitman. This study suggests that while people are able to coexist with wilderness without altering it, the Amazon isn't simply a resource that can be destroyed and regrown from scratch in a matter of centuries.
"To me, these findings don't say that the Indigenous population wasn't using the forest, just that they used it sustainably and didn't modify its species composition very much," says Piperno. "We saw no decreases in plant diversity over the time period we studied. This is a place where humans appear to have been a positive force on this landscape and its biodiversity over thousands of years."
"It's an important finding, and a hopeful one, because it shows that people have been living in the Amazon for thousands of years, in a way that allows them to thrive and the forest to to thrive," says Pitman. "And since this particular forest is still being protected by Indigenous peoples, I hope this study reminds us all how important it is to support their work."
CAPTION
Soil samples collected in the rainforest.
CREDIT
Nigel Pitman, Field Museum
