The Amazon was Partly Planted by Humans Over 10,000 Years Ago
Research shows the Amazon isn't untouched by humans, but likely formed because of us.
Hiya!
I grew up learning that Antarctica, the Pacific Ocean, and the Amazon are the last places on Earth that remain mostly or completely untouched by humans. It may have been true when I was taught that (too) many years ago, but as technology and human ambition advance, it becomes less accurate each year. For instance, human activity is already harming Antarctica.
We may feel guilt, anger, and anxiety about the impact modern humans have on our (only) planet and the resulting climate change because of it. But it turns out that, once upon a time, Earth benefited from human activity — and the Amazon is one such example.
Is the Amazon Really Untouched By Humans?
The Amazon is the largest rainforest on Earth. Located in South America, the Amazon spans eight countries and one overseas territory, is roughly 28 times the size of the UK, and is home to an estimated 400 billion trees. It’s wild and mysterious, but is it really as pristine and untouched as experts thought?
Researchers have spent years debating the question. They want to know how much, if any, influence human activity has had on the Amazon, even though humans have inhabited it for at least 13,000 years.
Then, in 2017, a study involving hundreds of ecologists and social scientists worldwide discovered that at least part of the Amazon was intentionally planted 10,800 years ago and, at some point, was left to grow wild.
The Research
Carolina Levis led the massive undertaking as a PhD student at Brazil's National Institute for Amazonian Research and Wageningen University and Research in the Netherlands at the time, and the resulting research was published by Science in 2017.
For the study, Levis — now a faculty member and Research Fellow in the Graduate Program in Ecology at the Federal University of Santa Catarina (Brazil) and a Brazil LAB-affiliated scholar at Princeton University (US) — and her team focused on 85 specific tree species known to be useful for, and domesticated by, Amazonian people for many millennia.
The team laid a map of the Amazon marked with over 3,000 archaeological sites atop another map with data from over 1,000 forest surveys. Then, they analyzed the rainforest’s tree composition at various distances from the archaeological sites to create the first generated analysis of how pre-Columbian Amazonian populations (the people who lived in the Amazon before Christopher Columbus arrived) influenced the Amazon’s biodiversity.
The Results
The researchers discovered that compared to non-domesticated species, those 85 tree species were five times more common in mature upland forests. In an article by Chicago’s Field Museum published by Science Daily, Nigel Pitman, the Mellon Senior Conservation Ecologist at Chicago's Field Museum and a co-author of the study, said:
"That's even the case for some really remote, mature forests that we'd typically assumed to be pristine and undisturbed."
Levis and her team also found some domesticated plants clustered in specific areas of the basin where pre-Columbian settlements have been found. Levis explained to the Field Museum,
"For many years, ecological studies ignored the influence of pre-Columbian peoples on the forests we see today. We found that a quarter of these domesticated tree species are widely distributed in the basin and dominate large expanses of forest. These species are vital for the livelihood and economy of Amazonian peoples and indicate that the Amazonian flora is in part a surviving heritage of its former inhabitants."
More specifically, the researchers analyzed the distribution of the 85 domesticated species across the Amazon and found that nearly 20 percent appear to have been influenced by humans and 30 percent were likely from environmental factors.
Interestingly, the results also showed human activity accounted for about 30 percent of the domesticated tree species in the southwestern part of the Amazon, where pre-Columbian populations existed — while less than 10 percent were from environmental conditions in the same areas. In the Field Museum’s article, Pitman explained:
"Some of the tree species that are abundant in Amazonian forests today, like cacao, açaí, and Brazil nut, are probably common because they were planted by people who lived there long before the arrival of European colonists."
The 85 known domesticated tree species the researchers used for the study are few compared to the over 16,000 Amazonian tree flora estimated to exist in the Amazon. Still, 85 species was enough to reveal a strong human connection to today’s rainforest.
Considering the researchers identified such a link, they believe humans likely had even more involvement in shaping the Amazon than their study suggests since hundreds more Amazonian species were used and domesticated by pre-Coloumbian populations that haven’t been studied yet.
The team hopes to continue untangling the Amazon’s history to better understand the ecological, historical, and environmental factors that created this remarkable overgrown garden.
In the years since Levis’s study, technological advancements, especially LiDar laser scanning, have revealed thousands of previously unknown ancient structures and cities throughout the Amazon — what might the tree flora diversity show there?
Additional Influences
Of course, the results of Levis’s 2017 study don’t necessarily prove that ancient human actions were solely responsible for distributing domesticated plants — and the researchers don’t claim otherwise.
Scientists have already learned to be careful with such assumptions after a larger-than-expected number of breadnut trees, brosimum alicastrum, around ancient Maya ruins once led scientists to believe the Maya civilization cultivated the tree.
However, in another 2017 study published a couple of months before Levis’s, ecologist Charles M. Peters at Yale University showed that bats could be responsible for the wide distribution of breadnut tree seeds in the same areas. Earlier research suggested the trees may have grown near the ruins, not because they were intentionally planted there, but because of the nutrients in the limestone the ruins provide the soil.
Plus, it’s not like the area hasn’t been inhabited since these civilizations lived there. Crystal McMichael, a palaeoecologist at the University of Amsterdam, told Erin Ross of Scientific American:
“It’s quite well known that ancient people and modern people both settle in similar areas. So it’s possible that more modern groups influenced the ecosystems we see today as much as ancient ones,”
Levis also told Ross that, ultimately, her and her team’s research doesn’t mean the domesticated portions of the Amazon were the result of ancient populations to the exclusion of modern peoples — but their study does show that the Amazon isn’t an untouched jungle, but an ecosystem humans have helped craft for millennia. And that, if we look closely, we can still see their marks all these years later.
Perspective Shift
Our technology has made us arrogant. We create rocketships and gadgets and think we know everything while viewing our ancient ancestors as naive know-nothings. Yet, while they didn’t have the technology we have, I’d argue that, in many ways, our ancient ancestors understood Earth a whole lot better than we do.
In fact, research since Levis shows that thousands of small mound forests of around 300 trees scattered across the Amazon in northern Bolivia were created by humans over 10,000 years ago and are one of the earliest known centers for plant domestication in the world.
Further, ancient Amazonian populations composted their food, waste, and charcoal to produce black earth, which is highly fertile soil that healed Amazonian soil and enabled it to sustain large, complex societies — and the practice is still used today by modern inhabitants.
Other ancient populations worldwide constructed massive cities and aqueducts that are still around today — some still work — rather than the cheap, ephemeral, and sometimes toxic construction we’ve used over the last few decades. All this time, we assumed that the Amazon, as wild as it is, was relatively untouched by human hands. Now, we’re learning just how wrong we were. Our ancestors were intimately connected with Nature in a way we’ve lost sight of while sequestering ourselves away, but it’s not too late to learn from them.
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Interesting and perspective-broadening. Thanks
So, Johnny Appleseed had a bunch of southern spiritual ancestors ten or more millennia ahead of his time? ¡Qué interesante!