Why Does the Amazon Rainforest Has So Many Edible Plants? The Legacy of Ancient Agriculture

“The hyperdominance of edible plants in modern forests in the eastern Amazon” has to do with agricultural practices started at least 4,500 years ago, scientists say.

The image of the Amazon rainforest often conjures a scene of pristine wilderness, untouched by human influence. Lush greenery stretches as far as the eye can see, teeming with an unmatched diversity of life. However, recent scientific discoveries are challenging this notion, painting a picture of the Amazon as a landscape subtly shaped by human interaction for millennia.

One of the most interesting questions emerging from this new perspective is the potential role of early human activity in shaping the abundance of edible plants found in the Amazon today. While the exact number of edible plants directly traceable back to human influence 4,500 years ago remains unknown, evidence suggests a long and complex relationship between humans and the Amazonian ecosystem.

One piece of the puzzle comes from a 2017 study by Levis et al. published in Science. This research explored the “persistent effects of pre-Columbian indigenous populations on Amazonian forest composition.” The study suggests that these populations may have engaged in practices resembling early agriculture, potentially influencing the distribution of certain plant species over time.

The Levis et al. study goes beyond simple presence, however. By analyzing the distribution and abundance of 85 woody species known to have been domesticated by pre-Columbian peoples across the Amazon basin, the researchers found that plants domesticated by these peoples are much more likely to be dominant in Amazonian forests today than other species. Furthermore, forests close to archaeological sites often have a higher abundance and richness of domesticated species. This strong correlation suggests a cause-and-effect relationship, implying that modern-day Amazonian tree communities across the basin remain largely structured by historical human use.

Going deeper, a 2018 study by Maezumi et al. published in Nature Plants offers a more specific perspective on early agricultural practices in the Amazon and their lasting impact. The research focuses on the concept of “polyculture agroforestry” (an agricultural approach involving the cultivation of multiple crops alongside existing trees), by examining clues left behind: charcoal, pollen, and plant remains buried in ancient settlements and lake sediments of eastern Brazil. By piecing together these bits of evidence, they were able to reconstruct the story of vegetation and fire use in the region.

Their findings revealed a surprising fact: as far back as 4,500 years ago, people in this part of the Amazon were actively farming! Crops like maize (corn), sweet potato, manioc (cassava), and squash were cultivated to supplement their diet, and they managed to grow these plants through closed-canopy forest enrichment and limited clearing for crop cultivation.

The Maezumi et al. study also highlights a key innovation: these early farmers actively improved the soil’s fertility to boost their harvests. They developed a nutrient-rich soil called Amazonian Dark Earths (ADEs), also known as terra preta, by adding a mixture of charcoal, bones, broken pottery, compost and manure to the low fertility Amazonian soil. These fertile patches contrasted sharply with the generally poor soils of the rainforest.

Dr. Yoshi Maezumi, from the University of Exeter, who led the study, explains the significance of ADEs: “This was a much more sustainable way of farming. The development of ADEs allowed the expansion of maize and other crops, usually only grown near nutrient rich lake and river shores, to be farmed in other areas.” This innovation likely increased food security for the growing Amazonian population.

Perhaps even more interestingly, the millennial-scale polyculture agroforestry systems have left a lasting impact on the modern composition of forests in the eastern Amazon. Modern botanical inventories show a heightened enrichment in the relative frequency, richness, and abundance of edible plants (trees and palms) on ADE soils compared to non-ADE soils.

“A disproportionate number of plants, accounting for half of all trees in the Amazon, are hyperdominant, and domesticated species are five times more likely to be hyperdominant than non-domesticated species. This is particularly prevalent in archaeological sites, suggesting the effect of pre-Columbian people on modern flora is more pronounced than previously thought,” the researchers wrote.

The Maezumi et al. study also highlights the potential lessons for modern conservation efforts. “Ancient communities likely did clear some understory trees and weeds for farming,” says Dr. Maezumi, “but they maintained a closed canopy forest, enriched in edible plants which could bring them food.” This contrasts sharply with modern practices of large-scale deforestation and industrial agriculture, which have devastating consequences for the Amazon ecosystem.

Professor Jose Iriarte, from the University of Exeter, emphasizes the lasting impact of these practices: “The work of early farmers in the Amazon has left an enduring legacy. The way indigenous communities managed the land thousands of years ago still shapes modern forest ecosystems.” Understanding these sustainable practices becomes even more crucial as modern deforestation and climate change threaten the Amazon’s future.

The Amazon is more than just a vast expanse of green; it’s a living patchwork woven by nature and human interaction. While the exact number of edible plants directly linked to human activity remains elusive, the evidence points towards a long and complex relationship. This newfound understanding of the Amazon challenges the notion of a pristine wilderness and offers valuable lessons for sustainable practices that can ensure the continued health of this irreplaceable ecosystem. If we could just learn from the past, for a change, we could find ways to coexist with the Amazon and safeguard its biodiversity for future generations.