Amazon agriculture shapes the landscape

The Amazon region of South America has been a hub of food production for longer than previously thought, according to two new studies.

The first study, conducted by Jennifer Watling and colleagues at the University of São Paulo, Brazil and published in the open-access journal PLOS ONE, unearthed remains of domesticated crops such as squash and beans from an archaeological site in the lowlands of south-west Amazonia. 

The region has long been identified as a major crop-growing centre in the early history of New World agriculture, but these findings have been drawn from genetic analysis of plant species, and little has been presented in the way of systematic archaeological evidence until recently.

The new evidence has been extracted from recently-exposed layers of the Teotonio archaeological site, on the banks of the Upper Madeira River in north-west Brazil. The researchers describe the site as a “microcosm of human occupation” in the area because it preserves a nearly continuous record of human cultures dating back to the Holocene period.

Watling and colleagues analysed the remains of seeds and other plant materials in the most ancient soils of the site as well as residue found on artefacts used for processing food. In addition to beans, squash and brazil nut, they found some of the earliest evidence of cultivated cassava, a crop which geneticists say was domesticated in the region more than 8,000 years ago.

Areas of disturbed forest and a soil type called ‘anthropogenic dark earths’ were also evident, further indications of human alteration of the land.

The researchers believe these results point to the Upper Madeira as a key locality in the genesis of crop cultivation in the Americas. “This discovery at the Teotonio waterfall in Southwest Amazonia is some of the oldest evidence for plant cultivation in lowland South America, confirming genetic evidence,” Watling notes.

The second study, reported in Nature Plants, made similar findings in the east of Brazil. 

A team of researchers from the University of Exeter, UK, found land in the region’s supposedly ‘untouched’ rainforest had been managed more intensively than previously thought, with farmers introducing crops to new areas, growing more edible tree species and using fire to improve the nutrient content of the soil.

The study is the first detailed history of long-term human land use and fire management in this region, and shows how early farmers introduced new crops, grew more edible tree species and used fire to improve soil quality, instead of clearing new areas of the forest.

The research team examined charcoal, pollen and plant remains from soil in archaeological sites and sediments from a nearby lake, tracing the history of vegetation and fire in the area. This provided evidence that the likes of maize, sweet potato, cassava and squash were farmed as early as 4,500 years ago in this part of the Amazon.

The findings also showed that farmers increased their harvests by improving the nutrient content of the soil through burning and the addition of manure and food waste. The researchers believe this could explain why forests around current archaeological sites in the Amazon have a higher concentration of edible plants.

“People thousands of years ago developed a nutrient rich soil called Amazonian Dark Earths (ADEs). They farmed in a way which involved continuous enrichment and reusing of the soil, rather than expanding the amount of land they clear cut for farming. This was a much more sustainable way of farming,” lead author Yoshi Maezumi explains.

Farmers in areas with poor soil quality were able to harvest maize and other crops usually grown only near nutrient-rich lake and river shores through the development of ADEs. This increased the amount and variety of food available for the growing population in the region at the time.

The researchers hope that in an area hit by extensive deforestation, lessons can be learned by the sustainable farming models employed by the early indigenous population. “The way indigenous communities managed the land thousands of years ago still shapes modern forest ecosystems,” adds archaeologist José Iriarte.

“This is important to remember as modern deforestation and agricultural plantations expand across the Amazon Basin, coupled with the intensification of drought severity driven by warming global temperatures.” 

The findings of both studies also suggest that the people of the Amazon region transitioned from early hunter-gatherer lifestyles to cultivating crops much earlier than previously thought.