Forest islands: ancient traces of plant cultivation

The flood savannah in the lowlands of Bolivia is littered with small forest islands. (Image: Umberto Lombardo)

Researchers report that thousands of forest islands in the southwestern Amazon are evidence of an astonishingly ancient cultural landscape. Analyzes of plant remains show that pumpkin and cassava were cultivated on the artificially raised areas over 10,000 years ago. According to the scientists, the area is one of the oldest known regions of origin in agriculture.

Instead of collecting nutrient-rich plants, people once began to cultivate them in a targeted manner: The development of agriculture was a revolution in human history that led to the emergence of all civilizations. So far, at least four independent centers of plant domestication in the early Holocene have been assumed: in the Middle East and China and two in what is now Mexico. The southwest of the Amazon region has also been considered a possible fifth region of origin for some time.

So far, however, the information has been indirect: in this region there are wild forms of important crops such as cassava, pumpkin, peanuts, chilli and beans. So far, however, there have been no clear archaeological traces documenting domestication of these globally important crops in the southwestern Amazon. In the case of cassava and pumpkin, the researchers led by Umberto Lombardo from the University of Bern have now succeeded.

Striking traces of settlement

The archaeological evidence comes from the Moxos Plain in the northern lowlands of Bolivia. It is an approximately 110,000 square kilometer flood savannah: it is flooded in the rainy season – on the other hand, it is extremely dry from July to October, which is why the region is largely characterized by grassy areas. However, there are numerous islands in this savannah landscape: these are areas with an average size of 0.65 hectares, which are slightly elevated and therefore not flooded. Trees and bushes grow on them, making them stand out clearly from the grass landscape even in the dry season.

An earlier investigation had already shown that many of these forest islands are shaped by the presence of humans. Findings of skeletons, charcoal and food residues have shown that they were home to people from around 10,000 years ago. As part of the current study, the researchers led by Umberto Lombardo from the University of Bern now come to the conclusion that there are 4700 forest islands on the Moxos level that were created by human settlement. In 30 of them, the scientists also carried out archaeobotanical investigations to obtain information about the use of certain plants.

Agriculture – over 10,000 years ago

To do this, they analyzed plant microfossils that can remain in the soil for tens of thousands of years – so-called phytolites. These are silica particles, the characteristics of which are typical of certain plants. “Sometimes these plant remains only say something about which family a particular plant comes from, but in some cases – especially with domesticated plants – it can be concluded in a very specific way,” explains Lombardo.

As the researchers report, they were able to use this method to prove that people grew two prominent crops in the area of ​​the forest islands at an astonishingly early stage: “We were able to show that the earliest age for cassava in the Amazon is 10,350 years, for pumpkins 10,250 years and for Corn 6,850 years, ”says Lombardo. “Our study shows that small communities that operate a mixed economy began to shape the Amazonian landscape about 8000 years earlier than previously thought,” said Lombardo. The results also confirm that the southwestern Amazon was one of the few early centers for the domestication of plants, the scientists say.

As you emphasize, the study also shows how early man began to shape entire landscapes: “The very early spread of people in the region had far-reaching effects on the environment,” says Lombardo: The approximately 4,700 artificial forest islands changed the ecological character of these seasonally flooded savannas. “Our study is also changing our understanding of the chronology and intensity of the human footprint in the Amazon region,” said the scientist.

Source: University of Bern, technical article: Nature, doi: 10.1038 / s41586-020-2162-7

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