The Amazon: A Savannah before a Forest
The Amazon is the largest tropical forest on the planet, covering about 6.5 million square kilometers, although much has been lost (around 18-20 percent) in recent decades. The great forest also, very likely, contains the highest biodiversity of species on land; for example a single hectare in Yasuni National Park contains more tree species than all of the U.S. and Canada combined. Yet new research published in the Proceedings of the National Academy of Sciences (PNAS) finds that quite recently—just 500 years ago—a significant portion of the southern Amazon was not the tall-canopied forest it is today, but savannah.
"These results were very surprising. We went to Bolivia hoping to find evidence of the kinds of crops being grown by ancient Amerindian groups, and to try to find how much impact they had on the ancient forest. What we found was that they were having virtually no effect on the forest, in terms of past deforestation, because it didn't exist there until much later," said lead author John Carson with the University of Reading.
For centuries scientists believed the Amazon rainforest had been largely unsculpted by man, only inhabited by small bands of hunter-gatherers with a light environmental footprint. However, that view has been challenged in recent years. Deforestation across the southern band of the Amazon has revealed clear marks of human societies: large geometric earthworks, whose purpose remains unknown, but whose construction was definitely the work of people.
The discovery of hundreds of these geoglyphs—in the form of ring ditches—has led a number of researchers to argue that the Amazon was, in fact, densely inhabited prior to the arrival of Christopher Columbus with his Old World diseases. This theory is also supported by many of the historical accounts of the Amazon by early travelers, some of whom describe large, complex civilizations in the forest and dangerous warriors. In fact, it was a description of a particularly fierce band of female warriors that gave the forest its name. Proponents of a more civilized Amazon further argued that these large populations hugely impacted the ecosystem through millennia of large-scale slash-and-burn farming. Instead of a wilderness, they say, the Amazon was more like a garden; only after Columbus brought genocide with him, did the forest become what it is today.
However, the new research rejects both these theories at their most extreme.
"Our unexpected findings reveal a surprising third scenario, in which earthwork builders took advantage of a naturally open savanna landscape, which existed under drier-than-present climatic conditions before around 2,000 years ago," the paper reads. "This finding suggests lower environmental impact, less labor, and possibly a smaller population than previously assumed."
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Amazon forest image via Shutterstock.