Farming isn鈥檛 all bad
Don鈥檛 tell Sting, but human activity may not be all bad news for the Amazon. A study of South American savannahs suggests that even before Europeans arrived, farmers were changing ecosystems with a landscaping method previously unrecognised in the region. What鈥檚 more, the pre-Columbian alterations may have increased biodiversity.
鈥淗uman actions cannot always be characterised as bad for biodiversity,鈥� says of the University of Montpellier聽2, France. 鈥淪ome might be good.鈥�
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McKey and his colleagues came to their conclusion after studying some strange features of the savannahs of French Guiana. These plains are flooded during the rainy season, dry and parched in the summer, and often burned by fires. It was while walking through this landscape that McKey started wondering about undulations in the terrain.
It turned out that they are mounds, mostly about 1.5聽metres across and 30聽centimetres high. McKey thinks that pre-Columbian farmers made them as beds for crops that drained well in the rainy season. Sure enough, when the team tested the mounds鈥� drainage capacity, they found it was nine times as high as the seasonally flooded savannah.
New tenants
Once these fields were abandoned between 800 and 400 years ago, plants and animals colonised the mounds, creating a new ecosystem. Specifically, McKey鈥檚 team found that the leaf-cutter ant , the predatory ant and the subfamily of termites preferred to build their nests on the raised beds.
The Acromyrmex, which are fungus-growing ants, even transported large quantities of organic matter to their nest. This in turn has caused the plants on the mounds to grow bigger and their roots deeper. The consequent structural integrity of the mounds and their excellent permeability to water has protected them from erosion by flood waters.
McKey expects that the alterations have been beneficial for the biodiversity of the area. 鈥淚t鈥檚 clear that a savannah with this heterogeneity will have a higher biodiversity than just a flat savannah,鈥� he says.
Besides French Guiana, such mounds can be found in Surinam, Belize, Venezuela, Ecuador, Bolivia and Mexico. The new study is bound to further fuel the debate over whether most of the Amazon rainforest and the associated savannahs are pristine ecosystems. 鈥淭o my mind, the debate has been too black-and-white,鈥� says McKey. 鈥淣ature and culture are interacting to produce interesting things, and maybe that is the way this debate should go.鈥�
, an archaeologist at the University of Illinois, Chicago, and an expert on human prehistory in Amazonia, agrees. Her own research has shown 鈥渁 long, complex sequence of human occupation in that area, despite the fact that many had assumed only a light and late occupation鈥�. The work of McKey鈥檚 team and her own show that 鈥渘ot only have people lived in and altered most of the area of Amazonia, but several habitat types assumed to be natural were not鈥�, she says.
Journal reference: , DOI: 10.1073/pnas.0908925107
