12 October 2009, by Sara Coelho
The Nazca people of ancient Peru were partly responsible for the collapse of their environment and the downfall of their own civilization as they cleared old forests for agricultural use. Without the trees, the valley they lived in was exposed to dry winds and catastrophic flooding.
The river valleys of southern Peru are an arid landscape, swept by some of the strongest winds on Earth. Water flows in the river beds only a few months per year and vegetation is sparse. But until 600 AD, the valleys were covered with trees and agricultural fields and were home to the ancient Peruvian civilization that built the world-famous Nazca lines.
'We have found very obvious evidences of changes in land use in the lower Ica Valley,' says Dr David Beresford-Jones, an archaeologist from the University of Cambridge. 'This land was once very productive and is now a desert - we wanted to know why.' Given the global interest in the Nazca lines, 'it's surprising how little we know about how this people actually lived,' he adds.
'By understanding past mistakes we can learn how to manage our present resources better.'
David Beresford-Jones,
University of Cambridge
Beresford-Jones and colleagues surveyed the lower Ica Valley, about 200 km south of Peru's capital Lima, searching for signs of human occupation. They were looking for the archaeological remains of the Nazca people, including pottery and ancient rubbish heaps that provide information about daily routine.
The team also looked for physical traces of environmental change. Microscopic pollen grains, preserved by the area's dry climate, revealed that the Nazca people grew maize, cotton and other domesticated plants in the floodplains of the river Ica in a landscape dominated by the huarango, a large, slow-growing hardwood tree of the genus Prosopis.
An ancient Prosopsis Usaca tree.
'The huarango was an important source of food, firewood and building materials,' says Beresford-Jones. The tree is well adapted for life in an arid environment, with a huge root system reaching up to 50 metres deep. The huarango was not only useful for the Nazca: 'the tree was the ecological keystone that kept the soil fertile, protected the valley against the wind and held the floodplain together with its roots,' explains Beresford-Jones.
Beresford-Jones and colleagues found over 60 huarango tree stumps preserved in the arid climate of the Samaca Basin and evidence that the forests were progressively replaced by agricultural fields. 'They removed the big trees to clear land for agriculture,' he says. 'After a while, they must have crossed a tipping point without realising it.'
For without the protection afforded by the huarango, the lands of the lower Ica Valley became exposed to strong winds from the Pacific. The valley sediments also tell a tale of a severe flood around 600 AD, probably the result of a strong El Niño climatic event.
'In normal circumstances, the floods would have been welcome for the agriculture,' says Beresford-Jones. But without the trees to hold the floodplain in place, the flood cut the valley open leaving their irrigation system high and dry, according to the paper published in the journal Catena.
To Beresford-Jones, these findings contradict the popular view that Native Americans always lived in harmony with their environment. 'What happened in the past is an important lesson for today,' he says. 'By understanding past mistakes we can learn how to manage our present resources better.'
David Beresford-Jones, Helen Lewis, Steve Boreham. Linking cultural and environmental change in Peruvian prehistory: Geomorphological survey of the Samaca Basin, Lower Ica Valley, Peru. Catena, 2009. doi:10.1016/j.catena.2008.12.010.
Source http://planetearth.nerc.ac.uk/news/story.aspx?id=558
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