An ancient civilisation brought about its own demise by destroying forests which kept its delicate ecosystem in balance, according to researchers who claim the discovery has important implications for the modern world. Archaeologists examining the remains of the Nazca, who once flourished in the valleys of south coastal Peru, discovered a sequence of human-induced events which led to their 'catastrophic' collapse around 500 CE. "There are rearrangements of settlement, there is evidence from human bodies that life expectancy was falling and infant mortality rising, and the orthodox understanding is that something awful happened," said David Beresford-Jones, of the McDonald Institute for Archaeological Research at the University of Cambridge. "The major ceremonial site at Cahuachi was also abandoned."
     The Nazca civilisation, noted for creating vast patterns in the desert that can only be seen from the air, disappeared partly because it damaged the fragile ecosystem that held it in place, a study found. Author Oliver Whaley, of the Royal Botanic Gardens, Kew, said: "The mistakes of prehistory offer us important lessons for our management of fragile, arid areas in the present."
     In the study published in the journal Latin American Antiquity, the researchers found that the Nazca cleared areas of forest to make way for their own agriculture over the course of many generations. In doing so, the huarango tree, which once covered what is now a desert area, was gradually replaced by crops such as cotton and maize. But the tree was crucial to the desert's fragile ecosystem as it enhanced soil fertility and moisture and helped to hold the Nasca's narrow, vulnerable irrigation channels in place, the researchers said. The Nazca eventually cut down so many trees that they reached a tipping point at which the arid ecosystem was irreversibly damaged. An El Nino-style flood then occurred, but its impact would have been far less devastating had the forests which protected the delicate desert ecology still been there, they said.
     Dr David Beresford-Jones said: "These were very particular forests. The huarango is a remarkable nitrogen-fixing tree and it was an important source of food, forage, timber and fuel for the local people. It is the ecological 'keystone' species in this desert zone, enhancing soil fertility and moisture, ameliorating desert extremes in the microclimate beneath its canopy and underpinning the floodplain with one of the deepest root systems of any tree known. In time, gradual woodland clearance crossed an ecological threshold - sharply defined in such desert environments - exposing the landscape to the region's extraordinary desert winds and the effects of El Nino floods." He said the study contradicted a popular view that Native American peoples always lived in harmony with their environment until the Spanish Conquest.

Sources: Telegraph.co.uk (1 November 2009), The Guardian, Times Online (2 November 2009)