New research says the extinction almost 1,500 years ago of the ancient South American civilisation behind the enigmatic Nazca Lines was largely self-inflicted as mass deforestation helped to irreversibly destroy the fragile ecosystem they inhabited.

Archaeologists from the UK and France examining the remains of the Nasca, who once flourished in the valleys of south coastal Peru, say they have uncovered a sequence of human-induced events that led to their collapse around 500 AD.

Best known for the Nazca Lines, giant geoglyphs etched into the surface of the vast, empty desert plain between the Peruvian towns of Nazca and Palpa, Nascas prospered during the first half of the first Millennium AD then collapsed into a bloody resource war and eventually vanished.

While some argue that a massive El Niño, which hit the region around that time, may have been the cause for the Nasca's downfall, a team of researchers led by Dr David Beresford-Jones from the McDonald Institute for Archaeological Research at Cambridge University, suggest in an article in the journal Latin American Antiquity, that the Nasca wrought their own demise.

Using plant remains gathered in the lower Ica Valley, the team found evidence that over many generations, the Nasca cleared areas of forest to make way for their own agriculture.

Studies of pollen samples taken by co-researcher Alex ChepstowLusty, of the French Institute of Andean Studies in Lima, showed that the huarango tree, which once covered what is now a desert, was gradually replaced by crops such as cotton and maize.

But the huarango was crucial to the desert's fragile ecosystem, enhancing soil fertility and moisture and helping to hold the Nasca's narrow, vulnerable irrigation channels in place. Eventually so many trees were felled that the ecosystem became irreversibly damaged, exaggerating the effects of El Niño which led to floods the scientists believe would have been far less devastating had the forests been there to protect the desert ecology.

"These were very particular forests," Dr Beresford-Jones said of the huarango. "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 the absence of huarango cover, when El Niño struck, the river downcut into its floodplain, Nasca irrigation systems were damaged and the area became unworkable for agriculture.