Wednesday, November 4, 2009
The civilization disappeared mysteriously around 1,500 years ago, after apparently prospering during the first half of the first millennium A.D. in the valleys of south coastal Peru. Scientists have previously suggested a massive El Niño event disrupted the climate and caused the Nasca's demise, but new research suggests that deforestation may have also played an important role.
The Nasca are best known for leaving behind large geoglyphs called Nazca lines carved into the surface of the vast, empty desert plain that lies between the Peruvian towns of Nazca and Palpa. Though the lines have spawned many interpretations, including the suggestion that they were created by aliens, most scholars now think they were sacred pathways that Nasca people followed during their ancient rituals.
The enigmatic society that once flourished apparently collapsed around 500 A.D. after a bloody resource war. To investigate this event a team of archaeologists led by David Beresford-Jones from the McDonald Institute for Archaeological Research at the U.K.'s Cambridge University gathered plant remains in the lower Ica Valley. Based on this evidence and pollen samples collected by co-researcher Alex Chepstow-Lusty of the French Institute of Andean Studies in Lima, the scientists found that the Nasca cleared huge areas of forest to make way for agriculture. The native huarango tree, which once covered what is now a desert area, was gradually replaced by crops such as cotton and maize.
This vital tree was a crucial part of the desert's fragile ecosystem, serving to enhance soil fertility and moisture and help hold the Nasca's narrow, vulnerable irrigation channels in place.
Eventually, the people cut down so many trees that they reached a tipping point at which the arid ecosystem was irreversibly damaged, the researchers found. At this point a major El Niño event likely occurred, triggering floods made much worse by the lack of forests that used to protect the delicate desert ecology.
"These were very particular forests," Beresford-Jones said. "The huarango is a remarkable nitrogen-fixing tree and it was an important source of food, forage, timber and fuel for the local people. Furthermore, 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 Niño floods."
Without the huarango cover, when El Niño did strike, the river down-cut into its floodplain, Nasca irrigation systems were damaged and the area became unworkable for agriculture. This finding fits with other evidence that shows that the generations that came afterwards did not fare as well as their predecessors: infant mortality rose, while average adult life expectancy fell. The crops cultivated by their ancestors disappeared in the lower Ica Valley and the area was probably afflicted by a severe drought.
The research also stresses the importance of huarango woodlands for sustaining livelihoods and creating fertile areas in these environments. There are now no undisturbed ecosystems in the region and what remains of the old-growth huarango forests is being destroyed in illegal charcoal-burning operations.
"The mistakes of prehistory offer us important lessons for our management of fragile, arid areas in the present," said co-author Oliver Whaley of the Royal Botanic Gardens in Kew, England.