The ancient South American Nasca civilization may have caused its own demise by clear-cutting huge swaths of forest, a new study has found.
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.
The new study is detailed in the journal Latin American Antiquity.
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