Clearing key trees left pre-Inca culture exposed to floods and drought
Steve Connor, The Independent 2 Nov 09;
At the height of their power, the Nasca had mastered the craft of weaving elaborate textiles and the art of painting fine, multicoloured pottery. They etched giant figures in the desert that only made sense if seen from the air, and they irrigated their crops with a network of underground aqueducts.
For more than eight centuries, the Nasca culture prospered in the coastal valleys of Peru until its sudden downfall around 600 AD, which many experts put down to the torrential rains and dramatic flooding brought on by one of the worst El Nino events in a millennium.
But a team of archaeologists has now found convincing evidence that this was only part of the story. The researchers believe the decline was self-inflicted and began with the cutting down of a tree that could have protected them from devastating climate change.
The Nasca, one of the most important of the pre-Inca civilisations of South America, are most famous for the "Nasca Lines", a series of elaborate geoglyphs etched into the desert covering huge areas, depicting animals, deities and geometric shapes.
After the Nasca Lines were discovered by the first passenger flights over the region, some pseudoscience authors suggested that since they could only be seen frome above, they must have been made with the help of space aliens. It is now accepted that the geoglyphs were created mundanely with long ropes tied to stakes in the ground, rather like present-day crop circles.
The Nasca survived in the semi-arid region by building irrigation canals to grow crops such as maize, squash, sweet potato and manioc. This reliable food supply enabled them to build a relatively sophisticated civilisation based on art and ritual, which nevertheless included the unpleasant practice of collecting severed heads as trophies.
All this came to an abrupt end, according to a new study, because the Nasca made the mistake of cutting down the huarango tree which would have protected them from the El Nino flooding and subsequent soil erosion and drought that turned the lush agricultural land into desert.
"The huarango is a remarkable nitrogen-fixing tree and it was an important source of food, forage, timber and fuel for the people," said David Beresford-Jones, an archaeologist and Nasca expert at the University of Cambridge. "It is the ecological keystone species in the 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."
The researchers have excavated the lower Ica Valley of the Nasca domain and found clear evidence that vast swathes of huarango trees had been cut down to make way for crops. Dr Beresford-Jones believes that the Nasca eventually changed the landscape forever. "In time, gradual woodland clearance crossed an ecological threshold, which is sharply defined in such desert environments, exposing the landscape to the region's extraordinary desert winds and the effects of El Nino floods."
The huarango tree plays a "profound role" in preserving the sort of semi-arid environments where the Nasca lived, the scientists say in their study. "Successful agriculture is just not possible here without the protection afforded by trees. Indeed, these findings have undoubted contemporary resonance."
When the El Nino struck, the river cut into its floodplain, washed away the soil and destroyed the Nasca irrigation systems, making the farmland unworkable. The generations of Nasca that followed suffered higher infant mortalities and lower adult life expectancy.
Eventually, the Nasca capital of Cahuachi was abandoned and all that was left of the culture were archaeological artifacts.
Lost civilisations: Destroyed by nature
*Easter Island
It is thought that the native people felled the majority of the island's trees between 1200 AD and 1500 AD. The loss of palm trees upset the eco-system, driving away wildlife and drying up water supplies.
*Maya
Mayan civilisation stretched across the Yucatan Peninsula until 900 AD when cities were mysteriously abandoned. It is believed that the culture was wiped out by a series of droughts.
Deforestation Sped Demise Of Nasca In Peru: Study
Reuters 3 Nov 09;
BARCELONA, Spain - The mysterious people who etched the "Nasca Lines" across deserts in Peru hastened their own demise by clearing forests 1,500 years ago, according to a study on Monday.
The Nasca people, famed for the lines that depict animals or geometric shapes most clearly visible from the air, became unable to grow enough food in nearby valleys because the lack of trees made the climate too dry, scientists said.
The report, led by Cambridge University in England, said that the findings showed a need for more action now to protect the world's arid lands.
"An ancient South American civilization which disappeared around 1,500 years ago helped to cause its own demise by damaging the fragile ecosystem that held it in place," the university said in a statement.
The Nasca people cleared valleys for farming by felling huarango trees -- a key species which can live more than 1,000 years and helps regulate soil fertility and moisture.
"Eventually, they cut down so many trees that they reached a tipping point at which the arid ecosystem was irreversibly damaged," it said of the findings published in the journal Latin American Antiquity.
Previously, the disappearance of the Nasca people has been blamed by some archaeologists on an extreme El Nino weather event that caused rains and catastrophic floods.
"These were very particular forests," said David Beresford-Jones, leader of the study. "The huarango is a remarkable nitrogen-fixing tree and it was an important source of food, forage, timber and fuel for the local people."
Its extremely deep roots helped create a moist microclimate and its leaves provided fertilizer. Remaining huarango forest in the region is now being destroyed by illegal charcoal-burning operations.
The statement said that most scholars believe the Nasca lines, on a desert plain, were sacred pathways used in rituals. It said "wild theories" included that they were etched by aliens.
"The mistakes of pre-history offer us important lessons for our management of fragile, arid areas in the present," said co-author Oliver Whaley of the Royal Botanic Gardens, Kew.
Climate negotiators from 175 nations will meet in Barcelona, Spain, from November 2-6 for a final round of talks before governments are due to agree a new U.N. pact to combat global warming in Copenhagen in December.
In Barcelona, measures to protect tropical forests will be under consideration to curb greenhouse gas emissions. Trees soak up carbon dioxide as they grow and release it when they rot or are burned.
Logging 'caused Nazca collapse'
Jody Bourton, BBC News 2 Nov 09;
The ancient Nazca people of Peru are famous for the lines they drew in the desert depicting strange animal forms.
A further mystery is what happened to this once great civilisation, which suddenly vanished 1,500 years ago.
Now a team of archaeologists have found the demise of the Nazca society was linked in part to the fate of a tree.
Analysing plant remains they reveal how the destruction of forests containing the huarango tree crossed a tipping point, causing ecological collapse.
The team have published their findings in the journal of Latin American Antiquity.
"These were very special forests," says Dr David Beresford-Jones from the McDonald Institute for Archaeological Research, University of Cambridge, UK who led the team.
The huarango tree ( Prosopis pallida ) is a unique tree with many qualities and played a vital role in the habitat, protecting the fragile desert ecosystem, the scientists say.
"It is the ecological keystone species in the desert zone enhancing soil fertility and moisture and underpinning the floodplain with one of the deepest root systems of any tree known," Dr Beresford-Jones says.
The tree was also a useful resource.
"This remarkable nitrogen-fixing tree was an important source of food, forage timber and fuel for the local people."
Researchers have previously found evidence that suggests the disappearance of the Nazca society was a due to catastrophic flooding event as a result of El Nino around 500 AD.
El Nino is a cyclical event that occurs as a result of a change in ocean temperatures that can cause a change in climate and severe flooding to the the west coast of South America.
The researchers have now found new evidence that suggests the society would not have been so easily destroyed if they had not cut down the forests around them.
Analysing plant remains and pollen in soil 1.5m deep, the team was able to trace an important sequence of events which show the clearing of woodland for agriculture.
"At the bottom of the profile there is a lot of huarango pollen and little evidence of human impact," explains Dr Alex Chepstow-Lusty from the French Institute of Andean Studies in Lima, Peru who also took part in the study.
"Then, at 80cm deep, maize pollen becomes common, showing the importance of this crop, suggesting a greater need for food and an increasing population," he says.
"It is now we notice a big impact on the huarangos and a major decrease in their pollen." "Then suddenly corresponding with the El Nino event at AD 500 or shortly afterwards, the pollen is dominated by weeds in the family Chenopodiaceae, which are adapted to salty conditions and this landscape is now the desert seen today."
The Nazca are famous for creating complex line drawings that can only be seen from the air in the Nazca desert, Peru 400km south of Lima.
They were created between 500BC and 500AD and depict animals such as monkeys and whales as well as geometric figures several kilometres long.
As well as the lines, the Nazca also formed a sophisticated society, constructing complex irrigation systems for agriculture.
However, despite their skills and expertise, the researchers say the Nazca society inadvertently contributed to their own demise through the removal of the tree species.
"The landscape only became exposed to the catastrophic effects of that El Nino flood, once people had inadvertently crossed an ecological threshold," explains Dr Beresford-Jones.
"Such thresholds or 'tipping-points' are sharply defined in these desert environments."
"Our research contradicts the popular view that Native American peoples always lived in harmony with their environment until the Spanish Conquest," Dr Beresford-Jones says.
Dr Beresford-Jones explains that with sufficient huarango cover, El Nino's were in fact not great disasters and actually created years of abundance replenishing water aquifers.
Once too much clearance had occurred the landscape was exposed to the effects of the El Nino floods.
"The river down cut into its floodplain and that floodplain narrowed hugely, irrigation systems were left high and dry," he says.
"Human induced gradual change is just as important to the full story of Nazca collapse as the major climatic impacts that eventually precipitated them."
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