Alex Chepstow-Lusty

An example of a huarango tree, a leguminous hardwood tree that enhances soil fertility and moisture. Alex Chepstow-Lusty

The ancient Nazca people, who once flourished in the valleys of south coastal Peru, literally fell with the trees they chopped down, new research has concluded.

The Nazca caused their own collapse when they cleared their forests in order to make way for agriculture, thus exposing the landscape to wind and flood erosion, according to a study published in the journal Latin American Antiquity.

Best known for carving hundreds of geometric lines and images of animals and birds in the Peruvian desert that are fully visible from the air, the Nazca flourished between the first century B.C. and the fifth century A.D.

During these centuries they made sophisticated ceramics and textiles and amassed one of South America's largest collection of human trophy heads.

Then, between 500 and 600 A.D., this enigmatic civilization slid into oblivion.

"It was not just that they were hit by a huge mega El Nino in about 500 A.D., but that they had already cleared their forests of huarango, a tree that lives in highly arid zones and stabilizes the soil with some of the deepest roots of any tree known-and can live up to 1000 years," Alex J. Chepstow-Lusty a palaeoecologist from the French Institute for Andean Studies in Lima, Peru, told Discovery News.

Stretching down as deep as 180 feet to subterranean water channels, the huarango roots not only suck up water for the tree, but bring it into the higher subsoil, creating a water resource for other vegetation.

"This is one of the most fragile ecosystems on Earth. It hardly ever rains here and the huarango tree is indeed a keystone ecological species," David Beresford-Jones, from the McDonald institute for archaeological research at Cambridge University, told Discovery News.

A leguminous hardwood tree, the huarango (Prosopis pallida) enhances soil fertility and moisture, while being a source of food for humans and animals.

"If you remove it, you destroy the ecosystem," Beresford-Jones said.

That was exactly what the Nazca did. Analysis of pollen from an excavation area of the lower Ica Valley of the Nazca domain, which is in complete desert today, has revealed a sequence of human-induced events that led to the Nazca's catastrophic collapse.

"At the bottom of the profile, I found lots of huarango pollen. This indicates that large forests were originally growing in that area.

Subsequently, I saw cotton pollen and other weeds, but still a lot of huarango pollen. It seems at this stage farming was in balance with the environment," Chepstow-Lusty said.

Then, about 400 A.D., the Nazca apparently stopped growing cotton, switching to large crops of maize.

The researchers found a major reduction of huarango pollen, indicating that people started clearing the forests to plant more crops.

But the agricultural gain from clearing forests was short-lived. When a mega El Nino event hit the south coast of Peru in about 500 A.D., there were no huarango roots to anchor the landscape.

The fields and canal systems were washed away, leaving a desert environment. Today, only pollen from plants adapted to salty and arid conditions can be found, Chepstow-Lusty said.

"The bottom line is that the Nazca could have survived the devastating El Nino floods had they kept their forests alive. Basically, the huarango trees would have cushioned that major event," Beresford-Jones said.

According to the researchers, some important lessons can be learned today from the Nazca's disastrous environmental strategies.

Indeed a similar scenario threatens Peru as the few remaining pockets of old-growth huarango trees on the south coast are being cleared by illegal charcoal burning.

"With most of Peru's glaciers predicted to disappear by 2050, the Andes need trees to capture the moisture coming from Amazonia. A major program of reforestation is desperately required both in the Andes and on the coast " Chepstow-Lusty said.