From the Discovery News article: Peruvian Desert once a Breadbasket:
Throughout human history unsustainable agricultural practices have turned fragile ecosystems into wastelands and left people starving. During the Dust Bowl, American farmers learned the consequences of removing the deep rooted grasses from the Great Plains when the soil blew away in tremendous dust storms. Icelandic shepherds learned that the sheep rearing practices their ancestors used on the European mainland destroyed the thin soils of their island and left them with starving herds and little to eat.
The ancient inhabitants of what is now Peru also learned the unhappy consequences of farming in a delicate ecosystem. The Ica Valley, near the coast of southern Peru and the famous Nazca lines, is now a barren desert, but was once a fertile floodplain, anchored by the roots of the huarango tree.
People were able to raise a variety of crops there for several centuries. But intensive agriculture in pre-conquest times led to ecosystem collapse. The history of the land was recently reconstructed by bioarcheologist David Beresford-Jones of the University of Cambridge by looking at plant remains left in ancient garbage heaps.
Beresford-Jones and a team of archeologists studied plant remains associated with settlement sites spanning roughly 750 B.C. to 1000 A.D. They observed the change as the valley inhabitants went from eating mostly gathered foods, to a period of intense agriculture, then back again to surviving on what they could eke out of nature’s diminished bounty.
“The farmers inadvertently crossed an ecological threshold and the changes became irreversible,” says Dr. David Beresford-Jones of the University of Cambridge.
. . .In less than two thousand years, the people went full circle and ended up eating what their ancestors had, but without the huarango forests. To this day, the land is barren, with only the ghostly outlines of irrigation canals to suggest that the land once supported an agrarian society.