The arrival of European diseases after Columbus crossed the Atlantic in 1492 may also have hastened the growth of forests by killing indigenous people farming the region, the scientists wrote in the U.S. journal Proceedings of the National Academy of Sciences (PNAS).
The scientists said that a shift toward wetter conditions, perhaps caused by natural shifts in the Earth’s orbit around the sun, led to growth of more trees starting about 2,000 years ago.
The scientists studied man-made earthworks, uncovered by recent logging in Bolivia, that included ditches up to about a kilometer (1,100 yards) long and up to 3 meters deep and 4 meters wide.
They found large amounts of grass pollen in ancient sediments of nearby lakes, suggesting the region had been covered by savannah. They also found evidence of plantings of maize, pointing to farming.
PRISTINE
The PNAS study suggests a new idea – that the forest simply did not exist in some regions.
In one lake, Laguna Granja, rainforest plants only took over from grass as the main sources of pollen in sediments about 500 years old, suggesting a link to the arrival of Europeans.
The purpose of the earthworks is unknown - they could have been defensive or for drainage or religious purposes.
And understanding the forest could help solve puzzles about climate change.
(Reporting by Alister Doyle; Editing by Lisa Shumaker)
