At www.eurekalert.org/pub_releases/2017-02/uoe-hoa020617.php … an update on the earthworks and human impact on the western Amazonian rainforest. Research s ongoing – aided and abetted by logging and felling. Human settlement in this part of the rainforest is known about and rather than being the province of a few maverick archaeologists it has now become of interest to the Brazilian government and state sponsored archaeology. The image below looks like LiDAR (radar images from the air) but it is mainly the clearance of trees and undergrowth that has enabled the archaeologists to expand on what was limited knowledge.
whilst it looks like the kind of earthwork you might find in Neolithic Europe the article defines it as a geoglyph for some reason. It then adds, these could have been gathering places (which is how they define causewayed enclosures and henges).
The authors of the study say they have reconstructed 6000 years of vegetation growth but only at 2 of the sites. They discovered that humans had been altering the landscape and creating their own fire history, through the course of thousands of year. Clearings were made to accommodate the geoglyphs and other constructs but it did not involve wholesale destruction of the forest. Instead, certain plants/ trees were encouraged – at the expense of others, somewhat like forest gardening (specific plant husbandry). A similar thing was going on in the rainforests of central America. Certain plants were favoured – such as vanilla (at the expense of others). One can imagine nuts and fruits were encouraged and trees with little immediate use to the people were taken down. In other words, the rainforest was not eliminated to accommodate humans (unlike in modern times) but was adapted to human requirements – and when human demographics declined the rainforest came back very quickly.
Note … some of the evidence comes from pits dug by archaeologists in and around the geoglyphs. See also https://phys.org/print405598398.html … and the link provided by Gary at www.livescience.com/57775-humans-altered-amazon-rainforests-geoglyphs.html