The amount of human conversion in the Amazon is mind blowing, from the fertile ground to the trees in the forest, much was shaped by human intervention. In Bene, a province of Bolivia, there is a 30,000 square mile area that archeologist Clark Erickson believes was completely created by humans in an advanced society more than two thousand years ago (Mann, Charles). What can be seen of it now from an airplane view is an archipelago of islands, some hundreds of acres across and quite round, that come up 10-30 feet above the floodplain and are connected by causeways. Some believe that there were dense zigzagging weirs between the causeways to catch fish. .
Many have heard about how poor the soils of the amazon are, all its nutrients are swept away with the rain, leaving soil that's pretty much useless. Two thousand years ago the Native Americans knew this as well, but they found a way to create fertile soil that scientists today don't know how to do. Scientists believe that the Native Americans found a special kind of microorganism with a transforming bacterial charge and inoculated bad soil with it. This soil has been found to regenerate itself, thus acting like an organism itself, resisting being swept away with the rain. This soil, called Terra preta, has been found in at least 10% of the amazon, an area roughly the size of France, which means that many, but probably not all, Native American societies had much more scientific ability than previously thought. .
If one were to try clearing a field to crop using simply stone tools, they would find it exceedingly difficult, therefore they would not want to have to do it every year. One way to get around this is to plant trees, from a tree you can get twenty or more years productivity, so the Native Americans found. There is a very abundant source of nuts and fruits in the amazon, and the Native Americans used this very much to their advantage.