This article from National Geographic talks about a really interesting discovery of towns in the middle of Amazonia. Interestingly enough, it seems that the inhabitant where practicing a form of forest gardening!
I had read from some permaculture sources that it appeared the native americans were practicing a form of permaculture, but I had never investigated the question further. This article also talks about the natives in New England managing the chestnut, hickory and walnut trees. Pretty cool!