TropicBreeze. Yes. As you mentioned slash-and-burn creates a mosaic of different fields at different stages of returning from human cultivation back to wild re-growth within an ecosystems. I think some of these use a 20 year cycle or more, but under population pressure are forced to re-cycle less land more often.
Im not really sure if terra preta soils are simply successful slash-and-burn or if there is something different going on there. But it is true, that ethnographic practice of slash-and-burn is considered to be temporary, not permanent. At the same time it creates a complex man land relationship in that there are different fields at different stages of regrowth at any given time. This means more food resources are available not only to the human community, but to game animals as well. Lots more for the dinner table.