The projects worked on by Mike Hands, after almost 20 years of research and testing of sustainable, or non-sustainable alternative systems, have some answers:   

1. Fundamental insights have been gained into why the practice of slash and burn is temporarily successful; but also into why it fails widely after one or, at most, two crops have been grown.  In other words : "What drives shifting cultivation?"
2. Exhaustive basic research has led to the development and successful testing of a sustainable alternative system which will enable the farmer and his family to remain on one cleared site and not to have to seek fresh forest to burn in order merely to stay alive.