Had an interesting conversation about the problem tree activity with some people who are using it in the context of a migrant worker organizing project. As part of a series of monthly worker assemblies, they are facilitating a three part problem tree activity -- one session for generating the leaves, another for the branches/trunk, a third for the roots. Where to go after that is not settled, it seems, but they seem to be thinking of some kind of discussion of solutions.
No popular education technique has spread as far and wide as this one. I first learned it from Eleonora Castano Ferreira and Joao Castano Ferreira, thanks to Maureen LaMar at the old International Ladies Garment Workers Union Worker-Family Education Program. To my mind the authoritative version is the one found in Volume 2 of Alforja's Tecnicas Participativas Para La Educacion Popular.