Pit fire ovens are often steam heating arrangements and I've read at least on account of native Americans using such an arrangement to heat shape elk horn strips for horn bows. Dry heat was used on green and dry wood. (Again based on reading, I can't site sources.) Shaping wood by bending the wood green and then tying to a form and allowing the wood to cure in the form was also used. That suggests that all three methods were used by prehistoric ( in the sense of before written records) peoples. That sort of makes a definitive answer impossible. Ron
