Actually, Sawz, he did not say anything about cutting trees down. He said that among other processes and resources (which he enumerated) clean burning of wood could also be considered.
1. The word clean must have escaped your attention, or you have no concept how it could be done.
2. The word wood, in your mind, means cutting down rees. But there are many other sources of wood, including chips and sawdust from other lumber processes, shrubs, and recycled wood to name a few.
Wake up and think in English, and all will be well.