Trees grow, Wood is the end product.
Wood is probably the oldest BioFuel in existence. Probably when some early human predecessor discovered fire, it was Wood that they burnt.
One of the great things with Trees is that woodland can in a large variety of different habitats. Once the woodland is there, it's actually fairly stable. If a tree falls down another one will grow all by itself. This means that it doesn't actually take a lot of effort to manage an enormous area of Wood. By and large, you can just leave it alone. This means that if you could extract energy from the woodland, using, for example, EnvironmentalSlashAndBurn, then over time the Wood will just regrow with very little effort.