Thinking about my response to the earlier post in Huffington post about using food crops to make biofuels, I started looking at the amount of fuel that could be generated from existing forest materials such as brush wood. There's a paper on Science direct which gives this as the yield from scrub in Galicia (northern Spain).
Bushes occupy around 15% of the forest surface of Galicia , approximately 450 000 ha. A rational planning would allow to obtain about 4x 6 ton of forest residues every year.
The thrust of the piece is in terms of electrical energy generation, but this kind of forest waste could be used to make liquid fuels. It could also be generated during forest management that could reduce the level and intensity of forest fires.