Transportation cost is a big element of any bioenergy system. The estimate I gave that maybe 15% to 20% of our current fossil fuel liquid energy consumption could be replaced with bioenergy produced from residues from forestry and farming takes into account both sustainability criteria and technical criteria, as well as, to some extent, production cost.
The estimates of how much residue is available generally come from spatial analysis that considers where this stuff is relative to our transportation networks and our major processing hubs. The higher the value of that fuel, the further afield you might go to get it. Without a doubt, there are certainly some remote logging operations for which it won't make sense to bring in that residue and there are others for which it will make sense.