Certainly tree bark is a component of coal. But tree bark is only a small
fraction of the biomass of a tree. If we don't have enough biomass using
the whole tree, how is using just the bark going to help? I may not be
understanding your point, but making coal out of tree bark doesn't help
alleviate the apparent discrepancy between the present biomass and the
organic mass represented in coal and oil. Better to use the tree, the
leaves, the forestfloor litter, the bark, the fruit, etc., if you want to
make a lot of coal.
Art
http://chadwicka.swau.edu