With careful management and modern forestry techniques I believe sustainable (or close to sustainable) charcoal production is possible, I can remember seeing CS

With careful management and modern forestry techniques I believe sustainable (or close to sustainable) charcoal production is possible, I can remember seeing CSIRO do a study using Australian Mallee trees. These grow fast enough such that you can rotate which part of the plantation you are harvesting to enable something close to continuous production. I can't find paper https://publications.csiro.au/rpr/pub?pid=csiro:EP115427 https://publications.csiro.au/rpr/pub?pid=csiro:EP115427 is closest thing google turns up. You also get eucalypt oil as a by-product from harvesting these trees wikipedia tells me this has a high enough octane rating to serve as a fuel in it's own right. https://en.wikipedia.org/wiki/Eucalyptus_oil https://en.wikipedia.org/wiki/Eucalyptus_oil Now this might be difficult to achieve in a near collapse. I'm not sure the size of plantations you would need I assume would be pretty massive.