You can pyrolize the wood by cooking it in an oxygen-free environment, cooking off almost all of the nitrogen and other nutrients and leaving nearly pure carbon

You can pyrolize the wood by cooking it in an oxygen-free environment, cooking off almost all of the nitrogen and other nutrients and leaving nearly pure carbon in the form of charcoal. Off the top of my head, for a given amount of wood biomass, you can get about a 70% ratio of product to fuel if you use a high-efficiency wood fire to cook the wood itself. Then you can take that carbon, bury it in decommissioned open pit mines, or use it as a soil additive (biochar), where it will sequester the carbon for thousands of years and act as a fertilizer. You could also pair the biochar with a fast-growing swamp tree (willow?), re-incorporating the char into the areas around the willow plantation to create a sort of artificial peat bog which could also be useful for water storage and filtration.