as long as for each tree taken down another tree is planted, fire wood can be under this circumstance a sustainable (but not the most sustainable) heating method ^_

problem is that some cities have then a large firewood consumption, and loggers have to travel further and further out to log trees without planting new trees for the future.

currently projects like ecosia (a search engine that uses profits to plant trees) are planting back trees in africa, but i see some interesting projects developing like AI tree planting drones