I think you could add ash as a resource.
Ash could be used in a wide variety of things:
- wood/charcoal ash for fertilizing plots of land (ash is rich in Phosphorus, Potassium and Sodium)
- wood/charcoal ash for glassware (potash[K²Co³ content of ash] was used in glassware as a flux)
- wood/charcoal ash for cooking (potash[K²Co³ content of ash] was used for baking as baking soda)
- coal ash contains less nutrients but a high amount of radioactive material (use in late game atomic reactors after enriching?) that pollutes the ground if not contained like tailings so you can go either way, deforest more rapidly or risk pollution of ground
- use in gunpowder (e.g. ash+any coal+ iron, if guns for hunting are ever added in late game. (ash can be used to extract nitrates from various sources which are used in gunpowder)