Ashes - new feature/improvement?

[Optimizer]

I have thought of adding Ashes, as a new terrain feature or terrain improvement.

Ashes would appear after pillaging, clearing forest/jungles, and maybe randomly.

It would decrease the productivity of a tile and provide a defense penalty. It would disappear automatically in one or a few turns.

 

[mayonaise]

considering the absolutely mamoth size that each tile portrays that would be a lot of ashes