Forest fires are out of control in this game (meant in a game-mechanic perspective, not a realism perspective). Plus, I don't know of many non-magical creatures that could endure a true forest fire - they should be expelled from the tile with a random amount of damage (if they have nowhere to go, the damage increases with a chance for death). And the game should go back to the old mechanic of burnt forest appearing under the flames. This burnt forest turns into new, then regular forest over time. If the burnt forest is removed (i.e., some builds something on it, even elves), then there is nothing to grow back.