Hm, I like the ancient forest looks, it gives more satisfaction to know that you've turned your whole empire into a uniform dark mysterious land of trees. I've never noticed the row pattern.
On the burning thing, I agree it's very annoying, do ancient forests have a lower chance of catching fire? if you have good roads you can always shuttle around adepts with spring, but that's annoying. The real problem is that the moment flames appear, your towns vanish. I'd say that it'd be nicer if the got pillage one level per turn by flames, except when you stop flames manually, the forest diassapears altogether, and you have to raze your town anyway, if you want to bloom again. Maybe towns should also lowered the chance of flames, after all, most people have a mild aversion to seeing their homes burned to the ground

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On the other hand, playing against the fellowship, I'm always reluctant to try to fireball/meteor their lands to death because there's a good chance that a treant will show up to punch my face in.