I love tree crusaders and bucket grinders. It would be wonderful for them to die in accidents here and there...
So.
If there are a lot of trees cut down in a short period of time, the disaster happens in the location. It can be invasion of rats/army of bears/forest spirit/Chuck Norris and so on. Just need to make it unefficient to grind on this purposely (make it once-a-day event, for non-trivial proposal.)
It maybe better not to protect all forests by such a way, but only "sacred" or "dark" ones. Accidents will be fun enough. This also can make population density less monotonous.
edit: Oh, I forgot to put lightning in the list.