In my latest game, I got my capital in an all plains zone, with only one big source of food. Big production in the beginning, I cut all the forests, got quite a few wonders done, but after that, as the game progressed, It stayed around 10 pop, and remained a second grade city.. Haven't even bothered building stuff around it (not more than I needed, anyway). So I got forested (about 9 or 10 in th fat cross). Than, guess what?... Medicine -> Natuonal Park-> presreves-> and now my capital is again one of my best cities.
It kinda fits in nicely with my being Sitting Bull. (philosophical and all)