Thanks for the crits and comments everyone
Raging and Gilles, my idea was to actually create this "empty" plains-line atmosphere from the tree tops. Anyway if I have time tonight I'll make another one, with height and color variation, to see if it looks better.
About the fog, I removed it 'cause it looked kinda toxic and depressing. While I liked the effect on the first pic, the rest are not as empty and they don't need it. Instead I used a very light dark orange fog.