Second try... Quite changed!
Completly revisited clouds, disposition and shading of the trees, fake stones and atmo.
I also tried to make the grass more realistic.
I am not satisfied of the lowest-level clouds, I am going to play with them during the weekend.
And I also want to work on the surface layer under the grass.
What do you think?

Oh... everything is procedural exept of the texture of the bark.