thanks for your helpfull comments !!!
I did the render once more and resized the terrain. The problem was, that it is an old WM-Terrain with a mountain height of 2000m. But when loaded in TG2, the altitude of this terrain grow up to over 22000m!
I added 3 fake stone layers (large, medium and small) and changed the POV
This is now the original render - no colours, staturation, brightness manipulation in PS. Only the trees and the birds are added in PS.
But I don't know which version is better: this one with the part of the tree on the left side or the image without the left tree ...
What do you think?