Weird lighting artifacts on displacements?

I have made a lot of displacements in my map. However the lighting is not uniform on them:

(Latest three screenshots)

You can see that the rocks on the right bottom side of the third picture are darker than they should be.

Any help is greatly appreciated.

The displacements don’t share an edge and therefore produce this lighting.
Make sure the two adjacent displacement-bushes do share an edge…

Are you sure that you only turned the visible faces into displacements? You might have some unneeded displacement faces inside the cliff, causing these weird shadows.

You can use an info_lighting to deal with the lighting on that rock