Blending material problem

I am trying to blend 2 textures based on height to create moss effect (see picture of nodes)
And get a problem with lightning. When there is only original texture on the mesh everything is fine, but when i add moss dark areas appear. No matter is lightning build or not. Why it is happening?
Any ideas can help. Thank you!! [alt text][1]

Not sure what’s wrong with your setup exactly, but this is a different way to mask the top of the mesh. it’s a bit more flexible, if you want the moss the grow more on the north side of the tree just tweak the 0,0,1 vector.

Thank you, I’ll check it out!