Lines of contrast appearing between meshes?

I am creating a map which is comprised of multiple mesh tiles. The problem that I am running into is that whether I use realtime shadows or baked lightmapping, there is a distinct separation between the lighting of each mesh, so that each mesh appears to be getting shadows without input from the others. I have included a picture of the problem I am trying to solve.

http://imgur.com/2DqwZvO

Obviously the ideal situation is to have shadows flow evenly between meshes, without having to consolidate the entire map into one mesh.