Wow... your first tg2 image, mine was never this good. I agree with the displacement breaking the mesh, it's bit extreme in the lateral direction maybe. But really damn good job. I think your trees maybe not sitting on the surface correctly, you could add a compute terrain after your last big displacement shader and link the trees population to that rather than the one just after the terrain, or alternatively put the displacements into the terrain tab before the Compute Terrain Node there. Generally you want to put BIG displacements into the Terrain Tab and small ones in the Shader Tab.
Cheers, Simon.
