No displacement applied to any objects. The model does look weird, I believe that was after welding vertices in Pose Ray. The tutorial I followed uses individual cylinders duplicated along a curve, but I re-meshed in blender, and again in Poseray, the mesh looks better but still the same issue.
That's an Xfrog model loaded into the same location, so I'm now less concerned about my model quality. In some of my previous renders there have been similar looking issues but ignored them - see the blocky tree (leaves removed).
At the start of the project I centered the planet at 0 0 0, so the scene is located somewhere near 30669, 6160570, 1653730. I guess this is my problem. I don't think it's feasible to shift my entire scene as the fractals will get messed up etc.