Thanks for your comments, guys. The purple is blossoming heather. As it happens we live near a nature reserve with many acres of the stuff, which is blazing purple each fall. Even more so than here. This is a mix of rough grass and heather. The heather is made of little fake rocks and displacements, was quite tricky to get it to mimic the rough heather structure.
Yes, it's easy to paint in the tree trunk, but I just wondered why it happens. I'll make a crop render.
It may look like cattle country, but this is Holland. We had these rough areas (heather, grass, swamps) where people had herds of sheep rather than cattle. The shepherd has to be drawn in in afterwork. This is based on archeological finds of the hills and circular trenches, so an 'exact' replica of what it might have looked like back then. Nobody knows why these lines of poles were there, perhaps some kind of worship thing. I made a huge black image in PS to get the dots as precise as possible, and attached a displacement shader.
---Dune
