Farquard

Probably a bit late, but hopefully helps anyone else who stumbles along this post. I had the exact same problem and it was simply because of me misreading the instructions for the Trees HD mod. I had accidentally hidden the trees folder located in textures instead of the one in meshes. To clarify, ensure that you have hidden or deleted meshes/landscape/trees (entire folder) and not textures/landscape/trees (entire folder) in MO file tree for the Trees HD mod. Hope this helps someone else!