I harvest vine maple in an area where a smooth green bark variety co-exists with a rough brown bark variety. In this area I don't think the differences have anything to do with moss. I like to remove the bark shortly after cutting (because it is such a bit*h to get off if you let it dry) and I've noticed that the brown variety will often check along the surface of the back whereas the green variety does not. I've also noticed that the brown variety does not seem to respond as well to belly tempering as the green variety.