The foliage setting that made the largest difference for realism was radius. It stopped the trees from being almost inside of each other, and the same goes for the ferns. Adding vegetation makes the world so much less flat. It makes the grass texture less of an imitation of foliage and more of an addition to the foliage. Forests and fields can set the mood, depending on density, human touch, and time of day. They can also serve to add walls for the player.