I'd recommend using something like http://ltrees.codeplex.com/ as it uses billboard foliage rather than the individual polys for leaves as in your example screen. is also fairly easy to convert it for instanced drawing as well . (have a look at http://code.google.com/p/xexuxjy-xna-games/source/browse/trunk/MagicCarpet/MagicCarpet/com/xexuxjy/magiccarpet/terrain/TreeManager.cs)