I think the shadows make the screens look as cool as they do. You've done really well there. This may or may not work for you, if you get z-buffer issues with trees and have to apply a material to stop it, you may want to separate the trunk from the leaves so that the trunk isn't using the material, this way you may have more control over it's lighting and shadows. Also you can set up bone or vertex animation of the leaves and animate them in script to get them to sway in the wind.