AThis is a very rough iced buttercream, so you could get this effect by icing your cake in a base color of beige buttercream, then tint several bowls of buttercream in dark green and brown, and light brown and lighter green. Then you apply it like with a small spatula or pallet knife. Just get a dab of it on the end of the knife and smear it across, then repeat.
AThanks Anna! Doesn't it look like its a smooth buttercream, airbrushed?
It may supposed to be smooth, but my crumb coat is smoother, so it is hard to say ;-) I like the thought of applying it with a spatula.
AThank you! I'll try the spatula with green and choc b/c! Thanks!!