I've used rock populations for fake trees before, but you've shown how creative you can be with fake stones yet again.
A working practise I use that you may find helpfull, is by saving a scene in increments like "TreePop01" "TreePop02" etc, except, when I experiment with a scene, I now save as "TreePop02x01" and expand on that until I make a breakthrough to then call it "TreePop03". So that I have obvious markers of when I'm happy with something. I also have a renders folder that I save images as the same file name on the initial increment. I admit I'm a lazy bastard when fooling around and tend to only use this on work projects, but it has proven useful when wanting to roll back a scene.