Beautiful work Cubs, the hair on the first one is just spot on 
I'm really pleased you noticed that actually, because I'm trying to improve my results with long hair. I keep staring hard at things like shampoo adverts, to see how the light moves about on people's hair and the places where you get unexpected deep shadows. It's not easy to get it looking natural and I'm still working on it.
I love the bases the moss on the stones is a great idea and I may steal that if I can work out how its done?
Now that's an old trick I nicked from the WaMP site a few years ago. You gather any old bit of garden moss (roots and all) and then leave it to soak in a solution of 1 part glycerine to 8-10 parts water for about an hour or two. This preserves the moss and stops it from rotting. Glycerine isn't anything scary, it's just a sugar solution - the stuff they use as a base for cough syrup and such. You can get a bottle very cheaply at the chemist, or order it in.
Then after the moss has soaked for long enough, you take it out and leave it on a piece of kitchen roll to dry thoroughly (overnight is good). Then just stick it in a tub or a bag and pinch bits off to use on your bases. If there are bits of mud stick stuck to the roots, just make sure you soak it in plenty of woodglue before sticking it to your base.
I have had problems in the past where the moss yellows over time. This doesn't look too bad, just like dried ferns or something, but now I add a couple of drops of green ink to the glycerine solution at the start and this keeps it nice and green.
Of course, having typed that, I'm wondering if you meant the green stipply moss effect on the little stones on the base? If so, it is what it looks like, just a bit of lime green-ish paint stippled gently on.