It's been some time since I've painted this, but if I remember correctly, this was the process (unless stated otherwise, all colours are Vallejo colours):
Everything was primed white
Whole base was covered with Khaki, then washed with Sepia Wash
A bit of Brown Ink was added to some parts of the base (around the roots/broken branches, for example)
Parts of the base have been lightly drybrushed with Khaki
"Grassy" parts were drybrushed with Camouflage Green and then washed with Green Wash
Rocks were painted with Stonewall Gray (I think), then washed with GW Nuln Oil
Rocks were then drybrushed with Stonewall Gray and Dead White
I hope this helps!