So people have been asking for tutorials so here is one! It's pixel but I use the same technique for regular hair shading as well. Uhm basically it's pretty simple. I personally don't use dithering...
Pixel Tree Tutorial by ~D-e-n-a on deviantART
Some pixels 2 on Behance
Isometric Pixel Art - Space Invaders. Illustration by Army of Trolls.
How I draw bushes by the-searching-one.deviantart.com on @deviantART
Tutorial: FASTER Pixel Art by ~Soprie on deviantART
Pixel Shading Tutorial