Hey. Thanks for the appreciation. I haven't had a chance to finish this one yet because of other things but I eventually will!

For the ground I simple use multiple layers filled with textures (or use the Pattern Overlay layer style, either way works) and then paint into a mask to expose that texture where I want it. I tend to use a set of grunge brushes I picked up for this painting, at less than full opacity. My layers are typically a cracked mud texture filling the map area, a sand texture, a dirt texture, and one or two grass or vegetation textures. Over that I'll use some more defined paint blobs on layers with vegetation textures (sometimes with bevel/emboss and/or a drop shadow) to suggest shrubs and larger plants. Trees are done similarly. I've been working unsuccessfully on a tutorial but haven't had much time to devote to it.
M