(If this post belongs in another section, just kick its butt where it does, I don't know my way around just yet )

I've decided to start a new world map using brushes I made myself instead of the premade/downloaded ones I have accumulated. I've been looking for a few tips, pointers, or (hopefully) tutorials for two things:

1. Trees.
2. Mountains.

Trees always float in the atmosphere, how do I get them grounded?
I've searched everywhere for beginner tutorials for drawing mountains, specifically for maps but I'm guessing my search keywords/parameters might be off because I haven't found anything on either DA or here at the guild. I was thinking of something similar to the Rivers sticky that's here? Any help would be MUCH MUCH appreciated and would save me from pulling out my hair.

Click image for larger version. 

Name:	pitamap.png 
Views:	69 
Size:	179.0 KB 
ID:	44230