actually it's pretty easy to create forests like the ones in redbaron's image.
just take an appropriate brush chose 2 foliage colours for background and foreground (a brown dark green and a yellow light green) then adjust the jitter/scattering/hue/size of the brush and paint your forests. then just add a drop shadow and depending on what you want add just a little bit of bevel. just a hint.
and the hills in redbaron's image are also easy to create. just take a brush and draw the general shape of the hill. then ctrl+click to select that area create a path from that selection. next stroke the path with a brush made of horizontal lines. then you can fiddle with it to get what you want. adjust the hue/saturation, or use a nice grunge brush to delete parts and bits, or add some speckle and noise.
“In the beginning God said, the four-dimensional divergence of an antisymmetric, second rank tensor equals zero, and there was light, and it was good. And on the seventh day he rested.”- Michio Kaku