It looks nice.

I don't know which software you are using, but maybe you could try bumping the flat ground a wee bit...

What I'd do, (In Gimp) is to select the mountains, increase the size of the selection and paint it in white on a different layer. I would also had a few whitish region here and there. Then I would blur this layer and then make it invisible, and use it to bumpe the land layer (and I guess, the forest layer too).
That way you would end up with a bit of gradual elevation surrounding the mountains...