The world has been dead. Not just people (otherwise we wouldn't need to bring life back to the land with channelers to make it habitable for people). Forests would have largely died out, too... So whatever forests there are would (story-wise, anyways) be fairly new growth along with the few holdout old growths. Kind of like Fangorn Forest in the LoTR. Fangorn Forest used to be part of the Great Greenwood, and used to encompass a huge area, including most of Gondor and I think even included the Mirkwood.

I agree entirely with the "little forest" idea.   I would have suggested the exact same thing.  (I would also suggest something other than "field" to be the empty space.   Things like rock formations (light rocks, so rough terrain), marsh (or just muddy areas), highlands, rolling hills, and the list goes on.  (I vaguely recall a thread on the subject)

Actually, I think "little forests" ared the way to go here: the world has been scorched to within an inch of its life. Surviving outside of the "channeler zone" is tough. Therefore, you would get areas of scraggly, unhealthy trees, that in my opinion fit the exact description of a "little forest"