rough forested?

"There were the sounds of bells, as the monasteries across the rough forested hills of Agion Oros tolled their times to God."

What does it mean by "rough forested"? That the forest is dense?

I'd say that the hills were rough.

... of course, you might interpret it as saying that the forest were rough ... but then, on the other hand, you might not really draw the line between forest and hill so sharply and rather interpret it more or less as indicating that the forested hill (as a single entity) were rough.

"Rough" is also used sometimes to indicate "wild" or "uncultivated". It could also be a visual description of the texture of forest seen at a distance. Or both.

Sometimes you'll see "rude" used in a similar way, although it's pretty archaic now -- a "rude hut" would not be an impolite little house making obscene gestures at you, but a simple one lacking in architectural flourishes.

I would say this refers to rugged forested terrain, that is not really mountanous but definately not flat.