Thanks for that comment, I have been wondering for the n-th time about the difference. So is it that hiljainen would imply the forest has an intrinsic quality of quietness (Adjective?); and hiljaa means the forest is just being quiet (Adverb?), maybe its actually a noisy forest but right now it is just being hiljaa. I would think using hiljaa instead of hiljainen for a forest might be slightly creepy?