It's hard for me to tell the scale, but that area doesn't really look big enough for a whole forest. Maybe a small patch of trees, but indeed I was picturing something like dod_forest when I first heard about it. You should do what skals suggested and put trees atop the rocks so it actually looks like you're surrounded by trees. Also, have some overhanging brush-based branches/leaves sticking out from the rocks (also much like dod_forest) and that should complete the feel.
Basically, just look at what they did in dod_forest and copy it.