I have one of the 6' KK rakes from TSC. Works like a charm on rocks, roots, etc. It's very heavy and solid. You didn't mention what kind of ground you have underneath the trees, but if it's good solid turf, you can still use the rake by keeping the tines as close to the ground as possible without touching. Even a little contact here and there isn't going to rip it too bad. But as Island mentioned, you'll still have piles to deal with. Hopefully you have a loader to finish that part.
And if the ground under your trees isn't all that grassy, then you can rake even more agressively without fear of damaging anything. Just make sure that you shorten your top link so the rake teeth are vertical. This less-agressive position will grab less dirt (thereby causing less damage). It will also allow a few more things to escape, which means another pass or two. But that means more seat time.