I've only cut down a few that were directly in the way (and removed leaves of others to unblock the path), but the forest is pretty much untouched, also I decided to follow the contour of the hill southward instead of cutting a tunnel through or making a stairway over it. I didn't do any digging in there yet, but i did leave a pathway of torches for the route I chose.
I stopped at the desert as I haven't decided for sure the exact route there.
If you want the dirt, sand, and saplings, I can give them to you, or put them in public storage.