It is a forest with some modifcated trees. Everything created without modification.
(from Minecraft Project City)
This is a small forest with a few birch trees, at the bottom still placed some mushrooms. Otherwise, Podzol or other building blocks could be used as soil. But that's still to come, you can decide for yourself.
This photo is from the Minecraft Project City.
I'm sorry for spelling mistakes, I'm from Finland.