Trees were more common for Japanese defenses then cement, by far. Really, they used their natural surroundings for as many things as possible, with in reason.
So, trees for wall barriers, entrenchment positions, bunkers and etc were very common and would be perfect for a map. If you look at some of the current FH.07 maps you'll notice a lot of wooden fortifications used.
I don't know a lot about it, but I hope that little bit I know helps.