Lumber as a Cheat
I think that lumber needs to be treated as a constructed object, thus once placed you pick it back up as lumber. As it is now if you learn the efficiency skill, you can place lumber down then chop it down back into logs. With this in place you can essentially create new logs from nothing and never have to cut another tree down, thus eliminating a key aspect to the ecological side of the game.
Yep, we've noted this as an exploit on github:
Its not really nothing it takes a lot more time and calories to produce logs from lumber. Only really worth doing if you have no tress to cut down or have no woodcutting efficiency.