I stopped playing after 10 minutes
Not because it was bad. It was a good game. The combat system was well thought out and the general feel of the game was good. You scored with the loading screen, hooked me before the game even began. I just couldn't take the lag and constant battling every 10 seconds.
I believe your lag issues stem from the fact that you are trying to move EVERYTHING at once. Instead of keeping trees completely invisible, try removing them from the stage by calling "removeChild." You should still have a reference to the tree somewhere. Remove trees that are out of the view of the game window and only add them when you need to see them. An efficient way to determine what needs to be affected within a certain area (such as your viewing plane) try using binary space partitioning (Wiki it).