What happens to trees from one life zone to the next

So a life zone is a place where both plants and animals live together--it's a specific habitat and there are many different life zones. Trees are planted in the ground, and once full grown can not be moved around, or else they will die. Their roots are in the ground and when taken out will be broken, it would be like taking the tree off life support. Therefore, trees cannot live in more than one lifezone because they cannot move without dying.