You don't even have to be out in the woods for this to happen. A good friend of mine was cutting his grass one day and heard a loud crash behind him. The only tree in his yard came down, an oak tree that was almost two feet across. And no it was not dead, we were having quite a bit of rain and apparently the ground had softened up and the roots just let go. The grass was much greener in the spot where he stopped for several months.