With considerable experience (I'm a trapper) I would say that the 1st. beaver did a poor job falling the tree and hung it up on another tree. Later the tree was sawed down by man and removed. Beavers don't eat wood just bark so eventually another beaver from the colony and dined on the rest of the stump. Beavers are very interesting and can do an enormous amount of damage with their choice of dam building sites. Some times many acres of timber or farm land are flooded and they have to be removed. They are also not rare or endangered, There are millions of them and are in every state and providence in U.S and Canada.