I am more than half Yankee, so I suspected a beaver, but a local friend whose family has been here for generations asked me what is was. I told him if you don't know, I sure don't.
If you have any ideas, please let me know. The wire has stopped the problem but I expect to lose the first tree.
Click on the pictures to enlarge.
I can’t say what caused that without a closer look at the teeth marks. But I can tell you a way to save your tree.
Have you ever tried your hand at grafting?
There’s a trick for saving girdled trees, called a bridge graft. Basically, you take a piece of fresh bark, or a nice springy twig, and graft one end to the living bark at the bottom of the wound, and the other end to the top. Do several per tree, in case some don’t take.
Here’s a good how-to guide: http://www.ladybug.uconn.edu/FactSheets/trees—bridge-grafting-and-inarching-.php
You can also do an image search and find some nice photos of the process.
As long as the tree can transport nutrients along these bridges, it should be able to recover.