Here's a pic of the damage after a year. I asked some Master Gardeners who were at the local hardware store about it when it first happened. They advised me to remove a couple of feet of the sod around the tree. The theory is that any animal inclined to chew on the trunk (in this case a small one like a rabbit since it was down low) would hesitate to cross the exposed area where they would be more visible to predators. I did that and it seems to have worked.