close up of lower branch with bark loss and regrowth

close up of lower branch with bark loss and regrowth
Originally uploaded by Heather Johnson

We're worried about the bark loss on our Red Oak. This tree is in our backyard and is a great tree! 40 feet tall and about ten years old. We've trimmed it up, so the lowest limb starts at about 15' high, and it's very healthy and healed over the cuts with new bark well.

I don't know what to do about this bark loss. I'm not sure what caused it, and we're afraid of more occurring.