I'm told this can't be fixed. We'll just have wait it out. See if the tree will survive. Is that the case?
Edit: Thanks all. I'll replace it and properly protect this time.
I've had some trees survive if they weren't chewed right down to the sapwood. I would coat the trunk with a wound coat or just get another tree. I cage vulnerable trees with at least 2 feet of hardware cloth, go 4 feet if you have a deer problem. If there are a lot of brambles or other small trees around rabbits usually prefer them.