need a pic.. for an opinion ...

ken

Is the tree dead or still alive?
If it is still alive leave it be.

If the tree is alive and doing well I wouldn't do anything. That does not sound like much of a scar, and the tree will likely just grow over it as time goes on.
Renais

I'm not sure if it's "not much of a scar" considering that the entire trunk is only about 2 inches in diameter. Remember I said the tree has only been planted for a couple of years so it's not very large at all. In the last month I've noticed a yellowing of the leaves, more yellow than it's neighbor that wasn't gnawed on and has no scar. :(

Not necessarily a goner. A photo might be helpful.
Wife backed a trailer into a 15-yr old bur oak in the yard here, 3 yrs ago. Knocked a 1-ft square(mostly) chunk of bark off. I replaced the loose bark and wrapped with parafilm(I have an 18" wide roll) duct tape & aluminum foil. The displaced bark did not 're-seat', but the tree has done an admirable job of closing over that defect - not quite there, but another year, and I think it'll be sealed over by callus tissue rolling in from the edges.

I'll try and get a photo and put it in here, what's really bothering me now is the yellowing of the leaves. I can't help but think that it has to do with the big open spot on the tiny little trunk. The trunk is only a couple inches in diameter and the opening is about an inch...ugh!