Hello and thank you for contacting AaE for help.

From the picture, it appears to be animal damage - more likely a rabbit or deer.  Since I don't see any other signs of disease nor do you describe anything that indicates disease that doesn't mean there might be disease involvement.  If you have additional information and pictures, feel free to post another question.

The wounds are clean and there is nothing you need to do.  Trees are very capable of healing themselves over time.  You might want to surround the tree with a barrier made of chicken wire or the like.  You could dig it a few inches into the ground to prevent rabbits and others from digging under the barrier.

I also suggest protecting your young tree from winter sun scald by shielding the trunk from sunlight reflected from the snow especially on its southwest side.  Doing so will protect it from cracking open during the warm sunny days that are followed by a sharp drop in temperature as the sun sets.

This can be done in your case (because of the multiple trunks) either by wrapping each trunk in special trunk tape or by putting up a durable piece of cloth stretched between two to three stakes about a foot away from the tree on the southwest and south sides of the tree.  Be sure to remove the tree wrap and shade cover in the spring. 

Good-luck!