|I have a new crabapple tree,|
|It's hard to say what may have caused the damage. It sounds mechanical (weed whacker, lawnmover), but it could be animal damage. Just to protect the trunk from further damage, why not drive a few bamboo stakes in the ground a few inches away from the trunk? The stakes only need to be 8-12 inches high and spaced 4-6 inches apart all the way around the trunk. This will keep lawnmowers, hoes, weed whackers, etc. from damaging the bark. Squirrels don't normally gnaw on tree trunks in the summer time; boring insects need more than just a few months to discover a tree trunk; field mice might gnaw on the trunk...
You won't need to do anything to the wounds except to allow them to heal over on their own. Don't apply wound dressings or wrap the trunk - these can cause further damage by holding too much moisture against the bark. Just allow the tree to mend on its own and it should be fine.