If the damage circumnavigates the entire trunk - removal of the bark, damage to the cambium - then the tree is most likely toast. Sorry. It affects the tree's vascular system or the ability to transport water and nutrients to the upper portions of the tree. If this is interrupted - a common issue with string trimmer damage - then the tree essentially will starve to death.

Don't give up. I have a tree with similar damage that is taking up nutrients and growing, also from careless landscaping. Outer bark gone around 75% of the trunk, about half the trunk missing, if that weren't bad enough what's left of the trunk cracked in half, so the only connection left between the leaves and the roots was a thin strip of outer bark that only went like 25% around.

The leaves of both the injured tree and a healthy tree beside it turned dark green in response to an application of mycorrhizal fungi, which increased nutrient uptake, so it's able to move nutrients. The leaves are still growing, although much more slowly. Leaves perk up at night and after watering.

The most important thing right now is to protect it from bugs, fungi, and disease that will attack an injured plant. I've been battling carpenter ants since the wound, and cinnamon seems to work, but I have to keep applying it every day or two and picking the ants out. Keep the wound dry and free of debris so it can heal over.

Keep the soil as moist as you can without overwatering, but be very careful not to get the wound wet, so that fungi and bacteria can't grow inside.

I would also pre-emptively stake it, because with that much trunk gone, it can break more easily. My tree's trunk might not have broken if I'd staked it to begin with.

10 years ago when we bought this house, there was a small maple with similar damage. While it had beautiful fall leaves,and appeared to have survived he damage, it was about the same size as it was 10 years ago..

Two years ago the top of the crown started to die and last spring the die back was worse. I finally had to take it out. I should have replace it 10 years ago and today would have had a nice tree.