Maybe try wrapping affected area with tree wrap or putting a narrow wire enclosure around the trunk for awhile.

Acer rubrum in case you're interested.

Dax

My guess is it might be squirrels, but they do most of their feeding like this in the late winter or early spring when other food is scarce.

Excellent. Maybe they're climbing the darn thing tearin it up. Any more and here comes the chicken wire!

To this point Dax it hasn't displayed very good fall color. Been blaming that on age or location. Maybe dumb luck.

Acer rubrum seedlings are almost always yellowish with dull fall color. You'd need to buy a named cultivar such as 'Embers', 'Red Sunset', 'October Glory', etc -

Those little scratches won't do anything to the health of your tree but I agree that it's time to protect it. Chicken wire is good.

Dax