Q: Nine years ago I planted 4 red maples . I am concerned about two of the trees. Their bark has long cracks in it. Why?

A: My initial answer is “That’s just what they do sometimes!” Notice how the split in the first picture has already closed and healed.

However I also notice that the roots beneath the splits have tightly encircled the base of the trunk. This could have caused the bark above that point to dry and be damaged.

You should carefully remove the circling root. Otherwise the tree will strangle itself in the future.

As far as treatment for bark splits. the reference below recommends bark tracing but I don’t think it’s necessary in your case. The splits will occur less frequently as the tree matures…but do attend to the bad root now.

See Bark Splitting on Trees