Home Improvement Questions? Ask a Handyman for Answers
Hi. It look like the tree suffered from root rot by too much water (there is never really too much water but too much standing water in the soil from poor drainage cause anaerobic bacteria). This may have climbed into the trunk a bit or it may have developed there from the start if you used mulch to close to the trunk or if you have other plant at the base.
The tree might recover but nothing is sure. Cut on the water for a while and do not fertilize until you really see the tree come back for good (trees in remission will not use it and it will stand there and burn the roots in no time).
Do not put anything on the exposed area, let them dry. The tree will grow over those wound over time.