We purchased a Mimosa (Silk Tree) a couple of years ago, and it's now putting out pretty flowers and appears to be doing fine. The trunk is about 2 inches in diameter and the tree's about 8 feet tall. I decided to re-stake it with some more substantial supports, and pulled some of the dirt away from the trunk to a depth of a couple of inches. I was disturbed by what I saw just above and just below ground level (pictured) and wonder if this is normal or a worry. The 'core' (for want of a better term) of the tree is visible through a 'natural' opening in the bark, natural in that there's been no trauma, although it appears that the bark is trying to grow into the opening. But since this is at a point where the roots branch out, can it eventually fill in? Should I try to fill it with something or otherwise protect what's there? We love the tree; many thanks for any pointers.

It's not natural, it's definately because of some trauma, propably mechanical.

The tree is trying to seal the wound by growing callus tissue around it to prevent any future bacterial or fungal infection. This will take years though. Best thing you can do is nothing; leave it alone. Don't go covering it with paints or whatever.