AusBonsai

I collected this Allocasuarina about 18 months ago and noticed some strange wound healing at the base.
As per the pictures, it looks like a wound that has callused over, possibly the remnants of the root sucker? The strange part is the bark is mature but markedly depressed in the centre of the callus. Any ideas how this might've happened?

As you can see it has caused obvious negative taper when viewed from the sides, I am thinking a might re-open the inside edge of the callus to get it to continue rolling in. I will probably have to flatten the internal bark so it has something solid to roll over. The callus is a complete circle around the mature bark centre.

Lastly, yes I know the trunk is straight and flawed, this was my first dig to gain practice before going after better stock. It was taken from a patch of weedy root suckering trees that were being cleared on a farm.

This might be good material to play with, learn how it responds to deliberate scarring or perhaps practice cosmetic surgery and glue some old bark on that area to see if you can achieve a realistic illusion.

Corky bark is the result of previous bark staying attached as new bark grows underneath. Reduced areas cannot catch up unless the bark grows at a faster rate that surrounding areas. Wounding may build scar tissue to bulk out the area and bring it up to the same level.
When I had this problem with corky Chinese elm I simply rubbed the bark off all the higher areas so everything started equal again. It doesn't really take long for the corkiness to return as the bark continues to grow.

Any ideas why the mature bark is situated inside the callus but not on it? I would have thought there'd be no living tissue in between the callus until it has completely closed over. I removed the bark today and re-opened the callus so will monitor how it responds over the next few years.

I had not realised that area was in the middle of the old wound if indeed that's what it is. More likely something else going on I think?

Yea that's the main reason I posted it as it doesn't seem possible for a normal wound but I don't know what else could've caused it