native gardenia

gmfruit1 starts with ...
Hi! On a suburban block in Brisbane, I have a native gardenia in a full sun, but protected (by the 90 degree corner of a 1.2-->1.8m high timber paling fence) location, which I am concerned about. It has been in the ground 5 years, and is about 2m tall. It generally looks healthy enough, the leaves are green and it has plenty of foliage all the way to the ground. However closer inspection raises some concerns. Those little black ants have infested it (to a degree; they are almost a plague in our suburb), and the trunk and branches show some "open sores" (dry broken black regions of the bark), which look like they're not supposed to be there. The ants don't appear to be affiliated with these sites, but I'm no arborist. I don't routinely fertilise or water the tree, as it is long established. I can submit photos if that helps. I'm wondering if these are serious issues, and how to treat them if they are.