Nick, the above ground tree parts look typical for the species, they often grow at an angle with their trunks resting on the ground. Light, tip-weight reduction trimming should be all they need, as in reduction cuts not thinning.
I would want to know a lot more about the tree/soil interface. Does that ring have a footing and how long has it been there. It looks like the grade has been changed, if so how many years? Even though P.racemosa grows in riparian areas, it still prefers good drainage. Do some digging and get a clear understanding of the soil profile, and not just 6" deep.
In this situation, as in many, what is happening underground could be of great significance.