Hello guy, great to have you visit and share with us, welcome mate!
You make some really important points and they are interestingly greatly overlooked here, perhaps we just don't have urban tree populations of an age to reveal the consequences of both Stem Girdling Roots SGR's and buried trees as yet to stimulate widespread recognition of the problems...though they surely do exist, and many of us have seen the results of both. Here's one that I probably should have identified as being SGR as much as buried
Wind throw.
Reading NATSPEC there is a section on Height of the root crown
"The root crown is the junction between the below-ground parts and above ground parts of the tree. Regardless of the size of the tree the root crown belongs at the surface of the root ball. Burying the root crown can lead to fungal infections, serious disruptions of the root system's structure and function or to the death of the tree (see Fig 2.4)
Height of the root crown assessment criterion:
- The root crown must be at the surface of the rootball. "
There's a diagram to show what the root crown is and the location it has to have for sustainable long term healthy growth.
I really think Ross Clark has done a great job in developing NATSPEC and very strongly recommend that all Arborists in Oz buy a copy of his book, trust me it will assist and simplify much of your interactions with clients in relation to not only buying new trees, but the early stages of their care.