It is never appropriate to remove the top to compensate for root loss (unless growing houseplants in a container). The leaves are the 'factories' for new root growth.

Plants cannot do too many tasks at the same time. If you damage a significant portion of the roots, most plants will gear up to replace those roots at all costs. The energy to do that requires photosynthates from the leaves.

If you chop the top, too, your plant will likely devote its energy to the manufacture of new leaves....at the sacrifice of root development.

I suggest that you water, water your plant. I don't know where you live but it looks like adding a substantial layer of mulch to that portion of the root system that remains won't happen.

Considering that half of the roots have been severed or buried, I would consider planting a new, young tree in a more suitable location so that it can grow in unrestricted soil. They grow rapidly if given decent, well drained soil and sufficient water.

I see. So are you suggesting that I should chop this down as the roots are probably in a bad shape and plant another one?

i suspect rhiz meant ... you have little in your yard ... properly water and mulch this tree ... and otherwise leave it alone .. and as a fail safe ... plant another ...

in tree time.. 3 to 5 years ... you either have one good new plant.. or you have 2 nice trees ...

and if that is not what she meant ... then its what i mean ... dont want to be putting words in her mouth ...

is that the wall that was built in the first pic??? .. if so.. im thinking that was not the issue with this plant ...

how long has this been there.. where are you.. etc.. give us more info to work with ...

here is a good guide to planting and caring for trees and shrubs ...

ken

https://sites.google.com/site/tnarboretum/Home/planting-a-tree-or-shrub

@ken_adrian Adrian MI cold Z5 I'm in Australia and it has been quite dry where I am. Yes, that's the wall. When we tore down the old wall with a bobcat, it was very clear that the tree's roots went behind the wall. We ripped out about 5m-6m of roots (it was actually one long root). I don't remember how long it has been there -- probably 20yrs.

btw ... one of my chief thoughts in my garden ... if its pissing you off.. just get rid of it ... lifes to short to be irritated by plants in your yard .. there is some therapeutic value in removing a problem .. ....

perhaps its time to start over.. or try something else ..

perhaps 20 years is enough patience ...

and if you plant something else.... mother earth net zero...

ken

ps: there might be some great joy in hooking it up to a bobcat.. and dragging that sucker a

round the yard for a few laps ... and even better.. if you could burn it ... lol

Yes: it's faltering because of the root damage. And is not in fact, a large impressive example - they get much bigger than this. And the way the barrier is right against it is not attractive - removing the tree might be the best idea.

Yes, John, getting rid of that tree is my suggestion. So much of the root system has been killed that it seems unlikely that it do anything but continue to decline.

I must say, though, that I am completely inexperienced about how this tree, which is native to Australia, responds to this kind of damage when in its natural environment. I only know it as a container grown houseplant.