Reduction Is The Local Answer
In most towns, light is what gets crown thinning and canopy reduction specified. Here it gets specified for anchorage, and that is the difference this soil makes.
A tree standing on forty to a hundred centimetres of sand over clay has a plate, not an anchor. Every metre of limb reaching out from the trunk is leverage applied to that plate, and shortening the longest limbs is the only thing anybody can actually do about it.
So on these lots, reduction is the treatment that gets recommended and thinning is the one people ask for. Both crown thinning and canopy reduction are on offer; the assessment will say which yours wants.
Crown Thinning And Canopy Reduction For Light, Properly Done
Where the complaint really is a dark garden, thinning is the right answer — a proportion of the finer branches taken evenly through the whole crown so daylight gets through, with the outline and the size unchanged.
Done properly it is invisible from the pavement. Done badly it is called lion-tailing: everything stripped from the inside of the limb and a tuft left on the end, which increases the leverage rather than reducing it. That is the opposite of what a shallow-plated tree needs, and it gets sold as thinning regularly.
What Crown Thinning And Canopy Reduction Will Not Do
Neither treatment makes a tree safe. Both take load off, and less load is less risk, which on a plate this shallow is money well spent.
Nothing done up in a crown improves a rotten butt. Nothing done up in a crown restores a plate that has already lifted. And nothing done up in a crown stops a bank eroding.
Anyone selling any of those three as crown work is selling something else.
Reduction Against Topping
Reduction ends the limb at a side branch substantial enough to take over. That leaves a growing point in place, the outline intact, and a wound the tree is able to seal.
A topping cut stops wherever the saw got to. Back comes a crowd of shoots anchored in callus rather than timber, and in five years there is more crown than before, denser, weaker, and sitting on stubs that are rotting inward.
A topped tree cannot be restored. It can be managed on a cycle — best regrowth kept, the rest taken, repeat — but it will not be the tree it was, and whoever says otherwise has an eye on the next invoice.
Limits, Named In Advance
Beyond a certain proportion of living crown, recovery in an old tree becomes unreliable. On stressed ground that share is lower than the textbook figure.
So the scope names a percentage and keeps it modest. If you want a substantially smaller tree the honest routes are staged work over several seasons, or a tree removal with something better suited planted in its place.