In message , Stan The Man
writes
Should I paint the trunk with something in the hope that it will protect
the tree from infection, given that quite a bit of bark is missing?

If the full circumference is stripped I fear you will lose the tree as
the sap won't be able to travel up to the leaves. In any event it is
likely that there will be no new growth above the stripped bark albeit
you may get some new growth at ground level. Cork trees seem to cope
well when their bark is stripped/harvested but they are an exception.

It is stripped the way something with claws would do it, and actually
mostly on one side, so there is a bit that is still intact. Is there
some sort of first aid I can apply, to try to salvage it? (It's a lovely
little tree, and, of course, an anniversary gift from our three
daughters....)

There is a lot of new growth from below that point, but that would turn
more into something like a bush....
--
Klara, Gatwick basin