Broadback writes

Thanks, of course it could have been that a mad cow broke in and
trampled it! :-) I'll take your advice as regards stakes in the Autumn,
also I will try cutting off at the damaged point and see if it regrows,
but I doubt it.

Don't be too pessimistic. I've seen advice on growing clumps of silver
birch by growing one, then cutting it back almost to base, whereupon two
or three new trunks will happen - don't follow these instructions which
are almost completely forgotten, but it demonstrates quite a keenness to
regrow.
--
Kay