I've no idea what a Japanese pine is but I have one Chinese black
Pine. Around here they mulch themselves as do the white pine.. However
I rob it and add the needles to my foot paths. If you are have a
general malaise with the whole tree involved I'm clues less. I've have
many white pine with some sort of borer that kills the new top growth
but the tree's seem to be able to carry on sometimes sending up a new
leader.

This usually happens to white pines grown out in the open. It is called the
"white pine weevil". You can train one young branch to be the new leader.
Maybe about what, 15 year old trees?


--
Sincerely,
John A. Keslick, Jr.
Consulting Forester & Tree Expert
http://home.ccil.org/~treeman
and www.treedictionary.com
Beware of so-called tree experts who do not understand tree biology.
Storms, fires, floods, earthquakes, and volcanic eruptions keep reminding us
that we are not the boss.