1) Anyone have a good idea what chance a small pear tree like this
would
have of healing such a large gap in the sapwood?
If the tree did not outright die nor show signs of die back in the
canopy this year it would indicate there was a good vascular flow
from roots to shoots, I would not be so alarmed that it" just sat
there" in its first year, it apparently was healing up and I bet it
will catch up to be where it is supposed to be in a few years There
can be many reasons it did not grow out. It just needs some time ( &
some TLC) to repair itself, which it will do.
2) Can attempting to do a trunk graft in a
situation where the live portion is only about 30% of the way around
cause more harm than good?
Again don't get hung up on the 30%. the main issue here it to keep it
stabilized ( see 1 above) so it will continue to grow on its own. It
appears it has, further It will repair itself and continue to grow,
most likely catching up with other of its age group. Now, you did
open up a lot of area ripe for infection so protect the tree this
winter and prune/fertilize properly, (not just follow old folk lore)
You should fertilize it not just for fruiting, but for building the
trunk back up ( avoid excessive N) and give it a couple of years to do
this
There are many things to try if you want to experiment w/ it. Perhaps
try bridge grafting as in the 1st two links below. If you determine
that it is still going downhill and beyond repair, consider root
layering further up the trunk to where you can still get all the
varietal grafts, yet still find some healthy bark or at least enough
that you can cover up. Perhaps I would not have a problem grafting
your graft onto new root stock. Lots of methods/techniques you can
try it you have the inclination and time.
BTW, I have a rescued 70+yo Golden plum with major trunk damage. The
tree walled off a 3-4 " strip running down an ~8" trunk and she still
produces quite a lot of fruit. I just have to protect the old wood as
best I can from insects and rot, Lime Sulphur works well for this.
http://www.omafra.gov.on.ca/english/...cts/98-003.htm
http://www.extension.umn.edu/distrib...re/dg0532.html
http://www.gardeningknowhow.com/tree...ark-damage.htm
good luck