Theoretically it can be done!
Lots of work! Sweat and tears!
You can it's called grafting. You could even graft some types of pears on that rootstock.
Have you cut and pruned a couple to see if that helps? Also a really good fertilizer can help out. What your doing during pruning and scaffolding is opening up the tree and getting rid of old dead stuff and channeling the energy into fruits, so if the tree is loaded or bending branches rub some of the blossoms off, this will channel the energy into the fruit left on the tree.
So yea you could cut the trees down and graft into that bigger tree. How and why? Because the roots store energy and the grafting is a technique where you mate the cambium layer of the rootstock and the scions.
For example you cut the rootstock tree down to 2-3 feet above ground at a 45 degree angle (allows water to drain off and not get diseased. Then you use a knife and a thin wedge to open that bark and cambium layer. Get your scions prepped and angle cut and cambium layer clear and slide that into the rootstock and pull that wedge out, then put wax and or wrap the new graft with plastic you don't want water to get in and rot. Some grafts may take and some may not. However if that rootstock is a 12" trunk and you have like 8 grafts (same or variety) you have 8 flavors, try grafting again! 😂
I hope that helps, it's just a bit of the game trying to figure out rootstocks, the problem is you would have to figure if those are natural grown rootstock or if those existing trees are grafted on to rootstocks which means the rootstock is different that's the apples you getup top. There should be a bunion graft about 8-12" off the ground
Yes, at the graft point is where the trunk will be, there's several different grafts I like the splice graft nice and clean, these grafts for you will look funky but they work, some orchards do this when they have a an established variety that isn't very good.
So the theory is all that stored energy in the roots will push up into that cambium into the scions, you'll start to see new growth and you can even graft onto those new sections down the road for cross pollination.
There was an artist that did like 30 grafts onto a rootstock and the variety of blooms, blossoms and fruit, I'm not sure if it's still alive or where it's at but it is real and it's out there.
Lol a side note! What if those are Arkansas Black? Store them for a couple months then try them, also pick after first temperature frost. That will set the fruit. Some folks don't have patients.
I'm excited for you buddy! I have a similar plan, but I would get some rootstock and air root and plant new rootstock then graft onto it! Hahaha!
