Good news and Bad news........ Im guessing you will see some new growth (your trees are not toast yet)
but..........They may send up new growth from shoots below the graft which will then be a tree from the root stock variety not the apple tree you wanted.
- How much tree is left (1 foot 2 foot 5 foot)?
- Are there any limbs below the snap and above the graft (assuming your trees are grafted apple trees) or just trunk?
- Do you have trees of the same variety as the damaged originals or another variety that you want as a replacement growing elsewhere where you would have access to the scion wood this spring?
- Is it a true 3 year old apple tree or did you buy a tree and have it for three years making it a 4-6 year old tree?
- What is the actual diameter of the tree at the new cut?
For now Seal the cut. Start there.
I have topped 3 year old apple trees and they come back but I know where and why Im making that cut. That being said:
Then, there is no reason why you could not top work the tree this spring - and - wait and see if the tree sprouts new growth. A 3 year old tree may have some viable buds on the trunk to make a new leader branch. If it is a larger tree and does not throw a new leader and you have some lower branches on the tree dont cut them all off now. The end wood on those branches may come in handy with where I'm going here.
At a minimum This spring top work the tree - if there is new growth (scion) on an existing lower branch end you can take that as scion and top work the tree trunk preserving the same tree variety. You could top work it with any variety scion you want as another option. If the tree does sprout a new leader below your top work you can always cut the top work off and run with that new up shoot leader or make a choice of keeping what looks better.
Worst case is the tree dies - I doubt its a total loss and that almost certainly will not be the case. Thee best worse case is it sends up root stock suckers and you grow them out as apple trees/crabs or next spring graft to one or more of those shoots and later pick the best and keep it. You have established root systems that is a huge plus.
Best case is it develops a new central leader from a bud on the trunk and you dont have to do anything. You have choices in between those possibilities.
So you potentially have many options........ and what a wonderful way to get into grafting (get yourself a grafting knife for x-mass) and let the madness
(addiction)
begin!
oh ya as a side note invest in some good fencing materials. You will often have more $$$ into T posts and wire then the trees.