Are those reliably hardy in your area?
I just googled for their hardiness range and was surprised to see they were hardy down to zone 3 but everything that listed zone 3, actually said 3-b.
So winter kill would be my first guess. Bone meal would be my second guess. That stuff is more potent than people often think.

First of all, I'm pretty sure that 'Autumn Brilliance' is not a grafted plant (which is good).

Will these sprouts at the base slow the main trunk from breaking dormancy or suck the life out of it?

Usually sprouts at the base mean that the upper portion of the tree has died and it is sending up new growth.

Do a scratch test on the upper branches to see if there is any green underneath the bark (lightly scratch with your fingernail). If there is no green, the upper part has died and you should just let those sprouts form the basis for the new shape.

Thank you iforgot, yes technically it's out of range although there are others that have grown these successfully here. I was hoping I was gonna be one of them, appears no such luck atleast so far. I didn't realize bonemeal was toxic, I thought given the numbers it would help to stimulate root growth, it really wasn't alot of bonemeal perhaps a half a cup. Well I hope I didn't screw up there, that has always been what I have added to everything that i have planted. I may have to rethink that I guess.

Thanks esh ga I actually did the scratch test, I do see some green on one but nothing on the other. The green on the one was not all the branches and the other I couldn't get any green anywhere. They are both sprouting at the base with what appears to be several sprouts. Heavy sigh, cutting off the main trunk may be my only option but I am still playing the waiting game a little longer.
Thanks for the responses, it's appreciated.

Barb

Bonemeal isn't "toxic", I said it's more potent than people often think because it is a natural fertilizer commonly used for root stimulation but still can create a nutrient imbalance if you ask me.

Wait a month or two and if nothing then adios to the main stems and let the new ones give it a try.

I'm with esh_ga - I don't think AB is routinely propagated as a grafted selection, so the suckers from the crown/root collar are probably true to type. If it doesn't show some signs of life fairly soon, I'd cut it back and chose however many new stems you want to re-create your specimen and try to keep others pruned back/rubbed off.

Thanks iforgot, I didnt mean to twist your words but i certainly will give more thought to my bonemeal use next time so thanks for the heads up. Yes I may just have to decide now if I want a multistemmed tree in place of what I was hoping for as a small decorative single trunk. Lucky, there appears to be so far atleast 4 to 5 pink nubs bursting from the trunk. I guess these could eventually make a small tree, meanwhile a small shrub. I wonder how much time it would take to make a small multistem tree, 20 years maybe. I have to say, I just assumed these where grafted, I never asked (bad me). They have what I thought was a typical grafted area on the bottom of the trunks but now that I really think about it perhaps that was removal of another main trunk since these are naturally multistem. Ya know I knew better than to try to fight mother nature, she always wins in the end as in this case it seems aswell.
Thanks for all the replies and advice.
Barb

No not grafted. Propagated vegetatively through cuttings.

I have single stemmed AB that suckers a lot. It really, really wants to be multistemmed. I constantly have to remove the sprouts. So keep that in mind for single stems it is a bit more maintenance.

I think the root of the matter is that AB is not well adapted to your winters. A bigger question would it be a better investment of time to reassign the planting location to something that isn't going to die back on you.

Yes, iforgot I do agree, we did have a substantually colder winter than usual so that made it more of a gamble but I planted them so I should make an effort to so what I can with any success quite possibly ending up in wasted time. Well I am not quite giving up yet, I was checking on them today and there may be a few buds breaking on one, OR it may be that I am just wishful. I will see what June brings and then rethink it all if I have to take the main stock off. Maybe this fall I will replace them with something less of a gamble.
Thanks for the reply,
Barb