Nick, now would be a perfect time to air layer.
I don't understand what you mean about shoots growing from the roots? Toni

By new shoots, I mean will the lower half of the plant send up more stems after I cut off the air-layered portion of stem? Will I have two plants at the end, or does the original root system die? Thanks.

It should if you have a node left after you lop the top off.

GH

No need for a node. Tissues in cambium will dedifferentiate and then redifferentiate to form adventicious buds. It just takes a little longer.

There's probably no reason to go through the effort of layering unless you want to. The plant comes easily from cuttings. Early spring is not a good time to layer this plant, btw. It is at it's lowest energy point of the growth cycle & will be pressed hard to make roots. I would have waited until the tree has gained some stored energy and layered it come mid June. Allow a month for roots to form, sever it and plant.

Al