Could you describe to me what an air layer is?
An air layer is another form of vegetative propagation that is used on larger, more mature wood. In nature sometimes a branch will droop and touch the ground and then spontaneously strike root. This has been know as 'layering'
The same thing can be accomplished higher in the tree, hence the term 'air layering' The general process is to remove a ring of bark from the branch, apply rooting hormone and wrap the site in damp sphagnum moss, and enclose the whole mess with plastic to keep the moisture up.
After a time (species specific) new roots will emerge from the upper portion of the wound. The newly rooted portion is then severed and begins its new life as an independent plant.
I have a few pictures of the process on the third and fourth page of [url=https://www.helpfulgardener.com/forum/viewtopic.php?t=4176&postdays=0&postorder=asc&start=0]this thread.[/url] Unfortunately it seems one of my pictures has been lost at Image Shack
and I don't recall exactly what I was showing in it. Probably a close up of the bark removal.
This is an example of layering, although I suppose it is not strictly air layering and I used a different medium than moss but the basic concept is the same. In this case I used the technique to replace an inferior root system with a more balanced and flat one.
Usually this is done in the spring or early summer so you have some time to do some research and to get your materials lined up. You can even purchase special pots that are hinged and specifically designed for this technique.