Pines are difficult to air layer. Not that it can't be done, but it may not work. If it doesn't work, you may have killed the top part, or it may just fuse back together, and then you have a horrible scar.
If they layered well, there would be no need to graft them.
All that aside, two special types of JWP are known to air layer well: Kokonoe and Zuisho. They are more of a dwarf type, and have shorter needles than the typical JWP. They are somewhat rare, but not impossible to find. Good ones command a lot of money.
Julian Adams sells rooted cuttings and rooted airlayers of Zuisho. Before you get too excited about making cuttings, Julian told me that only 6 percent of his cuttings live. And he has special equipment for cuttings. That helps explain the high price.
In Japan, they will graft Zuisho and Kokonoe onto JBP stock. And develop the tree. But, they design the tree knowing that the long term plan is to airlayer it once the tree is near its final size. The JBP rootstock is more vigorous than the native roots so the top will develop quicker than if grown on its own roots.
Zuisho and Kokonoe grow more slowly than the JBP rootstock. Eventually, the grafts fail. That is the JBP Stock thickens faster than the JWP part and the cambium layers break apart. Once the airlayer has taken, the JBP roots can be removed, and the tree can continue to live in definately on its own roots.
I know of two trees developed in this manner; one Zuisho and one Kokonoe.
