What is happen during the air layering?

Air layering is a method of plant propagation. Making a new plant from the branch of another one. You cut off a ring of bark, then apply moist sphagnum moss and a plastic bag to keep in the moisture. The branch above that cut will respond to the water and nutrients being cut off from it by producing roots. If you manage to keep the area moist long enough, usually 2-3 months, roots will develop inside the moss and bag. Then you can cut it off and plant. Rooting hormone is often applied to the cut area to help encourage the roots.