https://www.rhs.org.uk/advice/profile?PID=405
Royal Horticultural Society
Air layering is a method of propagating new trees and shrubs from stems still attached to the parent plant. The stem is wrapped with damp moss to encourage roots to form.
Air layering is an effective propagation method for some plants that do not root readily from cuttings and which often lack low-growing shoots suitable for conventional layering, such as magnolia, hazel, Cotinus and flowering Cornus species.
Other suitable plants for air layering include: acers, camellia, Chaenomeles, daphnes, Ficus, Forsythia, Hamamelis, jasmine, Philodendron, rhododendron and azalea, lilac and viburnums.