Marcoting
Marcoting is a well-known technique in horticulture that is often used when propagating bonsai.
Here on the right, we see an old Crataegus (hawthorn) where the right branch is marcoted. This means: by partially cutting away the bark and tying a plastic bag of moist phagnummos around the trunk, new roots are created at the upper edge of the wound.
When enough roots have formed, the branch can be cut off from the “mother tree” and we have a new tree that already has a thick old trunk. It must be firmly anchored in its pot, without hurting the young roots.
This new starter plant can quickly grow into a second bonsai.