Every time I talk about pruning off low limbs from pecan trees, I end up describing how to make the proper pruning cut. Typically, I've talked about removing a limb by cutting just outside the branch collar (photo at right). Removing limb in this manner promotes quick healing, reducing the spread of wood rotting organisms. But is there an anatomical reason this pruning method works so well? Let's look under the bark to see.
Last summer I cut a pecan sampling and carefully pealed the bark off the main stem and all the side branches (photo at left). After drying, the patterns of wood grain formation really became pronounced. You can see a raised branch collar formed by wood fibers that flow vertically around the side limb. By cutting limbs off outside this collar you don't disrupt the flow of water and nutrients from the roots to the upper portions of the tree. Cutting into the collar causes a disruption to sap flow and creates a wound that takes much longer to heal.