What specific action related to extensive drilling can cause a branch or trunk section of a tree to die back?

Wells drilled too closely together can girdle the branch or trunk, cutting off nutrient flow.

Although a healthy, mature tree can usually withstand the drilling from a single Sapsucker or a small family unit, extensive activity can lead to localized tree damage, particularly in younger or stressed specimens. The damaging factor occurs when the bird drills its sap wells too close together around the circumference of a branch or trunk. If these closely spaced holes connect or sufficiently intersect, they effectively girdle the area, meaning the drilling severs the necessary pathways for the flow of water and nutrients. This cutting off of resources results in the death or die-back of the section distal to the girdled area, which is why homeowners sometimes mistake this behavior for malicious destruction.