Slide show: The Tree Doctor

Based on the results of the scan, Allison asks Adam Alves, an arborist in the university’s Grounds Department, to perform a micro-drill resistotest to help pinpoint the exact location, size and nature of the defect inside the President’s Burr Oak. During the resistotest, Alves bores into the trunk with a tiny, 3-millimeter micro-drill, which measures the resistance of the wood. Resistance is high when the drill passes through hard wood, but dives towards zero when it hits hollow spots, cracks or decay inside the tree.