MEASUREMENTS OF THE DRILL RESISTANCE IN B ROAD-LEAF TREES AND THEIR WOOD-ANATOMICAL INTERPRETATION

The determination of the drill resistance is a technique for assessing the stability of trees. In the case of broad-leaf trees, however, the interpretation of these measurements is still unreliable. Therefore, profiles of the drill resistance of broad-leaf trees have been made an d compared to the local wood anatomy. Intrinsic factors such as wood d ensity and moisture content were considered, as well as pathogenic alt erations in the wood and factors involved in the measuring technique. The drill penetration measurements provide information on the structur e and status of the interior wood of tree trunks. They also indicate t he growth level and any abrupt changes in growth, but do not enable th e complete identification of all tree-ring borders. The profiles are m odified by the wood moisture. Factors connected with the drilling proc ess have to be taken into account when interpreting the measurements. In the case of pathogenically altered wood, the peaks of the drill res istance profiles were explained by means of scanning electron microsco py. In comparison to white rot, brown rot causes a reduction in drill resistance even at lower values of dry weight loss.