Northern red oak (Quercus rubra L.) is considered as having a good potential for natural pruning. This is especially the case of dense stands whereas in less dense stands, as well as plantations established at spacing over 2 x 2 m, artificial pruning, sometimes considered only as complementary to the natural one, is necessary to produce knot-free wood, with potential end-uses in furniture or lumber industry. In this respect the paper emphasizes the results of a research project carried out in two privately owned sub-compartments (no. 81B% and 81E), planted back in 1997 (81B%) and 2004 (81E) respectively, with northern red oak as the dominant species. The project deals with the wood discolouration of northern red oak trees subject to artificial pruning of their lower branches of variable sizes. The main outputs of the project can be summarized as follows: A. The size (length) of discoloured wood depends on the size of branch removed by pruning. The size level of 3 cm can be considered as the threshold for a quick closure of pruning wounds and avoidance (or reduction) of risk infections. B. No wood discolouration has been detected above the pruning cut; the only area showing this defect was located exclusively under the pruning cut, as a prolongation of various lengths of the part of branch removed by pruning towards the pith. C. In all cases the wood layers (growth rings) formed after artificial pruning outside the pruning cut area as a result of cambium activity are 100% free of defects.
