Occlusion of pruning wounds on northern red oak (Quercus rubra) trees in Romania

This study focuses on the occlusion of pruning wounds on northern red oak (Quercus rubra L.) trees grown in two plantations established in the south-east of Transylvania, Romania in 1997 and 2004. In total, 184 green branches of elliptical cross section (i.e. with the horizontal axis Ha shorter than vertical axis Va and ranging between 0.6 cm and 4.5 cm) were pruned in April 2007 and May 2009. Of these branches, 161 (88%) were fully occluded after five growing seasons and, the majority of these, 148 wounds (80%), had occluded in three seasons. The main factors affecting the wound occlusion on trees subject to artificial pruning are diameter at breast height increment and branch size: the occlusion is more rapid in trees with faster diameter growth rates and on small branches of maximum 3 cm Ha. Consequently, artificial pruning should be concentrated on small branches on well formed, vigorous and evenly spaced final crop trees which can subsequently be favoured by heavy and targeted thinning from above, allowing the production of large diameter, high-quality trees in 5070 years.