Self-pruning of pedunculate oak (Quercus robur L.) stems and the diameter at breast height of trees in commercially managed stands

The focus of this study was on the knottiness and self-pruning of trees at 10 study sites from which 30 trees were selected for observation. These areas represent two main forest site types (fresh mixed deciduous forest - LMśw and fresh deciduous forest - Lśw) characteristic of the silvicultural regime of oaks in Poland's lowland area. Sample trees were selected according to the principles of the Urich method (with the same number of trees in the diameter class) and Kraft's biosocial classification. Trees from the dominant stand (class I, II and III according to Kraft's classification) were subjected to analysis.Normal distribution of length parameters was found for the majority of analysed zones of sample trees. On this basis correlation values were calculated describing the relationships between the diameter at breast height (dbh) and self-pruned zones on the stem: with knobs visible on external surface of tree stem, with snags remained after the dead branches, with the still unbroken dead and dying branches, live crown (active with regard to transpiration and photosynthesis).The length of the self-pruned tree stems from the fresh deciduous forest was greater in comparison with the trees from the fresh mixed deciduous forest. In turn, the length of the knob and snag zones was greater in trees from the fresh mixed deciduous forest. The variation in these parameters was rather insignificant. No statistically significant differences were detected in mean lengths of the examined zones between the two forest site types. Trees in the oldest age classes (VI and VII) showed a higher mean length of individual stem zones compared with those in younger age classes.