EN
Harvested timber has many various wood defects. Analyses were carried out on material collected in Zaporowo Forest District (northern Poland). Results show that various defects were found in 35% of harvested timber on average. The share of timber with defects varied among individual species (pine – 44%, spruce – 22%, oak – 14%, birch – 9%, beech – 5%, lime and larch – 2% each, hornbeam and alder – 1% each). The individual wood defects appeared in harvested timber with following frequency: knots – 55%, knobs – 22%, foreign bodies – 7%, curvature – 5%, inner rot – 5%, galls – 2%, blue stain – 1%, insect holes – 1%, false heartwood – 1%, and cracks – 1%. Timber defects resulted in reduction of income from the sales. A decrease in income caused by various defects amounted from 0.07 PLN/m³ for brown sap stain to 68.83 PLN/m³ for knots. The greatest effect of wood defects on the reduction of income from sales was recorded for oak timber (518.30 PLN/m³), while the smallest for aspen (4.63 PLN/m³). Due to the fact that in almost all analysed tree species the dominant effect on the reduction of income from timber sales was caused by knots (open knots and knobs) systematic solutions need to be found in order to reduce the effect of this defect. It is particularly important in the case of oak timber, where a decrease in income from timber sales connected with this defect was the greatest.