A comparison between wood quality and growth in planted and naturally regenerated Scots pine (Pinus sylvestris L.) stands in Sweden and in Poland

Abstract: Scots pine Pinus sylvestris L. is one of the most important trees species for wood industry in Sweden and in Poland. The silviculture is aiming for high quality timber. This study compares different regeneration methods, initial densities, improved planting material and their impact on wood quality and growth. The study areas were located in Linnebjörke and Värnamo Forests (southern Sweden) and in Potrzebowice State Forest district (western Poland). In total 30 circular plots were set up in Sweden and 8 in Poland. The results shows stand characteristics such as height, diameter, mean annual increment, volume and timber quality traits, i.e diameter of the thickest branch, crookedness, spike knots occurrence, damages and judged overall quality . Planted stands had on average greater mean heights (34%), diameters (39%), mean annual increment (242%) compared to the naturally regenerated stands. The volume of pines planted under the normal shelter was on average (121%) of those planted under the dense shelter. Similarly the volume of the naturally regenerated pines under normal shelter was (346%) of the ones regenerated under the dense shelter. In Värnamo and Potrzebowice the plots planted in the lowest spacing (10.000/ha and 13.000/ha respectively) had the highest mean height, total volume per ha and MAI. The trees originated from improved planting material characterized high external quality and good growth. On average the growth of height and volume was 5% and 4% greater compared to the not improved plots planted on the clear cut. Naturally regenerated pine stands will have superior overall quality compared to the planted stands on the clear cut. On average the mean branch diameter was (20%) lower in the naturally regenerated plots compared to the planted ones. In general, fewer severely crooked stems were recorded in the natural regeneration. Longer shelter period improved the quality of planted pines. The stem straightness was considerably poorer and diameter of branches higher in the wide planting (1600/ha) compared to the closer planting (10.000 and 13.000/ ha). According to the linear correlation between the diameter of the thickest branch and the diameter at breast height the naturally regenerated stands will give higher selection possibilities than the planted stands.