SAW TIMBER RECOVERY AND SELECTED PHYSICAL AND MECHANICAL PROPERTIES OF WOOD FROM SCOTS PINE ON DRAINED PEATLANDS IN FINLAND

摘要

Abnormally large between-stand variations may be expected for peatland forests in stand structure, tree dimensions as well as wood and timber quality. In addition, variations may be larger within stands, and are very obviously larger within trees compared to trees on mineral soils. In this paper, 29 mature or close to mature Scots pine stands from drained peatlands in Finland are studied for the recovery and technical quality of the saw logs. In total, 1000 saw timber trees were examined standing. On average, the age, dbh, height and tree volume (o.b.) of the stands were 115 years, 21.7 cm, 17.1 m and 337 dm~3, respectively. Percentage of defect-free stems was 31%. The stem defects caused reject of full saw logs in 9 %, and reduction in the saw timber section owing to butt jumps, off-cuts and top cuts in 61 % of the trees. At the stand level, true recovery and percentage of conventional saw logs were on average 89 m~3/ha (s=63) and 55% (s=68). Decreasing the requirements for log diameter and length, i.e. counting also small saw logs, increased the figures up to 112 m~3/ha (s=78) and 69% (s=74). Compared to stands on mineral soils, the technical quality of Scots pine was at the similar level, but, owing to the smaller tree dimensions, the recovery of saw timber was lower. For a sub-sample of clear wood specimens, wood density (MC 12%) was 487 kg/m~3. Bending stiffness, i.e. modulus of elasticity (MOE), and strength (MOR) were 11180 MPa and 86 MPa, on average. These values were clearly higher in butt logs vs. middle or top logs, and, rather unexpectedly, in sideboards vs. centre yield. Compared to pine from mineral soils, density and MOR were at a clearly higher level in centre yield, but at a lower level in sideboards. MOE was a little lower on peatlands, irrespective of radial location of wood. For centre yield, the differences were more pronounced in butt logs compared to all logs on average.