The unique Northern pine
Scots pine wood grown in the northern latitudes (map) has several good properties that could be utilized in a variety of end products. The high quality of northern Scots pine mainly originates from the slow growth due to demanding climatic conditions and the suitable natural soil types.
Due to the slow growth the annual rings are narrow and the whorls are located quite close to each other. Narrow rings and minor ring width variation are advantageous properties of northern Scots pine wood for end uses where dimensional and form stability are important. In addition, it has been found that the narrower the rings, the better the machineability. The amount of technically and mechanically low quality juvenile wood (10 to 25 first rings around the pith) is very limited due to the same reason. Generally straight stems have little reaction wood, as well.
Slow growth advances the higher share of heartwood - at a given diameter the trees are older in the north, thus, the proportion of heartwood is higher. This enables an efficient utilization of Scots pine heartwood, which has an enhanced resistance against humidity variations and weather stresses. This is shown in better durability and stability in demanding end-uses in joinery and exterior products, for example. High heartwood proportion is an advantage also in log houses and gardening and landscaping products, for example.
Scots pine wood has a lower basic density in northern regions than in southern regions. The density is highest in the middle latitudes of the natural distribution area, that means, in central Finland and Sweden. However, pith-to-bark and butt-to-top density variations are smallest in the north, as is the variation in shrinkage and shrinkage anisotropy. Stable density and shrinkage together with narrow rings and heartwood offer dimensional stability and durable joints during drying processes or in varying humidity conditions.
Most of the strength and stiffness properties of clear Scots pine wood degrade towards northern latitudes mainly due to lower basic density in the north. However, in the pieces of sawn timber the strength properties could be higher in the north due to smaller knots and straighter grains in wood. The low share of juvenile wood in northern Scots pines significantly contributes to the overall strength and stiffness properties.
Susceptibility for checking is lower in the north due to better perpendicular-to-grain tensile strength. High tensile strength and shear strength also give mechanical durability to joints and mechanical connections. Together with the high heartwood proportion the low checking tendency enables the manufacture of stable and durable products for exterior claddings and other demanding outdoor end uses.
In Scots pine, colour is darker and more saturated in heartwood than in sapwood. The large heartwood content, together with narrow growth rings and lower latewood proportion, smaller knots and shorter whorl intervals provide northern Scots pine panels and boards with harmonious surfaces and an impressive, natural appearance.