Small-sized pulp roundwood falls from all logprocurement, both from thinnings and in practice every time sawn logs are cut.
In thinnings the proportion of pulp wood is always high. Conversely: the bigger the trees, the bigger the sawn log volume.
Pulp roundwood falls from all log procurement:
- Bigger trees, which produce sawn logs, yield from the minimum sawn log top diameter still one or two pieces of pulp wood in sufficient length.
- Bigger logs, which would be unsuitable as sawn logs because of poor quality, will be cut into pulp wood.
- In Spruce the most common reason for doing this would be butt rot. Other reasons for not accepting logs to sawmills can be bow, deformation or excessive knots.
Because of felling conditions and the aim to reduce the felling damage to the roundwood, thinnings are normally taking place during the winter period – especially with spruce.
Mills try to increase also the summer fellings, when it is suitable. Because of the variation in available raw material volumes and because the demand for pulp wood is still very stable all year round this raw material is stored for quite a long time to ensure sufficient volumes.
End-use requirements steer the raw material requirements. Main rule is that in mechanical pulping (groundwood pulping) the raw material needs to be fresh in order to retain its lightness also in the end products.
In the chemical pulping process lignin and extractives are removed either partly or totally. Requirements for this type of pulp wood are not as tight as they are for mechanical pulping, for instance some rot and discolouration are allowed.
