There is an often-quoted maxim that the pig is the most economical animal to eat because ‘you can eat everything but the squeal’. In timber production, trees can be seen rather similarly. There is almost no part of the tree that does not have a part to play.
With high-efficiency production, as seen for example in Scandinavian softwood forests, branches and leaves will be stripped off in the forest and left to rot on the forest floor – not wasted but putting nutrients back into the soil to assist future growth.
Waste such as bark and sawdust is used as a fuel in sawmills. In Sweden this forms part of a government strategy for the country to become carbon free by 2020. Any excess waste materials can be used for biofuel.
But what about the usable timber? Not all parts of a tree are equal. Esa Mikkonen of Crown Timber has analysed where the value comes from in pine (redwood) from Scandinavia. The figures will be slightly different for different species and different locations, but the underlying message is the same
– most of the value of a tree is in the lowest part of the trunk, which is cut into logs.
These pages show how trees are cultivated and how the various parts are used, while overleaf there are details of the different materials that can be produced from trees.
Thinning stages of Scots Pines
Not all trees reach maturity. In order to give the best trees room to grow, thinning – the selective removal of trees – will take place. In Scandinavia there will typically be two thinnings over 70 years.
In the first thinning, after about 15 years, the small trees removed will only be suitable for pulp production.
The time of the second thinning varies depending on the site, but 20 years after the first thinning is typical. One third of the felled material can be used for sawn goods in construction, the rest going to pulp and paper production. Needles and leaves are left on the forest bed as a nutrient.
Using all the different parts of a mature Scots Pine
First/bottom log: This log produces the most valuable timber. This is not just because it is the
largest but because all the branches will have fallen off with growth, so there will be very few knots. There will be high-quality ‘sideboards’ – the outer boards of the tree. Uses will be for high-quality mouldings – skirtings, architraves and other decorative mouldings.
The inner section will produce high-quality timber in large section sizes – typical uses include high-quality pine windows and other joinery products.
Used to make plywood, glulam, veneer and LVL.
Second/middle log: Branches are likely to be attached, but not all of them are still alive. When the log is sawn, dead branches will be found to have created black ringed and sometimes dead knots. Used in lower end joinery and construction work.
Used to make OSB and some veneers.
Third/top log: The top branches of a pine tree are younger and often still alive. When the sawn section is produced you get knotted material, which can be
Used to produce furniture, mouldings and floors.
Top of the tree: Used for pulp and paper production. The branches and even the stump are increasingly
Used for energy production in the sawmill.
Byproducts from the sawmilling process: Chips are converted to paper and the bark is burned to produce energy.
Used to make particleboard and MDF (made from sawdust).