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Sources of wood fuel

Conifer forest and felled timber

Conifer forests

In Scotland, the primary source of wood fuel arises from our extensive conifer forests. These are commercially established crops of Spruce, Pine, Fir and Larch varieties. Such forests provide wood for fuel either directly in the form of thinnings, or indirectly as sawmill co-products.

When conifer plantations are established, trees are planted very close together to encourage them to grow straight up, and with a minimum of branches. This increases their usefulness as sawn timber. Periodically, every 15 years or so, as the trees grow, the forest must be thinned so that it doesn't become overcrowded. The trees that are removed are called thinnings. First thinnings are typically trees of 100-200 mm diameter. These trees are generally too small to be useful to a sawmill, but are perfect for chipping to make fuel. Second thinnings will also be relatively small in diameter. Some trees will be useful for the fencing industry but many will also find their way directly into the wood fuel supply chain.

The brash from conifer harvesting operations can also yield biomass fuel, but this is relatively uncommon, as it is quite expensive to do so. When this does occur, the resulting fuel is of quite poor quality due to the high proportion of bark and the presence of soil contamination. It is really only suitable as an industrial fuel for use in specialist, generally large boilers and power stations.

Once trees enter a sawmill, they will still yield an element of fuel. Bark is peeled off and chipped for use in horticulture. The debarked logs are then cut into square sections, the resulting outer edges being referred to as slabs. These slabs are then either bundled together or, more commonly, chipped for use as biomass fuel. The sawdust from mills is often used to produce wood fuel pellets and briquettes. Wood chips arising from sawmills are an increasingly significant element of the wood fuel supply chain.

Hardwood Woodlands

Scotland's hardwood woodlands will also yield an element of biomass for fuel. Branches and tops from hardwood trees lend themselves better to conversion into firewood logs.

Street, Garden and Park Trees

The management of street, garden and park trees, also yields wood for fuel. These arboricultural operations will produce either chips, or hardwood branches. The former can be used as fuel, although they are not ideal as they will contain a high element of leaf and bark matter. As a fuel, this would produce high quantities of ash. The chips can also tend to be too small in size. Whole branches lend themselves to firewood production.

Recycled Wood

Recycled wood may be an option in some situtations.  Read more about using recycled wood for biomass.

Other

There are other types of biomass material which can be used as fuel, such as straw, coppice willow, and Miscanthus, but the production of these, for this purpose, is quite limited in Scotland.