Draft PPS18: Renewable Energy
Annex 1 Technology: Residues from Forestry Harvesting
B15. Forestry co-product harvesting makes use of those parts of the tree which, with conventional timber extraction and tree thinning, are normally left on the forest floor. The tops and branches of a tree are known as brash, and can account for 30-40 per cent of the gross weight of a conifer crop and over 50 per cent of the weight of a deciduous crop. Not all brash is available as biomass feedstock, as environmental impacts, extraction methods and ground conditions may render it unusable or undesirable to use.
B16. Whole tree comminution is the mechanical felling and chipping of whole small trees, usually undertaken in thinning operations. The main product is wood fuel chips, although higher value ‘white’ stemwood chips can be screened out for use in the wood processing industry. The use of SDR is becoming the preferred option for most forestry operators, due to diversification into new markets.
B17. Integrated harvesting is the mechanical extraction and processing of whole trees in a single operation. The tree is separated into stem wood and fuel wood products on site. This method leaves clear ground that can be immediately replanted and is considered to offer the most significant long term potential for the cost-effective harvesting of fuel wood. However, whole tree harvesting is not appropriate on all sites, and on some sites loss of nutrients and organic matter as well as soil compaction can be a significant factor.
B18. Although most of the fuel in this category arises from commercial softwood production, the use of arisings from the management of smaller hardwood woodlands can also be important to the rural economy, and can form a significant proportion of a small biomass heating plant in a rural area. It has the added advantage of providing another source of income for small woodland owners and farmers.