Where residues for woodfuel are to be harvested alongside sawlogs, there are a number of harvesting options. Optimum choice will depend on terrain, equipment available, tree size and species.
In addition, there are a number of pre-preparation alternatives to help minimise the moisture content of the wood. These include:
Once the produce has been felled and extracted from the forest there is the option of whether to process on site to the desired type of woodfuel, or to transport it in its harvested form.
Wood chips can be conveniently transported, but the bulk density is lower than for SRW, and because airflow through a heap of chips is not good drying can be less efficient. In addition there are potential problems with composting in heaps of chips that can lead to loss of biomass and raised temperatures that can cause spontaneous ignition.
It is therefore advised that heaps of chips not be constructed greater than 10 m high to prevent excessive heat build up. If managed carefully, however, the heat from composting can help to drive moisture out from a pile of chips.
Branches and brash are the lowest density form, however they will give good drying rates.
Once dried to a suitable level they can be chipped. However there will be a high proportion of bark and leaves which are high in mineral (ash) content.
Equipment to bundle up brash into 'residue logs' has been developed in Sweden to assist the harvesting and handling of this low density material. However it is specialized equipment and is not widely available in the UK.