Biomass refers to a wide range of organic material including timber, straw and energy crops. The DARE report looked at set aside land in 2006 as having the potential to produce energy crops, however since that report, the Government announced in 2008 a reduction in set aside to zero to allow that land to come back into full production. As conventional energy supplies decline, there are many competing issues that are likely to be hotly debated when considering land use for energy crops. More land will be brought under cultivation for food production, construction and clothing materials and these changes will also need to take into account local impacts on biodiversity in particular when bringing uncultivated areas back into more intensive productive use.

The enthusiastic interest in crops for biofuels for transport of a few years back has dwindled considerably in the recognition that land in a densely populated country like the UK will not be able to spare the large space this would require.

Biomass capacity

As specific information about woodland cover and set aside for Totnes and District has not been obtainable, and the district as an area within South Hams is broadly similar, the agricultural statistics in the DARE report have been used and adjusted to scale proportionally. The total landholding area for South Hams is 90,650 hectares (ha.); the area of T & D is approximately (24%) 21,500 hectares. This therefore indicates the following:

Woodlands

Wood fuel is probably the oldest known fuel to humans and is usually derived as a secondary product from other timber production processes. Anecdotal evidence suggests that on primary clearance, previously unmanaged, mixed woodland can yield 15 tonnes of timber per hectare and thereafter a sustainable 2.5 tonnes per ha per year.

Harvesting woodland

There are four primary ways of using timber: as slab wood, logs, woodchip and pellets (see Appendix C for details)

The estimation is that woodland in T &D can be exploited on a sustainable basis and provide in 2008:

The energy value of this yield will depend upon how the timber is processed. The more handling involved, the higher the cost of the resource and lower the energy balance. To maximise the benefit of harvesting existing woodlands, it will be necessary to develop local markets and timber handling processes that minimise the energy involved in getting timber to the user.

Increasing Woodland Cover by 2030

It is unlikely that much of the former set aside land will be available to plant new woodland. However in line with biodiversity considerations, 30% woodland cover by 2030 has been indicated as desirable and more hedgerow, amenity and garden woodland may be planted. This would mean increasing the current 3.5% current cover by a factor of almost 9. Rather than over assess the energy which may be available on the basis of woodland not yet in existence, this can be considered as a possible bonus at a later stage. However as agriculture reverts to a less intense and less mechanised system and more people are active on the land, and soil erosion may need to be addressed, fields and land areas may be reduced in size; if fields were to be reduced in size by a factor of 4 this could double the length of hedgerow and significantly increase the amount of timber available for wood fuel.

Assuming an increase of woodland cover by 2030 to 14% would quadruple the amount of timber becoming available. However as there is likely to be increased competition for its use for building, we will assume here that only 75% of this is available for fuel:

Short Rotation Coppice (SRC)

This term describes a system of harvesting a timber crop. Some tree species can be cut back to a ground level ‘crown’ and the re-growth of a large number of long thin stems harvested. Coppicing is a well-established method of tree management for fuel, charcoal and fencing. Several species can be used, but Willow (Salix sp) is the most commonly used for energy crops. Once established, stems can be cut back on a 3-year rotation.

SRC is normally harvested in winter when the moisture content is low and can be stored as long stems or chipped. The fuel can be used in 3 ways:

• Combustion to provide heat to boil water, produce steam for a turbine to generate electricity
• Gasification to produce a combustible gas for burning in an engine or turbine
• Pyrolysis to produce gas, oil or charcoal fuels.

Miscanthus

Miscanthus is a perennial grass, originating in the tropics but grows well in the UK climate. Once the rhizomes have been planted and become established, the crop requires minimal inputs, creates a strong root structure (tolerant to tractors) and typically grows to 3 meters high in season. At the end of the growing season, the chlorophyll retracts into the roots leaving just the cellulose stem above ground, this has two benefits; most of the soil nutrients stay in the ground and the stems have very low moisture content at the time of harvesting (Feb./Mar.), typically between 25-30%.

In line with the local topography, yields will vary considerably across the area. Growing over 3m in height, Miscanthus is susceptible to wind damage and is not suitable for areas with an average wind speed over 7m/s. While there are no areas of red (19 dt/ha/y), the more favourable areas are in yellow and green, it therefore reasonable to assume that T&D could sustainably support an average yield of 15 dt/ha/y.

Comparing Short Rotation Coppice and Miscanthus, the latter appears to be the better choice. Although planting costs are higher, the crop needs fewer inputs, converts solar energy more efficiently and has a low moisture level when harvested. Existing farm machinery can be used to harvest and it is not necessary to oven dry the crop to reduce its moisture content. Miscanthus can be left as long stalks, chopped or pelleted and has other uses such as animal bedding, so in some circumstances could be used twice and thereby adding value. It is possible to split areas between SRC and Miscanthus if soil circumstances dictate that one crop is better suited to a particular soil type.

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