Scottish Government

Executive summary

Yield of short rotation biomass and availability of suitable land

• On lowland sites yields of 8 oven-dry tons (odt) ha ^-1 per year can be expected from Short Rotation Coppice ( SRC) and 5-10 odt ha ^-1 from Short Rotation Forestry ( SRF).
• But on marginal land yields of both SRC and SRF ( SRB) may only be around 4 odt ha ^-1.
• Estimates of the amount of land suitable for SRC production Scotland range from 19,000 to 90,000 ha, 1-4% of the country. This limited area is due to much of the country being too wet or too cold.
• These potential areas are close to population centres and hence have the potential to supply biofuels within short distance of demand.
• Based on these estimates of suitable land, and the breakdown between more productive lowlands and less productive uplands, then the potential total annual yield of SRB could be between 125,000 and 600,000 odt.

Economic viability

• The major factors which determine the financial returns from SRC and SRF are wood chip yields and prices and the establishment costs (and hence the availability and level of establishment grant available).
• How the return from SRB compares with the alternative, agricultural, use of the land is also important.
• The current price for SRB is around £31 per oven dry ton (odt).
• At this price our estimates indicate that on marginal land SRC produces a smaller return than upland sheep, while SRF would lead to a net loss in income.
• In order for SRC to be as cost-effective as upland sheep the yield or price of SRC would need to increase by 15% or a 75% establishment grant provided.
• For SRB the yield or price would need to increase by 380% or a grant provided which includes an additional 10% over the full establishment cost.
• The main barriers to uptake of SRB are the establishment costs and the delay before any return can be realised. In contrast upland sheep, for example, offer an annual income.
• It is also worth noting that the LFA scheme has a major impact because it does not allow land in SRC to be classed as forage, and so results in a reduction in payments.
• The lower SRC establishment grant (50% in the LFA, up to £770/ha maximum) under the SRDP compared with the previous position under woodland grants (up to £1,000 per hectare) has a major impact on viability.
• The support which might be available for SRF is unclear. It does not fit the criteria, such as plant density, for SRC support, yet does not fit typical forestry criteria and standard costs.
• It would take relatively small additional benefits (planting in shelter strips to improve lamb survival, modest environmental payments) from SRC to allow it to compete with sheep in the better upland sites.
• Larger payments would be needed for SRF.

Carbon storage

• The planting of SRB for up to 30 years offers some potential for C storage. A greater proportion of biomass is likely to be harvested from SRB than from traditional commercial forests. Hence this utilisation of forest harvest residues on poor sites could be detrimental to site productivity and long-term soil C storage.
• A large proportion of land in Scotland is under grass, or on peat soils (or both), situations where SOM is already fairly large. The cultivation and drainage needed to establish SRB on such sites could lead to a net loss of soil C.
• It is important therefore that caution is exercised when considering the establishment of SRB on peat soils.
• Planting SRB on sandy soils that have been in long-term arable cropping offers the greatest potential for C storage.
• Average rates of soil C storage of 0.3 t C ha ^-1 yr ^-1 (range 0-3.0 t C ha ^-1 yr ^-1) by forestry has been reported. The considerations reported above suggest the potential for SRB will be at the lower end of that range.
• Above-ground C storage, i.e the C stored in the trees and litter minus the wood removed for fuel, could range from 0.2-0.6 t C ha ^-1 yr ^-1.
• In order to maximise the potential of sequestration, longer rotation periods have been proposed as the most effective. Therefore by definition, SRC is likely to be unable to be as effective as traditional forestry in maximising the potential for C sequestration.
• Much of any stored C is likely to be lost if the SRB is subsequently cultivated to establish arable crops or grassland.

Environmental impacts

• The soil cultivation needed to establish SRB may lead to increased emissions, of the GHGs nitrous oxide and methane as well as nitrate leaching during preparation of the site and during establishment of the crop.
• Once established SRC should have smaller nitrous oxide emissions than conventional crops.
• Once established nitrate leaching is expected to be less than from agricultural crops.
• But emissions of both will be greater than from natural grasslands, moorlands and woodlands.
• Uprooting the SRB stumps will disrupt the soil environment, and may wipe out the benefits of the carbon storage by SRB. In addition emissions of nitrous oxide and nitrate are likely to increase after uprooting.
• The pattern of polluting emissions will be an increase following soil preparation for establishment, a decrease in comparison with emissions from arable land and grazed grassland once SRB is actively growing, followed by another large increase after stump removal and cultivation for subsequent land use. Due to the lack of reported data on emissions from SRB it is not possible at this stage to estimate the likely average size of emissions in comparison with arable or managed grasslands.
• In the drier parts of Scotland use of SRB may reduce the volumes of drainage water.
• This reduction in the volume of drainage water might lead to concentrations of pollutants such as nitrate being maintained in drainage waters, even though losses as kg per hectare are reduced.
• SRB has the potential to be used in the treatment of wastewaters and sewage sludge via filtration through the vegetation. Such an approach can be carried out at a low cost compared with conventional treatment and minimises use of finite resources (materials, energy). This approach is already used in some other European countries.

Biodiversity

• In general, SRB plantations composed of willow or poplar support greater numbers of birds and more species than arable croplands and managed grasslands during spring and autumn. However, SRB provides a poorer habitat than woodlands, wet meadows and some grasslands.
• SRB plantation design and management should emphasise the maintanance of existing species assemblages and to avoid habitats such as wetlands and woodlands that support greater levels of biodiversity than occur in SRB plantations.
• As SRB plantations are often located within a combination of other land-use types, they may act as a stepping-stone to other land-use types and so some authors have considered SRB plantations to be an ecological corridor.
• Willows and poplars are intolerant of weed competition and hence some management guidelines advocate a "no-weed" approach.
• Few species of conservation concern have been observed in SRB.
• Attempts to introduce shade-tolerant wildflower species to improve the floristic diversity of the understory have met with little or no success.
• In general, SRB plantations composed of willow or poplar support greater numbers of birds and more species than arable croplands and managed grasslands during spring and autumn.
• But SRB provides a poorer habitat than woodlands, wet meadows and some grasslands.
• Rare bird species that prefer open habitats could be threatened or become locally extinct with the addition of large tracts of SRB plantations to the landscape.
• It has been suggested that to maximise avian biodiversity, SRB plantations should be designed in small blocks or in plots with a large edge-to-interior ratio.
• SRB plantations do not appear to provide high-quality habitat for small mammals, although un-weeded plantations contain a greater abundance of mammals than frequently weeded sites.
• Red-listed species such as the dormouse and red squirrel are unlikely to find suitable habitat in SRB plantations due to the absence of the mature trees required for nesting sites.
• The red-listed brown hare is expected to benefit from the infrequent disturbance and increased landscape complexity associated with SRB management and production.
• As SRB plantations are often located within a combination of other land-use types, they may act as a stepping-stone to other land-use types and so some authors have considered SRB plantations to be an ecological corridor.

Conclusions

• Short rotation biomass does not appear to be an attractive alternative to current enterprises on marginal land.
• However, an increase in the price of SRB woodchip to around £50 per odt, or grants that covered at least 75% of establishment costs could make SRC viable.
• While there is potential for C storage in the coppiced stools and in soil, and reductions in polluting emissions during the productive phase of SRB, these benefits may be lost on restoration to other land uses.
• Biodiversity may be increased, in comparison with arable land and managed grassland, particularly if plantations provide a large edge to land area ratio.
• However, at this stage there do not appear to be any compelling reasons to increase the area of SRB as a means of improving air or water quality or increasing biodiversity.