Identifying potential environmental impacts of large-scale deployment of dedicated bioenergy crops in the UK

Abstract

There is momentum, globally, to increase the use of plant biomass for the production of heat, power and liquid transport fuels. This review assesses the evidence base for potential impacts of large-scale bioenergy crop deployment principally within the UK context, but with wider implications for Europe, the USA and elsewhere. We focus on second generation, dedicated lignocellulosic crops, but where appropriate draw comparison with current first-generation oil and starch crops, often primarily grown for food. For lignocellulosic crops, positive effects on soil properties, biodiversity, energy balance, greenhouse gas (GHG) mitigation, carbon footprint and visual impact are likely, when growth is compared to arable crops. Compared to replacement of set-aside and permanent unimproved grassland, benefits are less apparent. For hydrology, strict guidelines on catchment management must be enforced to ensure detrimental effects do not occur to hydrological resources. The threat of climate change suggests that action will be required to ensure new genotypes are available with high water use efficiency and that catchment-scale management is in place to secure these resources in future. In general, for environmental impacts, less is known about the consequences of large-scale deployment of the C4 grass Miscanthus, compared to short rotation coppice (SRC) willow and poplar, including effects on biodiversity and hydrology and this requires further research. Detailed consideration of GHG mitigation and energy balance for both crop growth and utilization suggest that perennial crops are favoured over annual crops, where energy balances may be poor. Similarly, crops for heat and power generation, especially combined heat and power (CHP), are favoured over the production of liquid biofuels. However, it is recognized that in contrast to heat and power, few alternatives exist for liquid transportation fuels at present and research to improve the efficiency and energy balance of liquid transport fuel production from lignocellulosic sources is a high current priority. Although SRC, and to a lesser extent energy grasses such as Miscanthus, may offer significant benefits for the environment, this potential will only be realized if landscape-scale issues are effectively managed and the whole chain of crop growth and utilization is placed within a regulatory framework where sustainability is a central driver. Land resource in the UK and throughout Europe will limit the contribution that crops can make to biofuel and other renewable targets, providing a strong driver to consider sustainability in a global context.