Perennial energy crops and their potential in Scotland: evidence review

If Scotland is to achieve its ambitious net-zero greenhouse gas emissions target by 2045, bioenergy crops present one option as an integral part of the energy supply system.

The Committee on Climate Change (CCC) has identified that under net-zero emissions scenarios, bioenergy supplied in the UK could reach 200TWh (with 170TWh of this sourced from the UK) by 2050. The CCC considered that UK-produced energy crops could be an important source of bioenergy and assumed that around 700,000 ha could be planted in the UK to help achieve this target, although it did not consider where. If it were evenly spread across the arable area of the UK, Scotland’s ‘share’ would be about 70,000 ha.

This report examines the potential for a sustainable expansion of perennial bioenergy crop production on low-grade agricultural land or underutilised land, focusing on short rotation coppice (SRC), miscanthus and short rotation forestry (SRF). The aim was to understand the potential implications of any expansion, as a basis for further discussion.

Key findings

The theoretically suitable total land area identified across all three crops and land types, which include grassland, is more than 900,000 ha; suggesting that Scotland could make a substantial contribution to the area of UK energy crops, and meet its ‘share.’ The theoretically suitable total land area is shown to decline when grassland areas are excluded.

In terms of total area, geospatial modelling shows a theoretical potential for each crop type in Scotland (based on current data) of :

• 912,600 ha of suitable land is currently available for planting of SRF,
• 219,100 ha is available for SRC and
• 51,800 ha is available for miscanthus.

The areas can overlap and are therefore not mutually exclusive.

The majority of this theoretically available land is located in the east of Scotland and the lowlands. The availability of this land will be limited by a range of other factors, for example the need for land for other uses, such as fodder production, forestry (non-energy) etc.

The theoretically available land could provide the following energy yields:

• 50TWh/yr and 5.78Modt/yr for SRF,
• 25TWh/yr and 1.75Modt/yr for SRC and
• 59TWh/yr and 0.52Modt/yr for miscanthus.

Overall constraints are more severe for miscanthus than for SRC or SRF. The following constraints have high impacts on potential production area:

• Winter hardiness of miscanthus is a major constraint for this crop in much of Scotland.
• Current varieties of miscanthus are constrained by climate to the south and south east of Scotland (Towers, 2013).
• Soil carbon loss is a constraint for SRC expansion. There is a large area of land in Scotland with high levels of soil organic carbon and this land is susceptible to loss of soil carbon when it is cultivated. For SRF this constraint is less relevant because there is less soil cultivation but planting of trees on blanket bog (peatland) should be avoided (as recommended in the UK Forestry Standard (Forestry Commission, 2017)) because of habitat loss and carbon loss as a consequence of drainage.

Using a UK Climate Projections 2009 (UKCP09) medium emissions scenario for a changing climate, we found that the expansion in suitable land is between:

• 22-25% of the current theoretically suitable land area out to 2030 and between 29-30% of the current suitable land area out to 2045 for SRC and miscanthus.
• However, the suitable land available for SRF is shown to decline by 3% by 2040.

Overall, the data do show that there are opportunities for energy crop expansion both currently and under a changing climate.