Consensus, uncertainties and challenges for perennial bioenergy crops and land use

Abstract

Perennial bioenergy crops have significant potential to reduce greenhouse gas (GHG) emissions and contribute to climate change mitigation by substituting for fossil fuels; yet delivering significant GHG savings will require substantial land‐use change, globally. Over the last decade, research has delivered improved understanding of the environmental benefits and risks of this transition to perennial bioenergy crops, addressing concerns that the impacts of land conversion to perennial bioenergy crops could result in increased rather than decreased GHG emissions. For policymakers to assess the most cost‐effective and sustainable options for deployment and climate change mitigation, synthesis of these studies is needed to support evidence‐based decision making. In 2015, a workshop was convened with researchers, policymakers and industry/business representatives from the UK, EU and internationally. Outcomes from global research on bioenergy land‐use change were compared to identify areas of consensus, key uncertainties, and research priorities. Here, we discuss the strength of evidence for and against six consensus statements summarising the effects of land‐use change to perennial bioenergy crops on the cycling of carbon, nitrogen and water, in the context of the whole life‐cycle of bioenergy production. Our analysis suggests that the direct impacts of dedicated perennial bioenergy crops on soil carbon and nitrous oxide are increasingly well understood and are often consistent with significant life cycle GHG mitigation from bioenergy relative to conventional energy sources. We conclude that the GHG balance of perennial bioenergy crop cultivation will often be favourable, with maximum GHG savings achieved where crops are grown on soils with low carbon stocks and conservative nutrient application, accruing additional environmental benefits such as improved water quality. The analysis reported here demonstrates there is a mature and increasingly comprehensive evidence base on the environmental benefits and risks of bioenergy cultivation which can support the development of a sustainable bioenergy industry.

Switchgrass and Giant Miscanthus Biomass and Theoretical Ethanol Production from Reclaimed Mine Lands

“…Switchgrass and giant miscanthus (hereafter, miscanthus) are warm-season (C 4 ) perennial grasses with promising biofuel production capabilities due to their productivity on marginal land such as reclaimed mine lands [14][15][16][17][18][19][20]. This is consistent with the emerging view that cellulosic bioenergy feedstock production should be based on perennials grown on marginal lands that are unsuitable for annual cropping [9,15,21,22].…”

Measured and modelled effect of land‐use change from temperate grassland to Miscanthus on soil carbon stocks after 12 years

“…In the United Kingdom, Welsh agriculture is primarily grass based (Welsh Government, ) and spatial modelling has suggested that there may be 0.5 M ha suitable for the planting of perennial bioenergy crops (such as Miscanthus and short rotation coppice; Lovett, Sünnenberg, & Dockerty, ). However, there are concerns that losses of soil carbon (C) caused by soil disturbance (Balesdent, Chenu, & Balabane, ; Conant, Easter, Paustian, Swan, & Williams, ) could reduce the C mitigation benefits gained from the conversion of grasslands into the production of bioenergy crops (McCalmont, Hastings, et al, ; Whitaker et al, ).…”

“…However, to date, most studies have taken grassland sites adjacent to Miscanthus plantations as representative of pre‐cultivation conditions (Clifton‐Brown, Breuer, & Jones, ; Foereid, Neergaard, & Høgh‐Jensen, ; Rowe et al, ; Schneckenberger & Kuzyakov, ; Zang et al, ; Zimmermann, Dauber, & Jones, ), and while the use of such sites where soil and climate conditions are similar can provide a reasonable indication they may not accurately replicate baseline SOC stocks (McCalmont, Hastings, et al, ; Richter et al, ). Therefore, there is a need to reduce some of the uncertainty around the impact of this LUC from grassland to Miscanthus on SOC (Whitaker et al, ), especially over the longer term.…”

“…For example, Robertson et al () investigated SOC as part of their LCA involving LUC to Miscanthus but this was from a previous arable land use with annual cultivation; potential losses at grassland sites, with less regular soil disturbance, could have a significant impact on LCA results (Hillier et al, ). Changes in SOC over the lifetime of the crop also have the potential to impact on greenhouse gas balances to a greater extent than other LUC associated costs such as increased soil nitrous oxide (N 2 O) emissions (Whitaker et al, ).…”

A Framework for Tracing Social–Ecological Trajectories and Traps in Intensive Agricultural Landscapes

“…The Climate Adaptation Scenario focuses on the alteration of existing social-ecological feedbacks for increased resilience to the agricultural effects of climate change [29], whereas the Perennial Transformation Scenario involves the transformation of the CPNRD FEWES nexus from producing food [30] and bioenergy [31] from perennial instead of annual crops. Each scenario focused primarily on a feedback(s) identified in the causal loop diagram (Section 3.2).…”