What have we learnt?
What have we learnt?
Over the past decade, our research across empirical, modelling and life-cycle studies has demonstrated that perennial biomass systems (willow, eucalypt, robinia, radiata pine, poplar, among others) as well as energy grasses can reliably supply renewable feedstocks, sequester carbon, provide ecosystem services and support rural economies.
Management by crops and plantation systems. Large-scale mapping of potential yields across Europe indicates that willow short-rotation coppice can produce an average of 6.8–9.5 oven-dry tonnes per hectare annually under optimal conditions (Mola-Yudego, 2010). Analysis of Swedish commercial yields shows that the highest-performing growers increased willow stand outputs by approximately 2.06 odt ha⁻¹ yr⁻¹ per decade through refined management practices (Mola-Yudego, 2011). Comparisons between experimental trials and commercial harvests reveal that small-plot yield estimates can overstate real-world performance by up to threefold (Mola-Yudego, 2011, Mola-Yudego et al., 2015). Poplar coppice plantations achieve mean annual yields of 6.9 Mg ha⁻¹ with optimized cutting cycles (Mola-Yudego & Aronsson, 2008). Kernel-density evaluations demonstrate that poplar and willow plantations cluster in areas of medium-fertility soils, indicating that site selection strongly influences biomass production (Mola-Yudego & González-Olabarria, 2010).
Net-energy return studies report that unfertilised poplar plantations in Sweden produce 179 GJ ha⁻¹ yr⁻¹, rising to 190 GJ ha⁻¹ yr⁻¹ with moderate fertilization (Nordborg et al., 2018a). In willow SRC systems, increasing nitrogen application from zero to high rates raises net energy from 86 GJ ha⁻¹ yr⁻¹ to 175 GJ ha⁻¹ yr⁻¹, albeit with diminishing energy-use efficiency at higher inputs (Nordborg et al., 2018b). Investigations into harvest scheduling show that adjusting rotation lengths can optimize the balance between yield and stand longevity (Papamatthaïaikis et al., 2021). Mixed-species trials combining grasses and legumes within perennial rotations have demonstrated yield stability under variable weather conditions (Pineda & Mola-Yudego, 2025). Plant density experiments indicate that closer spacings can increase early-stand biomass but may reduce long-term yield per hectare (Dimitriou & Mola-Yudego, 2017 BR). Field trials comparing irrigation regimes in willow SRC highlight the importance of soil moisture management for sustained biomass growth (Dimitriou & Mola-Yudego, 2017 FEM). Studies on coppice cycle lengths reveal that shorter rotations maximize annual yield but require more frequent replanting, affecting overall system costs (Dimitriou & Mola-Yudego, 2017). Fertilisation experiments on poplars find that moderate nitrogen rates (75 kg N ha⁻¹ yr⁻¹) provide optimal growth responses while minimizing nutrient losses (Dimitriou and Mola-Yudego, 2017).
Environmental effects of these crops and plantations. Long-term willow SRC plantations exhibit 9 % higher topsoil organic carbon compared to adjacent arable fields after 10–20 years (Dimitriou et al., 2012b), and similar in poplar plantations (Dimitriou and Mola-Yudego, 2017). Across 16 commercial willow sites, nitrate leaching was significantly lower than in neighbouring cereal systems (Dimitriou et al., 2012). Life-cycle assessments indicate that nitrogen-fertilised willow plantations can achieve up to 40 % higher yields but incur increased eutrophication impacts (González-García et al., 2012). Unfertilised willow stands deliver superior greenhouse-gas savings per unit biomass relative to their fertilised counterparts (González-García & Mola-Yudego, 2012b). Multifunctional perennial grass systems reduce nitrogen runoff by over 30 % while producing biomass for biogas feedstocks (Englund et al., 2022). Riparian biomass strips sequester soil carbon and intercept nutrient loads, contributing to water-quality improvements (Englund et al., 2020). Mixed grass rotations sequester soil carbon at rates sufficient to offset 13–48 % of agricultural GHG emissions when used for biogas (Englund et al., 2023). Studies on evapotranspiration covers show that willow shelters reduce percolation on saline substrates by approximately 20 % compared to grass covers (Zalesny Jr. et al., 2019). Environmental modelling highlights that mature SRC stands can improve biodiversity metrics for birds and pollinators (Mola-Yudego et al., 2014b). Comparative soil-residue analyses reveal that willow biomass has low heavy-metal concentrations, meeting ISO standards for energy use (Mola-Yudego et al., 2015).
Strategic deployment and landscape integration. Spatial hotspot analyses identify that converting 10 % of EU arable land to SRC could deliver 6–9 odt ha⁻¹ yr⁻¹ while reducing erosion risk (Englund et al., 2020). Scenario modelling shows that riparian buffers and windbreak biomass strips on 5–10 % of agricultural land can cut nitrogen emissions by 20–30 % (Englund et al., 2021). Regional assessments demonstrate that dedicating grass rotations to 7 % of farmland can supply biomass displacing natural gas, saving 13 % of agricultural GHG emissions (Englund et al., 2023). Kernel-density mapping reveals four major pellet-mill clusters in Europe—Central, Scandinavian, Finnish and Baltic—accounting for over half of 11.5 Mt yr⁻¹ capacity (Mola-Yudego et al., 2014). Adoption studies show that Sweden’s district-heating plant expansions in the 1990s drove a 28 % increase in willow plantings within 30 km (Mola-Yudego & Pelkonen, 2011). Adoption-curve modelling indicates that planting subsidies and CO₂ taxes increased willow cultivation by nearly 70 % across municipalities (Mola-Yudego & Pelkonen, 2008). Meta-analysis of supply-chain resilience finds that stable off-taker contracts and research networks mitigate grower risk and accelerate crop adoption (Mola-Yudego et al., 2021). Continental-scale yield-potential comparisons show that plantations out-yield natural forests in 19 of 91 NUTS2 regions under 5 % land-use allocation scenarios (Mola-Yudego et al., 2017), and similarly in the Nordic area, at 1x1 km2 (Mola-Yudego, 2017b).