Assessing the potential of poplar short rotation plantations to contribute to a low-carbon bioeconomy under water-limited conditions

Poplar short rotation coppice (SRC) systems are important for biomass production and for short-to medium-term carbon (C) sequestration, contributing to a low-carbon bioeconomy and thus helping to mitigate global warming. The productivity and profitability of these plantations are, however, challenged under restrictive irrigation associated with climate change. This study compares the above- and below-ground C sequestration potential and economic viability of a 12-year plantation cycle (4 rotations of 3 years each) under Mediterranean conditions with optimum irrigation (T1) and 50% irrigation reduction (T2), analysing other promising biomass uses in the form of bioproducts. A total of 138 trees of the highly productive hybrid ('AF2') in a SRC-trial were sampled monthly (first rotation). Additionally, data from an extensive poplar plantation network (30 sites) was used to complete data for the plantation cycle. The average C content for above- and below-ground biomass was 17.04 Mg C ha-1 yr-1 (T1), falling by 24% in T2. The net present value (NPV) in T1 (6461 € ha-1) was 52% lower under T2 conditions. Extra payments for C sequestration increased the NPV to 8023 for T1 and 4331 € ha-1 for T2. Roots represent an important C storage in the soil, accumulating 29.9 Mg C ha-1 (T1) and 22.8 Mg C ha-1 (T2) by the end of the cycle in our study. The mitigation potential is strongly fortified when the share of bioproducts in biomass end-use increases. Assuming a distribution of 50% bioenergy and 50% bioproducts, emission were reduced between -114 Mg CO2eq ha-1 (T1) and -88 Mg CO2eq ha-1 (T2) compared to BAU until end of the century. This scenario plays a crucial sink-effect role by storing C contained in biomass, which is not immediately released into the atmosphere.