Development and evaluation of ForestGrowth-SRC a process-based model for short rotation coppice yield and spatial supply reveals poplar uses water more efficiently than willow

Woody biomass produced from short rotation coppice (SRC) poplar (Populus spp.) and willow (Salix spp.) is a bioenergy feedstock that can be grown widely across temperate landscapes and its use is likely to increase in future. Process-based models are therefore required to predict current and future yield potential that are spatially resolved and can consider new genotypes and climates that will influence future yield. The development of a process-based model for SRC poplar and willow, ForestGrowth-SRC, is described and the ability of the model to predict SRC yield and water use efficiency (WUE) was evaluated. ForestGrowth-SRC was parameterized from a process-based model, ForestGrowth for high forest. The new model predicted annual above ground yield well for poplar (r2 = 0.91, RMSE = 1.46 ODT ha-1 yr-1) and willow (r2 = 0.85, RMSE = 1.53 ODT ha-1 yr-1), when compared with measured data from seven sites in contrasting climatic zones across the United Kingdom. Average modelled yields for poplar and willow were 10.3 and 9.0 ODT ha-1 yr-1, respectively, and interestingly, the model predicted a higher WUE for poplar than for willow: 9.5 and 5.5 g kg-1 respectively. Using regional mapped climate and soil inputs, modelled and measured yields for willow compared well (r2 = 0.58, RMSE = 1.27 ODT ha-1 yr-1), providing the first UK map of SRC yield, from a process-based model. We suggest that the model can be used for predicting current and future SRC yields at a regional scale, highlighting important species and genotype choices with respect to water use efficiency and yield potential.