Predicting the yield and water-use of poplar short rotation coppice under a future climate

Under the current climate there is significant spatial variation in the yield and water-use ofbioenergy crops such as poplar short rotation coppice (SRC). Marked changes in patternsof precipitation and temperature are predicted globally as a result of anthropogenic climatechange. This is likely to significantly impact on the yield and transpiration of poplar SRC.The response of poplar SRC to future climate change is unknown and represents asignificant knowledge gap in the path to a sustainable future.This thesis used a land-surface scheme, JULES, to investigate the response of poplar SRCyield and transpiration to the interaction between changes in atmospheric CO2concentration and changes in climate. Empirical work generated poplar SRC specificparameter values for use JULES. It was found that Vmax, a key model photosyntheticparameter, was significantly lower when estimated under the assumption of infinite leafinternal conductance to CO2. This invalidated the assumption that internal CO2 transfer hasa negligible impact on the drawdown of CO2 from ci to cc. The photosynthesis model inJULES is based on this assumption; however, inclusion of this additional CO2 transferpathway in the model did not impact on the accuracy of the simulated carbon assimilation,because the value of Vmax used in the model compensated for the presence/absence of thispathway. It was concluded that, given the model’s high sensitivity to Vmax, it is essential tocalibrate the model with a parameter value estimated under assumptions appropriate for themodel. Further modification, calibration and validation enabled JULES to simulate thedynamic growth and water-use of poplar under a managed SRC cycle, which is a novelapplication for the model. Changes in climate were simulated using an ensemble of GCManomalies and atmospheric CO2 concentration was simulated using the SRES A1Bemissions scenario. Results of this work highlighted the influence of climate in modifyingthe yield and transpiration responses to elevated concentrations of atmospheric CO2.Additionally, for a future climate scenario, these simulations indicated higher yields butalso higher water-use of poplar SRC, although the magnitude and direction of responsewas highly spatially variable