Modelling climate change impacts on the productivity of short rotation coppice

摘要

Fast growing hybrids of Salix and Populus can be grown in a short rotation coppice (SRC) system to produce renewable energy. This PhD investigates the interactions between the environment and productivity, with a view to finding the key limiting factors to yield and the potential of these crops to fulfil UK renewable energy obligations, now and in the future. An empirical modelling technique, using partial least squares regression was developed to extrapolate actual field observations to a national scale. Genotype x age x environment interactions were studied to examine the key limiting factors to productivity. Modelled yields differed between genotypes, with mean annual aboveground biomass ranging from 4.9 to 10.7 oven dry tonnes (odt) per hectare for Populus trichocarpa x P. deltoides genotype ‘Beaupré’ and Salix triandra x S. viminalis genotype ‘Q83’, respectively. Variation in yield was primarily described by spring and summer precipitation, suggesting water availability is the key limiting factor to yield. Output from the model was up-scaled across the UK using a geographic information system (GIS), and scenarios were developed to better understand the role and impact of land use management and policy development on potential crop distribution. For example, to meet UK biomass and biofuel targets without compromising food security or ecosystem services, would require 5 % of grade 3 land, 56 % grade 4 land and 47 % of grade 5 land. This quantity of biomass would produce 7.5 M tonnes of biomass per annum and would theoretically generate 15.5 TWh yr-1 of electrical energy, displacing 3.3 M tonnes of oil – approximately 4% of current UK electricity demand. The South West and North West alone producing over a third of this figure (5.2 TWh yr-1). These results suggest that SRC has the potential to become a significant component of a mixed portfolio of renewables. Furthermore, climate change is predicted to have far reaching consequences on crop growth. Process-based models can help quantify these interactions and predict future productivity. Here we use ForestGrowth-SRC, a process-based model originally designed for high-forest species and parameterised for a coppice system. Climate change scenarios (UK Climate Projections) were run with the model to assess the impact of a changing climate on the growth and spatial distribution of SRC poplar. Results suggest ForestGrowth-SRC is capable of accurately simulating growth over a large spatial and temporal scale. However, pests and disease were found to significantly affect yield. In the absence of pests and disease, productivity could increase by 20 % nationwide by 2080 (under a medium emissions scenario), suggesting we will see a future increase in the value and production of these crops as feedstocks for heat, power and liquid transportation fuels