Model-based optimisation of the trade-offs between biomass production, CO2 balance and water consumption in short rotation coppice forestry
30 September 2016
UAntwerpen, Campus Groenenborger, U0.25 - Groenenborgerlaan 171 - 2020 Antwerpen (route: UAntwerpen, Campus Groenenborger
Organization / co-organization:
Department of Biology
Toon De Groote
PhD defence Toon De Groote - Faculty of Science, Department of Biology
Biomass for energy is one of the most interesting renewable energy sources, because it can provide a continuous flow of electricity and it can be converted into liquid biofuel. Short Rotation Coppice (SRC) plantations are intensively managed perennial energy crops with fast growing tree species in a coppice system. This plantation system allows a fast woody biomass production. Theoretically, this biomass for energy production is carbon neutral, but in practice plantation management adds an extra cost.
The objective of this thesis is to find an optimized management, i.e. a combination of good yield with low environmental impact, for SRC poplar (Populus spp.) plantations accross Europe for current and future climate.
The land-surface model ORCHIDEE was modified to predict biomass yield and CO2 uptake of poplar SRC plantations for different management scenarios. The biomass yield was predicted well within the range of measured values. The model estimated GPP and ecosystem respiration well and latent heat flux reasonably well compared to measurements.
For all scenarios the biomass was assumed for electricity production by gasification. We selected 22 sites across Europe, with a variety of soil types and climates. For each of these sites, we compared the biomass yield, the net CO2 balance, the net energy balance and the actual evapotranspiration for 20 different management scenarios under current and future climate.
The simulations showed that careful site selection is most important in establishing an SRC plantation. Plantations in temperate climates performed better than plantations in Mediterranean climates. Further optimizations pointed to two year rotations. Varying planting densities between 5,000 and 15,000 trees per hectare did not have an impact on yield, the net CO2 balance or the net energy balance. In temperate climates irrigation is not advised, as it is too costly from an energetic point of view. In Mediterranean climates, however, irrigation overcomes limited water supplies and summer droughts. In a future climate, the positive effect of increased atmospheric CO2 concentrations on water use efficiency was stronger than the increase in drought. Elevated atmospheric CO2 concentrations caused a yield increase and CO2 uptake, making SRC an even more promising renewable energy option.