Physiology and productivity of short-rotation coppice: genotypic differences and impacts of harvesting
30 June 2017
Campus Drie Eiken, O7 - Universiteitsplein 1 - 2610 Antwerpen-Wilrijk (route: UAntwerpen, Campus Drie Eiken
PhD defence Stefan Vanbeveren - Faculty of Science, Department of Biology
Biomass was, is and will always be an important source of renewable energy. Short-rotation coppices (SRCs) are plantations that combine forestry species with agricultural management: trees are planted at high densities and harvested regularly by removing all of the above-ground woody biomass (AGWB) from the field. The harvested stems are chipped and the resulting wood chips are used to generate renewable heat and/or green electricity. To correctly assess the feasibility and the potential of SRC, it is important to examine its productivity. On the one hand, this dissertation focused on the influence of the abiotic environment on the productivity of an SRC during the first two (two-year) rotations. On the other hand, the focus was on the harvesting, as this is the most important management intervention in the lifetime of an SRC.
Several abiotic factors were related to the productivity of the 12 different poplar genotypes. No significant correlations were found between the intercepted radiation (Iint) and the radiation use efficiency (RUE), but the RUE was significantly correlated to the AGWB. Furthermore, the leaf area index and the leaf area duration proved to be better indicators for the Iint than the AGWB for all 12 genotypes. The percentage of dry matter allocated to woody biomass increased with increasing productivity and significant genotypic differences were found. Furthermore, nutrient concentrations were always higher in leaves as compared to woody biomass. Lastly, the impact of harvesting on the SRC was investigated by assessing plant phenology with four approaches in the year before and the year after the first harvest. All approaches, except the satellite images, clearly showed a delayed spring onset (± 60 days) in the year after the harvest, while the end of the growing season remained unchanged, resulting in a shorter (63 days) growing season.
Harvesting-related literature was reviewed for the second part of this dissertation. The cut-and-chip harvesters are dominating the market, because of their high effective material capacity (EMC), which results from the significantly higher maximum engine power available. Furthermore, field stocking had a limiting effect on the maximum achievable EMC. During the second harvest of the POPFULL SRC the performance of manual harvesting proved to be 332 € MgDM-1 more expensive and 8 MgDM h-1 slower than mechanised harvesting. Finally, the revenue from integrated harvesting did not sufficiently increase under the current market conditions as compared to whole tree chipping.