© iForest -Biogeosciences and Forestry IntroductionEnergy security and greenhouse gas emission reductions are major challenges to meet the global energy demand and to mitigate climate change (IPCC 2014). In the light of these global concerns bioenergy could play a crucial role to achieve the EU's energy and climate targets (European Council 2009). The cultivation of lignocellulosic biomass, mostly poplar and willow in short rotation coppice (SRC) systems, has a high potential for the production of renewable electricity and the generation of "green" heat (Fischer et al. 2010). Despite the long-term experience with the commercial production in northern Europe (Rosenqvist et al. 2000, Langeveld et al. 2012, the implementation of SRC as a renewable energy crop is limited in European agriculture (AEBIOM 2010, Dimitriou et al. 2011, Don et al. 2011.Productivity is determined by light interception and by the efficiency of converting the intercepted radiation into biomass, i.e., the radiation use efficiency (RUE), as reported for both herbaceous (Sinclair & Horie 1989) and woody (tree) species (Cannell et al. 1988, Medlyn 1998. The crop's capacity to intercept radiation is determined by its photosynthetic area, generally assessed via the leaf area index (LAI), which is linearly related to the biomass production in poplar and willow plantations (Larson & Isebrands 1972, Cannell et al. 1988, Taylor et al. 2001a. In SRC systems, faster canopy closure and increased growth rates of sprouts from an established root system result in enhanced productivity of coppiced versus noncoppiced tree stands . Substantial genotypic variation exists in aboveground woody biomass productivity (AGWB) of SRC cultures in poplar (Ceulemans & Deraedt 1999, Dillen et al. 2011, Paris et al. 2011, Benetka et al. 2014). Variation in AGWB has been explained by variation in light interception, in biomass allocation, in leaf physiological factors related to RUE or in a combination of the aforementioned (Cannell et al. 1988, Green et al. 2001, Tharakan et al. 2008, suggesting inconclusive results on the relative importance of productivity determining factors in SRC. The quantification of genetic diversity and of genetic control contributes to future tree improvement and to yield maximization efforts towards sustainable bioenergy cultivation.In the present study, we analyzed the leaf area development, light interception and RUE of 12 poplar genotypes in a high-density SRC culture, before and after the first coppice of an experimental plantation. Assessment of LAI and woody biomass productivity was performed in a single versus a multi-stem culture, to analyze the effect of coppicing. We hypothesized significant genotypic, parentage and provenance variation in LAI, in leaf area duration (LAD), in RUE, in intercepted radiation (Iint) and AGWB. The objectives of this study were: (i) to determine the main differences between the first (R1) and the second rotation (R2) in the above mentioned parameters and in their relationships, i.e., before and after coppice,...

We compared four approaches to assess phenology in a short-rotation coppice culture with 12 poplar (Populus) genotypes. The four approaches quantified phenology at different spatial scales and with different temporal resolutions: (i) visual observations of bud phenology; (ii) measurements of leaf area index; (iii) webcam images; and (iv) satellite images. For validation purposes we applied the four approaches during two years: the year preceding a coppice event and the year following the coppice event. The delayed spring greenup and the faster canopy development in the year after coppicing (as compared to the year before coppicing) were similarly quantified by the four approaches. The four approaches detected very similar seasonal changes in phenology, although they had different spatial scales and a different temporal resolution. The onset of autumn senescence after coppicing remained the same as in the year before coppicing according to the bud set observations, but it started earlier according to the webcam images, and later according to the MODIS images. In comparison to the year before coppicing, the growing season -in terms of leaf area duration -was shorter in the year after coppicing, while the leaf area index was higher.