Assessing short rotation coppice poplar biomass and its determinants on former arable land in Czech Republic

Forest coppice biomass, fast growing short rotation coppice (SRC) trees such as willows (Salix) and poplar (Populus) have a substantial potential of storing carbon (C), and has been considered as a sustainable source of woody dry mass. Woody dry mass production, energy efficiency and economic profitability of poplar are important and essential to be studied in Czech Republic. The aim of this PhD thesis was to predict standing woody dry mass, maximize the productivity and quantify the determinants of poplar clone J-105 (Populus nigra × P. maximowiczii) under short rotation coppice (SRC) management on former arable in Czech Republic. This PhD study was carried out in Domanínek, Czech Republic (49°31´N, 16°14´E and 530 m a.s.l.). Plantations were established in high density (9,216 trees ha-1) with single stem hardwood cuttings for verification purposes and to test the performance of poplar clone J-105 on former arable land. The plantations were harvested above 15-20 cm from base in winter 2008/2009 (established in April 2001) and 2009/2010 (established in April 2002). In this thesis, short rotation woody coppice (SRWC) plantations are mentioned as SRWC1 (coppice established in 2009) and SRWC2 (coppice established in 2010), respectively. In spring 2009, SRWC1 was divided into four randomized blocks and treated with three different fertilizers such as minerals [Nitrogen (N), Phosphorus (P), and Potassium (K)], sewage sludge and ash, lime and control (without any treatment of fertilizer). In the plantation SRWC2, no further (at beginning of second rotation-coppice) fertilizer treatment was applied. For the prediction of standing aboveground woody dry mass (AGWDM) in fertilizer treatments and control, allometric equations were developed. The allometric equations thus developed may be considered robust and site specific for poplar clone J-105. After the successful development of allometric equations standing annual AGWDM was estimated followed by annual inventory at the end of each growing season. There were no significant differences observed in allometric equations for AGWDM among the fertilizer treatments (including control) within the year over four years of study from 2011-2014. This experiment was repeated in plantation SRWC2, for which the allometric equation was developed separately, for the purpose of allocation of the aboveground and belowground woody dry mass (BGWDM) at the same site. In this plantation for estimation of AGWDM, allometric equation was developed in 2011 (after two years of plant growth in coppice) and for BGWDM, the equation was developed in 2014 (after more than four years of plant growth in coppice). In SRWC2 plantation, dynamics of annual and cumulative above and belowground woody dry mass were estimated over four years from 2011-2014, where average AGWDM were observed from 8.29 to 11.02 t ha-1 year-1 and average annual BGWDM varied between 2.50 to 3.02 t ha-1 year-1. Growth and wood production mainly depend on photosynthetic area and light efficiency. Therefore, leaf area development including leaf area index (LAI) and leaf area duration (LAD) and radiation use efficiency (RUE) was studied to find a suitable determinant for aboveground woody dry mass production. In the results, maximum leaf area index LAImax was observed to be 9.5 after four years of plant growth in coppice, maximum number of LAD was 185 days after two years of plant growth in coppice and maximum RUE was observed to be 1.3 gMJ-1 in GS4 (growing season four) after four years of plant growth in coppice. LAI and LAD showed a strong positive correlation for AGWDM (R2 values ~1) while RUE showed a moderate positive correlation with AGWDM, where R2=0.50 (p=0.52). This implies that AGWDM is strongly dependent on LAI and LAD. To conclude a robust and site specific allometric equation was developed for poplar clone J-105 and also, this study confirmed that, there was no significant impact of fertilizers for maximizing the AGWDM production on former arable land. For determinants of AGWDM, it confirmed that LAI, LAD and RUE could be a good and reliable predictor of standing AGWDM in SRC poplar clone J-105 on former arable land