This paper reviews 23 studies on the financial feasibility and on the production/cultivation costs of bioenergy plantations of fast-growing poplars and willows (SRWCs), published between 1996 and ...2010. We summarized and compared methods used thus far to assess the economics of SRWCs, identified the shortcomings and/or gaps of these studies, and discussed the impact of government incentives on the financial feasibility of SRWCs. The analysis showed that a reliable comparison across studies was not possible, due to the different assumptions and methods used in combination with the lack of transparency in many studies. As a consequence, reported production costs values ranged between 0.8 € GJ−1 and 5 € GJ−1. Moreover, the knowledge of the economics of SRWCs was limited by the low number of realized SRWC plantations. Although specific numerical results differed, it became clear that SRWCs are only financially feasible if a number of additional conditions regarding biomass price, yield and/or government support were fulfilled. In order to reduce the variability in results and to improve the comparability across studies (and countries), we suggest the use of standard calculation techniques, such as the net present value, equivalent annual value and levelized cost methods, for the assessment of the financial viability of these woody bioenergy crops.
► We reviewed 23 studies on the economic feasibility of SRWCs. ► Methods used, shortcomings and government incentives were discussed. ► Different assumptions and lack of transparency hampered meaningful comparison. ► SRWCs only financially viable with subsidies and/or high yield/biomass sales price. ► Standard calculation techniques for SRWCs were suggested.
Photosynthetic carbon assimilation and transpirational water loss play an important role in the yield and the carbon sequestration potential of bioenergy-devoted cultures of fast-growing trees. For ...six poplar (Populus) genotypes in a short-rotation plantation, we observed significant seasonal and genotypic variation in photosynthetic parameters, intrinsic water-use efficiency (WUEi) and leaf stable isotope composition (δ13C and δ18O). The poplars maintained high photosynthetic rates (between 17.8 and 26.9 μmol m(-2) s(-1) depending on genotypes) until late in the season, in line with their fast-growth habit. Seasonal fluctuations were mainly explained by variations in soil water availability and by stomatal limitation upon photosynthesis. Stomatal rather than biochemical limitation was confirmed by the constant intrinsic photosynthetic capacity (Vcmax) during the growing season, closely related to leaf nitrogen (N) content. Intrinsic water-use efficiency scaled negatively with carbon isotope discrimination (Δ13Cbl) and positively with the ratio between mesophyll diffusion conductance (gm) and stomatal conductance. The WUEi-Δ13Cbl relationship was partly influenced by gm. There was a trade-off between WUEi and photosynthetic N-use efficiency, but only when soil water availability was limiting. Our results suggest that seasonal fluctuations in relation to soil water availability should be accounted for in future modelling studies assessing the carbon sequestration potential and the water-use efficiency of woody energy crops.
Short rotation woody crops (SRWCs) are being studied and cultivated because of their potential for bioenergy production. The harvest operation represents the highest input cost for these short ...rotation woody crops. We evaluated three different harvesting machines representing two harvesting systems at one operational large-scale SRWC plantation. On average, 8 ton ha−1 of biomass was harvested. The cut-and-chip harvesters were faster than the whole stem harvester; and the self-propelled harvester was faster than the tractor-pulled. Harvesting costs differed among the harvesting machines used and ranged from 388 € ha−1 to 541 € ha−1. The realized stem cutting heights were 15.46 cm and 16.00 cm for the tractor-pulled stem harvester and the self-propelled cut-and-chip harvester respectively, although a cutting height of 10 cm was requested in advance. From the potential harvestable biomass, only 77.4% was harvested by the self-propelled cut-and-chip harvester, while 94.5% was harvested by the tractor-pulled stem harvester. An increase of the machinery use efficiency (i.e. harvest losses, cost) is necessary to reduce costs and increase the competitiveness of biomass with other energy sources.
•Three different harvesting machines were evaluated at one SRWC plantation.•Harvesting costs differed significantly among harvesting machines.•The harvesters differed in the efficiency to harvest the total available biomass.•The specific advantages and disadvantages of the harvesters were discussed.
The temperature sensitivity of soil respiration (SR) is often estimated from the seasonal changes in the flux relative to those in soil temperature, and subsequently used in models to interpolate or ...predict soil fluxes. However, temperature sensitivities derived from seasonal changes in SR (from here on denoted seasonal Q10) may not solely reflect the temperature sensitivity of SR, because seasonal changes in SR can also be affected by other seasonally fluctuating conditions and processes. In this manuscript, we present a case study of how the seasonal Q10 of SR can be decoupled from the temperature sensitivity of SR. In a mixed temperate forest, we measured SR under vegetations with different leaf strategies: pure evergreen, pure deciduous, and mixed. Seasonal Q10 was much higher under deciduous than under evergreen canopies. However, at a shorter time scale, both vegetation types exhibited very similar Q10 values, indicating that the large differences in seasonal Q10 do not represent differences in the temperature sensitivity of the soil metabolism. The seasonal Q10 depends strongly on the amplitude of the seasonal changes in SR (SRs), which, under the particular climatic and edaphic conditions of our forest study site, were significantly larger in deciduous forest. In turn, SRs was positively correlated with the seasonal changes in leaf area index (LAIs), a measure of the deciduousness of the vegetation. Thus, in this temperate maritime forest, seasonal Q10 of SR was strongly influenced by the deciduousness of the vegetation. We conclude that the large differences in seasonal Q10 were not entirely due to different temperature sensitivities, but also to different seasonal patterns of plant activity in the evergreen and deciduous plants of this site. Some coniferous forests may be more seasonal than the one we studied, and the deciduous–evergreen differences observed here may not be broadly applicable, but this case study demonstrates that variation of plant phenological process can significantly contribute to the seasonality of SR, and, hence, calculated Q10 values. Where this occurs, the seasonal Q10 value for SR does not accurately represent temperature sensitivity. Because the strong seasonal correlation between SR and temperature does not necessarily imply a causal relationship, Q10 values derived form annual patterns of SR should be used with caution when predicting future responses of SR to climatic change.
One of the strategies to ensure energy security and to mitigate climate change in the European Union (EU) is the establishment and the use of short rotation woody crops (SRWCs) for the production of ...renewable energy. SRWCs are cultivated in the EU under different management systems. Addressing the energy security problems through SRWCs requires management systems that maximize the net energy yield per unit land area. We assembled and evaluated on-farm data from within the EU, (i) to understand the relationship between the SRWC yields and spatial distribution of precipitation, as well as the relationship between SRWC yield and the planting density, and (ii) to investigate whether extensively managed SRWC systems are more energy efficient than their intensively managed counterparts. We found that SRWC yield ranged from 1.3 to 24tha−1y−1 (mean 9.3±4.2tha−1y−1) across sites. We looked for, but did not find a relationship between yield and annual precipitation as well as between yield and planting density. The energy inputs of extensively managed SRWC systems ranged from 3 to 8GJha−1y−1 whereas the energy ratio (i.e. energy output to energy input ratio) varied from 9 to 29. Although energy inputs (3–16GJha−1y−1) were larger in most cases than those of extensively managed SRWC systems, intensively managed SRWC systems in the EU had higher energy ratios, i.e. between 15 and 62. The low energy ratio of extensively managed SRWC systems reflected their lower biomass yield per unit area. Switching from intensively managed SRWC systems to extensively managed ones thus creates an energy gap, and will require more arable land to be brought into production to compensate for the yield loss. Consequently, extensification is not the most appropriate path to the success of the wide scale deployment of SRWC for bioenergy production in the EU.
► Here we report CO2, CH4, and N2O fluxes measured using eddy covariance above a short-rotation bioenergy plantation. ► During the first six months the total CO2, CH4, and N2O emissions was ...5.36±0.52MgCO2eqha−1 in terms of CO2 equivalents. ► Nitrous oxide loss mostly occurred during a week-long peak emission which represented 52% of the entire N2O loss. ► The sum of the CH4 and N2O losses was an order of magnitude higher (3.51±0.52MgCO2eqha−1) than the net CO2 uptake (−0.75±0.58MgCO2eqha−1). ► Climate change and altered rainfall pattern could increase the negative environmental impacts of bioenergy plantations.
The increasing demand for renewable energy may lead to the conversion of millions of hectares into bioenergy plantations with a possible substantial transitory carbon (C) loss. In this study we report on the greenhouse gas fluxes (CO2, CH4, and N2O) measured using eddy covariance of a short-rotation bioenergy poplar plantation converted from agricultural fields. During the first six months after the establishment of the plantation (June–December 2010) there were substantial CO2, CH4, and N2O emissions (a total of 5.36±0.52MgCO2eqha−1 in terms of CO2 equivalents). Nitrous oxide loss mostly occurred during a week-long peak emission after an unusually large rainfall. This week-long N2O emission represented 52% of the entire N2O loss during one and an half years of measurements. As most of the N2O loss occurred in just this week-long period, accurately capturing these emission events are critical to accurate estimates of the GHG balance of bioenergy. While initial establishment (June–December 2010) of the plantation resulted in a net CO2 loss into the atmosphere (2.76±0.16MgCO2eqha−1), in the second year (2011) there was substantial net CO2 uptake (−3.51±0.56MgCO2eqha−1). During the entire measurement period, CH4 was a source to the atmosphere (0.63±0.05MgCO2eqha−1 in 2010, and 0.49±0.05MgCO2eqha−1 in 2011), and was controlled by water table depth. Importantly, over the entire measurement period, the sum of the CH4 and N2O losses was much higher (3.51±0.52MgCO2eqha−1) than the net CO2 uptake (−0.76±0.58MgCO2eqha−1). As water availability was an important control on the GHG emission of the plantation, expected climate change and altered rainfall pattern could increase the negative environmental impacts of bioenergy.
•We compared the performance of 12 poplar genotypes in a bioenergy plantation.•Multiple characteristics were assessed at leaf, tree and population levels.•Hierarchical cluster analysis was used to ...analyze causal relationships.•Clustering clearly reflected parentage and genetic origin.•Bioenergy production depends more on the biomass produced than on the caloric value.
The success of the production of renewable bioenergy with short-rotation coppice (SRC) cultures primarily depends on their sustainability and biomass yield. The choice of the genotypic materials largely determines how much biomass can be produced; therefore there is a need to study the performance of genotypes in situ to select the best performing ones. Twelve poplar (Populus) genotypes, of which two only recently commercialized, were planted in a large-scale operational SRC culture for the production of biomass for bioenergy. The objectives of the study were: (i) to describe and compare the 12 genotypes based on their growth, structural and developmental characteristics, and (ii) to analyze causal relationships between determining traits and productivity characteristics assessed at leaf, tree and population level by performing a hierarchical cluster analysis. The clustering of the poplar genotypes was clearly determined by parentage and genetic origin. Distinct differences between clusters were expressed in the biomass related traits; genotypes of similar parentage and origin showed comparable characteristics. Populus nigra genotypes were the least performing among the studied genotypes. The recently commercialized P. trichocarpa×P. maximowiczii hybrids on the other hand, were among the most productive genotypes. The P. deltoides×P. nigra hybrids showed intermediary results, with genotype Hees showing the highest biomass production among the 12 genotypes. As higher heating value was rather uniform among the genotypes, biomass production appeared the primary trait with regard to bioenergy production. This has significant implications for SRC cultures aiming at maximization of biomass production for maximum bioenergy yield. Besides the direct measurements of woody biomass growth (i.e. stem diameter), leaf area index is one of the most important early selection criteria for poplar with bioenergy purposes. The negative correlation of biomass and leaf rust infection reconfirmed the importance of disease vulnerability in breeding and selection programs.
Poplar (Populus spp.) and willow (Salix spp.) short rotation coppice (SRC) are attractive feedstock for conversion to renewable electricity. Site managers typically optimize biomass production at ...their sites. However, maximum biomass production does not necessarily equate an optimal CO2 balance, water use and energy production. This is because many operational actions consume water and energy and emit CO2, either on-site or off-site. Coupling a land surface model (ORCHIDEE-SRC) with life cycle assessment enabled us to determine the optimal management for SRC in Belgium. We simulated 120 different management scenarios for each of two well-studied Belgian SRC sites (i.e. Boom and Lochristi). Simulated soil carbon changes suggested substantial carbon losses of 20–30 Mg ha−1 over a time period of 20 years, which were within observation-based uncertainty bounds. Results showed that in Belgium, which has a temperate maritime climate, optimal management of SRC has a rotation cycle of two years without irrigation. Energy inputs for this optimal management were 5.2 GJ ha−1 yr−1 for the Boom site and 5.3 GJ ha−1 yr−1 for the Lochristi site, while the biomass yields at Boom and Lochristi were 9.0 Mg ha−1 yr−1 and 9.4 Mg ha−1 yr−1, respectively. The energy ratio (i.e., ratio of bioelectricity output to cumulative energy input) for this optimal management was 12, on average. Planting density turned out to be unimportant, while rotation length turned out to be most important to obtain the highest energy ratio and still maintain high biomass yield. Scenarios with high energy-input generated more bioenergy outputs, but the energy gains did not compensate for the increased energy inputs. Reductions in energy consumption per unit of bioenergy output should target the agricultural stage since it accounted for the largest energy share in the production chain.
•Water use, CO2 and energy balance of SRC were compared across managements regimes in Belgium using a modelling approach.•Variation in planting densities from 5000 to 15000 trees ha−1 showed no effect on SRC yields.•Irrigation benefits biomass production, but is energetically too costly to apply.•High energy ratios proved that SRC-based electricity production is energy efficient.•Optimal rotation length was two years without irrigation.
Although poplar short-rotation coppice (SRC) systems as an alternative to fossil fuels have been intensively studied, little is known about their biomass potential during several consecutive harvest ...cycles. For the very first time, this study reports on aboveground biomass yield and energy balance of a 16-year-old poplar SRC with a mixture of 17 pure species and hybrid Populus spp. clones. The plantation established on degraded land in Boom, Belgium, was maintained as a low-energy input system, i.e. no irrigation, no fertilizers and no fungicides were applied. The average dry biomass yield during the fourth rotation was 4.3 ± 3.4 ton ha⁻¹ year⁻¹ across all clones, but the most productive clones yielded up to 10.5 ton ha⁻¹ year⁻¹. After 16 years, stool survival ranged from 6 to 91% among clones. Our results demonstrated the sustained biomass potential and resprouting capacity after a severe leaf rust attack and after several harvests of the studied Populus nigra and Populus trichocarpa clones as opposed to hybrids between Populus deltoides and P. trichocarpa which hardly survived the fourth rotation. These findings suggest that pure species might perform better than hybrids under suboptimal conditions, e.g. on degraded lands, throughout several harvest cycles and/or after leaf rust infestations. Despite the relatively low yields, the investigated system on degraded land had a positive energy balance producing 7.9 times more energy than it consumed from cradle to plant gate.
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