Poplar Short Rotation Research Articles

Economic and environmental assessment of a multifunctional poplar plantation for roundwood and wood chip production in Spain

Aim of study: To analyze the environmental and economic performance of a multifunctional poplar plantation (MPP), which was managed to produce timber for sawn wood and chips for bioenergy. Area of study: The plantation was located in Southern Spain producing roundwood and woodchips (from tops and branches). Material and methods: The life cycle assessment (LCA) methodology was chosen to perform the environmental impact assessment from a cradle-to-gate perspective. Capital goods, including machinery-manufacturing processes, were included. One oven dry tonne (odt) of forest biomass was chosen as functional unit. The economic analysis was performed using present costs and common indicators: net present value (NPV) and internal rate of return (IRR). Main results: The harvest operations are the most environmental impacting subsystem and cultivation the costliest. Chipping was the process contributing the most to the environmental burden. The use of fertilizers, within the cultivation subsystem, had a notable impact on certain midpoint categories. In terms of climate change potential, 1 odt of delivered wood chips generated 64.1 kg CO2-eq. When considering the whole system (including the roundwood fraction), this value was 45.2 kg CO2-eq odt-1. MPP was hardly profitable with land rental and irrigation being the most expensive items. NPV, including harvesting and transport subsystems, was 1,582 € ha-1, while IRR reached 6.3%. Research highlights: Our results allow to identify the costliest operations and those with the greatest impact to improve the system. Finally, these figures can be compared with other crop alternatives such us poplar short rotation coppice (SRC).

Torrefaction of Portuguese woody biomasses and the evaluation of its properties

Torrefaction is an option for improving biomass properties for fuel application. Biomass undergoes chemical changes reflected on the upgrading of its properties as a biofuel, such as higher calorific power, lower O/C and H/C ratios, lower higroscopicity or better grindability. The objectives of this experimental study were to analyze the effects of torrefaction, under standard conditions of 265 ºC, and residence time of 15 minutes in a nitrogen atmosphere and during a total 1h45m heating period, on a set of sixteen woody biomasses coming from poplar short rotation coppice (SRC) and other Portuguese roundwoods. Average mass loss was higher than 40%. The set of poplar clones and common broom provided torrefied products with higher quality than the set of roundwood forest species. The results on other parameters for proximate and ultimate analysis corroborate this global picture. Correlation analysis showed a higher degree of interconnectedness between LHV and proximate analysis results, for poplar clones and common broom, comparatively with roundwood biomasses.

Assessing the potential of poplar short rotation plantations to contribute to a low-carbon bioeconomy under water-limited conditions

Poplar short rotation coppice (SRC) systems are important for biomass production and for short-to medium-term carbon (C) sequestration, contributing to a low-carbon bioeconomy and thus helping to mitigate global warming. The productivity and profitability of these plantations are, however, challenged under restrictive irrigation associated with climate change. This study compares the above- and below-ground C sequestration potential and economic viability of a 12-year plantation cycle (4 rotations of 3 years each) under Mediterranean conditions with optimum irrigation (T1) and 50% irrigation reduction (T2), analysing other promising biomass uses in the form of bioproducts. A total of 138 trees of the highly productive hybrid (‘AF2’) in a SRC-trial were sampled monthly (first rotation). Additionally, data from an extensive poplar plantation network (30 sites) was used to complete data for the plantation cycle. The average C content for above- and below-ground biomass was 17.04 Mg C ha−1 yr−1 (T1), falling by 24% in T2. The net present value (NPV) in T1 (6461 € ha−1) was 52% lower under T2 conditions. Extra payments for C sequestration increased the NPV to 8023 for T1 and 4331 € ha−1 for T2. Roots represent an important C storage in the soil, accumulating 29.9 Mg C ha−1 (T1) and 22.8 Mg C ha−1 (T2) by the end of the cycle in our study. The mitigation potential is strongly fortified when the share of bioproducts in biomass end-use increases. Assuming a distribution of 50% bioenergy and 50% bioproducts, emission were reduced between −114 Mg CO2eq ha−1 (T1) and −88 Mg CO2eq ha−1 (T2) compared to BAU until end of the century. This scenario plays a crucial sink-effect role by storing C contained in biomass, which is not immediately released into the atmosphere.

Adapting 3-PG foliar variables to deciduous trees in response to water restriction: poplar short rotation plantations under Mediterranean conditions

Abstract Poplar plantations growing in short rotation are a crucial biomass source of raw material for bioenergy and/or bioproducts, making an important contribution towards achieving a low-carbon bioeconomy. To optimize yield predictions of poplar plantations, this study aims to adapt the foliar variables of the process-based model 3-PG (Physiological Principles Predicting Growth) to a deciduous species like poplar. A total of 138 trees were sampled from a poplar plantation of the highly productive hybrid P. x canadensis (‘AF2’) over a first rotation at a planting density of 10 000 trees ha−1. Two irrigation scenarios, full soil field capacity (FC) and 50% FC, were considered to take into account the impact of climate change in the context of irrigation restrictions. Based on this information, the objectives were not only to determine the required species-specific foliar parameters but also to adapt the 3-PG model architecture to a pattern of variation along each growing season and identify the foliar parameters which present a significant response to restrictive irrigation. For this, specific leaf area (SLA) changes were modelled and the litterfall rate (${\gamma}_F$), and maximum canopy quantum efficiency (${\alpha}_{Cx}$) were calculated. SLA follows a similar dynamic in terms of water availability and year, with SLA for mature leaves being 19.9 m2 kg−2 and the SLA at the beginning of the growing season 10.4 m2 kg2. Leaf litter season begins in late August and lasts until early December, with 26 per cent litterfall by October. Additionally, the highly sensitive parameter ${\alpha}_{Cx}$ was calibrated and a proposed value of 0.093 molC mol PAR−1 was used. The validation of the proposed parameterization showed realistic estimates of the changes of leaf biomass and LAI during the growing season. These results will enable improved 3-PG-based estimations of the real variation along the growing season of variables such as Net Primary Productivity, leaf litterfall or analysis of the soil–plant nutrient cycle.

Agronomic performance of soybean and sorghum in a short rotation poplar coppice alley-cropping system under Mediterranean conditions

The transition from conventional arable towards silvoarable systems can increase the delivery of ecosystem services. Nevertheless, the assessment of crop yield under agroforestry condition is crucial to evaluate of the reliability of these systems and to increase the knowledge base needed to support their design. Although the feasibility of poplar short rotation coppice (SRC) silvoarable alley-cropping systems has been widely investigated, few studies have addressed the agronomic response of crops intercropped with poplar SRC in narrow alleys, especially in Mediterranean environments. Thus, this paper treats the effects of SRC poplar rows on soybean and sorghum productivity in a 2-year rotation implemented in an alley-cropping system. A field experiment was carried out in 2018 and 2019 with the objective of measuring and evaluating effects of light availability variation, as affected by the growing rate of 2-year coppice cycle poplar SRC rows, and the soil characteristics on soybean-sorghum and sorghum–soybean rotations. Above-ground biomass, grain yield and crops residue showed a significant reduction in the tree–crop interface up to 74% and sorghum proved to be less tolerant to light reduction compared to soybean. Our results demonstrated that light is the most important factor for sorghum cultivation, despite grain yield was also influenced by the soil characteristics such as pH, while soybean is affected also by soil moisture and water retention capacity. The design of crop rotation in an SRC-based agroforestry system needs to consider the different agronomic performance of different crops and the harvest cycle of tree rows.

Growth and Mortality of Hybrid Poplar Short Rotation Culture (AF8 Clone) in Response to Clostera anastomosis L. (Lepidoptera: Notodontidae) Defoliation

The increasing worldwide interest in renewable energy and carbon storage has led to the development of relatively fast solutions to obtain wood biomass. The cultivation of fast-growing tree species in short-rotation crops, such as hybrid poplar clones, is one such solution, at least in temperate areas. Sometimes these monocultures are affected by disturbing factors, including severe insect defoliation, with strong destructive effects. The impact of defoliation on the growth and productivity of poplar crops is often estimated in the context of artificial defoliation. There have been few studies in which the effect of defoliation was calculated after natural defoliation. Among defoliating insect species, Clostera anastomosis L. is one of the most important defoliators of young poplars. This species developed severe defoliation in a 4-year-old poplar clone AF8 crop, from the northeastern part of Romania, in the spring and summer of 2017. The study aimed to assess the impact of defoliation both on the growth and mortality of defoliated trees and the productivity of the affected crop. To reach this goal, the height and radial growth of 150 trees with different defoliation rates (50 non-defoliated, 50 partially defoliated, and 50 completely defoliated) were measured and the defoliation symptoms and mortality were also evaluated for 4780 poplars (10% of the analyzed population). The defoliation caused a significant decrease in the annual height growth (28.6% of the partially defoliated trees and 38.5% of the completely defoliated trees) and a severe decrease in the radial growth, between 82.2% and 90.4%, respectively, depending on the defoliation rate. These strong decreases led to a significant decline in tree-level biomass accumulation, approximately 74.8% for partially defoliated trees and 83.1% for completely defoliated trees, for the year of defoliation. As a result, the loss in total biomass (for the four years of the rotation) was between 28.1% and 34.6%, respectively, depending on the defoliation rate. Therefore, the total biomass loss was 5 t·ha−1, representing approximately 70% of the forecasted production for 2017 only (approximately 7 t·ha−1).

First trial of a prototype chainflail delimber for the European short rotation poplar plantations

Small tree size represents a main challenge for single-tree handling techniques and caps harvesting productivity in short rotation poplar (SRP) plantations. That challenge is best met by a shift towards mass-handling. Chainflail delimbing is one of the best solutions for multi-tree processing, but commercially available equipment is often too heavy and expensive for European operations. Therefore, an Italian company developed a compact chainflail delimber-debarker (CFDD) specifically designed for small-scale SRP. The machine was tested in Western Slovakia in early March 2022. The test included a five-days endurance trial and a controlled experiment on 16 carefully measured wood piles representing “strong” and “weak” trees, i.e. trees with a mean diameter at breast height (DBH) of 12 and 10 cm, respectively. The endurance trial was quite successful since no mechanical problems were recorded during the five-days period. Delimbing and crosscutting quality were as good as those obtained with a standard processor head, while log yield was generally better, averaging 42% and 68% for the “weak” and the “strong” trees, respectively. Productivity was on a par with the alternative cut-to-length technology options and can be significantly increased once the prototype will be further developed. In general, the new compact CFDD may become the best option for handling the small trees offered by underdeveloped SRP plantations, which cannot be efficiently harvested with the cut-to-length system.

Productivity of Short-Rotation Poplar Crops: A Case Study in the NE of Romania

In Romania, the productivity of the new clones of hybrid poplar has not been tested in recent years. This case study aims to fill a gap on the productivity map of the new poplar clones, estimating, by biomass measurements, the productivity of two clones (AF2 and AF8) with different planting densities (from 1333 trees·ha−1 to 2667 trees·ha−1). The short-rotation woody crops (SRWCs) were established in homogeneous conditions, in North-East (NE) Romania and the northern part of Suceava County. Using a specifically developed method, biomass production was estimated using destructive methods, with 190 poplar trees being harvested, measured, and weighed to compute the accumulated biomass for each growing season The biomass production of the crops with 1667 trees·ha−1 planting density highlighted significant differences in productivity in favour of the AF2 clone after five growing seasons. The crops shared similar annual growth patterns, and the stem biomass represents approximately 73–80% of the total biomass of the trees. The second research question concerning planting density influence on productivity showed fluctuations of biomass accumulations at different planting densities (1333 trees ha−1, 1667 trees ha−1 and 2667 trees ha−1) for a 5-year rotation. The outcomes emphasized the influence of the annual weather conditions—primarily the rainfall in May–June—on poplar growth, showing that productivity also depends on the genotype, density and biotic disturbances.

Time-course foliar dynamics of poplar short rotation plantations under Mediterranean conditions. Responses to different water scenarios

Poplar (Populus spp.) Short Rotation Coppice (SRC) systems are characterized by high short-term biomass productivity and play a key role in promoting employment in rural areas as well as supplying environmental benefits. However, in the context of climate change with expected reduced water availability in the Mediterranean area, the productivity of these plantations may be seriously limited. In this regard, the aim of this work is to analyse the monthly dynamic responses of relevant variables at foliar level throughout the entire first rotation of a poplar short rotation plantation under two water scenarios: optimal scenario (with irrigation to field capacity (FC)) versus restrictive scenario (with 50% FC irrigation).This data came from 590 trees in a poplar short rotation plantation of the highly productive genotype ‘AF2‘. LAImax values of 2.39, 7.47 and 9.34 were found for the three-year rotation cycle, pointing to significantly lower values after the establishment year under the restrictive water scenario. SLA mean values displayed a downward trend, with 12.25 m2 kg−1, 10.82 m2 kg−1 and 10.47 m2 kg−1 for years 1, 2 and 3 respectively, no significant differences being observed between water scenarios. NPK foliar concentrations decreased over the rotation, being the values lower under the restrictive scenario. Additionally, the selected genotype, ‘AF2’, displayed tight stomatal control under conditions of water stress, maintaining high photosynthetic levels.The responses observed in this study can potentially be used to better understand the behavior of these variables which most affect production of poplar plantations in face of climate change.

Beyond Monetary Cost-Benefit Analyses: Combining Economic, Environmental and Social Analyses of Short Rotation Coppice Poplar Production in Slovakia

Rising demand for bio-based products exerts a growing pressure on natural resources such as wood. Sustainable solutions are becoming increasingly important to meet the demand. In this study, 20-year poplar Short Rotation Coppice (SRC) plantations located in Western Slovakia are investigated with respect to (socio)-economic, environmental and social sustainability. The cost–benefit methodology is applied to assess the economic profitability of a switch from conventional annual crops (corn maize and winter rye) to perennial SRC. To compare economic profitability of the land management, net present value (NPV), payback time (PBT), internal rate of return (IRR) and benefit–cost ratio (BCR) are calculated. The study was enhanced by adopting the concept of regional value added to indicate the local value creation. The results for the three scenarios yield an NPV equal to 12,156 euros ha−1 for corn maize, 9763 euros ha−1 for winter rye and 2210 euros ha−1 with a PBT of 14.13 years for poplar SRC production. The regional value added for the corn maize scenario was estimated with 10,841 euros ha−1, the winter rye with 7973 euros ha−1 and the poplar SRC with 1802 euros ha−1. To appraise non-monetized social values, semi-structured interviews (N = 4) were conducted among experts familiar with SRC management in Eastern Europe. Non-monetary benefits for the stakeholder groups society, farmers or landowners and the industry were identified in terms of land fragmentation, carbon sequestration and an increase in biodiversity within the plantations, farm diversification and higher independency from wood markets. The relatively poor image of SRC, farmers or landowners having concerns about being tied on long-term contracts and legal restrictions may become obstacles in the establishment of SRC. For estimating the capability of carbon sequestration in SRC plantations the RothC model was utilized, resulting in the potential soil organic carbon (SOC) average increase of 29% during the 20 years. However, a transition in land use patterns must involve thorough considerations of all three pillars of sustainability to ensure long-term viability of the establishment.

Influence of Soil Characteristics on the Growth of Poplar Short Rotation Coppice (SRC) under Suboptimal Conditions

Several studies have discussed the growth of poplar short rotation coppices (SRC). Soil characteristics have a large effect on the yields of sites with no access to surplus water sources – especially on their physical and chemical properties contributing to water storage, all of which limit growth. We conducted our research on a fourth rotation plantation established with two different poplar clones (‘AF2’ and ‘Kopecky’) on a site without groundwater in the rooting zone to describe the influence of topography and soil parameters on biomass production. For both hybrids, 5–5 sample areas were planted. Systematic soil sampling, a tree inventory, and a destructive tree survey were completed to provide an equation of site and clone specific biomass estimation. Our results revealed that the shallower, eroded areas presented low-yield patches, particularly when compared to the parts with deeper rooting zones and soil richer in mineral and organic colloids. The amount of the plant available water, pH value, organic matter content, and CaCO3 content have the most significant effect on growth. No meaningful growth difference emerged between the two clones. The previously mentioned soil properties greatly influence tree growth on sites with no direct access to the groundwater; therefore, a detailed site description is indispensable for plantation planting.

Lengthening single-stem rotation improves biomass yield and water use efficiency in black poplar genotype multi-stem rotation coppice plantations

Poplar short rotation coppice (SRC) plantations have great potential for supplying environmentally friendly bio-based industries. However, little research has focussed on the linkages between SRC management regimes and the consumption of water for biomass production in the Mediterranean environment. Therefore, we compared six hybrid clones and four native black poplar genotypes with an aim to examine how two different lengthening periods (3 vs. 5 years) of single-stem rotation affected growth performance in the following three years of multi-stem rotation coppice. To achieve this goal, we assessed the aboveground dry biomass production and variation in water use efficiency (WUE) of the genotypes annually. A longer single-stem rotation increased biomass productivity and WUE in the multi-stem rotation of the native black poplar, rather than that of the hybrid genotypes. In contrast, biomass and WUE performances did not diverge between the native and hybrid genotypes under the shorter single-stem phase. These findings underline the importance of lengthening the rotation of single-stem SRC plantations in hot and dry Mediterranean climates. Native black poplar genotypes managed in SRC should be strongly considered as environmentally compatible genetic resources both in protected areas and in areas where water supply constrains biomass production.

Nutrient Release through Litterfall in Short Rotation Poplar Crops in Mediterranean Marginal Land

A detailed knowledge of how poplar leaf litter decomposes under Mediterranean marginal conditions can help to minimize fertilization inputs and determine the profitability and sustainability of energy crops established in these particularly sensitive areas for bioenergy. Leaf litter decomposition was monitored for 32 months using the litterbag technique in a poplar crop under short rotation conditions in a marginal Mediterranean area. In addition, nutrient dynamics, together with the production and composition of the woody and foliar biomass produced, were studied for a period of four years. Leaf litter decomposition was relatively slow, particularly during the winter months, and accelerated in early spring, coinciding with the rainy season. At the end of the decomposition study 50% of the initial litterfall was decomposed, releasing roughly 60% of the N, 40% of the K, and 70% of the P initially present in fresh leaves. Annual yields of 6.0 dry Mg ha−1 were obtained. The aerial biomass produced the first year of the second rotation cycle extracted 83, 8.7, and 29 kg ha−1 of N, P, and K, respectively, whereas the amount of nutrients that were estimated to be naturally supplied to the system through leaf litter decomposition were 180 kg ha−1 of N, 19 kg ha−1 of P, and 30 kg ha−1 of K. Therefore, four years after establishing the energy crop, leaf litter was able to release higher amounts of primary macronutrients into the environment than the nutrient uptake by the produced aboveground biomass (woody and foliar biomass).

An economic overview of Populus spp. in Short Rotation Coppice systems under Mediterranean conditions: An assessment tool for decision-making

Poplar Short Rotation Coppices can provide lignocellulosic raw material, promote employment in rural areas, contribute to achieving a low carbon bioeconomy and supply environmental benefits. Nevertheless, the economic feasibility of these plantations is a matter of concern and hampers the expansion of commercial initiatives. In this regard, this work aims to identify the most critical cost factors of poplar plantations under Mediterranean conditions. Data from an extensive network located at 30 different sites were used, in particular, detailed cost data for 2 rotations was available for 6 sites within the network. This study evaluates the critical factors that affect profitability, analysing the influence of the discount rate and biomass price under two productive scenarios derived from the network and evaluated as green biomass yield for the first rotation: Baseline (30.56 Mg ha−1 yr−1) and an Optimum (56.52 Mg ha−1 yr−1). Net Present Value after 12 years (4 rotations of 3 years each), ranges from −1105.54 € ha−1 (Baseline) to 9620.30 € ha−1 (Optimum). According to the findings of this study, profitability of poplar plantations will be achieved by ensuring optimum productivity, through an increase in current market prices (40 € Mg-1) or by valuing the ecosystem services, which are not currently quantified. Sensitivity analyses were performed for the most critical cost factors: land rent (31.88 %), irrigation (16.61 %), and cut-and-chip harvesting (11.87 %), revealing that the influence of the former factor was decisive. Management diagrams that combine the discount rate, yield and biomass price are provided as tools for decision makers.

Models for the Evaluation of Productivity and Costs of Mechanized Felling on Poplar Short Rotation Coppice in Italy

The forest biomass, as a renewable energy source, can significantly contribute to the progressive replacement of fossil fuels in energy production, with a positive final balance in terms of greenhouse gas emissions. One of the different sources of woody biomass supply is represented by short rotation coppices (SRC) plantations, currently present in various European countries for a total of about fifty thousand hectares. In Italy, part of the SRC surface has been converted into other more profitable crops, both the low levels reached by the woodchips market price and the scarce availability of specific public incentives. In this study, the authors expose the results of the models for evaluating work time, productivity, and costs of the felling operation on SRC poplar plantations with 8- and 11-year-old trees. The aim is to evaluate the economic sustainability in the use of advanced mechanization on these plantations. The machine was a crawler excavator equipped with a shear head. In the 11-year-old plantation, the productivity estimation model returned a range of 1.09–18.93 Mg h−1 (average 5.56 ± 3.88 SD) when the weight variation of the trees was 20–491 kgw (average 100.41 ± 87.48 SD). In the 8-year-old poplar, the range was 1.02–11.60 Mg h−1 (average 3.80 ± 1.71 SD), for weight variation of 17–137 kgw (average 50.57 ± 18.82 SD). The consequent variation in unit cost was EUR 2.82–51.63 Mg−1 and EUR 4.05–49.65 Mg−1, corresponding to EUR 1252.17–3463.78 ha−1 and EUR 922.49–2545.11 ha−1 for 11- and 8-year-old trees, respectively.

Environmental Sustainability of Heat Produced by Poplar Short-Rotation Coppice (SRC) Woody Biomass

As demonstrated for some time, the reduction of greenhouse gases in the atmosphere can also take place using agroforestry biomass. Short-rotation coppice (SRC) is one of the sources of woody biomass production. In our work, the supply of woody biomass was considered by examining four different cutting shifts (2, 3, 4 and 5 years) and, for each, the Global Warming Potential (GWP) was evaluated according to the IPCC 2007 method. Regarding the rotation cycle, four biomass collection systems characterized by different levels of mechanization were analyzed and compared. In this study, it was assumed that the biomass produced by the SRC plantations was burned in a 350 kWt biomass power plant to heat a public building. The environmental impact generated by the production of 1 GJ of thermal energy was assessed for each of the forest plants examined, considering the entire life cycle, from the field phase to the energy production. The results were compared with those obtained to produce the same amount of thermal energy from a diesel boiler. Comparing the two systems analyzed, it was shown that the production and use of wood biomass to obtain thermal energy can lead to a reduction in the Global Warming Potential of over 70% compared to the use of fossil fuel.

Economic Modelling of Poplar Short Rotation Coppice Plantations in Hungary

No study has been previously completed on the range of sites, potential yield, and financial characteristics of poplar short rotation coppice plantations (SRC) in Hungary. This paper conducts a literature survey to reveal the biomass production potential of such plantations and presents a model that is used to analyze their financial performance. The results indicate that the break-even-point of production is between 6 and 8 oven-dry tons per hectare per year once a minimum cost level and wood chip price within a 10% range of the 2020 value are considered. The higher the wood chip price, the lower the break-even-point. Since the model excluded the administrative costs that depend on the type and size of the management organization, the break-even-points can be significantly higher in reality, which suggests that short rotation energy plantations can be a financially reasonable land-use option in above average or even superior poplar-growing sites. The rotation period of industrial poplar plantations that produce high quality veneer logs ranges from 12 to 25 years. Though such sites can provide higher returns on investment, short rotation plantations have the advantage of providing a more evenly distributed cash flow. To facilitate the wider application of poplar SRC, the related policies need to apply specific subsidies and allow the rotation cycle to be extended up to 20–25 years, which is currently limited to 15 years.

An assessment of the harvesting and fuel performance of a single-pass cut-and-chip harvester in commercial-scale short-rotation poplar crops as influenced by crop and weather conditions

There is a need for data on commercial-scale harvesting operations in hybrid poplar short rotation crops to better understand costs and logistics, especially for modeling large scale biorefineries. An investigation was conducted on the in-field performance of a single-pass cut-and-chip harvester operating in commercial fields for over 370 individual wagon loads representing a range of crop and field conditions. Mean material capacity peaked at 70 Mg h−1 in dry conditions in lower biomass (<60 Mg ha−1), but was only 28 Mg h−1 during wet conditions and often higher standing biomass. Wet ground conditions require the harvester to divert additional power to maintaining forward movement, which results in decreased material capacity and increased fuel consumption. Crops with higher standing biomass had taller trees that do not always feed as smoothly into the harvester, slowing forward progress and lowering material capacity. Mean crop specific fuel consumption, L of fuel per Mg of biomass processed, generally decreased as standing biomass increased. When standing biomass was above 40 Mg ha−1 mean crop specific fuel consumption (FCC) was 1.69 L Mg−1 in dry conditions and 3.98 L Mg−1 in wet conditions, but when standing biomass was below 40 Mg ha−1 FCC increased drastically (as high as 5 L Mg−1) because the harvester is putting more effort into forward speed instead of material processing. Developing relationships between material capacity and fuel consumption based on standing biomass and ground conditions at representative scales are essential for conducting environmental and economic analyses of these systems.

Partial overlap of fungal communities associated with nettle and poplar roots when co-occurring at a trace metal contaminated site

Stinging nettle (Urtica dioica L.) raises growing interest in phytomanagement because it commonly grows under poplar Short Rotation Coppices (SRC) set up at trace-metal (TM) contaminated sites and provides high-quality herbaceous fibres. The mycobiome of this non-mycorhizal plant and its capacity to adapt to TM-contaminated environments remains unknown. This study aimed at characterizing the mycobiome associated with nettle and poplar roots co-occurring at a TM-contaminated site. Plant root barcoding using the fungi-specific ITS1F-ITS2 primers and Illumina MiSeq technology revealed that nettle and poplar had distinct root fungal communities. The nettle mycobiome was dominated by Pezizomycetes from known endophytic taxa and from the supposedly saprotrophic genus Kotlabaea (which was the most abundant). Several ectomycorrhizal fungi such as Inocybe (Agaricomycetes) and Tuber (Pezizomycetes) species were associated with the poplar roots. Most of the Pezizomycetes taxa were present in the highly TM-contaminated area whereas Agaricomycetes tended to be reduced. Despite being a known non-mycorrhizal plant, nettle was associated with a significant proportion of ectomycorrhizal OTU (9.7%), suggesting some connexions between the poplar and the nettle root mycobiomes. Finally, our study raised the interest in reconsidering the fungal networking beyond known mycorrhizal interactions.

The Impact of Poplar Short Rotation Coppice on Topsoil Physical Properties and Related Water Conditions

In Europe, the establishment of short rotation coppice (SRC) systems for biomass production has been expanding in the last decades. Several studies have considered the impacts of SRC on soil properties; many have focused on studying its effect on biochemical properties while only a few have addressed physical and hydraulic properties. This study reports the assessment of soil physical and hydraulic properties on two SRC sites on sandy soils planted with 3-year-old poplar trees and an adjacent conventional agricultural field in Western Slovakia. All sites contain a comparable sandy loam soil texture and both SRC fields differed only in the groundwater accessibility. Water infiltration experiments were conducted in the field with subsequent sampling of the upper topsoil (0–5 cm depth). The samples were further processed in the laboratory to obtain the water retention and hydraulic conductivity functions of the soil covering a wide range of soil pore saturation. These hydraulic functions were fitted by using the bimodal version of Kosugi-Mualem’s hydraulic model to estimate the pore-size distribution (PSD) of the soils. The comparison between the SRC field neighboring the agricultural field and the latter showed similar hydraulic soil properties such as the topsoil water retention. However, macropore content, bulk density (BD) and infiltration capacity differed under SRC particularly in the tree row. Analogously, the two SRC fields showed similar topsoil water contents. Other soil properties differed presenting an increased macropore content and higher BD in the SRC field with distant groundwater connection. Our findings suggest that the SRC management may influence the topsoil properties.