Soil Carbon Modelling in Salix Biomass Plantations: Variety Determines Carbon Sequestration and Climate Impacts

Short-rotation coppice (SRC) Salix plantations have the potential to provide fast-growing biomass feedstock with significant soil and climate mitigation benefits. Salix varieties exhibit significant variation in their physiological traits, growth patterns and soil ecology—but the effects of these variations have rarely been studied from a systems perspective. This study analyses the influence of variety on soil organic carbon (SOC) dynamics and climate impacts from Salix cultivation for heat production for a Swedish site with specific conditions. Soil carbon modelling was combined with a life cycle assessment (LCA) approach to quantify SOC sequestration and climate impacts over a 50-year period. The analysis used data from a Swedish field trial of six Salix varieties grown under fertilized and unfertilized treatments on Vertic Cambisols during 2001–2018. The Salix systems were compared with a reference case where heat is produced from natural gas and green fallow was the land use alternative. Climate impacts were determined using time-dependent LCA methodology—on a land-use (per hectare) and delivered energy unit (per MJheat) basis. All Salix varieties and treatments increased SOC, but the magnitude depended on the variety. Fertilization led to lower carbon sequestration than the equivalent unfertilized case. There was no clear relationship between biomass yield and SOC increase. In comparison with reference cases, all Salix varieties had significant potential for climate change mitigation. From a land-use perspective, high yield was the most important determining factor, followed by SOC sequestration, therefore high-yielding fertilized varieties such as ‘Tordis’, ‘Tora’ and ‘Björn’ performed best. On an energy-delivered basis, SOC sequestration potential was the determining factor for the climate change mitigation effect, with unfertilized ‘Jorr’ and ‘Loden’ outperforming the other varieties. These results show that Salix variety has a strong influence on SOC sequestration potential, biomass yield, growth pattern, response to fertilization and, ultimately, climate impact.

Non-domestic building stock energy and carbon modelling for policy advice – a user requirements survey

In recent years, many building stock models have been developed to advise and guide policymakers. In most models, however, user needs were not formally established. Therefore, the aim of this paper is to formally undertake a user needs‘ assessment for building stock energy and carbon models. To achieve this aim, a bilingual exploratory online user requirements’ survey was developed. The survey was designed to gather information in the following areas: the general interests of the potential model users; their experiences with related studies and models; the desired properties of non-domestic building stock energy models; and any technical limitations, such as computational resources. A total of 19 responses were obtained. Users favour tools which are: usable, transparent; flexible; compatible with other tools; and provide clear, understandable results.

Sustainable Cereal Straw Management: Use as Feedstock for Emerging Biobased Industries or Cropland Soil Incorporation?

Sustainability goals regarding biobased chemicals and fuels can lead to increased demand for cereal straw, which could lead to undesirable effects on soil organic matter (SOM) content. The aim of this study was to evaluate the effects of removing straw on SOM, using a life cycle approach based on agricultural statistics and soil carbon modelling. This regional evaluation in southern Sweden showed that the general restrictions on straw removal recommended in many European studies, with demands on the incorporation of at least half of the aboveground straw, is not an efficient means of SOM preservation. Unrestricted straw removal in combination with the cultivation of intermediate crops leads to a much higher SOM build-up. Such measures will increase the availability of removable straw 2.5 times, at little extra cost. The findings of this study demonstrate the necessity of regional evaluation, taking new findings on the impact of straw incorporation on SOM into consideration. This is important for both regional emerging biobased industries, where unnecessary restrictions on straw removal might hamper the development of new production pathways, and for future sustainability in agriculture, where well-intended but inefficient SOM preservation strategies might hinder the implementation of more efficient measures. Graphic Abstract

Dynamic Sustainability Assessment Tool: Case Study of Green Biorefineries in Danish Agriculture

In this work, a novel, dynamic sustainability assessment tool is presented and validated in a case study. This tool combines two methods—system dynamics (SD) and temporal soil carbon modelling. The case study for sustainability analysis of Danish agriculture and green biorefineries supply chains in Denmark is used. The development of the Danish agriculture sector is simulated and assessed in relation to the ecosystem’s carrying capacity until 2050, defined as 1.4 livestock units per hectare. The results show that under the current development, the agriculture sector would exceed this carrying capacity shortly after 2030. The results obtained from the dynamic sustainability assessment tool show a more precise and less optimistic projection of future development than the assessment using constant soil carbon modelling values only. The study, therefore, suggests that the use of the temporal aspects in the sustainability assessment should be included and further developed.

Land use shapes the relationship between tree cover and carbon stocks in the tropics

<p>Tree cover (TC) and biomass carbon stocks (CS) are key parameters for characterizing the states and dynamics of tropical ecosystems. Despite the presence of several datasets with high spatial resolution, differences among data products prevail and systemic inter-relations between TC and CS remain poorly quantified. Further, the role of land use in explaining disagreements among datasets remains largely unexplored. Here, by combining established spatially-explicit estimates of TC and CS over contemporary timescales, we analyse uncertainties between these two ecosystem parameters across the global tropics (~ 23.4°N to 23.4°S). We quantify land use effects by contrasting actual and potential (ie. in the hypothetical absence of land use) states of vegetation and by correlating TC and CS changes with land use intensity. Our results show that land use strongly alters both TC and CS, with disproportionate impacts on CS and large variations across tropical ecozones. Differences between potential and actual vegetation CS remain above 50% across the tropics except for rainforests (34%). Differences within corresponding TC estimates are more variable, and higher among sparsely-vegetated landscapes (81% for shrublands), highlighting the overwhelming extent of land use impacts. Cross-comparisons across available TC and CS datasets reveal large spatial disagreements. More than a third of all identified co-located TC and CS change datasets show disagreements in the direction of change (Gain vs Loss), and these divergences persist as a function of land use intensities. Our results provide a characterization of the prevailing uncertainty structures of input datasets and the spatial patterns of land use-induced disturbances at the pixel and ecozone-levels. This assumes added significance in light of the stock-taking exercises envisaged as part of the Paris Agreement, the advancement of terrestrial carbon modelling initiatives as well as emerging, novel remote sensing products.</p>