Mixed-species forests are increasingly recognized for their role in buffering ecosystems against climate stressors; however, the effects of species mixing ratios and tree sizes on drought resilience remain insufficiently explored, particularly in temperate regions. This study investigates the impact of species composition and structural diversity on drought resilience in mixed Pinus tabuliformis and Quercus variabilis stands. We collected 180 tree core samples (60 per species ratio) from three specific mixing ratios—90% P. tabuliformis and 10% Q. variabilis (P9Q1), 60% P. tabuliformis and 40% Q. variabilis (P6Q4), and 20% P. tabuliformis and 80% Q. variabilis (P2Q8)—and further stratified samples by dominant, intermediate, and suppressed size classes. Field sampling at breast height utilized increment borers to obtain tree cores with minimal impact, which were subsequently air-dried, mounted, and polished in the lab to enhance ring clarity. Growth ring widths were measured using a high-precision system, with cross-dating techniques ensuring chronological accuracy. To evaluate drought resilience, we calculated resistance (Rt), recovery (Rc), and resilience (Rs) indices and employed the Palmer Drought Severity Index (PDSI) to analyze growth sensitivity across the ratios and size categories. Mixed-effects models were applied to assess the effects of species composition, tree size, and climate factors on drought resilience. Results showed that the P6Q4 ratio optimally supported Q. variabilis resilience during extended droughts by fostering hydrological niche benefits, while P. tabuliformis showed declining Rt, Rc, and Rs values as Q. variabilis proportions increased. PDSI analysis revealed dominant trees had stronger responses in P6Q4 and P2Q8, while intermediate and suppressed trees responded more in P9Q1. These findings underscore the importance of species-specific mixing ratios and structural diversity for enhancing forest resilience under climate change, supporting a framework for sustainable forest management that prioritizes mixed-species configurations to reduce climate vulnerability and promote long-term ecosystem stability.

Replacing winter fallow in midwestern corn and soybean rotations with cover crops could offer significant environmental benefits, including increased soil carbon sequestration and reduced nitrogen leaching. Although winter cover crops are currently planted on only a small fraction of agricultural fields in this region, two emerging markets may incentivize broader adoption: demand for biofuel feedstocks could create markets for harvested cover crop biomass, and carbon credit programs could pay farmers for using cover crops to sequester carbon in the soil. This study examines how these emerging markets may influence the economic feasibility of winter rye cover crop strategies in the Midwest and the resulting environmental impacts. Our objectives were to: (1) estimate the costs to farmers of winter rye strategies, including potential yield impacts on corn and soybean; (2) explore the profitability of these strategies under different market scenarios; and (3) assess the environmental impact of profit-maximizing strategies, including spatial variation in these impacts.

We assessed harvested and unharvested winter rye management strategies within corn-soybean rotations across Iowa, Illinois, and Indiana. In total, we evaluated 19 strategies, including a no-cover-crop baseline and combinations of three fertilizer rates and three planting dates. We used the biogeochemical model Ecosys to assess yields, soil organic carbon, nitrogen leaching, and N2O emissions of each strategy compared to the baseline over a 20-year period. We also estimated the economic feasibility of each strategy under three scenarios: 1) farmers receive market price for harvested rye biomass or a cost share payment for unharvested rye, 2) farmers receive market price for harvested rye or a cost share plus carbon credits for unharvested rye, and 3) the same as scenario 2, but with a higher carbon credit value. Carbon credits are unlikely to apply to harvested rye due to additionality rules. In all scenarios, costs included fuel, labor, fertilizer, and potential corn and soybean yield losses, while revenues included the market value of harvested rye, cost share payments, and carbon credits.

Our results show that the profitability of winter rye strategies varies regionally, with harvested rye being more profitable in southern areas and unharvested rye in northern areas. This is because increased winter rye yields produced more revenue when harvested, but caused greater corn yield decreases, particularly when not harvested. Unharvested winter rye was not economically feasible in most locations when the cost share was the only financial support. Fertilization increased economic feasibility of unharvested strategies by decreasing corn losses and in some cases increasing soybean yields, but led to greater environmental damage. Introducing a modest carbon credit did not change the economic feasibility of unharvested strategies, but the high carbon credit increased the feasibility of low-yield unharvested strategies and produced the highest total environmental benefits. These insights demonstrate how availability of harvested biomass and C credit markets could influence farmer choices and environmental impacts, particularly highlighting the issues of corn yield changes and regional variability. This could inform policy and program development toward promoting sustainable agricultural practices.

Background:

Life cycle assessments (LCA) have consistently demonstrated that biobased chemical production methods can yield significant reductions in greenhouse gas (GHG) emissions when compared to fossil-based incumbents [1]. However, many types of biomass are incompatible with existing biobased chemical production methods [2]. Biological systems and living organisms are naturally capable of converting contaminated, low-quality, and heterogeneous materials into complex organic chemicals, including high-value products that have historically been produced with fossil resources. Synthetic biology facilitates industry-optimized biological production pathways, reduced reliance on fossil feedstocks, an extended range of viable biobased feedstocks, and potentially decreased process energy demands.

Nonetheless, few systems analyses have been conducted to understand which combinations of biobased feedstocks and synthetic biology processes are both environmentally and economically sustainable. To address this gap, we have built a dynamic materials flow analysis (MFA) for 1,3-propanediol (1,3-PDO) in the United States. While this important intermediate material was originally made mostly from fossil feedstocks, the supply chain has recently expanded to include biobased feedstocks, which are microbially upgraded using synthetic biology. Additional waste-based feedstocks are also poised to enter the supply chain using synthetic biology conversion techniques. Dynamic MFA enables us to elucidate supply chain responses to changes in synthetic biology process technology, as well as external market factors.

Significance:

This assessment constitutes the first MFA of 1,3-PDO and is one of few that explores chemical products and integrates dynamic systems analysis. On the supply side, we show that although direct use of fossil feedstocks in the 1,3-PDO production conversion process is limited, the total upstream fossil feedstock requirement is significant. Furthermore, we reveal the wide variety of fates of 1,3-PDO once it enters various use phases and end of life, stages that are underexplored, if not entirely unaddressed, in published LCAs. Our complimentary analyses will determine the supplies and prices of crude oil and biomass that lead to a total production capacity that is completely bio-based and the systems-level environmental impact of 1,3-PDO production in the US. Overall, we believe this offering brings important insights into the potential viability of a bio-based supply chain for a large-market chemical product and may serve as a framework for exploring other products that could be generated using synthetic biology means.

Methods:

MFA data sources include government databases, industry reports, and published scientific and technological literature. For additional insight into the factors that may impact the feasibility or preferability of certain biobased feedstocks, we will also employ dynamic systems analysis to determine market conditions under which a 1,3-PDO could be entirely bioproduced in the United States. We disaggregate biomass by type using data from the most recent Billion Tons Study (BT23) to provide deeper granularity than previous models [3]. We will also use the GREET database to determine the overall water, land, and energy, and emissions burden of the entire 1,3-PDO value chain to quantify the environmental effects of the material flows of the system.

1 Zuiderveen et al. 2023. DOI: 10.1038/s41467-023-43797-9.

2 Scown et al. 2022. DOI: 10.1016/j.copbio.2023.103017.

3 BETO: Billion-Ton 2023. https://tinyurl.com/2p9wxc3b.

Renewable natural gas (RNG) has long been seen as a replacement for fossil natural gas (FNG), given its compatibility with existing infrastructure. However, previous life cycle assessment (LCA) studies have shown that, from a greenhouse gas perspective, RNG results in a lower global warming potential (GWP) than FNG only in a consequential framework, where an avoided emissions credit is applied to the RNG to offset emissions that would have occurred if the RNG had not been produced. While such an accounting strategy has been useful in supporting development of RNG production in the United States, the policy direction of the Low Carbon Fuel Standard points toward phasing out such methods. It is thus prudent to evaluate the GWP of RNG from a true attributional perspective, with careful consideration of system boundary and biogenic carbon accounting.

This study aims to evaluate U.S. RNG production pathways using an attributional framework that includes (1) anaerobic digestion (AD) of animal manure (AM), landfill gas (LFG), municipal solid waste (MSW), and wastewater sludge (WWS), and (2) thermal gasification (TG) of woody waste feedstocks using a catalyst, air, or steam. The scenarios evaluated vary depending on upstream emissions framework (true waste or attributional), co-product management method, fuel for internal heating of the conversion process (FNG or RNG), and inclusion of carbon capture. The true waste scenario (i.e., cutoff) excludes upstream emissions (including atmospheric carbon uptake) except for transportation emissions from waste site to conversion facility. The attributional scenario includes both the life cycle upstream impacts of the feedstock and the original product. The co-product management scenario uses mass and energy allocation to attribute some portion of the upstream emissions to the co-product that was formerly a waste (and not the main product), which only applies to the AD of AM and AD of WWS pathways. The rest of the scenarios include whether to use a particular technology and are self-explanatory. All the data compiled for our study was retrieved from publicly available sources such as the Federal LCA Commons, GREET, EPA (i.e., WARM), NETL, and peer reviewed literature, except for the data for animal manure from dairy cows, which was provided by USDA upon request.

The results indicate that pathways resulting in a lower GWP than FNG (about 7 g CO2e/MJ) are AD of AM (–108 to –218 g CO2e/MJ) and TG using Air with CCS (–44 g CO2e/MJ). Other pathways about an order of magnitude higher than FNG are TG using Air without CCS, AD of LFG and AD of MSW. Meanwhile, all three AD pathways of WWS yield a GWP result that is several orders of magnitude higher than FNG, likely due to the energy intensity of wastewater treatments. Interestingly, the attributional GWP was higher than when treating feedstocks as true waste only for the AD of WWS pathways. These results highlight the value of using an attributional framework to compare RNG and FNG production pathways.

The pulp and paper industry (PPI) is an integral part of the manufacturing industry in the United States. Despite the industry’s success in reducing energy use, it remains an energy-intensive industry, accounting for 11% of the manufacturing sector’s energy consumption. There have been many initiatives to decarbonize the PPI and many novel innovations to make it more energy efficient. One of the novel approaches to decarbonizing this industry is through converting existing pulp and paper mills into integrated pulp and paper biorefineries (IPPB) and transforming wastes or lower-value by-products into value-added products.

Studies have shown that one of the key value-added products of IPPBs is soil amendment. Soil amendments can be produced from by-products such as sludge, lime mud and dregs. The sludge of PPI mainly consists of wood-fibers, paper products and non-wood fibers; therefore, using it to produce soil amendments can improve soil quality and increase soil organic matter. Lime mud and dregs can also be beneficial to the soil and its quality. In this study, we use life cycle assessment (LCA) and techno economic analysis (TEA) to investigate and compare the costs, carbon, and energy impacts of IPPB-based soil amendments. The objectives of this analysis are to show the environmental and economic impacts of this IPPB-based value-added product, and to identify the main drivers for these impacts.

In this analysis, we use the system expansion methodology with substitution to account for the avoidance of conventionally produced products that the IPPB-based soil amendments replace. Our expected results will identify the carbon and energy hotspots in the processes that can be improved and assess what the main environmental and economic impacts hinge on. IPPBs are industrial symbiosis systems that share materials and energy between the production processes of pulp and value-added products. This results in reduced usage of virgin materials, energy use, emissions, and waste generation. Therefore, targeting specific product markets could lead to net improvements in the total environmental impacts of the system. Lower production costs could also contribute to a more competitive market. The value-added products produced can replace petroleum-based, virgin materials, impacting material and resource consumption of multiple industries. Thus, the results of this study can help decision makers with their judgement related to this product as compared to others in the market with respect to their economic and life-cycle impacts.

The urgent need for sustainable agricultural solutions has positioned Climate Smart Agriculture (CSA) practices at the forefront of global efforts to counteract climate shifts and ensure food security. These practices have great potential to safeguard agricultural productivity, bolstering resilience, and mitigate greenhouse gas (GHG) emissions. However, a limited understanding of their environmental implications hinders their optimization and widespread implementation of CSA practices. Addressing this knowledge gap is crucial for realizing the whole potential of CSA practices and promoting a healthier, more resilient and sustainable agricultural future.

The present work will provide thorough meta-analysis of life cycle assessment (LCA) research to analyze the environmental impacts of several CSA practices. The meta-analysis consolidates and examines existing LCA studies for identifying trends in GHG emissions, energy efficiency, and resource use efficiency. By systematically reviewing and synthesizing findings from diverse studies, this work aims to uncover underlying patterns, identify critical gaps in current knowledge, and provide a comprehensive understanding of the subject matter to guide future research and practices. Furthermore, as the most LCA results highly sensitive to methodological choices such as system boundary, functional units and the data sources, this study will evaluate the heterogeneity in environmental performance across CSA practices, which might be driven by regional, technological, and methodological variances in the underlying studies. Analyzing these variances will provide a deeper understanding of how and why environmental outcomes differ among practices and contexts.

The anticipated findings will highlight the importance of targeted implementation strategies that consider regional and system-specific factors, guided by integrated life cycle insights. This research contributes to a broader understanding of effectiveness of CSA practices, offering practical and evidence-based guidance for different stakeholders including farmers aiming to foster sustainable agricultural transformations globally. By doing so, study seeks to support sustainable agriculture, helping to align CSA efforts with environmental and resource sustainability goals.