Sustainable intensification or natural climate solutions? Case studies assessing opportunities for land-based biological carbon mitigation on former and current agricultural lands

Climate stabilization scenarios rely heavily on land-based biological carbon mitigation, including both increased ecosystem carbon storage and sustainable intensification to produce feedstocks for low-emissions bioenergy and bioproducts. However, previous assessments have suggested that these two paradigms are often in conflict. Process-based ecosystem models can be useful for assessing the intensification potential of agricultural landscapes, and the implications thereof for soil carbon storage and biogenic greenhouse gas (GHG) emissions. Here we present the results of two such case studies using the process-based DayCent model.The first study considers the potential for intensification via stover removal in a corn–soybean landscape in northwestern Iowa. We utilized county-scaled data on crop yields, fertilizer application rates, and tillage intensity to estimate baseline trends in soil organic carbon (SOC) and biogenic GHG emissions, and simulate the effect of stover removal and co-adoption of complementary natural solutions (specifically, tillage intensity reduction and winter cover cropping). Using a newly-developed multi-product landscape–life-cycle assessment approach, we show that stover collection can significantly improve the mitigation potential of the landscape through the production of fossil fuel-displacing cellulosic biofuels, though co-adoption of complementary natural solutions is required to maintain or improve upon the baseline trend of increasing SOC.The second study compares using former agricultural land for the cultivation of switchgrass as a bioenergy feedstock, versus for reforestation or grassland restoration. We considered current-day cellulosic biofuel production technology as well as anticipated future improvements in switchgrass yields, cellulosic biorefining, and the integration of carbon capture and storage (CCS) technology to sequester biorefinery by-product CO2. Tracking carbon flows from the atmosphere through managed feedstock-sourcing ecosystems and biofuel supply chains, we show that current-day biofuel production has mitigation value comparable to reforestation and substantially greater than grassland restoration, whereas future carbon-negative biorefinery systems could achieve several-fold higher mitigation