Growth and yield models are an essential tool for predicting the long-term response of forests to management and disturbance. Model evaluation and calibration are challenging, however, given data limitations for observing stand structural changes with age across heterogeneous forest landscapes. Here we present an approach for calibrating the lodgepole pine (LP) forest model in the Central Rockies variant of the Forest Vegetation Simulator (FVS-CR) using Forest Inventory and Analysis (FIA) plot data from the US Forest Service. Previous evaluation showed the FVS-CR LP model is generally successful in reproducing known patterns of stand dynamics. However, the default model settings tend to result in unrealistic stand successional behavior and over-estimate the density, basal area, and especially carbon density of mature lodgepole pine forest stands as compared to expectations. Here we develop a generalized model calibration procedure based on simulating bare-ground re-growth of a single mixed lodgepole stand and comparing to a forest growth chronosequence constructed from FIA plot measurements in Colorado and Wyoming. We set parameters such as basal area increment and maximum tree size to match corresponding characteristics observed directly in the FIA plot data. The remaining ‘free’ parameters (notably small tree height increment and tree mortality parameters) were then tuned for best fit against the FIA chronosequence in terms of five different stand characteristics: live and dead basal area, trees per hectare, quadratic mean diameter, and average height. Improving model fit against all five stand characteristics simultaneously required substantial increases to mortality-related parameters, particularly for the shade-tolerant species present in mixed stands. These parameters had to be adjusted empirically rather than based on literature values, suggesting some underlying model structural challenges. However, the resulting recalibrated FVS-CR LP model achieves much better representation of expected lodgepole stand structure and successional behavior, and can more credibly be used to evaluate carbon storage outcomes for different forest management choices in the region.

Sustainable aviation fuels (SAF) produced from lipid feedstocks are an increasingly mature and low-cost option for aviation sector decarbonization. Ethiopian mustard (Brassica carinata) is a non-food oilseed crop that can be grown on winter fallow land in the southeastern US and used as a feedstock for SAF, with a high-protein livestock feed co-product. Integrating carinata into existing annual crop rotations produces an additional revenue stream for landowners, with potential co-benefits for soil carbon and other ecosystem services. The Southeast Partnership for Advanced Renewables from Carinata (SPARC) is a USDA-funded research consortium to advance carinata production and associated SAF and bioproduct supply chains in the region. A SPARC research team used the DayCent ecosystem model to estimate the potential production of carinata across the tri-state region of Alabama, Florida, and Georgia, and assess associated changes in soil carbon storage and emissions of nitrous oxide (N2O), the main biogenic greenhouse gas (GHG) emissions from agriculture. First, we calibrated DayCent to reproduce the phenology, harvest index, productivity response to nitrogen application, root-to-shoot biomass ratio, and tissue nitrogen content data observed for a set of carinata field trials in the region. Next, we simulated the integration of carinata into a typical cotton/peanut rotation across the 2.3 million hectares of annual cropland within the climate suitability range for this crop, grown once every third winter. We show an annual production potential of greater than 1 billion liters of SAF from this feedstock in the region. Our base carinata management case is approximately neutral in biogenic GHG emissions, with modest soil carbon sequestration that offsets the associated small increase in N2O emissions. However, adopting conservation management practices such as no-till establishment or poultry litter soil amendments results in a more substantial net soil carbon sink, reducing the GHG footprint of carinata-derived SAF by up to 20 grams of CO2-equivalent per megajoule of fuel. This work supports SPARC’s ongoing efforts to develop improved crop varieties and management practices that simultaneously improve the economics and ecosystem service value of carinata production.