Landscape Carbon and Greenhouse Gas Model Quantifies Net Impacts and Tradeoffs of Land Use and Land Management Strategies at the Sub-National Scale

Comprehensive landscape carbon models are needed to support the implementation of climate policy and land management strategies at the sub-national scale. However, quantification tools often do not account for multi-dimensional interactions of land use, land management, climate change, and wildfire. Here we quantify the net greenhouse gas (GHG) emissions (i.e., CO₂ and CH₄) impacts and associated uncertainties of two portfolios of land use and land management goals (moderate and high intensity) established by the State of California in the 2030 Draft Natural and Working Lands Implementation Plan using the California Natural and Working Lands Carbon & Greenhouse Gas Model (CALAND), which we developed for this purpose. Importantly, the two scenarios not only aimed to enhance carbon storage in vegetation and soil, but also prioritized other ecosystem services with competing goals, such as resiliency to wildfire, which involved controlled burning of biomass carbon. We show that through immediate Sate-supported actions, including conservation, restoration, forestry, and others, California has the potential to reduce cumulative net emissions of GHG by -34.5 Tg CO₂e to -109.2 Tg CO₂e by 2050 relative to a baseline scenario of no State-mandated interventions. This range spans two future climate projections (Representative Concentration Pathways RCP 4.5 or RCP 8.5) and the uncertainty bounds of the two scenarios. Both scenarios resulted in near-term increases in GHG emissions relative to the baseline, largely due to the intensity of forest fuel reduction activities. Our analysis demonstrates that trade-offs in management strategies in terms of GHG emissions and wildfire mitigation can be overcome in the long run through balancing the intensity of forest fuel reduction practices with technologies that have immediate GHG emissions benefits through CO₂ removal and avoided GHG emissions (e.g., wetland restoration, expansion of urban forests, and less intensive forest management). Furthermore, we have created a modeling framework for scenario exploration and GHG quantification that can be used for regional goal setting within the State of California, as well as serve as a template for model development in other States.