Simulated Impacts of the 2023 Megadrought on Black Spruce Potential Productivity Across Canada

Black spruce ( Picea mariana ) is a dominant tree species across the Canadian boreal forest and a key contributor to national carbon dynamics. However, its growth and stand productivity are increasingly threatened by intensifying droughts, rising temperatures, and associated disturbances such as wildfire. In this study, we used the process‐based StandLEAP model to simulate black spruce potential net primary productivity (NPP pot ) annually from 1950 to 2024, with a focus on estimating the impact of the exceptional 2023 climate conditions across the species range. While simulated NPP pot in 2023 remained close to the long‐term mean at the national scale, our results reveal strong spatial heterogeneity: some regions, particularly in western and central Canada, showed simulated NPP pot declines of up to 32%, while others recorded above‐average values. These anomalies were closely associated with extreme vapor pressure deficits and low precipitation. Many of the regions experiencing the strongest simulated NPP pot losses also burned during the 2023 wildfire season, reflecting a spatial co‐occurrence between drought‐driven reductions in productive potential and areas affected by wildfire. Long‐term simulations further suggest that black spruce NPP pot has stagnated since the 1980s in many areas, especially west part of its range. Our study shows that process‐based simulations coupled with up‐to‐date national vegetation coverage and weather data provide a rapid, spatially comprehensive means of monitoring NPP pot changes over annual to decadal scales.