Climate‐Driven Tree Mortality Alters the Timing and Magnitude of Forest Carbon Uptake in the Conterminous United States

Abstract Earth's forests are major carbon sinks that slow human‐driven climate change, yet climate‐sensitive disturbances are increasing tree mortality and altering carbon cycling. We assessed how forest mortality influences the magnitude, phenology, and drivers of carbon fluxes across the conterminous United States. Using changes in normalized difference vegetation index (NDVI) and terrestrial gross primary production (GPP) before and after mortality events across spatial scales, we found mortality consistently advanced the midpoints of Greenup and Greendown. At fine (30 m) to moderate (500 m) resolutions, 60%–80% of sites showed declines in NDVI or GPP, whereas only ∼15% did so at coarse (8 km) resolution, revealing strong scale dependence. Temperature or vapor pressure deficit (VPD) was the dominant factor modulating these responses. Overall, tree mortality affects both the timing and magnitude of forest carbon fluxes and underscores the critical importance of spatial resolution for detecting and modeling mortality effects.