Attributing carbon changes in conterminous U.S. forests to disturbance and non‐disturbance factors from 1901 to 2010

Recent climate variability (increasing temperature, droughts) and atmospheric composition changes (nitrogen deposition, rising CO 2 concentration) along with harvesting, wildfires, and insect infestations have had significant effects on U.S. forest carbon (C) uptake. In this study, we attribute C changes in the conterminous U.S. forests to disturbance and non‐disturbance factors with the help of forest inventory data, a continental stand age map, and an updated Integrated Terrestrial Ecosystem Carbon Cycle model (InTEC). We grouped factors into disturbances (harvesting, fire, insect infestation) and non‐disturbances (CO 2 concentration, N deposition, and climate variability) and estimated their subsequent impacts on forest regrowth patterns. Results showed that on average, the C sink in the conterminous U.S. forests from 1950 to 2010 was 206 Tg C yr −1 with 87% (180 Tg C yr −1 ) of the sink in living biomass. Compared with the simulation of all factors combined, the estimated C sink would be reduced by 95 Tg C yr −1 if disturbance factors were omitted, and reduced by 50 Tg C yr −1 if non‐disturbance factors were omitted. Our study also showed diverse regional patterns of C sinks related to the importance of driving factors. During 1980–2010, disturbance effects dominated the C changes in the South and Rocky Mountain regions, were almost equal to non‐disturbance effects in the North region, and had minor effects compared with non‐disturbance effects in the West Coast region. Key Points Disturbance factors were the determinant driver of C changes in U.S. forests Disturbance effects outweighed or were equivalent to non‐disturbance effects The disturbance and non‐disturbance effects had distinct regional patterns