Aboveground biomass and seedling responses to forest disturbances across the conterminous United States

Increases in the frequency and severity of forest disturbances over recent decades have raised concerns regarding the future health and functioning of forest ecosystems. Previous ground- and remote-sensing-based studies have quantified disturbance impacts and recovery, but we have limited understanding of the immediate impacts and short-term recovery of seedling density and live biomass across broad geographic regions. We quantified short-term impacts and recovery of seedling density and live biomass stocks following different disturbances (fire, harvest, and insect/disease) in forests of the conterminous United States (U.S.) using nationwide forest inventory data and a remote-sensing-based burn-severity product. Harvest and fire were the most common forms of severe (stand-replacing) disturbance in the eastern and western U.S., respectively. Insect/disease disturbances were common in both regions but were rarely stand-replacing. In the West, live tree aboveground biomass (AGB) was substantially lower following severe fire compared to other severe disturbances, although multiple disturbance agents (e.g., drought and insects) may interact to affect fire severity and its impacts. Furthermore, most conifer forests in the West impacted by large, severe fire remained classified as stand age zero with low seedling density (< 400/ha) for at least 10 years post-fire, indicating sparse and delayed regeneration. Our results show that in the western U.S., forests recover slowly from large, severe fire, and the short-term impacts of fire are more severe than other types of episodic disturbance. Given the ongoing intensification of wildfire regimes in the western U.S., these findings imply a threat to forest carbon stocks and other ecosystem services.