Abstract: Forests comprise a primary terrestrial carbon pool, and forest carbon uptake greatly slows climate change. However, increasing frequency and intensity of disturbances such as drought, fire, and biotic agents driven by climate change threaten long-term forest carbon uptake and sequestration. The goal of this study is to determine how climate-sensitive disturbances might alter the capacity of forest carbon sink in a changing climate. Here, we estimate the sensitivity of forest gross primary production (GPP) to drought stress based on regression between long-term GPP and Palmer Drought Severity Index (PDSI) and quantify the change of GPP sensitivity before and after severe disturbances such as drought, fire, and insect outbreaks. We find that GPP-drought sensitivity increased significantly after severe drought and fire events in the conterminous United States (CONUS) and decreased after insect outbreaks. Among different forest types, evergreen broadleaf forests and deciduous broadleaf forests show increased sensitivity after all three disturbances. However, evergreen needleleaf forests present decreased sensitivity after fire and insect disturbances. Additionally, hot and dry regions tend to show increased sensitivity after disturbances, while cold and wet regions are more likely to reveal decreased sensitivity. Overall, this study highlights the increasing sensitivity and vulnerability of forests to disturbances under climate change, illustrating the negative impacts of climate driven disturbances on carbon sequestration.
