A two-decades mountain forest Carbon sink affected by increased disturbance and drought

Temperate mountain forests are critical to global carbon (C) cycling, acting as significant sinks for atmospheric CO₂. This study investigates two decades of stem C sequestration dynamics in a 90-ha forest in the Northern Limestone Alps in Austria, a region subjected to intensifying climate disturbances, including storms, droughts, and spruce bark beetle outbreaks. Utilizing a high-resolution, long-term dataset, the analysis reveals that disturbances reduced stand density, increased the proportion of deciduous tree species, and drove a decline in Norway spruce populations. Stem C sequestration decreased significantly during disturbance-intensive periods, particularly in conifer-dominated stands, while mixed forests exhibited higher resilience and recovery. Drought effects were limited to the extreme events, such as the 2003 drought, which caused transient reductions in C sequestration, likely due to cumulative pre-drought stress. Conversely, other drought years, that affected forest’s C sink whole over Europe, showed minimal impact, attributed to the humid mountain climate. Warming trends, marked by increasing minimum temperatures, enhanced C sequestration in beech-dominated stands, demonstrating the species' adaptability to higher temperatures and extended growing seasons. These findings underscore the influence of forest composition, soil properties, and climatic trends on landscape-scale C sink dynamics and provide valuable insights for adaptive forest management and climate resilience in temperate mountain ecosystems.