Natural disturbances increasingly affect Europe’s most mature and carbon-rich forests 

Europe's forests store nearly 40 PgC and provide a critical carbon sink of ~0.2 PgC yr-1, yet climate-driven disturbances increasingly threaten this capacity. Although disturbance rates from windthrow and bark beetle outbreaks have risen in recent decades, it remains unclear whether these events increasingly affect the oldest and largest trees, which store a disproportionate share of carbon. Here, we combine three decades of satellite-derived disturbance maps with spatially explicit data on forest age, biomass, and species composition to reveal patterns of structural selectivity across Europe. We show that natural disturbances have shifted toward older, carbon-rich stands, with disturbed forest area > 60 years old nearly tripling since 2010 (from 0.38 to 1.06 Mha). This structural shift is most pronounced in spruce-dominated regions of Central Europe (effect size = 1), where compound heat and drought events have amplified susceptibility to bark beetles. Biomass losses from natural disturbances in spruce forests increased eightfold between the early (2011-2016) and recent (2017-2023) periods. Trend-based projections indicate that, if current patterns of structural selectivity persist, natural disturbances could expose biomass carbon stocks equivalent to approximately 20 % of Europe’s contemporary forest carbon sink by 2040 (~0.05 PgC yr -1 or ~0.7 PgC cumulative). Our findings reveal a previously unquantified vulnerability: climate-driven disturbances increasingly affect forest structures with high per-hectare carbon stocks, amplifying disturbance-related carbon exposure and weakening the long-term effectiveness of Europe’s forest carbon sink. Adaptive management strategies that promote structural and compositional diversification in high-risk regions will be critical to stabilise forest carbon storage under continued climate change.