Natural disturbances from bark beetle outbreaks and windthrow increasingly affect Europe's most mature and carbon-rich forests

Résumé fourni par la source

Abstract. Europe's forests store nearly 40 PgC and provide a critical carbon sink of ∼ 0.2 PgC yr−1, yet climate-sensitive 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. Focusing on bark beetle outbreaks and windthrow, the dominant natural disturbance agents in temperate and boreal European forests, 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 forest patches, with disturbed forest area >60 years old nearly tripling since 2010 (from 0.38 to 1.06 Mha). This pattern reflects a qualitative shift in disturbance dynamics, from historically episodic, wind-dominated impacts to increasingly persistent, climate-amplified bark beetle outbreaks that preferentially affect mature spruce forests in Central Europe (effect size = 1.1). As a result, biomass losses from natural disturbances in spruce forests increased fivefold between the early (2011–2016) and recent (2017–2023) periods, outpacing the expansion of the disturbed area. 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 ∼ 0.8 PgC cumulative). Our findings reveal a previously unquantified structural susceptibility: climate-sensitive disturbances increasingly affect forest structures with high per-hectare carbon stocks, amplifying disturbance-related carbon susceptibility 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.