No Refuge at the Edge for European Beech as Climate Warming Disproportionately Reduces Masting at Colder Margins

Reproduction is vital for forest resilience under climate change, enabling tree populations to recover from disturbances and migrate. Yet projections of habitat suitability often overlook seed production. For European beech (Fagus sylvatica), viable seed production depends on year-to-year variability and synchrony in reproduction (masting). Using data from 341 sites (mean record: 31.7 years), we show that, especially in colder sites, increased frequency of the main reproductive cue is linked to strong declines in masting (CVp decline up to ~54%). This suggests that high latitudes and elevations offer no refuge, countering common assumptions and trends in other demographic processes. Severe disruptions to masting are projected to become the norm, with the greatest reductions (up to ~83%) at colder margins. Masting disruption may threaten forest regeneration and have far-reaching ecological impacts. Monitoring recruitment and testing adaptive forest management in vulnerable areas will be essential to mitigate reproductive constraints on forest resilience.