European beech reproduction is resilient to drought, including the 2003, 2018, and 2022 extremes

Jakub Szymkowiak, Michał Bogdziewicz, Dave Kelly, Jessie Foest, Sabine Braun, Burkhard Beudert, Francesco Chianucci, Andrea Cutini, Rachel Gaulton, Georg Gratzer, Angelika Koelbl, Georges Kunstler, Jonathan Lageard, Henning Meesenburg, Francesco Mezzavilla, Martina Mund, Anita Nussbaumer, Mario Pesendorfer, Wolfgang Schmidt, Anne Thimonier, Peter A Thomas, Stanislav Vacek, Zdenek Vacek, Arne Verstraeten, Markus Wagner, Andrew Hacket-Pain

Climate change is intensifying drought stress in temperate forests, but its effects on tree reproduction, central to forest regeneration and migration capability, remain poorly understood. In mast-seeding species such as European beech (\textit{Fagus sylvatica}), reproduction is regulated by temperature cues rather than current-year resource availability, raising questions about drought sensitivity once reproduction is triggered. Here, we analyse 221 time series of beech seed production across Europe to test whether drought, after reproduction has been initiated, reduces seed output. We isolate drought exposure during pollination and seed maturation phases, including severe events in 2003, 2018, and 2022. Seed production was not impaired by summer drought, and dry spring conditions were associated with increased output, likely via enhanced pollen dispersal. Thus, once triggered, beech reproduction is not reduced by drought. Considered alongside prior evidence that drought suppresses growth and elevates mortality, these findings indicate that vital rates can respond in opposite directions to the same stressor—reproduction is buffered while growth and survival decline. Such contrasts may sustain short-term regeneration during heat–drought events yet shift demographic balance toward higher mortality and turnover as climatic extremes intensify.