No refuge at the edge for European beech as climate warming disproportionately reduces masting at colder margins

Jessie Josepha Foest, Jakub Szymkowiak, Marcin Dyderski, Szymon Jastrzębowski, Hanna Fuchs, Ewelina Ratajczak, Andrew Hacket-Pain, Michał Bogdziewicz

Reproduction is vital for forest resilience to climate change, as tree populations depend on adequate seed production to recover demographically from disturbances and migrate to more suitable sites. Neglecting reproduction in projections of habitat suitability and range shifts risks overestimating forest resilience to climate change. For many tree species, including European beech (Fagus sylvatica), producing viable seeds depends on the variability of seed production from year to year (CVp), known as masting. Analysing data from 341 sites (average record length: 31.7 years), we find that rising summer temperatures in Central Europe are associated with declines in masting. Crucially, declines are more pronounced in sites with lower mean annual temperatures, indicating that higher latitudes and elevations may offer no refuge. Using the identified relationship between masting and climate, we project changes in masting across the species range under contemporary and future climates. The risk of masting decline is predicted to be widespread throughout the species range, due to ubiquitous summer warming, but the risk is highest in colder areas (up to ~54% decline in CVp). Large masting disruptions are expected to become the norm in future climates, especially at the cold margins, with declines of up to ~83%. With masting crucial for tree regeneration, and wider consequences including on seed consumer populations, its disruption under climate change could have far-reaching ecological impacts. To mitigate the impacts of masting disruptions, monitoring recruitment in vulnerable areas is vital, combined with testing forest management strategies to mitigate the effects of masting decline.