Climate warming flattens masting-driven resource pulses

Michał Bogdziewicz, Jessie Foest, Andrew Hacket-Pain, Maciej K. Barczyk , Maria Bogdańska, Marcin Dyderski, Rachel Gaulton, Jonathan Lageard, Peter A Thomas, Dave Kelly, Jakub Szymkowiak

Pulsed resources arise when environmental forcing synchronizes biological responses, creating years of low or high resource availability that structure food webs. Mast seeding is a major example, yet climate warming is disrupting the synchrony that underpins these fluctuations. Ecological consequences depend on whether populations fail together or produce large seed crops together across space.

We tested how warming-driven changes in European beech (\textit{Fagus sylvatica}) masting affect spatial synchrony in failure and high-seeding years, and how these changes arise from altered links between weather cues and reproduction. We analysed 45 years of individual-tree seed production data from the United Kingdom and 33 years of seed harvest records from Poland.

Synchrony declined strongly in high-seeding years, by 45\% locally and 54\% regionally. Synchrony in failure years also declined, although less strongly, by 34\% locally and 19\% regionally. The decline coincided with a restructuring of weather-cue responses: strong warm-summer T1 cues no longer generated uniform reproductive amplification, while unfavourable cue conditions that previously suppressed reproduction were associated with heterogeneous outcomes among trees.

Declining synchrony weakened both the spatially coherent seed shortages generated by widespread reproductive failure and the resource surges generated by mast peaks. The flattening of masting-driven pulses is likely to reduce the strength, spatial extent, and predictability of consumer responses and food-web effects.