General flowering in temperate forests arises from multi-timescale community synchrony

Valentin Journe, Jakub Szymkowiak, Jessie Foest, Marcin Dyderski, Szymon Jastrzębowski, Andrew Hacket-Pain, Michał Bogdziewicz

Community-wide “general flowering” has been regarded as a tropical phenomenon. Here, we show that temperate forests also exhibit community-wide flowering at the regional scale. Annual seed-production records for seven dominant tree species across 432 forest sites, analysed with timescale-explicit wavelet metrics, reveal landscape-scale synchrony structured by two periods — a 2–4-year band and a 5–8-year band — and associated with spatially coherent summer temperatures. This dual-band synchrony demonstrates that large-scale, cross-species reproductive alignment is an emergent property of temperate forest communities, implying shared climate cueing of reproduction and the potential for community-wide predator satiation. Since $\sim$2005, the short- and long-period synchrony has weakened, and the short-period signal has shifted towards $\sim$2 years (shorter period). Species-specific shifts in timescale structure no longer sum constructively, implying smaller, less predictable resource pulses at the community level, reduced community-wide predator satiation, and a decoupling of consumer–resource dynamics under continued warming.