Fire modulates millennial plant community assembly

Pablo Valgañón-Ruiz, Alessio Cardillo, Ana Cano, Hugo Sáiz, Adam T Clark , David García-Callejas, Lena Neuenkamp, Cristina Ramos-Capón, Penélope González-Sampériz, Graciela Gil-Romera

How ecological communities maintain resilience under recurrent disturbance remains unclear because the processes governing persistence often unfold over centuries to millennia. Using fossil pollen and charcoal records spanning up to 14,000 years from mountain ecosystems in Europe and Africa, we reconstructed temporal networks of community predictability to investigate the role of fire in long-term plant community assembly. Across both records, high-fire periods produced denser and more centralised communities dominated by a small number of highly connected taxa, whereas low-fire periods promoted more differentiated structures consistent with niche partitioning. Fire thus repeatedly reorganised communities along a continuum from differentiated to synchronised assembly modes. Despite these pronounced shifts, communities retained a robust giant connected component throughout the records, indicating persistent whole-community coherence. Our results suggest that long-term resilience arises not from compositional stability but from the capacity of communities to reorganise their internal relationships while maintaining an integrated architecture. This framework identifies mechanisms linking disturbance, community assembly and resilience across millennial timescales and provides a baseline for assessing ecosystem responses to ongoing global change.