Fire and Herbivory as Architects of Mediterranean Biodiversity

Reconstructing the long-term interactions between fire and herbivory is essential to understand how Mediterranean vegetation has historically responded to disturbance regimes which is a critical step for informing current biodiversity and fire management strategies. We reconstructed 8000 years of vegetation composition, habitat combustibility, and herbivore density in southern France using pollen data and coprophilous fungal spores. We show that periods of high-herbivore density systematically co-occur with open, highly flammable habitats, and significantly correlate with elevated palynological richness. Conversely, cooler and wetter climatic phases promoted the development of closed-canopy, low-combustibility forests, which consistently exhibited lower biodiversity levels. In recent centuries, a documented decline in mammal herbivory pressure has coincided with the expansion of fire-prone vegetation types such as garrigue and green oak coppice, exacerbating landscape combustibility under climate change. Our 8000-years reconstruction highlights herbivory as a persistent and quantifiable driver of habitat openness, heterogeneity, and fire regime modulation. Synthesis: Our study demonstrates that herbivores and fire have jointly shaped Mediterranean biodiversity over millennia. These findings highlight the need to reintroduce or maintain herbivory as a management tool in fire-prone Mediterranean ecosystems.