Evenness peaks in fire-resilient vegetation preceded ecosystem shifts in East Africa

Abstract Fire is often assumed to be a key driver in shaping tropical vegetation structure and composition in grass-dominated ecosystems, while forests experience infrequent but impactful fires that influence ecosystem resilience. Although short-term interactions between fire and vegetation are well-documented, long-term dynamics remain underexplored. This study examines fire regimes, vegetation dynamics, and its biodiversity over the past 17 000 years in southwest Tanzania, using sedimentary charcoal and pollen. Major ecological transformations of vegetation and fire regimes were recorded, with vegetation changes consistently preceded shifts in fire regimes. Increased grass pollen correlated with more frequent or larger fires, while high tree cover in Miombo woodland reduced fire activity. Interestingly, pollen evenness was a precursor to major ecological transformations as peaks preceded changes in ecosystem states. Changes in precipitation and moisture seems the major top–down drivers of these changes in vegetation and fire. Fire regimes were indirectly controlled by water availability, and vegetation exhibited resilience to fire at centennial timescales before reaching ecosystem shifts at 12 400 and 1700 cal BP. Our results emphasize the critical role of tree and grass cover in shaping fire regimes and highlight the interplay between climate, vegetation structure, and fire in East African ecosystems.