Doubled density and increased resilience: Consequences of seven consecutive annual dry‐season fires to the unburned Cerrado grass layer

Abstract Tropical grasslands and savannas are dominated by C 4 grasses, which are crucial for the biodiversity, structure and functioning of these ecosystems. Yet, grasses have been neglected in vegetation science, leading to a superficial understanding of their responses to fire and of the mechanisms/traits associated with it. This hinders the effective management and conservation of the tropical open ecosystems, especially because recent anthropogenic fire regimes have raised concerns about the long‐term effects of repeated dry‐season burns. Therefore, we investigated how prolonged frequent fires affect the Cerrado grass layer by exploring community properties, functional guilds, population responses and persistence mechanisms. We sampled all grass individuals within 120 permanent 1‐m 2 plots before the first fire in 2015 (single fire recorded in the last 30 years) and again after seven annual mid‐dry‐season fires in 2022. We also collected data on traits relevant to species' regeneration and persistence. The data were analysed using an effect size approach to assess changes in community properties and population sizes between sampling occasions. We also compared shifts in the proportions of functional guilds and partitioned the composition of populations to demonstrate persistence mechanisms. After seven annual burns, the grass layer maintained its composition, increased its homogeneity, increased its total richness (from 26 to 30 species) and doubled its density (from 8 to 17 individuals/m 2 ), but did not change its richness/m 2 (4 species/m 2 ). Functional composition was affected by fires, increasing the prevalence of traits related to fire tolerance and vegetative regeneration. Species responded differently to burns, with 25% benefited, 25% disadvantaged and 50% unaffected. Resprouting, recruitment and clonality contributed differently to species persistence, with clonal reproduction driving population growth. Synthesis and applications . The Cerrado grass layer benefits from frequent fires and is resilient even to an extreme fire regime, such as seven annual burns. Recurrent mid‐dry‐season fires are not harmful to the grass layer and should be less concerning than prolonged fire‐suppression regimes, which diminish grasses' biomass, cover, diversity and functioning. Maintaining frequent fires or reintroducing them after prolonged fire exclusion (as in our study) are suitable management actions for the conservation of the grass layer.