Effects of fire frequency on vegetation structure and woody species diversity in neotropical savannas

Tropical savannas are dynamic ecosystems where fire acts as a key driver of vegetation structure and biodiversity. In the Brazilian Cerrado, intensifying fire regimes driven by human activities can compromise species resilience and alter the biome's functional integrity. This study investigated the direct and indirect relationships among fire frequency, vegetation structure, and woody species richness across a mosaic of Cerrado phytophysiognomies. Utilizing the PPBio protocol, we established ten permanent 1-ha plots to quantify woody species richness, aboveground biomass, and vegetation greenness via the Normalized Difference Vegetation Index (NDVI) from remote sensing. We applied Structural Equation Modeling (SEM) to test the hypothesis that fire frequency affects woody species richness primarily through changes in vegetation structure. Our results showed that higher fire frequency was strongly and negatively associated with vegetation greenness (beta= −0.93) and aboveground biomass (beta= −0.93), whereas its direct association with species richness lacked statistical support (beta= 0.19). NDVI was positively associated with species richness (beta= 1.55), while aboveground biomass showed a significant negative conditional association with species richness (beta= −0.69). Furthermore, both the specific indirect path via NDVI and the total indirect path were statistically supported. We conclude that the relationship between fire history and woody species richness operates primarily through pathways involving vegetation structure and greenness. These findings highlight that conservation strategies must integrate fire history, vegetation greenness, and structural heterogeneity to safeguard the long-term resilience of the Cerrado.