Fire absence favours tree growth above the flame zone threatening South American Cerrado vegetation

Abstract

Tropical savannas, including the Brazilian Cerrado, face significant woody encroachment linked to fire suppression. We investigated floristic composition, horizontal and vertical structure, and Enhanced Vegetation Index (EVI) time series in a 1-hectare plot within Chapada dos Guimarães National Park. This area has been fire-excluded since 1997, and it was represented by scattered trees and shrubs over a grassy layer. We found 60 tree species, including a new Tabebuia species (not yet described), with a notable dominance of tree species typical of Cerradão forests (58% of individuals, 55% of species) and a high proportion (67%) of typical species of other forest formations. In closed savannas or forests, animals are the primary dispersers, as we observed in the study area, where zoochorous species represent 65%. Conversely, Styrax ferrugineus , a typical cerrado species, showed high dominance, indicating its favored status in the absence of fire. Our vertical structure analysis, particularly for the forest species Tachigali rubiginosa , revealed heights exceeding typical flame escape, suggesting a shift towards a forest-like physiognomy. The EVI time series corroborated seasonal variations and structural changes, with increasing values over time, indicating encroachment processes. Our findings suggest that prolonged fire exclusion promotes the replacement of open Cerrado by denser, tree-dominated formations. We recommend implementing prescribed fires to control woody encroachment and prevent forest species from establishing above the flame zone, which is essential to maintain the natural structure, biodiversity, and long-term resilience of fire-adapted savanna community.