Mid-to-late Holocene vegetation and paleofire dynamics of the last 6,000 years in the Southeast Brazilian highlands montane rainforest

The present study aimed to investigate the dynamic of the vegetation and the occurrence of local fires during the Mid-to-Late Holocene in the mountainous domain of the Serra do Mar (SE, Brazil). Investigation involved the analysis of charcoal particles, pollen samples and stable isotopes in colluvial sediment cores, in the upper portion of Macaé River's Basin (Rio de Janeiro State), in order to perceive the environmental changes. Previous studies conducted stable carbon isotope analysis and radiocarbon dating, indicating a timescale within the Mid-to-Late Holocene (last 6,000 cal yrs BP). Two cores were collected for palynological and charcoal particle analyses and the results indicated three significant shifts in the vegetation composition during this period. The analysis indicates that fires played a role in shaping the vegetation dynamics of the montane rainforest. Around 6,000 cal yrs BP, the montane rainforest was predominantly covered by herbaceous-shrub vegetation, characterized by an abundance of grasses and shrubs, along with frequent fires. Between 4,500 and 2,000 cal yrs BP, a transition occurred towards a denser canopy forest with increasing dominance of tree species such as Ilex, Alchornea and Machaerium, accompanied by a decrease in fire activity. Despite forest expansion, fires still occurred and became frequent in the last 900 cal yrs BP, leading to a decrease in tree density and opening of the canopy. Charcoal particles peaks reached maximum levels over the last centuries, being related to local anthropic action.