Late Holocene vegetation dynamics, fire regimes, and human impact in Southern Brazil: A multi-proxy palaeoecological record from the Matematico Lake

The long-term interactions between forest and grassland in Southern Brazil remain poorly understood, despite the region's ecological importance and the ongoing debate about natural versus anthropogenic drivers of landscape dynamics. In this study we present a multi-proxy palaeoecological study of the Matematico sediment core from the Southern Brazilian highlands, with the aim of disentangling the roles of climate and human activity in shaping late Holocene Araucaria Forest and Campos (grassland) dynamics. We combined pollen, non-pollen palynomorphs (NPPs), charcoal, and compound-specific hydrogen isotopes (δ 2 H) from leaf-wax n- alkanes, making this the first study in Southern Brazil to integrate these proxies within a single core. Between ~3.500 and 2.100 cal yr BP (calibrated years before present), the landscape was dominated by Campos under relatively dry conditions, with low fire activity and limited forest cover. Subsequent Araucaria Forest expansion happened in two phases, which were identified at ~1700 and ~ 500 cal yr BP. Both phases correspond with shifts to more negative δ 2 H values, indicating a forest expansion due to wetter climatic conditions. However, the earlier wet phase, corresponding to the wettest interval of the last 8000 years in Southern Brazil, did not trigger lasting forest establishment, suggesting that climate alone was insufficient to drive large-scale forest expansion. Meanwhile, the later expansion at ~500 cal yr BP a coincides with increased charcoal influx and archaeological evidence of intensived occurrence of Southern Jê groups of the Taquara/Itararé Tradition, suggesting potential human influence in this latter expansion. This integrated multi-proxy approach provides new insights into the ecological and cultural legacies of the today's threatened Araucaria Forest–Campos mosaic. • First multiproxy record combining δ 2 H isotopes and pollen in Southern Brazil. • Two distinct phases of Araucaria Forest expansion identified over the late Holocene. • Forest spread at ~500 cal yr BP linked to Southern Jê land use and increased fire activity. • Campos grasslands persisted for millennia, challenging degradation narratives. • Results underline the importance of mosaic conservation of forests and grasslands.