Wildfire associated with a deciduous broadleaved forest from the Neogene Baoshan Basin at the southeastern margin of the Tibetan Plateau

Wildfire bears a close relationship with vegetation as its fuel source. The southeastern margin of the Tibetan Plateau witnesses frequent wildfires among various types of vegetation, whereas such wide interactions between wildfire and vegetation remain poorly studied from geological times. In this study, we reported a local fire using sedimentary macroscopic charcoals from the latest Miocene to early Pliocene of the Baoshan Basin in this region, and then inferred the local vegetation at the time of the fire event based chiefly on the coexistent fruit and seed fossil assemblage. Our taxonomic results show that the charcoal assemblage is probably dominated by broadleaved plants and the fruit and seed fossil assemblage is apparently dominated by Salix (Salicaceae) followed by Sambucus (Adoxaceae), suggesting a deciduous broadleaved forest in which the fire likely occurred. Under a seasonally dry climate associated with the Asian monsoon, this type of vegetation might be prone to natural fire, because in the wet rainy season the plants grew well to accumulate biofuel and in the dry season abundant ground litter resulting from leaf decay would be desiccated to become highly flammable. Due to the fire-tolerant habit of Salix as the dominant plant, the forest might be in return adapted to the fire event or even more fires that potentially followed. All these may suggest a close relationship between the fire event and the reconstructed vegetation. Our finding documents a new type of wildfire–vegetation interaction, namely the interaction between wildfire and deciduous broadleaved forest, from the geological past at the southeastern margin of the Tibetan Plateau. It therefore sheds new light on the wildfire history coupling vegetation change in the region.