The contribution of fire to the late Miocene spread of grasslands in eastern Eurasia (Black Sea region)

Angelica Feurdean,Iuliana Vasiliev

doi:10.1038/s41598-019-43094-w

Angelica Feurdean, Iuliana Vasiliev

Open Access

https://doi.org/10.1038/s41598-019-43094-w

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Abstract

Grasslands are globally extensive, but the processes governing their ecology and evolution remain unclear. The role of fire for the expansion of ancestral C3 grasslands is particularly poorly understood. Here we present the first biomass combustion record based on late Miocene to Pleistocene (~10–1.9 Ma) charcoal morphologies (grass, herbs, wood) from the Black Sea, and test the extent of fire events and their role in the rise of open grassy habitats in eastern Eurasia. We show that a mixed regime of surface and crown fires under progressively colder and, at times, drier climates from the late Miocene to Pliocene (8.5–4.6 Ma) accelerated the forest to open woodland transition and sustained a more flammable ecosystem. A tipping point in the fire regime occurred at 4.3 Ma (mid-Pliocene), when increasingly cold and dry conditions led to the dominance of grasslands, and surface, litter fires of low intensity. We provide alternative mechanisms of C3 plant evolution by highlighting that fire has been a significant ecological agent for Eurasian grasslands. This study opens a new direction of research into grassland evolutionary histories that can be tested with fossil records of fire alongside climate and vegetation as well as with dynamic vegetation modells.

Highlights

Grasslands have among the world’s highest species diversity, harbor endemic and threatened plant and animal species, and provide critical ecosystem services[1]
To test the hypothesis that fire contributed to the rise of C3-dominated open habitats in eastern Eurasia, we used the charcoal morphology record of biomass burning from the Deep Sea Drilling Program (DSDP) 42B
The influx of Danube-supplied sediment to the southwestern Black Sea began after ~4.3 Ma16, the final arrival of Danube sediments into the Black Sea took place during the Pleistocene i.e., 571 mbsf (~2 Ma)[16,17,18]

Summary

Introduction

Grasslands have among the world’s highest species diversity, harbor endemic and threatened plant and animal species, and provide critical ecosystem services[1]. Several drivers have been put forward to explain forest loss and the expansion of an open grassy biome. The critical role of fire in the rise of the savanna mosaic has been confirmed from fossil pollen, charcoal, and leaf wax n-alkanes records in C4-dominated grasslands in southern Africa[10]. The involvement of fire is likely because the ancestral transition from forest to open grassy biome occurred in C3 species, but the rise of grasslands are explained based on processes that maintain tree-grass interactions in C4-dominated ecosystems[3]. Recent studies from non-forested ecosystems (grasslands, shrublands, savannas) question the view of climate as the only driver of vegetation, and increasingly emphasises the role of disturbance by fire and herbivores[11,12]. To test the hypothesis that fire contributed to the rise of C3-dominated open habitats in eastern Eurasia, we used the charcoal morphology record of biomass burning from the Deep Sea Drilling Program (DSDP) 42B www.nature.com/scientificreports/

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