The role of fire in Miocene to Pliocene C4 grassland and ecosystem evolution

Hoetzel, Sebastian; Dupont, Lydie M; Schefuß, Enno; Rommerskirchen, Florian; Wefer, Gerold

doi:10.1038/ngeo1984

Cited by 149 publications

(133 citation statements)

References 27 publications

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“…Fires are frequent in high-rainfall savannas and have been considered the major agents accounting for open ecosystems in climates that can support forests. Fossil charcoal, mostly from marine cores, shows a surge in fire activity from the late Miocene correlated with the spread of savannas (9,10). Phylogenetic studies have shown the emergence of fire-adapted woody plants from the late Miocene through to the Pleistocene in both Brazil and Africa, consistent with fossil evidence for increasing fire activity from this time (11,12).…”

mentioning

confidence: 58%

Spiny plants, mammal browsers, and the origin of African savannas

Charles‐Dominique

Davies

Hempson

et al. 2016

Proc. Natl. Acad. Sci. U.S.A.

135

151

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Savannas first began to spread across Africa during the Miocene. A major hypothesis for explaining this vegetation change is the increase in C 4 grasses, promoting fire. We investigated whether mammals could also have contributed to savanna expansion by using spinescence as a marker of mammal herbivory. Looking at the present distribution of 1,852 tree species, we established that spinescence is mainly associated with two functional types of mammals: large browsers and medium-sized mixed feeders. Using a dated phylogeny for the same tree species, we found that spinescence evolved at least 55 times. The diversification of spiny plants occurred long after the evolution of Afrotherian proboscideans and hyracoids. However, it is remarkably congruent with diversification of bovids, the lineage including the antelope that predominantly browse these plants today. Our findings suggest that herbivore-adapted savannas evolved several million years before fire-maintained savannas and probably, in different environmental conditions. Spiny savannas with abundant mammal herbivores occur in drier climates and on nutrient-rich soils, whereas fire-maintained savannas occur in wetter climates on nutrient-poor soils.Africa | Bovidae | coevolution | mammalian herbivory | savanna T he origin and spread of savannas have been topics of intensive research, but many questions remain. The C 4 grasses that dominate savannas emerged in the late Oligocene (∼30 Ma), but savannas only began to emerge as one of the world's major biomes in the late Miocene more than 20 My later (1). What changed to roll back the forests, allowing the rapid spread of grasslands? Ehleringer et al. (2) first linked the rise of savannas to a drop in atmospheric CO 2 , which would favor C 4 grasses over their C 3 grass predecessors. Low CO 2 can also reduce woody cover by increasing the risk of recruitment failure in woody plants whether from drought, fire, or browsing (3). However, the timing of the onset of low CO 2 is much earlier than the spread of savannas; therefore, although low CO 2 may have contributed to savanna expansion, it cannot explain the long time lag between C 4 origins and savanna spread. Climate change is the usual explanation for changing vegetation over time. Increased aridity in the late Miocene has been shown to cause the retreat of forests in North America and Eurasia, allowing grasslands to spread in their place (4, 5). However, large areas of extant savannas occur in climates that are wet enough to support forests and other closed woody types (6-8). Fires are frequent in high-rainfall savannas and have been considered the major agents accounting for open ecosystems in climates that can support forests. Fossil charcoal, mostly from marine cores, shows a surge in fire activity from the late Miocene correlated with the spread of savannas (9, 10). Phylogenetic studies have shown the emergence of fire-adapted woody plants from the late Miocene through to the Pleistocene in both Brazil and Africa, consistent with fossil evidence for increasing f...

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mentioning

confidence: 58%

Spiny plants, mammal browsers, and the origin of African savannas

Charles‐Dominique

Davies

Hempson

et al. 2016

Proc. Natl. Acad. Sci. U.S.A.

135

151

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“…However, the role of fire in the spread of African savannas can be traced from fossil charcoal, especially from marine cores. These show a sharp increase in charcoal fluxes also from the Late Miocene [34,35]. Increased fire activity within the last approximately 10 Myr, is a worldwide phenomenon with evidence for a surge in charcoal fluxes in the North Pacific, the North and South Atlantic off Africa, and terrestrial records in Australia [36].…”

Section: The Antiquity Of Savannasmentioning

confidence: 99%

The deforestation story: testing for anthropogenic origins of Africa's flammable grassy biomes

Bond

Zaloumis

2016

Phil. Trans. R. Soc. B

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Africa has the most extensive C4 grassy biomes of any continent. They are highly flammable accounting for greater than 70% of the world's burnt area. Much of Africa's savannas and grasslands occur in climates warm enough and wet enough to support closed forests. The combination of open grassy systems and the frequent fires they support have long been interpreted as anthropogenic artefacts caused by humans igniting frequent fires. True grasslands, it was believed, would be restricted to climates too dry or too cold to support closed woody vegetation. The idea that higher-rainfall savannas are anthropogenic and that fires are of human origin has led to initiatives to 'reforest' Africa's open grassy systems paid for by carbon credits under the assumption that the net effect of converting these system to forests would sequester carbon, reduce greenhouse gases and mitigate global warming. This paper reviews evidence for the antiquity of African grassy ecosystems and for the fires that they sustain. Africa's grassy biomes and the fires that maintain them are ancient and there is no support for the idea that humans caused large-scale deforestation. Indicators of old-growth grasslands are described. These can help distinguish secondary grasslands suitable for reforestation from ancient grasslands that should not be afforested.This article is part of the themed issue 'The interaction of fire and mankind'.

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“…A North American vegetation reconstruction from n-C 31 alkane data from a Gulf of Mexico core (DSDP Site 94) also suggests minor amounts of C4 vegetation by 9.1 Ma or possibly earlier (49). Two marine sediments cores (Ocean Drilling Program Sites 1081 and 1085) spanning ∼10 degrees of latitude from southern Africa both indicate the onset of expansion at ∼7.5 Ma based on n-C 31 alkane data, lagging eastern Africa by ∼2.5 My (102,103). A Neogene vegetation record from western Africa could provide information on mechanisms behind the expansion in Africa because it would show whether or not expansion occurred synchronously across eastern and western Africa.…”

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confidence: 99%

“…The Neogene plant wax record provides the opportunity to place the expansion of C 4 grasslands in eastern Africa into a global context. C 4 grassland expansion has been investigated most intensively in the Siwaliks of South Asia (48,51,53), the Americas (49, 54, 99-101), southern Africa (102,103), and, to a lesser degree, China (104,105), the Mediterranean (106), and the Middle East (85,86). The onset of expansion at 10 Ma in eastern Africa precedes by at least 2 My that of well-dated terrestrial records from the Siwaliks (∼8 Ma), North and South America (∼8-6 Ma), and South Africa (∼8-7 Ma).…”

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confidence: 99%

Neogene biomarker record of vegetation change in eastern Africa

Uno

Polissar

Jackson

et al. 2016

Proc. Natl. Acad. Sci. U.S.A.

114

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The evolution of C4 grassland ecosystems in eastern Africa has been intensely studied because of the potential influence of vegetation on mammalian evolution, including that of our own lineage, hominins. Although a handful of sparse vegetation records exists from middle and early Miocene terrestrial fossil sites, there is no comprehensive record of vegetation through the Neogene. Here we present a vegetation record spanning the Neogene and Quaternary Periods that documents the appearance and subsequent expansion of C4 grasslands in eastern Africa. Carbon isotope ratios from terrestrial plant wax biomarkers deposited in marine sediments indicate constant C3 vegetation from ∼24 Ma to 10 Ma, when C4 grasses first appeared. From this time forward, C4 vegetation increases monotonically to present, with a coherent signal between marine core sites located in the Somali Basin and the Red Sea. The response of mammalian herbivores to the appearance of C4 grasses at 10 Ma is immediate, as evidenced from existing records of mammalian diets from isotopic analyses of tooth enamel. The expansion of C4 vegetation in eastern Africa is broadly mirrored by increasing proportions of C4-based foods in hominin diets, beginning at 3.8 Ma in Australopithecus and, slightly later, Kenyanthropus. This continues into the late Pleistocene in Paranthropus, whereas Homo maintains a flexible diet. The biomarker vegetation record suggests the increase in open, C4 grassland ecosystems over the last 10 Ma may have operated as a selection pressure for traits and behaviors in Homo such as bipedalism, flexible diets, and complex social structure.

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The role of fire in Miocene to Pliocene C4 grassland and ecosystem evolution

Cited by 149 publications

References 27 publications

Spiny plants, mammal browsers, and the origin of African savannas

Spiny plants, mammal browsers, and the origin of African savannas

The deforestation story: testing for anthropogenic origins of Africa's flammable grassy biomes

Neogene biomarker record of vegetation change in eastern Africa

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