Africa's savanna grasses evolved in two distinct waves, not one
Schartman AK, Polissar PJ, Strömberg CAE
Climate Adaptation
The grass-tree balance in savannas and prairies today is a legacy of ancient climate tipping points, and understanding how small temperature shifts once flipped forests into grasslands helps predict how today's landscapes, from African reserves to your local prairie restoration, might respond to a warming, drying future.
Scientists studied waxy molecules from plant leaves that got washed into the ocean and buried in mud off the coast of northwest Africa millions of years ago. These molecular fingerprints show that around 15 to 14 million years ago, dense forests gave way to a strange grassland unlike anything alive today, and only later, between about 7.4 and 6.4 million years ago, did it transform into the C4 grass savanna we'd recognize now. The shift happened as Earth's climate cooled and dried, showing how tightly plant communities are wired to climate and to pressures like grazing animals and fire.
Key Findings
A nonanalog C3 grass-rich savanna replaced closed woodlands and forests during the middle Miocene, roughly 15 to 14 million years ago, coinciding with global cooling and aridification.
This unique ecosystem transitioned into a C4 grass savanna in stages during the late Miocene, with the most rapid shift occurring between 7.4 and 6.4 million years ago.
The timing roughly coincides with C4 grass expansions documented in other subtropical regions worldwide, suggesting a shared climate-driven trigger.
chevron_right Technical Summary
Ancient plant chemical traces buried in seafloor mud reveal how Africa's savannas actually formed: grasslands appeared first, millions of years before the grazing-adapted grasses we know today, as the climate cooled and dried out.
Abstract Preview
Original paper
The origin and development of the Miocene northwest African savanna.
Like many of Earth's subtropical open ecosystems, the African savanna originated in the Miocene Epoch (23.0 to 5.3 Ma), one of the best historical analogs for future climate states. The first C4 gr...
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