Accelerated Grass Growth in African Savannas Linked to Rising CO2

The international team, led by Dr Kimberley Simpson of the University of Sheffield, combined results from 70 CO2 enrichment experiments with a 32-year observational record covering 533 sites in Kruger. Analyses ruled out changes in rainfall, temperature, grazing pressure, fire frequency, nitrogen deposition, and species composition as primary drivers, leaving the rise in atmospheric CO2 as the most consistent explanation for the observed biomass boost. Climate-model simulations indicate that, despite projected warming and reduced precipitation, CO2-driven growth is likely to persist throughout the 21st century.

CO2 Surge Fuels Grass Growth in African Savannas

More abundant grass provides additional fuel for wildfires, potentially altering fire regimes across savannas that occupy roughly one-fifth of Earth’s land surface. The extra forage could support larger herbivore populations, yet the net carbon benefit remains uncertain because carbon stored in biomass may be rapidly released when grasses are grazed or burned. The study also notes a shift toward taller, more productive grass species, suggesting that rising CO2 may reshape plant community composition and competitive dynamics.

YaleGlobal Online

Lead author Simpson emphasized that the enhanced water-use efficiency of savanna grasses under elevated CO2 allows continued photosynthesis during drought, overturning previous assumptions about their responsiveness. Co-lead Carla Staver highlighted the potential ripple effects on fire activity, wildlife, and the global carbon cycle. Professor Colin Osborne called the convergence of experimental and long-term field evidence “strong evidence” of ecosystem change and indicated that future work will examine how species composition may further evolve.

CO2 Surge Fuels Grass Growth in African Savannas

• “The grasses that dominate savannas have often been considered largely unresponsive to rising carbon dioxide because they already use a highly efficient form of photosynthesis under hot and high-light conditions.” — Princeton University, of Sheffield

CO2 Surge Fuels Grass Growth in African Savannas

• “This increase could have important impacts on fire activity and on wildlife, as well as on the carbon cycle, in this sensitive ecosystem and others like it," said Carla Staver, Professor of Ecology at Princeton University and study co-lead.” — Carla Staver, Professor of Ecology at Princeton University and study co-lead

CO2 Surge Fuels Grass Growth in African Savannas

• “Finding the same pattern in controlled experiments and across more than three decades of observations in a natural savanna provides strong evidence that rising carbon dioxide has been changing these ecosystems for some time. The wider impact depends on where the extra grass ends up. If it is eaten by animals or burned in fires, much of the carbon is quickly released back into the atmosphere.” — Princeton University, of Sheffield

CO2 Surge Fuels Grass Growth in African Savannas

• “Our next step is to understand whether rising carbon dioxide is changing not only how much grass grows, but also which species thrive. Changes in competition between grasses could have important consequences for how savannas function in the future.” — Professor Osborne

CO2 Surge Fuels Grass Growth in African Savannas