This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Rising atmospheric carbon dioxide is boosting grass growth in Africa's water-limited savannas, according to a new study led by the University of Sheffield. The findings reveal an overlooked driver of change across African savannas, which cover half the continent's land surface, that could have a significant impact on wildlife habitats, fire risks and the global carbon cycle.
The research also challenges the longstanding assumption that C₄ grasses, which dominate many tropical and subtropical savannas, gain little benefit from increasing carbon dioxide. The paper, published in Nature, shows that higher carbon dioxide levels help wild savanna grasses reduce water loss through their leaves. This allows them to maintain photosynthesis and produce more aboveground growth when water is scarce.
Kimberley Simpson, research fellow in the University of Sheffield's School of Biosciences and the study lead, said, "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. "Our findings challenge that assumption. Under dry conditions, higher carbon dioxide helps these grasses conserve water, reduce drought stress and continue growing." The international research team analyzed 70 carbon dioxide experiments and a unique 32-year record of grass production from 533 locations in South Africa's Kruger National Park.
The data revealed a striking trend: Grass production in the park increased by 28% between 1989 and 2021. "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. The researchers examined other possible causes, including rainfall, temperature, grazing, fire, nitrogen pollution and changes in grass species.
However, none of these factors fully explained the dramatic increase. The trend was instead most consistent with the rise in atmospheric carbon dioxide over the same period. The relative increase in grass growth was also greatest in the park's driest areas, supporting the experimental results.
Professor Colin Osborne, from the University of Sheffield's School of Biosciences, added, "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." Savannas cover around one-fifth of Earth's land surface and contribute to around 30% of global plant productivity. While increased grass growth may sound positive, researchers warn it could have complex, wide-ranging consequences: Simpson added, "More grass does not automatically mean more carbon will be stored. The wider impact depends on where the extra grass ends up.
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