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Extinguishing old grazers sparked a global increase in fires

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From 50,000 to 6,000 years ago, many of the world’s largest animals, including iconic grassland grazers like the woolly mammoth, giant bison, and ancient horses, were extinct. The loss of these grazing species has triggered a dramatic increase in fire activity in the world’s grasslands, according to a new study led by Yale to be published on November 26, 2021 in the journal Science.

Working with the Utah Museum of Natural History, Yale scientists have compiled lists of large extinct mammals and their approximate dates of extinction on four continents. Data showed that South America lost the most grazers (83% of all species), followed by North America (68%). These losses were significantly higher than in Australia (44%) and Africa (22%).

They then compared these results with the records of fire activity revealed in lake sediments. Using charcoal records from 410 global sites, which provided a historical record of regional fire activity across continents, they found that fire activity increased after fire extinctions. mega-pastures. Continents that lost more grazers (South America, then North America) experienced larger increases in the extent of fires, while continents that experienced lower extinction rates (Australia and Africa) saw little change in prairie fire activity.

“These extinctions resulted in a cascade of consequences,” said Allison Karp, postdoctoral associate in the Department of Ecology and Evolutionary Biology at Yale and corresponding author of the article. “Studying these effects helps us understand how herbivores are shaping global ecology today.”

Widespread extinctions of megaherbivores have had major impacts on ecosystems, ranging from the collapse of predators to the loss of fruit trees that once depended on herbivores for their dispersal. But Karp and lead author Carla Staver, associate professor of ecology and evolutionary biology at Yale School of Arts and Sciences, questioned whether there was also an increase in fire activity in ecosystems. of the world, in particular due to an accumulation of dry grass, leaves or wood caused by the disappearance of giant herbivores. They found that in the prairies grass-fueled fires were on the increase.

However, Karp and Staver note that many species of ancient navigators – such as mastodons, diprotodons, and giant sloths, which used to feed on shrubs and trees in wooded areas – also became extinct during the same period. , but that their losses had less impact on fires in wooded areas. areas.

Grassland ecosystems around the world have been transformed after the loss of grazing tolerant grasses due to the loss of herbivores and increased fires. New grazers, including livestock, eventually adapted to the new ecosystems.

That’s why scientists should consider the role of grazing cattle and wild grazers in fire mitigation and climate change, the authors said. “This work really shows how important grazers can be in shaping fire activity,” Staver said. “We need to pay close attention to these interactions if we are to accurately predict the future of fires. “

Reference: “Global response of fire activity to late Quaternary grazer extinctions” November 26, 2021, Science.
DOI: 10.1126 / science.abj1580