Forest fires triggered by extinction of woolly mammoth, giant bison, and ancient horses

Forest fires in ancient times were triggered by extinction of some of the most iconic grassland grazers such as the woolly mammoth, giant bison, and ancient horses from 50,000 to 6,000 years ago, a new study has claimed.

Scientists say in a study that loss of these grazing species triggered a dramatic increase in fire activity in the world’s grasslands. The findings are published in the journal Science. Scientists compiled lists of extinct large mammals and their approximate dates of extinctions across four continents.

Comparing these findings with records of fire activity as revealed in lake sediments using charcoal records from 410 global sites they found that fire activity increased after the megagrazer extinctions. Continents that lost more grazers (South America, then North America) saw larger increases in fire extent, whereas continents that saw lower rates of extinction (Australia and Africa) saw little change in grassland fire activity.

Widespread megaherbivore extinctions had major impacts on ecosystems — ranging from predator collapse to loss of fruit-bearing trees that once depended on herbivores for dispersal. Scientists wondered if there was also an increase in fire activity in the world’s ecosystems, specifically due to a buildup of dry grass, leaves, or wood caused by the loss of giant herbivores. They found that, in grasslands, grass-fueled fires increased.

Grassland ecosystems across the world were transformed after the loss of grazing-tolerant grasses due to the loss of herbivores and increase in fires. New grazers, including livestock, eventually adapted to the new ecosystems.

That’s why scientists should consider the role of grazing livestock and wild grazers in fire mitigation and climate change, the authors said.

“This work really highlights how important grazers may be for shaping fire activity,” said one of the researchers. “We need to pay close attention to these interactions if we want to accurately predict the future of fires.

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