From 50,000 years to 6,000 years ago, many of the world’s largest animals, including such iconic Grasslands grazers as the woolly mammoth, giant bison, and ancient horses, went extinct. The loss of these grazing species triggered a dramatic increase in fire activity in the world’s Grasslands.The study’s authors collaborated with Utah Natural History Museum; Yale scientists compiled lists of extinct large mammals and their approximate dates of extinctions across four continents. The 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 findings with records of fire activity as 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 the megagrazer extinctions. Continents that lost more grazers saw more significant increases in fire extent, whereas continents with lower extinction rates saw little change in Grasslands fire activity.
Karp and Staver note that many ancient browser species—such as mastodons, diprotodons, and giant sloths, which foraged on shrubs and trees in wooded areas also went extinct during the same period but that their losses had less impact on fires in wooded areas. Grasslands ecosystems worldwide were transformed after the loss of grazing-tolerant grasses due to the loss of herbivores and an increase in fires. New grazers, including livestock, eventually adapted to the unique ecosystems.
Staver said that the scientists should consider the role of grazing livestock and wild grazers in fire mitigation and climate change, the authors said. This work highlights how essential grazers may be for shaping fire activity. They need to pay close attention to these interactions to predict the future of fires accurately.