Iconic grassland grazers such as giant bison, woolly mammoth and ancient horses went extinct from 50,000 years to 6,000 years ago, and their extinction has led to the triggering of a dramatic increase in wildfire activity in the world’s grasslands, according to a new study.
The Yale-led study in the journal “Science”, said that the continents that lost more grazers (South America, North America) saw larger increases in wildfire extent whereas continents that saw lower rates of extinction (Australia and Africa) saw little change in grassland fire activity.
MORE GRAZER LOSS, INCREASED FIRE
The study was held in collaboration with the Utah Natural History Museum. In the study, the researchers 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 per cent of all species). followed by North America (68 per cent). 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.
Corresponding author and a postdoctoral associate in Yale’s Department of Ecology and Evolutionary Biology Allison Karp said that the extinctions led to a cascade of consequences. The study found that large scale megaherbivore extinctions had major impacts on ecosystems – ranging from predator collapse to loss of fruit-bearing trees that once depended on herbivores for dispersal. Karp and others looked at the possible increase in fire activity in the world’s ecosystems due to a buildup of dry grass, leaves, or wood caused by the loss of giant herbivores.
However, the researchers noted 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. They said that grassland ecosystems across the world transformed after the loss of grazing-tolerant grasses due to the loss of herbivores and increase in fires. As such, new grazers, including livestock, adapted to the new ecosystems. The researchers note that the studies should consider the role of grazing livestock and wild grazers in fire mitigation and climate change.