Earth Science: Extinction of the World’s Largest Animals Caused Increase in Grassland Fires
The loss of Earth’s grazing megafauna between 50,000 and 7,000 years ago led to a dramatic increase in grassland fires around the world, a study has found.
These large herbivores — including the iconic woolly mammoth, giant bison and ancient horses — are said to have died out as the climate warmed.
However, experts led by Yale University have now shown that their loss had knock-on effects: The grasses they no longer ate provided fuel for wildfires.
The team added that their findings highlight the need to consider the role of herbivores in forecasting global fire activity in the present and the future.
The loss of Earth’s grazing megafauna — including woolly mammoths — 50,000-7,000 years ago led to a dramatic increase in grassland fires around the world, a study has found.
These large herbivores — such as the iconic woolly mammoth, giant bison (whose remains are pictured), and ancient horses — are said to have died out as the climate warmed
The study was conducted by paleoecologist Allison Karp of Yale University, Connecticut, and her colleagues.
“These extinctions led to a cascade of consequences,” Dr. Karp said, including, she explained, the collapse of predators and the loss of the fruit-bearing trees that had depended on the large herbivores to disperse their seeds.
“By studying these effects, we understand how herbivores are shaping global ecology today,” she explains.
The researchers wondered if — since the loss of giant herbivores would likely lead to a build-up of dry grass, leaves and wood — this could lead to a temporary increase in fire activity.
In their research, the experts compiled a list of large, now-disappeared mammals and estimated dates for their extinction on four continents.
Their analysis found that South America lost the most large grazers (83 percent of all species), followed by North America (68 percent), Australia (44 percent) and then Africa (22 percent).
The team then compared this data with data from previous wildfires, as recorded by the presence of charcoal in lake sediments from 410 sites around the world.
Not only did this reveal that wildfire activity appeared to be increasing in the wake of the megafauna extinction, but that the Americas, which lost more grazers, saw a greater increase in fire levels than in Australia and Africa, where the changes were less.
According to Dr. Karp and her colleagues, grasslands worldwide have been transformed by the loss of herbivores, the resulting fires and the loss of grazing-tolerant grasses. New grazers, including livestock, needed time to adapt to the new ecosystems.
However, the loss of large browser species, such as mastodons, giant sloths and Australian diprotodons, all of which forage on shrubs and trees, were not found to be associated with a comparable increase in wildfires.
In their study, the experts compiled a list of large, now-lost mammals and estimated dates when they became extinct on four continents — and compared this data with data from past wildfire activity as recorded by the presence of charcoal in lake sediments from 410 sites across the United States. whole world, as shown
The analysis found not only that wildfire activity appeared to increase in the wake of megafauna extinctions (as pictured) — but that America, which lost more grazers, saw a greater increase in fire levels than in Australia and Africa, where the changes were less
The findings, the team said, show how we should consider the role of wildlife grazers and livestock in reducing wildfires, especially given climate change.
“This work really shows how important grazers can be in shaping fire activity,” said author and ecologist Carla Staver, also of Yale University.
“We need to pay close attention to these interactions if we want to accurately predict the future of fires.”
The study’s full findings were published in the journal Science.
WHAT DO WE KNOW ABOUT THE ANCIENT MEGAFAUNA?
The Earth was once inhabited by a variety of gigantic forms of animals that would be recognizable to us today in the smaller forms that their ancestors had taken.
They were very large, usually over 40 kg and generally at least 30 percent larger than their living relatives.
There are several theories to explain this relatively sudden extinction. The main explanation from around was that this was due to environmental and ecological factors.
It was nearly completed by the end of the last ice age. It is believed that megafauna initially arose in response to glacial conditions and became extinct with the onset of warmer climates.
In temperate Eurasia and North America, the extinction of megafauna ended simultaneously with the replacement of the vast periglacial tundra by an immense forest area.
Glacier species, such as mammoths and woolly rhinoceroses, were replaced by animals better adapted to forests, such as moose, deer and pigs.
Reindeer and caribou retreated north, while horses moved south to the Central Asian steppe.
This all happened about 10,000 years ago, despite humans colonizing North America less than 15,000 years ago and non-tropical Eurasia nearly a million years ago.
Worldwide, there is no evidence that indigenous peoples systematically prey on megafauna or kill too many.
The largest animal regularly hunted was the bison in North America and Eurasia, but it survived for about 10,000 years until the early 20th century.
For social, spiritual and economic reasons, the First Nations peoples harvested game sustainably.