Ancient global warming fueled a fiery chapter in Europe's past

(CN) — The plants that took over after one of Earth’s greatest mass extinctions may have turned ancient Europe into a tinderbox.

Researchers say sprawling fern savannahs fueled widespread wildfires during a period of extreme global warming about 201 million years ago.

The study, publishedTuesday in Nature Geoscience, provides evidence that fern-dominated landscapes stretching across what is now northwestern Europe repeatedly burned near the end of the Triassic Period.

Researchers based their findings on fossil pollen and fern spores collected from sites across northwestern Europe, where they found signs of widespread burning preserved alongside charcoal and other fire-related compounds.

The mass extinction coincided with intense volcanic activity as the supercontinent Pangea began to break apart.

The eruptions released vast amounts of carbon dioxide into the atmosphere, raising global temperatures by an estimated 5 to 10 degrees Celsius and transforming forests into fern-covered savannahs.

Researchers analyzed fossil pollen and fern spores collected from rock cores across the United Kingdom, Germany and Denmark.

They found the microscopic remains had become progressively darker during the extinction interval, alongside high levels of charcoal and fire-related chemical compounds.

“The most important finding is that we quantified the amount of darkening of tree pollen and fern spores within the ‘fern spike interval,’” Bas van de Schootbrugge, a geologist at Utrecht University, said in an email.

The researchers linked that darkening to biomass that had been charred by wildfire. Because the same pattern appeared at sites spanning thousands of square kilometers, they concluded the fires were widespread rather than isolated events. They also say the darkened pollen and spores could provide a new way to identify ancient wildfires in other parts of the fossil record.

According to Van de Schootbrugge, the fern-covered landscapes themselves likely helped the fires spread.

“This is a very intriguing question. For one, ferns can form a lot of fuel. This is the main reason for any wildfire to get very big, is to have fuel available,” he said. “In the case of ferns, their biomass dries out, but it degrades very poorly, so it is possible to have thick cured matts of material that can ignite when you have droughts followed by storms and lightning strikes.”

He compared the ancient landscapes to parts of Florida’s Everglades today, where invasive ferns create dense vegetation that can help fires spread, even in wetlands.

The findings also offer new insight into how ecosystems recover after catastrophic environmental change.

After trees largely disappeared, ferns quickly colonized the barren landscape, forming sprawling savannahs that dominated the region during the recovery.

“Well, for sure, ferns are tough as nails,” van de Schootbrugge said. “They appear in association with the end-Permian, the end-Triassic, and even the end-Cretaceous extinction events. They are true disaster species, and they will likely be here for a long time.”

He said their ability to spread by spores and regrow from underground stems allowed them to rapidly reclaim devastated landscapes while outcompeting many other plants.

Researchers say the findings not only shed light on one of Earth’s most dramatic periods of climate change but also provide a new tool for tracing ancient wildfires preserved in the geologic record.

“I think there is a lot more to learn from how ferns deal with these conditions, growing under these extreme circumstances, where they had to deal with high CO2, extreme weather, metal poisoning, wildfires. True survivors,” van de Schootbrugge said.