Artist impression of the end-Triassic fern spike interval. Weeding and pioneering ferns are overgrowing the disturbed soils and remains of conifer forests. (Credit: Mark Garlick)
A Fire-Fed Feedback Loop Devastated Northwest Europe for Thousands of Years
In A Nutshell
- Fossilized pollen and spores from four European rock cores mysteriously darkened during the end-Triassic mass extinction, then returned to their normal pale color afterward.
- Scientists traced that darkening to a new culprit: repeated, intense wildfires that swept through fern-dominated landscapes as ancient forests collapsed.
- Fast-growing ferns colonized the wreckage of dying forests and, once dried out, became fuel for the very fires that helped keep them spreading.
- The fern-fire cycle likely lasted anywhere from 40,000 to 300,000 years, offering an ancient parallel to how climate extremes can fuel modern wildfire risk.
Two hundred million years ago, as the Triassic Period came to a violent end, a series of volcanic eruptions tied to the breakup of the supercontinent Pangea pumped roughly 100,000 gigatons of carbon dioxide into the atmosphere. Global temperatures spiked between 5 and 10 degrees Celsius. Rainfall patterns went haywire. And now, buried in ancient pollen grains pulled from rock cores across Europe, scientists have found the charred fingerprints of what happened next: a vast wildfire crisis across large parts of Northwest Europe that intensified the ecological damage during one of Earth’s five great mass extinctions.
An international team led by geologists from Utrecht University has traced the disaster back to an unlikely source: fossilized pollen and spores that mysteriously darkened from pale yellow to near-black in rock layers spanning Germany, Denmark, Luxembourg and the United Kingdom. The findings are published in the journal Nature Geoscience.
That darkening had puzzled scientists for years. Now researchers say fire is the most likely culprit, fueled by the very plants that took over the dying forests. As tree-dominated vegetation collapsed under climate stress, fast-growing ferns colonized the wreckage and formed sprawling, fire-prone savannahs across what is now Northwest Europe. The ferns did not just survive the chaos. They fed it.
Darkened Pollen Offers a New Way to Track Ancient Wildfires
Researchers examined four drill cores from ancient coastal and lake environments lining the Laurasian Seaway, including a newly drilled 640-meter-long core from the United Kingdom. Earlier studies had already found hints of fire in this period, using fossil charcoal counts and traces of smoke residue trapped in the rock, but both clues are notoriously messy: charcoal breaks into unreadable fragments over time, and smoke residue does not always land near the fire that made it. So the team added a simpler check. “The novelty of this study came from the analysis of color changes of organic microfossils,” said Dr. Bas van de Schootbrugge of Utrecht University, a senior author on the paper. Using a microscope camera, the team measured the color of more than 13,000 ancient pollen grains and fern spores, tracking exactly how dark each one had turned.
Normally, buried plant matter darkens gradually the deeper it sits, cooked slowly by heat and pressure over millions of years. That is not what turned up here. In all four cores, pollen and spores were light-colored in older layers, turned progressively dark brown during the extinction, then returned to pale yellow afterward. “We were quite puzzled by this phenomenon as it occurs in all four cores at exactly the same time, so it could not have been related to burial of the sediments,” van de Schootbrugge said.
Because the darkening showed up equally in tree pollen and fern spores, plant biology could be ruled out as the cause. “All plant groups show the same effect, which is a strong indication that it was the result of an outside force,” van de Schootbrugge said. That dark, scorched-looking layer lined up precisely with the charcoal and smoke-residue evidence already pointing to fire.
Ferns Fed the Flames That Kept Them Coming Back
Ferns might seem like an unlikely fire hazard, but that is exactly what makes the finding compelling. Explosive fern growth during the extinction resulted from a mix of deforestation, soil erosion, intense greenhouse warming and wildfire itself, feeding back into one another. Ferns burn easily above ground but regrow fast from root systems buried in soil, letting them outcompete slower-recovering plants and quickly repopulate scorched ground. “Ferns are truly remarkable plants that have withstood many crises throughout Earth history, and some species can adapt to some of the most extreme environments. They can be considered to be true disaster species,” van de Schootbrugge said. Researchers estimate the fern-dominated interval lasted from about 40,000 to as long as 300,000 years, with repeated fires likely helping ferns maintain their hold on the landscape.
Some fern species also functioned as fire ladders, smothering surrounding vegetation and letting flames climb from the ground into taller plants. “When the ferns dry out, the thick mats act as the ideal fuel to trigger massive wildfires,” van de Schootbrugge said. “Ferns responded to and delivered the fuel that fanned the flames, triggering repeated massive wildfires. A truly hellish world.”
Schootbrugge.
Ancient Wildfires Offer a Warning About a Warming World
Every piece of this puzzle points back to the same root cause: a climate spiraling out of balance. The ancient record shows how extreme heat, prolonged drought and major swings in rainfall can leave landscapes vulnerable to repeated fires, the same conditions that turned fern savannahs across Northwest Europe into repeated infernos 200 million years ago.
Van de Schootbrugge sees a warning in the wreckage. “The lesson we can learn from this is that the combination of climate change, deforestation, and the spread of opportunistic species can provide all the ingredients for a perfect storm,” he said. Two hundred million years later, the ashes of that ancient inferno are still telling the same story.
Paper Notes
Limitations
The study relies on pollen and spore samples from four drill cores concentrated along a relatively narrow band of ancient coastline, meaning the findings capture a regional signal that the authors extend more broadly using supporting evidence from previously published work elsewhere. Charcoal and PAH records each carry known interpretive limits, including fragment breakup and inconsistent preservation, which is part of why the team developed the darkness index as a cross-check rather than relying on either method alone.
Funding and Disclosures
The research received support from the Human Frontier Science Program, the Dutch Research Council, the UK’s Natural Environment Research Council, and the International Continental Scientific Drilling Program, which helped fund coring operations in the United Kingdom. Drilling of the Elvange core in Luxembourg was supported by that country’s Service Géologique. The authors declare no competing interests.
Publication Details
The study, titled “Continental-scale fern savannah wildfires during end-Triassic greenhouse warming,” was published in Nature Geoscience on July 21, 2026. The authors are T. P. Hollaar, M. S. Kent, B. H. Lomax, W. Meredith, S. L. Lindström, R. Bos, C. V. Looy, J. P. Benca, I. A. P. Duijnstee, S. P. Hesselbo, S. Richoz, H. M. Viðarsdóttir, T. R. A. Vandenbroucke, J. Vermeer, N. Kuhlmann, I. M. Waajen-Labee, F. Peterse, K. G. J. Nierop and B. van de Schootbrugge, representing institutions including Utrecht University, the University of Nottingham, the University of Copenhagen, the Geological Survey of Sweden, the University of California, Berkeley, the University of Exeter, Lund University, Ghent University, the University of Luxembourg and TNO–Geological Survey of the Netherlands. The paper’s DOI is 10.1038/s41561-026-02048-4.
