Ancient Ferns Helped Turn Triassic Europe Into a Wildfire Inferno

A fresh look at fossilized charcoal and pollen shows that weedy ferns kept regrowing after each blaze, feeding an extinction-era firestorm in what is now Northwest Europe.

About 201 million years ago, a catastrophe reshaped life on Earth. The end-Triassic mass extinction wiped out roughly half of all species, and geologists have long tied it to enormous volcanic eruptions during the breakup of the supercontinent Pangea. Those eruptions dumped vast quantities of carbon dioxide into the atmosphere, pushing global temperatures up by an estimated five to ten degrees Celsius. Forests dominated by slow-growing trees collapsed, and a new, stranger landscape took their place.

The fern spike

Across what is now Northwest Europe, the charred remains of a distinctive fossil interval tell a vivid story. Geologists call it the “fern spike”: a sudden, continent-wide dominance of fast-growing, soil-pioneering ferns sweeping in after disturbance. When forests burn or soil is scoured bare, ferns are often the first plants to return. The fossil record of the end-Triassic is full of them, so the fern spike became a convenient marker for the extinction itself.

A new international study led by geologists at Utrecht University, published in Nature Geoscience, asks what those ferns actually did in the ecosystem. The answer is unsettling: they may have helped keep the fires burning.

Reading ancient fire in rock

To reconstruct the blaze record from 200 million years ago, the team analyzed sediment from four drill cores — including a recently collected 640-meter core from the United Kingdom. They measured two kinds of fire signatures. Fossil charcoal records how much wood burned, while tiny smoke compounds called polycyclic aromatic hydrocarbons (PAHs) record the total amount of burning, including smaller fuels. Combining those signals with fossil pollen and spores, the researchers found that wildfire activity jumped sharply during the main phase of the extinction — and that the spike in fire matched the dramatic expansion of ferns.

Why ferns mattered

The mechanism is a kind of ecological feedback loop. Ferns grow fast, die fast, and leave behind large amounts of dry, flammable biomass. As each eruption-heated summer sparked wildfires, the ferns that repopulated the ash quickly regenerated fresh fuel for the next blaze. Traditional charcoal counts tend to underestimate that repeated small-scale burning, because broken charcoal fragments are hard to reconstruct. The PAH records, by contrast, caught the persistent, cumulative smoke of a landscape in constant renewal — a fuel-rich savannah that could not rest between fires.

A warning in the deep past

The end-Triassic fern spike is more than a curiosity of extinction ecology. It is a reminder that vegetation itself can shape climate disasters. When ecosystems are pushed past a threshold, the plants that step in to fill the gap may be the wrong kind — quick to colonize, quick to burn, and quick to set the stage for the next catastrophe. As today's warming planet reshapes forests around the world, the Triassic ferns offer a dark chapter worth remembering.