Continental fern savannah wildfires driven by end-Triassic greenhouse warming

Two hundred million years ago, vast CO₂ emissions from the Central Atlantic Magmatic Province helped trigger the end-Triassic mass extinction, a biological collapse that reshaped Earth’s ecosystems. Across drill cores from Germany, Luxembourg, Denmark and the UK, palynological records reveal a puzzling “dark zone”: pollen and spore assemblages become markedly darker at this critical interval. The effect is difficult to explain with straightforward thermal maturation, suggesting that an additional process altered the microscopic record.

To test what caused this sudden palynomorph darkening, researchers applied the Palynomorph Darkness Index, focusing on trilete spores produced by ferns and Classopollis pollen from conifer lineages. Because different groups preserve differently through time, pairing fern spores with conifer pollen provides a comparative view of how terrestrial vegetation responded during greenhouse-driven environmental stress.

Strikingly, the maximum darkness aligns with phases of forest collapse and the spread of fern-dominated pioneer vegetation. Peak values occur in the Triletes Beds in Germany and in correlatable strata elsewhere across Europe. The synchrony indicates that the darkening was not a local artifact of sedimentation or basin chemistry, but instead reflects a continent-scale disturbance.

The study then connects these observations to physical fire effects. Controlled heating experiments on spores from the modern clubmoss Lycopodium show that the magnitude and pattern of darkness observed in the Triassic best match scenarios where surface fires burn through fern savannas. In this model, repeated burning can darken palynomorphs in ways that mimic—or exceed—thermal maturation signals expected from burial heating alone.

Independent proxies strengthen the wildfire interpretation. Microcharcoal measurements indicate abundant charcoal production during the same extinction interval, consistent with frequent burning. In parallel, pyrolytic polycyclic aromatic hydrocarbons—molecules formed during combustion—further corroborate widespread, high-temperature events rather than purely geological heating.

Together, the evidence points to continental-scale fern-savana wildfires during end-Triassic greenhouse warming. Such fires would have amplified environmental volatility, degrading habitat, suppressing forest recovery, and stressing plant communities already under rapid climatic change.

By linking palynological “darkening” to combustion-derived changes, the work reframes how the terrestrial biosphere responded to extreme warming. It also implies that heat stress and prolonged drought—interrupted by episodes of intense precipitation—created conditions ideal for widespread ignition and fire spread.

Finally, the record suggests that ecosystem collapse was not driven only by atmospheric chemistry and oceanic disruption, but also by repeated terrestrial burning events that reshaped vegetation at a continental scale.