New research suggests that a rapid expansion of ferns during the end-Triassic mass extinction created a feedback loop of wildfires that ravaged prehistoric landscapes.

An international research team led by Utrecht University geologists has linked the end-Triassic mass extinction, which occurred approximately 201 million years ago, to widespread wildfire activity. As volcanic eruptions caused global temperatures to rise by 5 to 10 degrees Celsius, forests collapsed and were replaced by fern-dominated landscapes. These fern-covered regions became highly susceptible to fire, creating a cycle of destruction that persisted for tens of thousands of years.

Tracking Ancient Fires with Fossil Color

To analyze fire history, researchers studied sediment from four drill cores, including a 640-meter-long core from the United Kingdom. Beyond measuring charcoal and polycyclic aromatic hydrocarbons (PAHs), the team utilized a new technique called the Palynomorph Darkness Index. By measuring the color of fossil pollen and spores using the RGB spectrum, they identified a 'Dark Zone' that correlated with the extinction interval. While organic fossils typically darken due to burial depth and pressure, the fossils in this study showed a unique pattern. They darkened significantly during the extinction period before returning to a lighter color once the interval concluded. This consistent pattern across four different geological basins indicated that the darkening was caused by an external force rather than burial history.

The Fern-Fire Feedback Cycle

The study indicates that ferns acted as 'disaster species' that thrived in the wake of deforestation and soil erosion. Once established, these ferns created dense mats that served as fuel for massive wildfires. Because ferns can rapidly regrow from underground root systems after burning, they were able to dominate the landscape, crowding out other vegetation and providing fuel for recurring fires. Researchers estimate that this period of intense wildfire activity and fern dominance lasted between 40,000 and 300,000 years. This created a destructive feedback cycle where climate warming facilitated fern growth, which in turn provided the fuel necessary to sustain a 'hellish' environment of repeated wildfires.