Ferns Fueled European Fires for Millennia After Climate Warming

A hellish world of recurring fires and rampant ferns characterized parts of Europe during extreme climate warming, according to new research. The study, published in Nature Geoscience, links widespread fires to the massive proliferation of ferns following the mass extinction at the end of the Triassic period, approximately 201 million years ago.

This extinction event, associated with colossal volcanic activity as the supercontinent Pangaea broke apart, released an estimated 100 trillion tons of carbon dioxide into the atmosphere. This surge in greenhouse gases led to a global temperature increase of five to ten degrees Celsius. As forests collapsed under these harsh conditions, a world dominated by ferns emerged.

Ferns, acting as ecological pioneers, rapidly colonized the devastated landscapes. Their ability to sprout quickly from underground root systems after fires and their dry, dense foliage made them ideal fuel for subsequent blazes. This created a dangerous feedback loop where fires and fern growth mutually amplified each other, a cycle that researchers estimate persisted for at least 40,000 years, possibly up to 300,000 years.

Researchers analyzed sediment cores, including a 640-meter core from Britain, looking for evidence of past fires. Fossil charcoal and polycyclic aromatic hydrocarbons (PAHs), compounds formed in smoke, served as indicators. Combined with pollen and spore findings, this data painted a picture of a "fire hell" in the landscapes of northwestern Europe.

Further confirmation came from the unusual coloring of microscopic fossils like pollen and spores. Typically, these fossils darken gradually with increasing depth and temperature. However, in the extinction interval, these fossils uniformly turned extremely dark across all four cores, regardless of their geological history, while being significantly lighter before and after this period. This distinct pattern, calculated from 15,000 measurements, aligns with the increased frequency of fern spores and charcoal, supporting the researchers' findings.