One of the largest mass extinctions of the past 600 million years (Myr) occurred 200 Myr ago, at the Triassic/Jurassic boundary. The major floral and faunal turnovers1 have been linked to a marked increase in atmospheric carbon dioxide levels2, probably resulting from massive volcanism in the Central Atlantic Magmatic Province3,4. Future climate change predictions suggest that fire activity may increase5, in part because higher global temperatures are thought to increase storminess6,7. Here we use palaeontological reconstructions of the fossil flora from East Greenland to assess forest flammability along with records of fossil charcoal preserved in the rocks to show that fire activity increased markedly across the Triassic/Jurassic boundary. We find a fivefold increase in the abundance of fossil charcoal in the earliest Jurassic, which we attribute to a climate-driven shift from a prevalence of broad-leaved taxa to a predominantly narrow-leaved assemblage. Our fire calorimetry experiments show that narrow leaf morphologies are more flammable than broad-leaved morphologies. We suggest that the warming associated with increased atmospheric carbon dioxide levels favoured a dominance of narrow-leaved plants, which, coupled with more frequent lightening strikes, led to an increase in fire activity at the Triassic/Jurassic boundary.
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We thank J. Torero for providing access to test facilities and institutional support and R. Hadden for help in the FireLab at the University of Edinburgh. Thanks to P. Thomas (Royal Botanic Gardens, Edinburgh) for providing modern vegetation samples. L.M. thanks W. M. Kürschner for palynological guidance. We thank M. Popa for sample collection and floral taxonomy of the East Greenland samples, F. Surlyk and N. Nøe-Nygaard for their aid in C.M.B.’s and L.M.’s 2009 Greenland field season and also D. Sunderlin’s and F. Surlyk’s contributions during a 2004 field season. Technical assistance from B. Moran (UCD) and N. Welters and J. van Tongeren (Utrecht University) is gratefully acknowledged, as is that of P. Ditchfield (University of Oxford). We thank A. McGowan for comments that we feel improved the quality of the manuscript. We acknowledge financial support through a European Union Marie Curie Excellence Grant (MEXT-CT-2006-042531) and the National Geographic Society (7038-01) for funding the 2002 expedition.
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