How old are wildfires? Probably as old as terrestrial ecosystems . The origin of fire is tied to the origin of land plants, which are responsible for two of the three elements essential to the existence of fire: oxygen and fuel. The third element, a heat source, has probably been available throughout the history of the planet (mainly through lightning). There is charcoal evidencs of fires already in the Silurian (440 Ma). However, the existence of fire does not necessarily mean that fire was playing an evolutionary role at that time. So when did fire start to play an evolutionary role generating fire adaptations [2, 3]? By mapping fire adaptation onto a dated phylogeny of Pinaceae, we recently demonstrated  that at least, and for this family, fire was an agent of natural selection since about 90-125 Ma! This is far back from what was known until now . At this time, fire-protective thick barks were originated in Pinus species as response to surface fires. With increasing fire intensity, thicker barks and serotiny appeared by 70-90 Ma. These innovations appear at the same time as the Earth’s paleoatmosphere experienced elevated oxygen levels that led to high burn probabilities (mid-Cretaceous). That is, the fiery environments of the Cretaceous strongly influenced trait evolution in Pinus. Whether fire had an evolutionary role prior to this is a challance for future research.
Fotos: In many pines, the thick bark and the discontinuity between the canopy and the understory (self-pruning) allows survival after surface fires (left: Pinus nigra, eastern Spain). Serotinous cones allow a quick seed regeneation after crown fire (right: P. halepensis, eastern Spain). Photos: JG Pausas
 Keeley, J. E., J. G. Pausas, P. W. Rundel, W. J. Bond, and R. A. Bradstock. 2011. Fire as an evolutionary pressure shaping plant traits. Trends in Plant Science 16:406-411. [doi | trends | pdf] | For managers]