Stephen J. Pyne - Fire: Nature and Culture

The tree the carcass that remains of it lies within the Desierto de los Leones National Park in the Valley of Mexico. A large gash runs down the bole where lightning once split off a long splinter. The outside of the trunk is chunky with the black, deep etchings of a subsequent fire. Later, the tree died, it is believed, from ozone and other noxious gases in the poisonous atmosphere of the valley. Then it fell, and its scars now serve as a record for historical forensics while its composite of gouges, gnarly burns and sickened physiology speaks perhaps as an oracle.

What that fallen trunk reveals will vary with the eyes that look upon it. But for anyone curious about fire, that single tableau is a rude chronicle of earthly combustion. Usefully, that story has three parts the combustion community tends to think in terms of fire triangles in the same way the hydrological community thinks in terms of water cycles. One part of that fire story belongs to nature alone, the second to people working with nature, and the third to a Promethean humanity inventing a new kind of fire.

The first phase began in the early Paleozoic. Here, the first of fires triangles appeared as heat, fuel and oxygen alloyed to allow combustion outside cells. As plants spread across the land another organizing triangle crystallized, this one made of terrain, weather and coarser arrays of hydrocarbon fuels, that governed how the zone of combustion moved around the landscape. For over 420 million years the overwhelming source of ignition was lightning, as bolts blasted away at plants like the gouged conifer in the Desierto, some fraction of which kindled into flame.

Then, within the last two million years, the genus Homo acquired the capacity to preserve and eventually start fires. In the original triangle life created two sides fuel and oxygen but had to yield to a physical process, the act of kindling. Now, the living world could claim all three sides, shrinking the relative impact of lightning, and not only did a species begin replacing atmospheric electricity as a source of kindling, but only one species did. Homo sapiens enjoys a species monopoly over fires manipulation that it will surely never willingly allow another creature to possess.

Humans became the keystone species in fires ecology. People commandeered fire where it naturally thrived, took it to places that had never known it, and everywhere changed the patterns through which it flourished. By setting fires those in confined hearths and furnaces and those on the land they remade vast landscapes and rendered others habitable. The charring around the Desierto trunk is most likely the outcome of just such burning. This anthropogenic fire is the second side of fires historical triangle.

Burned tree trunk, Desierto de los Leones, Mexico.

The last phase is more recent, perhaps no older than two centuries. It is the era of industrial fire, defined simply by the combustion of fossil biomass. This is an artificial burning: it occurs in special chambers without the biotic checks and balances of season and place. The ancient power of fire to transmute makes a modern technological leap into pipes and wires. People burn fuels from the geologic past and release their effluents into a geologic future. The present they overload with noxious emissions and greenhouse gases. The famously polluted air in the Valley of Mexico the product of industrial combustion is the likely cause of death for the fallen Desierto conifer. Certainly the groves around it are pale and feeble from cloying ozone and deposited acids.

The Desierto conifer is a cameo of earths fire history. Until recently, there was little strange or unseemly about that saga. There is nothing alien about fire: the living world runs on combustion and has co-evolved with the open flame. Here is the true wildfire, the fire that can thrive quite apart from any human. It has its own logic and coded behaviour, however flamboyant it appears to untutored eyes. So too there is nothing peculiar about humanity using fire: it has been a species possession a defining trait since our origins. It defines our ecological agency and has gone on for so long in so many places that the prevailing regimen of fire, to which the ecosystem has adapted, is the one guided by people. This fire, too, has its prescriptions and codes. Fire is what we do that no other species does.

Industrial combustion is different, however, for it depends wholly on humanity; so powerful has the role of people become that observers have proposed that the era of fossil fuel burning constitutes a distinct geologic epoch, the Anthropocene, for which fire is not simply an index of global change but the primary driver of it. What makes the story especially fascinating is that the three fires do not simply evolve one after the other, but compete. They can all converge at the same time and place. They can all leave their imprint on the same single plant.

Nordic legends represented the living world as a colossal tree, the Yggdrasil, at the foot of which three Norns spin, weave and cut the threads that compose the tapestry of life. The Desierto conifer might serve as a symbolic Yggdrasil of fire at the base of which fuel, spark and oxygen braid together to keep the planet alive and craft its designs, for fire is truly a creation of life, without which all would turn dead and cold.