The Long Burn - history of fire ecology

Stephen J. Pyne

Seizing fire was our most daring, our most profound gamble. It made us the biospheric creature we are. It made the biosphere anew.

We didn't invent fire as we did things to make and use it, like candles and matches. It was already out there--has been on the planet for at least 400 million years. And it will outlive us, all of our monuments, all our words. When the Earth itself ends, it will likely do so in a flash of solar fire. But fire's Earthly origins were far less explosive.

The early Earth had plenty of sparks. Even today lightning is a more than ample source of ignition. But those bolts had to strike something that could burn, and in any event, burning required oxygen, which the early atmosphere lacked. Life furnished both: The atmosphere became saturated with oxygen, and plants encrusted the land. What photosynthesis put together, combustion pulled apart. The "slow combustion" of respiration acquired a more vigorous twin with the "fast combustion" we call fire. Beginning with the Devonian, fossil charcoal began to litter the sedimentary record.

So we did not invent fire. We captured (stole, seduced, tricked, pried, wrested) it away from nature. This was a profound moment for the natural history of the Earth because it changed how and where fire worked. Natural fire is lumpy. Naturally ignited fire occurs in patches and pulses, driven by a two-cycle climatic engine of wetting and drying, shaped by the kinds of biomass that may or may not thrive under such a regime, waiting on lightning's lottery to kindle. Much of the Earth doesn't burn. It is too wet, too icy, too sparsely vegetated. Over much of early Earth history the mix so often failed to kindle that vast quantities of biomass were simply buried. Nature's economy, in brief, lacked a broker that could match flame with fuel.

CAPTURING SPARK

That changed with the later hominids. It seems that Homo erectus could tend fire, could keep it alive in caves or hold it in torches or slow matches. Probably not until Homo sapiens, however, could humans start fire more or less at will. The standard technologies for kindling fire by striking, drilling, or rubbing are the same as those developed at that time for working stone and bone. Still, it was easier to keep fire alight than to constantly rekindle it; guarding the perpetual fire is a very old (and very practical) habit. The sputtering flame became constant, something that accompanied people wherever they went; and they went everywhere. One species had acquired a monopoly over fire that it would never willingly surrender.

Since the first tread of Homo sapiens, fire ecology has thus meant human ecology. The biosphere had long exercised some control over fuel and oxygen, since life produced both. In human hands, a living part of the biosphere--us--could in principle exert some power over ignition as well, and bring fire's triangle (spark, fuel, and air) more closely into the cycle of life.

But humans did not set fire by instinct. They were something new; they burned for their own ends. They inscribed lines and fields of fire that laid down a new mosaic; they kindled flame according to new rhythms. It was this regime to which biotas would have to adapt. Anthropogenic fire competed with natural fire, much as domesticated livestock would later compete with wildlife. Flame and all the landscapes fire touched entered the moral universe of humans.

WHERE IT WORKED

Ignition, of course, is not the same as fire. Not every spark took, not every fire could propagate. Human firebrands were most effective in wet/dry biomes, where fire already existed or where the conditions for fire were present but lacked a suitable spark. Thus, people favored fire-prone places and shunned sites hostile to flame. They sought out places with vigorous wet/dry cycles, where they could crack open a biome the way a frost/thaw cycle could crack rock. Into those fissures, people thrust their firesticks. They could patch-burn the landscape without waiting for lightning. The shock was greatest in places like Australia that had the conditions for burning but apparently lacked the regular spark of lightning or volcanoes.

People could further leverage their firepower by hunting and foraging. So intensive can human tweaking of a landscape become that Rhys Jones, scrutinizing aboriginal Australia, coined the term "firestick farming" to describe a scene that was often as intricately manipulated as outright cultivation. Especially important was the disappearance of megafauna (mammoths, giant sloths, mastodons). In fire-prone areas, such beasts competed with fire for biomass. Removing them ratcheted up the amount of fuel available and the spectacular nature of burns. In fire-intolerant areas, however, eliminating those biotic bulldozers allowed the now herbivore-free scrub and trees to overwhelm fire. In geographies of weak seasonality and extinct brush-toppling and scrub-girdling browsers, the firestick by itself could not overcome biomass productivity. It became a hammer without a chisel. This scenario likely helps account for the puzzling fact that wet/dry dosed-canopy forests exist on the planet.

The fact is, tough limits on anthropogenic fire remained. Mostly, people could only work with what nature presented them by way of weather and fuels. They could not often bring fire where nature would not sustain it. They seized fire-rich sites and those fire voids that lacked only ignition. But they could not break into shade-laden woods empty of dry tinder or hold the frontier against blurred seasons and chronic wetness. The firestick could nudge vast ecosystems, as it did much of Africa, or even wrench whole continents, as it apparently did Australia, but only if it had a suitably arranged fulcrum of tinder.

The flame's keepers knew full well both their power and its limits. Their fire starters were stone, wood, bone; their myths often told how fire leaped out of wood or flint when freed from its bondage by people. The possession of fire made them unique, distinct among creatures, yet their firepower itself flowed from nature, which inscrutably gave and withheld.

CULTIVATING FLAME

Until recently, people preferred to live in fireprone places whose firepower and combustible biomass gave them an advantage. If people couldn't burn, they could do very little. If they could burn, they could not only hunt and forage, they could also plant and herd. While there are systems of agriculture for which fire is irrelevant, that use water instead of flame to disturb, destroy, and fertilize, they are few and do not extend far from floodplains or hillside terraces. (Even these systems often burn their stubble.) Most agriculture requires fire somewhere in the chain of cultivation. But that requires fuel, and the ability to create fuel is--from a fire-history perspective--the defining feature of agriculture.

The reason for agriculture's flame-reliance lies in basic fire ecology. Flame purges and promotes. For a time, it drives off the local flora and soil microfauna, leaving a cleared space in which some exotic plant can thrive. The creative destructiveness of fire, moreover, shatters the biotic vault in which plants (particularly dead plants) hold critical nutrients. A quick jolt of flame sends nutrients coursing through the site. Shaded sites become open to sunlight, wet sites dry, and the scene more closely resembles those from which the cultigens originated. (Agriculture's hearths are, curiously, almost all fire-prone places.) Then, after the harvest, the local biota close in and the process must begin anew. With farming, caring for fuels joined caring for sparks.

Nonindustrial farming exploits a fire-driven cycle. Either the farm moves through the landscape (as with classic slash-and-burn) or the landscape in effect cycles through the farm (as with rotating fields). Either way, at some point, the system requires the push-pull of fire to turn the ecological crank. Which is to say it demands fresh fuel, such that the cultivator must seek out new sites or bring new fuel to the old site. Farmers could amass combustibles by cutting or by growing them; most easily by abandoning the field to weeds or invading woodlands (and perhaps folding the flock in for a while). But almost any biomass can serve as "fuel" if properly dried: wood, scrub, sod, peat, stubble. If on-site fuel can't be grown, the cultivator must bring in more and spread it over the plot: pine needles, dung, branch wood, or even Seaweed. The agronomic name for this fuel is fallow. And fallow; in short, was not burned as waste, but grown or gathered in order to be burned.

That was not, however, how urban intellectuals and officials read the scene. Whatever value peasants placed on flame, however critical in practical farming, the clerical classes saw fire through the prism of their habitat, the city. Overall, they detested open burning and distrusted the peasantry who used it. They knew fire in cities. They wanted it only in a furnace or lamp. They saw free burning fame stirring society, with swiddeners and herders especially always on the move, beyond the grasp of taxes and conscription. They knew fire as danger, as arson and weapon. They interpreted it as an index of social unrest, something that appeared like rats and plague when the prevailing order broke down. They saw fallow as a waste that a society pressed to its population limits could ill afford. Even the great Linnaeus was forced to delete some favorable remarks about swidden and pastoral burning from his published Skone journal and insert in their place a passage celebrating manure. The ideal European landscape was a garden in which every thing, and every body, had its assigned place. Flame belonged in the hearth or in the toolshed. Free-burning fire resided beyond the farm's fenced borders. Ideally, it did not belong at all.

COLONIZING FIRE

Fire, by its nature, puts people and places into motion. Cultivation is a kind of colonization, and agriculture proved a hardy traveler. It needed for its tool kit only something with which to slash and something with which to cast sparks. If the farmer also had livestock, so much the better; hoof and tooth were as powerful as ax and harrow. Flocks and herds replaced the megafauna that had earlier vanished, crunching and chewing the flora into more burnable forms. With ax and livestock as leverage, Mesolithic people could reenter places like central Europe (or at a much later time, Amazonia) from which their Neolithic predecessors had been expelled by climate. Elsewhere they remade aboriginal fire regimes into agricultural ones. Where fire had not previously existed, it now thrived. Where it had previously flourished, it changed character. The domain of fire expanded enormously.

The possible combinations of plants, animals, ax, plow, people, and fire are many. What matters is that all compel a controlled disturbance, and the form that best matches human desires with ecological possibilities is burning. What matters too is that cultivation placed fire ecology even more strenuously into human hands. How fire would behave on Earth became more closely bonded to the will and whim of human life, to a widening gamut of politics, trade, scholarship, war, and legal conceptions of land ownership. None of these had touched natural fire or shaped its regimes. Ideas and institutions proved as significant as storms and cone serotiny. Even today, farming and herding remain the planet's primary cause of open burning.

THE BIG BURN

Agriculture placed vastly more fuels at fire's disposal, but fire could not burn more than what nature could regrow. Limits remained. Nature still determined how much fuel was available. The cultivator could, within bounds, make and break biomass to fashion fuel, but could not evade the cycles of growth and decay that oversaw how much living biomass was available for converting into combustibles. Yet anthropogenic fire was only as powerful as the fuels that fed it. Close tending could smooth the cycles and tighten the links; it could push out the ecological perimeter of burning. Still, it could not breach it, or could do so only fleetingly and at serious costs. Humans could only hope to transcend this profound cycle if they could tap another source of combustibles.

With fossil biomass, they did precisely that. The combustion of coal, gas, and petroleum launched a new epoch in the Earth's fire history, the era of industrial fire--the Big Burn. Combustion now contains geologic time as well as geographic space. More fuel mass burns than before; probably more is burning now than at any time in the Earth's history. Fuel no longer limits combustion as it did. Fossil fuels abound, enough for centuries. The competition between lightning and torch for biomass continues, but both now face a combustion competitor for whom fuel is no longer limiting. Rather, the problem is one of sinks. Industrial fire burns without regard to ecological context. It burns day and night, winter and summer, through wet season and dry, in times of greenup and dormancy. It both ignores and overwhelms the traditional sinks for fire's by-products. The Earth is awash in its effluent, the pollution of combusted fossil biomass. The Big Burn has inspired a Big Dump. Above all, combustion competes for airshed. It may even perturb climate.

SUBSTITUTION AND SUPPRESSION

The competition takes more direct forms as well. In particular, industrial combustion has aggressively shouldered aside many older pyrotechnologies. Fire had early on bonded with toolmaking and proved as mandatory for technology as it had for manipulating landscapes. If the tended hearth was the core around which a domesticated life and landscape evolved, so cooking served as the model for chemistry. People were able to cook rock for glass, ceramics, metals, lime. They cooked the woods, not only by slashing and burning, but by converting them to potash, tar, pitch, and charcoal. Moreover, technology fed on itself, each tool improving others, mutually refining fuel and flame.

It was in the realm of domestic burning and prime movers that industrial combustion quickly replaced open fire. Steam engines and furnaces could strip a landscape of its fuels; they demanded a deeper, vaster source, which only the geologic past could supply. Yet coal and oil could only be burned meaningfully in specially constructed chambers. And, increasingly, humans sought to control the third leg of fire's triangle, air, as they previously had spark and fuel. Natural gas and controlled airstreams, as well as electricity from combustion-powered dynamos, swept candles, hearths, and wood-fired stoves aside. A mechanical fauna powered by fast internal combustion replaced a fauna of draft animals that had relied on their own slow combustion that, in turn, depended on the grown fuels of the field. In their built environment, industrial societies have all but extinguished open flame.

The substitutions did not end there, however. Industrial combustion has pursued its biomass-centered competition beyond the city and into the field. Fossil fallow has replaced living fallow, and a flaming front of pesticides, fertilizers, herbicides, and tractor-drawn plows has rendered fallowing irrelevant at all locales with access to industrial products. And the process has gone even further, has pushed even into wildlands, leading to active extinction of open fire. It is here in the wildlands that further problems bubbled up, because fire is as ecologically powerful removed as applied. Fire outside the built environment behaves differently from the way it behaves within it. In fields and woods, flame is not simply a technology, it is an ecological process. An electric range can neatly replace a wood-burning stove, but chain saws and caterpillar tractors do not so replace a crown fire and its biogeochemical complexities.

The Earth is separating into two great combustion realms: one dominated by biomass burning, the other by industrial fire. Industrial fire is competing with human-set open fire as human-set open fire had long done with natural fire. More, the creation of "pristine" wildlands by industrial societies has reduced controlled burning and encouraged more lightning fire. Together, natural fire and industrial fire are squeezing the long-dominant domain of human-abetted open fire.

Even fire control has changed its tactics. Since forever, controlled fire has been the primary defense against runaway wildfire. Protective burning shielded villages and fields and sacred groves; backfires broke the advance of fire fronts. Even while fighting fire, flame remained on the land. But the equipment of industrial fire has replaced hand-set flames as a landscape tool, and firefighters have sought to suppress free-burning by meeting it head to head with the power of internal combustion. Outfitted with vehicles, aircraft, power tools, and chemicals, fire agencies stopped the cycling flames in their tracks, then drove them back. We didn't pursue fire control, we sought fire exclusion. We quit lighting fires and we suppressed those that did occur. Had more of the old regime survived, the forest health crisis on America's public lands would likely not exist.

THE CULTURE OF FIRE

Industrial fire has bonded combustion more closely to culture. Its fire starters are a second-order technology like heated wires and electrical arcs, not natural objects. It burns within enclosed metal and ceramic chambers. It combusts biomass drafted from the geologic rather than the biologic realm.

Industrial fire cannot survive without its human tenders. It would expire, instantly. With industrial fire, we became more than the movers of ecological levers; we became the designers of novel ecosystems that cannot exist without us. More and more, the defining flow of energy through the biosphere is the flow of industrial combustion. More than ever, the mechanics of fire ecology are incomprehensible without including the mechanics of human society. What we know (or don't know, or wrongly think we know) matters as much as the moisture content of fuels. How we move knowledge through institutions affects fire's ecology as fully as the turning of the seasons. The flow of knowledge is as vital as the flow of nitrogen or phosphorus; the structure of institutions has molded biotas as surely as mountains and rivers and the rhythm of the seasons. Scientific periodicals, professional journals, books, popular magazines, television--all have packaged and shunted the information with which society decides how it proposes to manage fire.

What happens at a fire in California can thus affect fire practices in Georgia. A fire in South Africa can influence fire programs in Australia. The Yellowstone fires of 1988 shut down natural fire programs across the country for a while--and in some instances permanently--and gave pause to fire strategists around the world. Since the world widely regards the United States as a leader, if not the model, for handing the landscapes of industrial fire, decisions reach far beyond America's shores.

STILL A FIRE PLANET

The geography of Earthly fire remains today neither exclusively natural nor exclusively human. We have not put fire in significant ways into the Sahara, save through the flaring off of natural gas. Nor have we abolished fire from the Siberian taiga. But the geography of fire looks the way it does because of what we have done and not done.

Clearly there have been epochs in which fuels have exceeded fires, in which there has been more biomass than burning. And there are times--the present age, for example--when fire combusts more than what the biosphere grows. The overall fire load of the planet (the amount of yearly combustion) has increased; by how much is difficult to say. In many areas, human agency has meant a change in regime, not in the absolute presence or absence of fire. Only rarely, and then very recently, have humans removed fire from any significant realm.

Today the Earth suffers a vast maldistribution of burning. There are places, mostly in the developing world, that have too much open fire; places, largely in the developed world, with too little; places, along exurban fire frontiers, with volatilely mixed fires. There is too much of the wrong kind of fire and too little of the right. Probably the planet has too much combustion and too little fire.

Ultimately, even the fuel sources must shrink; anthropogenic fire will again have to restrict itself to the cycles of what can be grown. Humanity will have to transcend industrial fire technology, as anthropogenic fire did natural, to fashion sources of power other than controlled combustion. That prospect lies centuries in the future, however. It may not arrive by the end of the third millennium.

STILL KEEPER OF THE FLAME

Fire has meant many things to us, and we, many to fire. Yet throughout the span of centuries, and constantly, amid all our shifting roles--suppressor of lightning fire, promoter of anthropogenic fire, stoker of industrial fire--we have remained the keeper of the planetary flame. Viewed over geologic time, our presence may appear fleeting, but measured by its ecological effects, we have had the impact of a slow collision with an asteroid, throwing embers to all sides, overturning continents, altering climates, wiping out and restoring biotas. Such is the power of fire. And whether or not it was a power we sought, much less deserved, it was a power we gained and one we have never renounced. The seizure of fire was our most daring, our most profound gamble. It made us the biospheric creature we are.

Our prolonged crash into the biosphere has been, above all, a long burn. Beyond the next epoch of geologic time, well after this species expires and another examines its record, we may come to be seen as we have so often seen ourselves: as a flame--destroying, renewing, transmuting. The Earth's greatest epoch of fire will likely coincide with our own. Unquenchable fires will have marked our passage; charcoal will track our progress through history; flame--tended, suppressed; abandoned--will speak uniquely to our identity as creatures of the Earth.

As it should.

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