Burning Bush. Stephen J. Pyne

used to disperse throughout the continent. One theory argues for a coastal colonization. Watercraft were essential to make it to the Sahul, and rafts could continue to carry humans around the resource-rich perimeter. Movement inland followed rivers and clustered around the many lakes that splashed across Pleistocene Australia. Another theory suggests a more interior route, exploiting the watered savannas that wound between the desert core and the more heavily wooded coasts. In this instance, the rivers would lead to the well-lardered coasts and lakes; and from the grassy plains humans could gradually claim the forested bush and mountains. Obviously both patterns could coexist. What seems indisputable is that by 40,000 years ago humans had colonized the major landscapes of Australia. The more inhospitable environments—cold glaciated mountains, arid stony deserts—did not come under year-round human influence until the past few millennia. Whether or not other humans were on the scene, the newcomers wrote a separate record, one preserved not only in fossil bones and campsites but in the environment. Their primary tool was fire.

      Erectus or sapiens, robust or gracile, one variable population or two (or more) distinct groups—regardless, Homo brought fire with him and picked up fire from the new lands he entered. His techniques for preserving fire were adequate to survive short sea voyages. It may have been, as in historic times, that fires were simply maintained on the craft in dishes of clay and sand. It may well have been the case that foraging parties were alerted to the new islands and eventually to the Sahul by bushfires. Even small fires with columns on the order of 1,000 meters can be seen from distances of up to 110 kilometers, which would readily render the Sahul coastline visible from Timor; more intense fires are common in heavier fuels. At night the light from fires carries brilliantly, a beacon. It is habitual for voyaging peoples to identify fire with humans, so it is possible that the smoke not only alerted early parties that land existed but promised human society as well. Once humans did arrive, their own ignitions made that promise a reality.¹⁰

      The record of early hominids is, by and large, a record of fire. Fossil sites are universally associated with fire—with open hearths, with stony ovens, with charred bones, including cremations. Charcoal both preserves and makes possible dating by carbon-14 methods. It is obvious that the abrupt dispersal of humans around 40,000 years ago brought with it an unprecedented wave of burning that reinforced, if it did not catalyze, the internal revolution within the scleroforest that assured the dominance of Eucalyptus. Hearth fire contended with wildfire, broadcast fire with bushfire.

      While fire practices varied in detail, they showed a remarkable uniformity in intent and effect. By the time Europeans arrived, the structure of the forest reflected tens of millennia of Aboriginal fire, a profound modifier of climate and a selector of biotic stocks. Virtually the entire landscape of Australia was itself, as Josephine Flood concludes, “an artefact created by Aborigines with their fire-sticks.” Even forested bush often resembed an open woodland or savanna, astonishingly like the oak woodlands and champion fields of England. Large grassy corridors were carved by fire for access to prime foraging and hunting sites.¹¹

      Of course fire had its limitations. It could not roll back glaciers in the Tasmanian Alps, alter the patterns of the seasons, stay the rising seas, or, unaided, wipe out rainforest. Fire was a catalyst, a shaper, a multiplier of other effects and other practices. It was subtle, intimately tied to local sites and local practices. Without drought, fire could not invade rainforest, and anthropogenic burning could not indefinitely hold out against a wet climate intent on restoring rainforest over scleroforest. Fire could not promote thirsty flora in a dry climate. Fire interacted differently in various environments, affecting savanna in ways distinct from its effect on a Mediterranean terrain or a subalpine forest. Likewise, fire practices acted differently when used in concert with other human practices. Broadcast burning by one group would not be identical with burning by another group, or by similar groups at different times in their history.

      Still, of all the implements in the toolkit of the Aborigine, fire was the most powerful because it went to the dynamic heart of Australian life. As Norman Tindale expressed it, “for at least fifty millennia during the Late Pleistocene, and subsequently, man has ranked with climate as the arbiter of change in Australia.” The Pleistocene revolution was a human revolution. Gently, insistently, violently, the Aborigine put Old Australia to the torch.¹²

       FIRES OF REVOLUTION

      The tempo of environmental reform intensified as the Pleistocene approached the last of its glacial epochs. Global changes revised, then rewrote over and again the physical geography of Australia. Temperature and precipitation regimes fluctuated, storm tracks migrated, seasonality became more pronounced—and less so. During glacial maxima conditions cooled, dried, and spread uniformly over season and place, sea level fell, and increased moisture made otherwise inhospitable sites in the interior habitable. During the interglacial periods, the climate was warmer, often wetter, and more seasonal and regional in distribution; sea level rose such that as much as 25 percent of the Sahul flooded. Rapid change became itself an inexpungable feature of Old Australia.

      This climatic revolution paralleled a biotic revolution. The Pleistocene was a time of major extinctions and recolonizations. Extinction was a global phenomenon, but it affected different continents at somewhat different times and with different intensities. It was felt with special keenness in Australia. Among flora, scleroforest completed its accession over rainforest, and Eucalyptus claimed primacy among the scleromorphs. Among animals, megafauna were preferentially devastated. About a third of Australian megafauna—mostly giant marsupials like Sthenurus, a huge browser, and Thylacoleo, a lionlike carnivore—vanished between 50,000 and 15,000 years ago. The major extinctions, affecting the largest megafauna, occurred between 40,000 and 20,000 years ago. A slower rate of extinction, acting on somewhat smaller megafauna, continued for a few thousands years after than time. A third wave of extinction swept away two marsupial carnivores on the mainland—Thylacinus and Sarcophilus (the Tasmanian tiger and devil, respectively)—between 5,000 and 3,000 years ago. The magnitude of the Australian extinctions is comparable only to those in the Americas. Unlike the Americas, however, the species were not replaced, except by Homo and his sometime associate, the dingo.¹³

      These coincidences—the advent of humans, the disappearance of a rich megafauna, the sudden ascendancy of the eucalypt—have argued for a causal linkage. Clearly massive extinctions have occurred in the geologic record without human assistance. Equally, the record of human colonization in prehistoric times is a register of selective biotic extinctions, and megafaunal extinctions, in particular, have tended to trail human migrations. In Pleistocene Africa, where humans and megafauna evolved in collaboration, few species were exterminated; in Eurasia, there were more; in Australia and the Americas, extinctions were apparently rapid and extensive. The historical record is especially telling with regard to islands, whether invaded by Siberians, Europeans, Madagascans, or Polynesians. Because of their isolation from human migration routes, both the Americas and Australia were effectively vast islands. Humans exploded into them almost without control.

      Thus the Australian scene could be considered two ways: it was a climatic phenomenon, the last in a rhythm of Pleistocene extinctions from natural causes; or it was an anthropogenic artifact, among the first of the historic extinctions by marauding humans outfitted with spear and torch. The evidence is not unequivocal for either position. But it does appear that the extinctions occurred across all climate zones, that they preceded the onset of major aridity during the glacial maximum, and that the timing of migration and extinction is uncannily close.

      What is apparent is that the Aborigine moved into an environment which was undergoing dramatic, perhaps irreversible change. These were circumstances to which Homo—an ambulatory weed, a species nurtured in the Pleistocene, a torch-carrying pyrophile—was well adapted. Of all creatures humans were prepared to survive in a disturbed environment, and humans became in turn a contributing disturbance. Whether the Aborigine hunted megafauna to extinction, or whether he burned away critical environments, or whether he favored some species who subsequently outcompeted rivals, or whether he only hastened an irrevocable decline driven by distant sunspots and Milankovitch wobbles in the Earth’s orbit, he was an important, an unprecedented presence. While his hunting mimicked other carnivores and his torch mimicked lightning fire, the rapidity, the