triumph of scleroforest over rainforest—a driving force. Once established, however, it was difficult to extirpate. Fire created the conditions for more fire. So long as fire persisted, there could be no biological counterrevolution, no resurgent rainforest.9
Fire forced, fire stressed, fire quickened. Fire’s dynamism made it, over the short term, the most powerful of the environmental determinants shaping Old Australia. Soils changed only over geologic eons; aridity was, likewise, a product of infinitesimal change—the migration of the Australian craton into the tropics, the reformation of climates, the restructuring of storm tracks. But fire was abrupt, vigorous. Fire responded to brief bouts of drought, as well as to prolonged aridity; to storms, lightning, and winds, not just climatic change; to rapid ecological successions, environmental selections, restructured habitats, and mobilized nutrients, not merely to ponderous evolutionary coadjustments. Compared with soil degradation and climatic reform, fire was more mobile, more sensitive, more varied and malleable, more compelling. The dynamism of fire was inextricably bound to the dynamism of life.
In the drive toward sclerophylly, fire had a paradoxical role. Often it complemented aridity. It pushed biotas to greater sclerophylly as quickly as they could, within their genetic reserves, tolerate the move. Equally, fire released precious nutrients otherwise stockpiled in dead wood or cached in forms inaccessible to biological agents. While the overall nutrient level of average soils might be degraded, fire kept the existing stock in active circulation; it made nutrient caches into rapid nutrient cycles. It also recycled organisms and whole communities. It favored those plants that were already disposed to survive as scleromorphs and it burned maladapted competitors into oblivion or herded them into fire-safe enclaves. What had existed as generic adaptations to sclerophylly now often acquired more fire-specific signatures.
Among the scleromorphs fire constantly fine-tuned composition and dynamics, the balance between those organisms that needed more light and those that needed less, between those that reproduced by seed on mineral soil and those that propagated by vegetative sprouting or suckering, between those that needed access to surface water and those that reached deep into the water table. In the face of pressures toward geologic uniformity, fire helped inspire a biotic diversity. The many niches that had existed in the ancestral rainforest because of long stability now had, within the scleroforest, dynamic analogues, niches made possible because of frequent disturbances by fire.
A remarkable reciprocity developed between the scleroforest and fire. If fire helped differentiate the biota, so also that biota helped particularize fire. Different communities revealed different patterns of fire starts, spread, frequency, timing, and intensity. If rainforest ecosystems could be differentiated largely on the basis of precipitation regimes, then scleroforest ecosystems could be aptly characterized by fire regimes. Fire interacted with the uniquely Australian biota in spectacular, sometimes special ways. Fire created circumstances that promoted the spread of the scleromorphs, and the scleromorphs reciprocated by promoting the spread of fire.
Australian fire acted on and redirected those trends toward sclerophylly that preceded it. Those preadaptations gave fire an entree into Old Australia that it exploited with brilliant effect. Fire swelled into continental dimensions, a selective force that flamed across nearly the whole spectrum of Australian biotas, one that exhibited a special relationship, a positive feedback, with scleromorphs, grasses, and ephemerals—the most characteristic and unique of Australian floras. As fire spread, it became something more than a process; it assumed the character of a defining presence—or more, of an informing principle. The second upheaval, the internal revolution within the scleroforest, is unintelligible without reference to it. Bushfire became an inextricable part of Australian geography, history, and consciousness.
The history of Australia is not synonymous with the history of fire, but the history of neither can be told without reference to the other. Even as fire proliferated, the resistance to its spread was terrific; rainforest gave way grudgingly. But of all the environmental levers by which the landscape could be moved, fire was the most sensitive, subtle, and, in short spells, the most powerful. It was, more tellingly, the lever most accessible to humans. It thrived on instability, and humans destabilized. With each transformation, the pressures argued for more fire, not less.
WHEN GONDWANA BROKE UP, its rafting fragments had to search out new identities. They could no longer derive their meaning from the collective commonwealth of the supercontinent. With each passing eon their Gondwanic heritage faded, the imperative for a separate future became larger, and the possibility of new alliances among the continents and subcontinents more likely. India hurried to a violent union with Asia, massively deforming each in the process. South America rafted eastward toward an eventual, tenuous linkage with North America, part of a brave if wary New World. Africa reunited with Europe and Asia, suturing microplates in Asia Minor, warping borders into mountains and huge basins that filled to become separating seas. Along its great rift valley it nearly split, then halted—a place of origins, and a crossroads for the Old World. Madagascar, New Zealand, the Seychelles—all fragmented so badly that they became outright islands, too insular to share in continental history. That left Antarctica and Australia.
Antarctica drifted only slightly poleward. Its deteriorating climate, which culminated in its colossal ice field, was the product of its singular isolation around the South Pole. As the other Gondwanic plates deserted it, as its connections to other continental masses were removed, Antarctica acquired new patterns of circulation that made it not only cold, but wet. Precipitation fell in what had been a continental desert. Snow became ice, ice created more ice, and the entire continent evolved into a slab of glacial ice so immense that it deformed the shape of the planet. Its ice was ruthless, final, deathly. The ancestral biota it once shared with much of Gondwana failed, without replacement. In the ice of Antarctica, life all but vanished. Its ice, too, repelled humans.
Its Gondwanic twin, Australia, took an antithetical direction. Australia became steadily isolated because of its own positive plate motion, not merely the relative movement of the plates around it. Those travels, however, took Australia into the Pacific, away from the other continents; only to the north, where its edges ground against a submerged Asian plate, did it reestablish contact, and then with the upheaved islands of the Sunda arc; and as often as not even that land linkage was lost to deep channels and rising sea levels. As Australia entered the tropics, new circulation patterns not only raised its overall temperature but introduced aridity—seasonal, secular, selective. Aridity promoted the scleromorphs, and the scleromorphs brought fire. Where Antarctica was progressively informed by ice, Australia was increasingly shaped by fire. Rock had turned to dust, and dust to ash.
The Australian biota might have evolved in several directions. Sclerophylly encompassed a suite of traits that adapted organisms to a suite of environmental conditions; not every trait was specific to fire, and fire could hardly subsume the whole spectrum of adaptations. But among the dominant environmental pressures fire was the most active, and like Antarctic ice, Australian fire had self-reinforcing tendencies. It was as though the landscape had been gently tilted and its streams accorded a particular channel. Each subsequent event tilted the land further and the stream of fire history entrenched itself more deeply. The fire-proneness of the island continent ratcheted steadily upward, each event so tipping the balance that correction became impossible. Even before the arrival of humans, Old Australia had probably crossed a biotic threshold that bound it irreversibly to fire. The advent of humans, however, inexpungably committed Australia to the Pacific’s ring of fire.
Like Antarctic ice, Australian fire became more frequent, more intense, more pervasive, more domineering a presence. But there the similarity ends. Ice is profoundly abiotic; fire is inextinguishably tied to life. Where ice reduces, removes, and buries, fire enhances, multiplies, stimulates, recycles, and animates, a plural not a singular process, massaging a varied, subtle biota. It is above all vital—at times awesome but also playful. Always it is associated with life. Life made fire possible—and fire, in return, dramatized Australia’s life. Its history, natural or cultural, could not be understood without it. To invoke the lands that evolved from Old Australia is to conjure up a burning bush.
