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Prologue

Dust to Dust

… Flood, fire, and cyclone in successive motionComplete the work the pioneers beganOf shifting all the soil into the ocean.

—JAMES MCAULEY, “The True Discovery of Australia”

GONDWANA GENESIS

In the beginning—even 250 million years ago—all lands were one. Then they began to break apart. Great rifts appeared that opened and closed uncertainly over a period of tens of millions of years, and when the final tear ceased, Pangaea had become two continents. One, Laurasia, drifted north. The other, now known as Gondwana, moved south.

Over the coming eons the continental masses migrated, fractured, grew, and reoriented themselves. They massed mountains to their flanks, fresh lands swelled out of submerged basins, volcanic eruptions piled new rock onto old crust. Laurasia broke cautiously into Old World and New, Eurasia and North America. Gondwana was more prolific. As it fissioned, it spawned continents, subcontinents, and microcontinents. New island arcs broke through Gondwana’s peripheral oceans as colossal plates of crust grated, subducted, melted, and bubbled upward into chains of fiery volcanoes. Greater Australia, which included Papua New Guinea and Tasmania, moved northeast into an empty Pacific. By 80–60 million years ago, with the opening of the Tasman Sea, Australia segregated from New Zealand, the last of its Gondwana affiliates. In its travels it had rotated nearly 90 degrees, and it had rafted northward at roughly six or seven centimeters per year until it rammed into the submerged Pacific margins of Asia and helped raise the Sunda arc, punctuated by the towering mountains of New Guinea.

Australia’s geology preserved a Gondwana core, a continental craton, in the enormous plateau that sprawled over the western and central thirds of the continent. Its odyssey, however, had raised mountains along its eastern flanks—the Flinders Range, the Tasmanian Alps, and the Great Dividing Range, a plateau eroded into dramatic escarpments. Continental warping had raised basins and bulged crust into domed, long-wasted mountains in the center. Associated with the eastern uplift, too, were local outpourings of volcanics, largely Tertiary in age, occasionally sputtering into the Holocene.

But overall the post-Gondwana history of Australia was one of geologic quiescence. Australian tectonics were muted; mountains were relatively low in elevation; the principal periods of vigorous activity were old and circumscribed. Australia became the most level of continents. Small rises in sea level resulted in massive incursions of ocean, while small recessions exposed vast regions of land with catastrophic suddenness. The geologic story of Australia required geologic time to record—the minuscule migration of the craton, the relentless leaching and the implacable erosion of its surface. The rejuvenation proposed by the first failed to match the degradation of the second.¹

Where rainfall remained plentiful, deep weathering became the norm. Soils edged into acidity and deteriorated in those physical properties vital to groundwater. Laterization bound phosphorus to iron and aluminum complexes, chemically inaccessible to most organisms. Minerals once distributed more or less uniformly were reworked, concentrated, or removed from the scene. In some instances this led to localized lodes of gold, bauxite, and uranium, but overall the processes only encouraged the generic pauperization of soils, the loss of phosphorus and such critical trace elements as molybdenum, copper, cobalt, and boron. Without renewal by major tectonic forces, without intervention by some process like glaciation that could overturn or scrape away the surface debris or recharge lowlands with new minerals derived from mountain catchments, there was little chance to reverse the inexorable tread toward an entropy of emptiness. The process might be slowed, even locally defied, but it could not be resisted. In Western Australia, at Mount Narryer, weathering exposed zircon some 4.1–4.2 billion years old, incorporated into rocks formed 3.6 billion years ago. New landscapes emerged from the successive exfoliation, by erosion, of old landscapes. Australia’s biologic renaissance had to rise out of a geologic decadence.²

THE BREAKUP OF GONDWANA freed Greater Australia to pursue a separate destiny. That burden fell to its biota: its curious flora and fauna would proclaim the unique character of the island continent. Old Australia’s geology and its biology coexisted in weird counterpoint. Where one degraded and removed, the other exploded into a biotic efflorescence, a proliferation of species unlike those found anywhere else on Earth. Instead of much devolving into less, a relatively small Gondwanic inheritance evolved into more. Some components of green Gondwana not only accepted the geologic legacy—soil depletion and geographic isolation—but turned them to advantage.³

Its originating biota was one Old Australia shared with most of Gondwana. The ancestral forest was dominated by the gymnosperms—the southern conifers, the araucarias and podocarps—but just as Gondwana began to break up, and perhaps in partial response to the stimulus of that profound dislocation, the angiosperms—the flowering plants—proliferated. From a projected point of origin where Africa joined South America, the angiosperms spread throughout Gondwana. Their migration was selective, and the resulting geographies of the conifers and the flowering plants varied. Gondwana was too large, too unbroken a landmass for a single climate to characterize it everywhere, and as the giant continent fragmented, separate lines of biotic advance and exchange danced in slow choreography with geologic cratons. This meant that a single pan-Gondwanic biota did not exist everywhere in equal composition. What part of the ancestral forest the different continental fragments took with them depended on their relationship to Greater Gondwana and on the sequence of their fissioning, all played against the larger drama in which the angiosperms invaded and claimed greater proportions of the supercontinent.

It appears that Old Australia embarked with a solid complement of the ancestral rainforest, a Gondwanic ark. Among the dominant conifers were the araucarias and the podocarps; among the angiosperms, the dominant genus was Nothofagus, the Antarctic beech. Minor families included the myrtles, the grasses, casuarinas, chenopods, and xanthorrhoeas; important genera included Banksia, Hakea, Melaleuca, Eucalyptus. Much the same paleoflora characterized large portions of Antarctica, South America, and New Zealand. In all these lands the Gondwanic rainforest was sustained by a persistent, year-round moisture regime. The relentless rains leached and degraded soils, but the process occurred so slowly that the biota kept pace and adapted. The minor flora claimed special niches; many probably scavenged along the margins of rainforest, better adapted to disturbances, occasional dryness, a more fractured biotic environment.

When Old Australia broke away, about 30 million years ago, the rupture was remarkably final. There would be some late contamination along the north from Indo-Malayan biotas, though these would be restricted by the high mountains thrown up along the New Guinea border and by the deep waters, between islands, that only select species could cross. Together mountain and sea presented an effective biological filter. Greater Australia differ entiated into the Australian mainland, New Guinea, and Tasmania, to be reconnected and sundered from time to time with the geologic tides of a rising and falling global ocean. Not until historical times would there be a further, significant contamination of the biota.

The move to the tropics, while slow, induced climatic change, a new biotic force. Aridity did to the Gondwanic rainforest what tectonic stress did to the Gondwanic supercontinent. The ancestral rainforest fractured and multiplied, cleaving along biotic planes of weakness that divided those species that required uniform moisture from those that could accommodate dryness and change. The onset of aridity did not simply replace one enduring condition with another; it made regular and sporadic change a fundamental part of the biological calendar.

Australian aridity was seasonal, episodic, and chronic. It became, in places, part of an annual cycle of wet and dry seasons. In the tropics, the seasons followed the monsoonal winds, wet in the summer and dry in the winter. In the Mediterranean-like climates of the southeast and southwest, aridity took the form of a prolonged, parching summer, with moisture mostly a product of winter storms. Elsewhere aridity manifested itself as drought, extending regionally over several years. In the enormous center of the continent, aridity became a relentless presence, crowding moisture regimes to the coastal fringe and assaulting the littoral with desiccating winds. The southeast trades and the Great Dividing Range combined to raise moisture along the eastern seaboard, but the interior deserts, like a stony ice sheet expanding and contracting, defined the frontier. At times, like a red giant exploding among the stars, the desert core threatened to engulf the continent.

This transformation—the Great Upheaval—occurred over the course of the Tertiary period. It commenced with Greater Australia’s segregation from Gondwana during the Eocene epoch, and acquired a signature rhythm, long but emphatic, during the Oligocene. The Earth cooled and, overall, dried; Antarctica acquired an ice sheet; Australia continued its tread toward the equator; new circulation patterns established around the Southern Ocean and within and around the Australian continent; global changes in sea level catastrophically flooded then reexposed vast portions of the continental plains, reshaping the interactive meteorology of ocean and continent. By the Pliocene and Pleistocene epochs—over the past 5 million years—the trend became all but inevitable. Aridity became the norm and humidity the exception. The area of stony desert came roughly to equal the area of true forest. During the last glacial epochs, the transfiguration could be called irreversible. Australia’s low latitudes and low relief confined glaciation to Tasmania; there were no loess plains blown downwind, no fresh rocks exposed to weathering, no transfer of nutrients and sediments from mountain to plain. Where rainforest taxa reemerged, they bloomed like ephemerals after a desert storm. The Great Upheaval ended with a Great Inversion of the Australian biota.

In this biotic revolution once-minor constituents, now hardened and shaped by drought and disturbance, became dominant. The survivors evolved into scleromorphs (or sclerophylls)—literally, “hard leaves,” referring to the small, tough evergreen leaves that hoarded nutrients and resisted the transpiration of precious water. The scleromorphs adapted not only to soil impoverishment but to aridity—and, in fact, to disturbances of many kinds. By the mid-Miocene epoch (c. 15 million years ago), as the continental interior acquired its imperishable dryness, the relatively homogeneous biota of ancestral Australia began to differentiate.

What had been a more or less uniform cover of closed Gondwanic rainforest splintered into new, peculiarly Australian biotas. The hermetic forest became open; woodland surrendered to savanna, shrub and heathland, grasses, or outright sand and stony desert. The ancestral rainforest dominated by Nothofagus and Podocarpus gradually retreated before aridity like leaves before a blower. In its place emerged a scleroforest. Casuarinas succeeded araucarias. Tough grasses and scrubby scleromorphs seized understories formerly softened by fern, moss, and fungi. About 34 million years ago the eucalypts appeared, quiet and unannounced. Sometime around 25 million years ago acacias arrived, probably by sea from elsewhere in Gondwana. Thereafter the biotic isolation of the island continent was nearly total. By the time of European discovery the ancestral rainforest had retreated to minor enclaves in the Great Divide, where they occupied probably less than 1 percent of the total land surface of Australia.

The Great Upheaval had all but replaced a pan-Gondwanic biota with a marvelously endemic suite of biotas. About one-third of all Australian plant genera are endemic, nearly 90 percent of all plant species; Victoria alone has a flora twice as great as that of Britain. But such figures fail to convey the utter, continental-scale domination of the landscape by the scleromorphs. The revolution was comprehensive. With the new flora came new fauna and new patterns of interaction between sclerophyllous plants and sclerophyllous animals. Birds and mammals, not insects, typically pollinated the flowering scleromorphs. Placental mammals and reptiles repeated the radiation of specialized plants. Two genera, Eucalyptus and Acacia—gums and wattles—virtually tyrannized every forest and woodland biota, excepting only the relict rainforest. Two genera of grasses, Triodia and Astrebla—the hummocks and the tussocks—similarly dominated the grasslands. Scleromorphs invaded and reshaped forests, woodlands, grasslands, deserts. They penetrated every ecological niche—the canopy, the understory, the surface. They claimed relatively dry sites and relatively wet and those areas that were, on an annual cycle, both wet and dry. The rainforest eroded away like the plateaus of ancient Gondwana. What began as a Gondwanic ark ended as an island continent, Old Australia, that only remotely resembled anyplace else.⁴

The final expulsion of rainforest came relatively late. By the onset of the last glaciation (80,000 years ago) a rough balance still existed between forests consisting of scleromorphic angiosperms like the casuarinas and those composed of ancient gymnosperms like the araucarias. By 38,000 years ago, however, the araucarian forest had all but vanished. Aridity had decided the contest between rainforest and scleroforest, but as aridity settled in to an enduring presence, it became more complex and found new allies. During the final, near extinction of rainforest another biotic revolution broke out, this time within the scleroforest. Casuarinas receded, eucalypts advanced, and charcoal saturated the landscape. This second upheaval was decided by the renaissance of a new, vastly more complicated stress—fire.

WHAT ESCALATED THE GREAT UPHEAVAL was not the simple fact of aridity, but its rate of growth, the frequency of its oscillations, the way it introduced routine disturbances. Wet periods gave way to dry, and dry returned to wet, like a two-cycle engine. With the onset of the Quaternary era the frequency of oscillations increased. A gradual change could have been met with gradual adaptations, but rapid, frequent flux encouraged organisms that could respond with equal vigor and speed, that thrived amid disturbance. It encouraged the tough, the opportunistic. It promoted the weeds among the Gondwana greenery. What began as a tendency stiffened into a trend as Australia began to burn.⁵

There had been some fire in the past. Coal seams preserved, as pyrofusinite, the charcoal of Carboniferous- and Tertiary-era fires. Brown coals from the Yallourn-Morwell district of Victoria reveal ample evidence of burning, probably in the late Tertiary or early Pleistocene times. Where coal seams had been exposed as outcrops, they also ignited from surface fires. Burning Mountain in New South Wales, already smoldering when Europeans arrived, is a celebrated example. But smoldering coal and fiery basalt flows could not become a selective force of continental proportions. Lightning fire could—and did.⁶

What is required is not lightning per se, but the interaction of lightning with appropriate fuels properly cured and dried. The scleromorphs and grasses offered ideal fuels, and a pattern of seasonal aridity and lightning storms stirred the right mixture of fire and water. The storms had to arrive when the vegetation was cured, massed, and dried. Too much rain dampened the fuels; too few storms reduced the probability of ignition; and too prolonged aridity not only dried but killed the vegetation and starved the fire of fuel. During the Great Upheaval, however, the proper, improbable combination of conditions appeared and persisted.

Those circumstances are difficult to reconstruct in any detail. As scleromorphs emerged from the morass of rainforest taxa and as aridity evolved into seasonal or secular patterns, it is likely that fires appeared where they had not been present before, or became more active where they had gained footholds. For fire to be biologically effective, it need not occur annually, only at critical times within the life cycle of the prime species. For rainforest these cycles may involve decades, centuries, perhaps millennia. Elsewhere in what endures of Gondwana rainforest, there is evidence of fire. Thick lenses of charcoal of uncertain origin underly sites in Amazonia. The rainforest of East Kalimantan, Borneo, burns in long, relentless stringers from surface coal seams that act as a slow match, ready to kindle the surrounding terrain at times of severe drought. In the early phases of the Great Upheaval the fossil record suggests a pattern of swamp fires within a landscape of closed rainforest. The frontier between scleroforest and rainforest was almost certainly etched with fire.⁷

Current statistics furnish some insight into the potential power of lightning fire in Old Australia. A 1961 lightning barrage in the Australian Alps impressed fire professionals that “there is no doubt that if all the fires … had spread unhindered by firefighters, they would have burnt over most of the Snowy Mountains area before winter rain put them out.” During the 1970s in Victoria lightning was responsible for 24 percent of all fire starts. In terms of area burned it accounted for 60 percent of the acreage. A single storm in 1972 ignited thirty-nine fires in rugged terrain. While most fires began in the eastern mountains, the largest fires raced through the more interior grasslands. Some 80 percent of fires in western Queensland, it is estimated, originate with lightning. About 20 percent of fires in southeastern Australia and perhaps 12 percent of fires in the forests of the southwest, plus potentially large fractions in the north and center begin, on the average, from lightning. Perhaps 60 percent of the fires in Victoria’s Big Desert originate with lightning, as do about 12 percent of starts in the national parks of Western Australia. The onset of the tropical monsoon is a time of storm and sun, even of dry lightning—ideal conditions for fire starting. In the Mitchell grasslands of the subtropical north, where anthropogenic fire is infrequent, lightning remains an important cause. The capacity of lightning to kindle fires in the desert interior is largely limited by fuels, a product of rains. Many of the worst fire complexes of recent decades include multiple starts from lightning—the 1951–52 fires in New South Wales, the 1961 fires in Western Australia, the 1977 fires of the southeast, and the gargantuan fires of the central deserts in 1974–75. Perhaps 97 percent of the area burned in 1974–75—about 15 percent of all Australia—is attributed to lightning. (Lightning starts in Tasmania, however, appear to be negligible.) Such statistics, however, are allusive rather than conclusive. Millennia of human intervention have so distorted natural fire regimes that it is difficult to assign reasonable values. That lightning is most prominent where humans are least present is no accident. Yet the numbers do testify to the power of lightning to kindle fire in nearly every environment, and that is enough.⁸

Initially, fire reinforced the trend toward aridity. It is possible that fires dried out landscapes, further favoring scleromorphs and shaping microclimates that made future fires more likely: increases in fossil charcoal parallel increases in scleromorph pollen. Then, as its domain expanded and it established reciprocity with critical components of the biota, fire began to redirect the evolution of the Australian scene. Almost certainly fires are implicated in the emergence of sclerophylly, in the astonishing ascendancy of the scleromorphs from their obscurity within the ancestral rainforest, and in the rapidity of overall environmental change. It was no longer sufficient on the Australian ark to adapt to soil paupery and aridity; to thrive, organisms had to adapt also to a regimen of fire. Fire set to boil the whole biological billy that was Old Australia.

INFORMING FIRE

When it first appeared, fire was a minor phenomenon, and it supported minor elements of the biota. The rainforest thrived under a regimen of rain and stability. It adapted to soil degradation, tolerated minor disturbances, closely resembled its Gondwanic cognates. If fire infiltrated that environment, it did so marginally or episodically. With or without it the rainforest continued.

The advent of aridity expanded enormously fire’s potential habitats. It made available new fuels and served new environments that mingled wet and dry, the rain that flushed the landscape with fuels and the spark that kindled them. Yet fire remained one process among many that rallied around aridity, that drove Gondwana greenery toward sclerophylly. It was a catalyst, an accelerant, not—until the complex 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.