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The Universal Australian

… round the bases of the barkWere left the tracks of flying forest-fires, As you may see them on the lower boleOf every elder of the native woods.

—HENRY KENDALL, “A Death in the Bush”

The extreme uniformity of the vegetation is the most remarkable feature in the landscape of the greater part of New South Wales … In the whole country I scarcely saw a place without the marks of a fire; whether these had been more or less recent—whether the stumps were more or less black, was the greatest change which varied the uniformity, so wearisome to the traveller’s eye.

—CHARLES DARWIN, The Voyage of the Beagle (1845)

IT IS NOT CLEAR just when the first eucalypt emerged out of the welter of ancient rainforest taxa. The earliest definite pollen appears in the Oligocene, around 34 million years ago, long after Australia had separated from the bulk of Gondwana. Nor is it obvious whether the genus developed from a single protoeucalypt or from several related forms.¹

What is incontestable is the degree to which the genus Eucalyptus is endemic to Australia, the extent to which, by Holocene times, it came to dominate the forest and woodland environments of Australia, and the peculiar attributes to which it owes its evolutionary triumph. Its successful coup within the scleroforest, in particular, came from a powerful set of alliances, a triumvirate that Eucalyptus formed with fire and the genus Homo. Found virtually nowhere outside Australia, but within Australia found nearly everywhere, the eucalypt became the Universal Australian.

THE EUCALYPT AS COLONIZER

Amid the Great Upheaval, the family Myrtaceae—flowering trees and shrubs with fleshy or dry fruits—emerged as one of the scleromorphic winners. Although it probably originated in Australasia, Myrtaceae saturated all of Gondwana, a minor element in the ancestral rainforest. When Gondwana divided, so did Myrtaceae. Its fleshy-fruited genera concentrated in South (and Central) America, and its dry-fruited genera in the eastern cratons including Greater Australia. In Australasia the family Myrtaceae featured ninety-five genera, ninety-three of which were endemic. Australia contained sixty-nine genera, of which forty-five were endemic, among them Leptospermum, Melaleuca, Callistemon, Baeckea, Verticordia, and Eucalyptus. By the time Eucalyptus appeared in the fossil record, Myrtaceae had experienced perhaps 30 million years of evolutionary history.²

The Tertiary upheaval completely reformed the status of Eucalyptus. Its genetic inheritance included as a matter of course generalized Myrtaceaen traits and scleromorphic tendencies. Probably it appeared along the margins of rainforest, a weed searching out disturbed sites at least momentarily free of an obscuring canopy. Interbreeding was common; hybridization, frequent. As the Australian ark floated into the Pacific and experienced upheaval, a genus that thrived amid disturbance found itself on an increasingly disturbed continent. Quickly Eucalyptus began to diversify, to radiate into the new niches that blinked from a disintegrating rainforest, and to reshape those environments in its own image. Southeastern and southwestern Australia divided into biotic subcontinents, segregated first by intervening seas, then by different soils, and finally by endemic biotas. As the Australian plate threw up an arc of mountains to the north, a few eucalypts crossed the Torres Strait and found a marginal existence in drier, unsettled sites of New Guinea and beyond. The remaining genera discovered plenty of opportunity within Australia, first as scleroforest replaced rainforest and then as the proliferating eucalypts seized dominance over the scleroforest.³

The scleroforest revolution concluded between 38,000 and 26,000 years ago as the scleromorphs, led by Casuarina, completed their abrupt, all but catastrophic, expulsion of the araucarias. But almost as suddenly, between 20,000 and 7,500 years ago, Eucalyptus did the same to Casuarina. By the time of European discovery forests and woodlands comprised about 25 percent of the Australian land surface; perhaps 70 percent of those lands could be classified as pure eucalypt forest. Eucalypts claimed about 16 percent of the tropical eucalypt and paperbark biomes, and an estimated 11 percent of the cypress pine biome. Across Old Australia eucalypts comprised some 95 percent of the constituent tree species. They thrived almost everywhere—at the snow line of the Australian Alps, along the saltwater tide of tropical mangroves, along desert watercourses, on monadnocks; in relatively wet climates and in relatively dry, on impoverished sites and on more enriched; in Mediterranean climates, in true deserts, in wet-dry tropics, along the margins of rainforest and interpenetrating grasslands. They were absent only in the true, the relict rainforest. With minor exceptions, Eucalyptus dominated Australian forests. Every other organism had to accommodate that fact.⁴

“The remarkable plurality of the Eucalypts,” as Ferdinand von Müller called it—what staggered Charles Darwin as the “never-failing Eucalyptus family”—prevailed over the Australian continent to an extent unrivaled by any other genus on any other continent. Eucalyptus had exploded so widely that it is considered by some authorities as less a genus than an alliance composed of three suballiances, ten subgenera, and over six hundred species. The plasticity of the genus is extraordinary. Hybrids are common within subgenera, juvenile habits persist into adulthood, and even phantom species (apparently hybrid populations that now exist in the vicinity of only one parent) have been identified.

The eucalypt conveyed to Australia a special character. Marcus Clarke gave it poetic expression as “Weird Melancholy.” Here, where “flourishes a vegetation long dead in other lands,” is found the “Grotesque, the Weird, the strange scribblings of nature learning how to write,” a “phantasmagoria of that wild dreamland termed the Bush.” Others described or cursed it in more prosaic language, but no one could deny that Australia was different and that the eucalypt was to a large extent both cause and symbol of that difference. But if the eucalypt animated the bush, fire animated the eucalypt. The abrupt, smothering rise in Eucalyptus pollen that accompanied the scleroforest revolution paralleled an equally sudden increase in charcoal.⁵

THE EUCALYPT AS SCLEROMORPH

Eucalyptus was first a scleromorph and then a pyrophyte. Of the three suballiances that comprise the genus, Monocalyptus shows the greatest adaptation to impoverished soils but displays limited tolerance for drought or hostile soil microorganisms. By contrast, Symphyomyrtus avoids the worst soils, but shows considerable tolerance toward drought and microbes. Corymbia falls somewhere in between, and was probably intermediate in the evolution of the alliance. But degraded soils were something to which most members of the Gondwanic rainforest had to adapt. Eucalyptus, however, elevated nutrient scavenging and hoarding to an art form.

The eucalypts typically developed extensive, deep roots, capable of foraging widely. Rather than target particular nutrient niches, rather than hone their search with exquisite refinement, the eucalypts processed soil catchments in volume, partially compensating for the relative poverty of soil at a restricted site. In addition, eucalypts evolved chemical and biological aids to improve access to those nutrient reservoirs, particularly phosphorus, that did exist. Through various biochemical mechanisms, probably involving phosphataze enzymes or organic exudates, eucalypts could extract phosphorus from iron and aluminum compounds. Similarly, it appears that leachates from leaves and litter of some eucalypt species can percolate into the soil and mobilize phosphorus compounds that are otherwise inaccessible. And then there are the biological allies of Eucalyptus, soil microbes and mycorrhizae, that evidently improve phosphorus uptake. The scavenging eucalypt can grow where other trees starve.

Getting scarce nutrients is only half the equation. Once absorbed, eucalypts carefully, obsessively retain and recycle them. Seedlings develop lignotubers—enlarged storage organs in the roots. Here nutrients can be collected and stashed until needed. If the shoot is killed, new shoots promptly emerge. Some eucalypts retain their lignotuber into adulthood, and some can send out from it multiple stems. A lignotuber ensures that, when conditions are right for growth, the seedling will have adequate reserves of the nutrients it needs. Likewise, eucalypts store nutrients selectively within their bole. A nutrient gradient exists between inner heartwood and outer sapwood such that phosphorus, in particular, is cached where it will be most useful. If branches are destroyed, new sprouts shoot out from beneath the bark, and the nutrient reserves in the sapwood ensure that this process will be rapid. Thus not only the roots but also the crown are buffered against erratic and ephemeral changes. The effective nutrient reserve shifts from the soil alone to the tree itself and the immediate environs under its biological control. Eucalypts can thus acquire nutrients far in excess of their immediate needs, and they can cache that surplus for years, perhaps as long as a decade. When young, eucalypts prefer mechanisms of internal cycling; when more mature, cycling between the soil and the tree.

Recycling occurs as well in the crown. A eucalypt canopy is dynamic: old branches become senescent and die back, while new branches immediately spring forth from epicormic sprouts lodged just under the protective bark. The crown is thus continually reshaped for maximum efficiency, and nutrients are reabsorbed before the branch is vulnerable to breakage and loss. As an evergreen, the eucalypt retains its leaves, shedding them as infrequently as possible, tenaciously hoarding their precious supply of nutrients. Instead, eucalypts shed their impoverished bark. When leaves do fall, they are drained of vital nutrients to the fullest extent possible before deposition. And once on the ground, leachates from the crown quickly return residual nutrients to the tree through the soil.

These adaptations served Eucalyptus well during the Great Upheaval. The particular mechanisms it favored for the foraging and cycling of nutrients did double duty for water. But there were greater variances in coping with aridity; the range of responses to water stress among eucalypts exceeded their range of responses to soil degradation. In fact, Eucalyptus is not a true drought evader. Eucalypts do not close their leaf stomata, go into seasonal hibernation, or shed their leaves. Instead they tolerate drought. They search out new water sources, hoard existing reserves, shut down nonessential processes. When drought comes, they tough it out.

Like all the scleromorphs, eucalypts have hardened leaves that reduce moisture loss. (The same is true for the operculum, from which derives the name Eucalyptus—from the Greek eu, meaning “well,” and kalyptos, “covered.”) Their canopy drapes downward, evading excessive leaf temperatures. Their vast, plunging root systems; their lignotubers; the capacity of seedlings to reside in apparent dormancy within lignotubers for years, even decades; their ability to shrink their leaf stomata to reduce transpiration and conserve water—all ensure the survival of the eucalypt within a land that is seasonally dry or episodically blasted by drought. But eucalypts have a harder time conserving water than nutrients. Their physical geography is thus limited, in some regions, by cold and in others by water. Where aridity becomes chronic and pronounced, eucalypts surrender to grasses, scleromorphic shrubs like saltbush, and that prolific rival, Acacia.

Its acquired traits were adequate to keep Eucalyptus alive during the eons of soil impoverishment, and they were enough, within the context of the Great Upheaval, to liberate eucalypts among the emergent scleroforest. The reformation in the physical environment meant a reformation in the biotic environment as well, and organisms had to accommodate to both circumstances. The eucalypts were supreme opportunists, infiltrating sites more and more frequently disturbed. As they broadened their domain, entire biotas had to reorganize around the defining properties of Eucalyptus. Eucalypts were too effective as scavengers and as hoarders of scarce nutrients and water to ignore. They were aggressive competitors—and a vital focus for grazing by insects, mammals, and birds. They concentrated bionutrients into particular forms; their hard gum nuts, for example, were accessible to some species and not to others. They created special niches and coevolved unique associations with koalas, termites, possums, and parrots; while eucalypts covered 25 percent of the surface of Australia, they harbored some 50 percent of its avifauna. The patterns of eucalypt forests defined the structure of critical habitats; the processes of eucalypt life determined the flow of nutrients and water.

If they wished to survive, other organisms had to seek out an accommodation with the Universal Australian. But the revolution did not end with the breakup of rainforest into scleroforest. The last 20,000 years—the epoch of the eucalypt revolution—have been marked by massive biotic realignments and extinctions. Each stress inspired others. Selective aridity encouraged fire, and fire fostered another suite of conditions, both abiotic and biotic. If they wished to survive, flora and fauna had to adapt not only to fire in the abstract but to the kinds of fire their scleromorphic neighbors supported. How their associates burned and reproduced determined in no small way the kind of fire they confronted. Amid fire the eucalypts flourished.⁶

THE EUCALYPT AS PYROPHYTE

The spread of Eucalyptus traced the spread of fire. Charcoal and eucalypt pollen march side by side in the geologic record of the late Pleistocene and Holocene. Fire proliferated across the spectrum of Old Australian biotas—in scleroforest of course, but also in the grasslands, the acacia-splattered savannas, the heaths; it rolled back the rainforest into sharply bounded sanctuaries. The environments were varied, and so, not surprisingly, were the responses even among the prolific eucalypts.

Those inherited traits for contending with deteriorating soils and unreliable water preadapted the genus to survive fire. It knew how to cope with irregular nutrient fluxes, with an erratic tempo of too much and too little. Its quest for water already plunged roots safely out of the way of surface fires. Its weedy ancestry had groomed the eucalypt into an opportunist, ready to seize disturbed, opened sites. Eucalypts could capture nutrients released by fire, could store them until another release, could in emergencies live off internal caches in heartwood and lignotuber. Bark was thick, tough, and it shed as it burned like the ablation plate of a descending spacecraft. If branches were seared off, new ones could sprout from beneath the protected layer. If the bole burned, new trunks could spring from the buried lignotuber. A eucalypt could pour old nutrients into new growth, even as it scavenged liberated minerals from freshly burned ground. Fire could, for a couple of years, purge hostile microbes from the site; it might encourage better percolation of groundwater; it opened an area to sunlight, allowing the sun-worshiping eucalypt seedlings a chance to outgrow more shade-tolerant rivals. For most eucalypts, fire was not a destroyer but a liberator.

There were differences between fire and other pressures toward sclerophylly. Fire acted on a scale of minutes or hours, not over decades or millennia or eons. It was also interdependent with life in ways that leaching and drying were not. Soils degraded regardless of vegetative cover. Droughts arrived and departed whether there was anything on the surface or not; rocks or rainforest, it mattered little, for while organisms could alter the surface concentrations of minerals and water, while they could modulate the force of climate, they could not prevent rain or drought from appearing. But fire could only thrive in the presence of organic fuels. The character of those fuels profoundly influenced the character of the fires that resulted. And those fires, in turn, shaped the kind of biotas on which the fires fed. Fire and flora entered into a process of mutual selection, of positive reinforcement, that was far more rapid, intimate, and compelling than any of the relationships that preceded it.

Eucalyptus was excellent at extracting and hoarding precious nutrients; but so were most of the Australian flora. It was successful at persevering through dry seasons and episodic droughts; but so, again, were the other scleromorphs. Eucalypts, in fact, tended to occupy the relatively better sites of Old Australia—shunning the driest, the worst waterlogged, the most nutrient-degraded. In none of these attributes was there anything to account for its extraordinary ubiquity or its supremacy within the scleroforest. What made the eucalypt special was its extraordinary opportunism, a relationship reinforced by fire. Eucalypts accepted wretched soils and tolerated drought, but they thrived amid fire.

A eucalypt forest became a fire forest. The alliance between Eucalyptus and fire compelled other organisms to respond likewise to fire—and not just to any and every fire, but to fires occurring at certain seasons and across a specified range of frequencies and intensities, a fire ensemble to a considerable extent dictated by the burning properties of the eucalypt and its scleromorphic associates. No organism could survive in Quaternary Australia because of its fire-hardiness alone; but it became equally, increasingly true that generic sclerophyllous traits were by themselves inadequate. Fire was too sudden, too powerful. Fire could even allow the eucalypt, within limits, to defy climatic oscillations, to preserve a relatively dry environment against pressures to restore elements of rainforest or araucarian forest. This apparently explains the otherwise anomalous persistence of Eucalyptus and scleroforest pollen at Lake George on the Atherton Tableland during the wet cycle of the last glaciation. The growing prevalence of fire revolutionized the internal relations among the scleromorphs.⁷

As Pleistocene inflected into Holocene, Eucalyptus was primed for a biological explosion. Once torched, the burning bush resembled a spiral nebula, its fuels and fires like paired arms locked into an accelerating vortex. Anything that altered the bush altered the regime of fire. Any change in fire behavior, timing, or frequency rippled throughout the entire biota. One encouraged the other. Unlike many organisms—Acacia, for example—Eucalyptus did not mold microenvironments unfavorable to fire, or shape fuel complexes unlikely to burn routinely, or inhibit those environmental parameters that supported free-burning fire. It burned readily, greedily, and gratefully. A fire weed had discovered a fire continent.

The Universal Australian became the archetypal fire colonizer of Australia. Granted a certain abundance of water, its range was limited by fire, and fire, by the prevalence of ignition. The Pleistocene revolution dramatically expanded those sources of ignition. With fire the genus Eucalyptus and the genus Homo had common cause and shared a common future.

THE EUCALYPT AS EMIGRANT

Eucalyptus is almost, but not quite, confined to Australia, and the exceptions are revealing. A few eucalypts have crossed the Torres Strait (or its land bridge, the Sahul) northward, and an extraordinary quantity of eucalypts have, through human efforts, become established throughout the world. The contrast between the natural and the anthropogenic—the extra-Australian eucalypts and the emigrant eucalypts—is expressive.⁸

Some ten species of eucalypts have infiltrated northward, half of which belong to the Corymbia subgenus, and half to the Symphyomyrtus—the later branches of the grand Eucalyptus alliance to emerge. They represent, that is, Australian indigenes that have attempted to occupy extra-Australian sites. Some probably crossed the Sahul, the shallow plains that, from time to time, have joined northern Australia to Papua New Guinea. Others may have colonized afterward, a product of catastrophic windstorms that biologically bridged the strait. Of the ten, four are still found in Australia, and only two exist outside the provenance of Gondwanic Australia before it sutured with the Sunda arc.

The New Guinea eucalypts claim drier sites, outliers of rainforest. In effect, they have rediscovered more ancient niches, not unlike those that species of Eucalyptus occupied during the early tremors of the Great Upheaval. They are minor, marginal constituents of New Guinean rainforest. All but E. deglupta live in monsoonal climates where fire is seasonally important. Two species, however, continued their move away from Australia. E. urophylla entered Timor, the Lesser Sunda Islands, and New Caledonia. It claims seasonally dry or disturbed sites, but it shows few of the typical eucalypt traits, and it competes poorly with other scleromorphs of the Myrtaceae family such as Melaleuca.

By contrast, E. deglupta penetrated into New Britain, New Ireland, the Celebes, and the Philippines—the only eucalypt to cross the classic Wallace Line. In the process it shed most of its Australian traits and entered the rainforest, thronging gregariously onto wet, lowland sites. No longer did it seek out niches thrown up by disturbance or seasonal aridity; it chose another, alternative path. The farther it distanced itself from Australia, the further it sloughed off those attributes that accounted for the dominance of Eucalyptus within Australia. As a result, neither E. urophylla nor E. deglupta survived in Australia, and may, in fact, have emerged outside Australia altogether. E. deglupta, in particular, lost completely any affiliation for fire. Fire destroyed it.

Clearly the special status of Eucalyptus within Australia depended on its special circumstances—its isolation, its pattern of disturbance and aridity. Yet, paradoxically, this most indigenous of Australian flora has been successfully transplanted not only throughout ancient Gondwana but into Eurasia, Africa, and North and South America. In the early years the French more than the British actively promoted eucalypts (most often E. globulus, the blue gum). It was hoped that gums would become a valuable hardwood, provide fuelwood, assist agriculture by establishing windbreaks and shelterwoods, and decorate the countryside with attractive ornamentals. Eucalypt oil was promoted for medicinal and commercial purposes, as an antimalarial agent and as a chemical base for perfumes. French explorers to Australia returned to Paris with seeds, and from the Jardin des Plantes eucalypts were propagated throughout the Mediterranean littoral. Britain soon followed suit, moving Eucalyptus out of the category of an ornamental for estate aboriculture and extending it through Kew Gardens into its African and Asian colonies. Italy, in turn, became another center for export, largely into North Africa. The Trappist monks of the Tre Fontane monastery inaugurated perhaps the most celebrated experiment when, in 1868, they planted thousands of eucalypts in the Pontine Marshes in the pious hope that the mysterious, aromatic “gums” would purge the miasmic swamps of malaria. Only with the accession of the indefatigable Ferdinand von Müller to the status of colonial botanist in Victoria did Australia become an active distributor.

About twenty to thirty species define the emigrant eucalypts. Their chief liability is their intolerance to extreme cold—a reason why their range in central and alpine Australia is restricted, and another legacy of their Gondwanic heritage in a rainforest and of Australia’s migration toward the equator. But in Mediterranean climates, especially, Eucalyptus has proliferated. It thrives in Spain, Portugal, Italy, Turkey, Israel, and such islands as Corsica and Cyprus. It has been widely planted in Africa—the northern littoral of the Mediterranean, the southern and eastern veldt, the Ethiopian plateau, the Congo basin. Eucalypt plantations are extensive in Brazil, and they have reclaimed otherwise denuded plains in Chile, Ecuador, and Argentina. Gums are grown in China and India, where they are praised as fast-growing fuelwood and cursed as thirsty aliens. Eucalypts clothe patches of the Coast Ranges of California, where they were promoted by various interests (including the Southern Pacific Railroad), often as a surrogate for that enduring California passion, real-estate speculation. Eucalyptus has successfully transplanted to a panoply of islands from Madagascar to Mauritius, from Sri Lanka to the Seychelles, from Easter Island to Alcatraz. Eucalypts grace the royal palaces at Katmandu and Addis Ababa. Where Australian soldiers have fallen on foreign battlefields, local gravesites are framed with eucalypts. (Poignantly, they refuse to grow on the cold flanks of Gallipoli.)⁹

The reasons for the success of the emigrant eucalypts are several. They flourish in climates similar to those they knew in Australia. They were often unpalatable to local browsers (even goats). No less, there exists a strong fertility gradient between Australia and most other lands such that it is often easier to export indigenous plants from Australia than to import exotics into it. Only a special suite of organisms could thrive under Australian conditions, and then primarily if the native biotas were upset beyond their normal tolerances. But transplanting flora like eucalypts that had evolved in a nutrient-deprived and droughty environment into relatively rich, well-water sites was a formula for successful colonization. The outcome could be extraordinary. Between 1950 and 1974, for example, eucalypt plantations increased worldwide (including China) from 0.7 million to 3.7 million hectares—and continue to rise.

It is probable, too, that its alliance with humans explains the ubiquity of eucalypts in Australia. They moved overseas because humans took them into compatible environments. They did not have to transcend endless oceans or navigate through rainforest, a biota they had abandoned during their evolutionary history: they could appear directly on suitable sites. In most cases, those sites could not offer worse conditions of soil and aridity than they had known in Australia. Native organisms were kept off balance, the site chronically manipulated, by human intervention. With a few exceptions, free-burning fires were less pervasive, and when they came, they inflicted less damage than on native trees.

Its enlarged dominion has had a cost, however. The eucalypts’ interdependence with humans could not eliminate their more ancient interdependence with fire. They continued to behave as though fire were still a principal ally, persisted in littering fuels as though surface fires routinely passed over them, acted as though fire would remain instrumental in purging the biota of competitors, in restoring conditions for regeneration, in recycling scarce nutrients. Those environmental conditions that allowed emigrant eucalypts to prosper so gloriously also encouraged an excess of unchecked fuels. Interestingly, other fire-hardened scleromorphs from Australia like Casuarina and Melaleuca have also become major fireweeds in such exotic landscapes as south Florida. But these were weeds, unwanted escapees, not assisted emigrants.¹⁰

The environments that encourage eucalypt plantations also encourage eucalypt-dominated fire regimes. Not only commercial plantations, but other environments receptive to eucalypts have witnessed a rise in fire hazard. The transported eucalypts shed fuel as though they expected to burn. The Berkeley fire of 1923, which consumed about a fourth of the city and entered the University of California campus, was propelled in part by windfall and litter from extensive eucalypt plantings. The scene had little improved when an Australian fire specialist visited the Bay Area in the 1960s. Familiar with the intensity of eucalypt fires in their native setting, he gasped at the specter that greeted him—the intermixture of houses and giant eucalypts, branches and bark piled deep, a surreal scleroforest composed equally of Eucalyptus and houses. Shaken, he abandoned the conference tour and retired to his motel room, his head spinning with visions of holocaust.¹¹

THE EUCALYPT AS AUSTRALIAN

The Australian bush owes its peculiarity, more than anything else, to Eucalyptus. No other continental forest or woodland is so dominated by a single genus. Other biomes on Earth have scleromorphs, most have grasses, and few are spared wholly from fire, but none has the combination that exists in Australia and has given the bush its indelible character. Eucalyptus is not only the Universal Australian, it is the ideal Australian—versatile, tough, sardonic, contrary, self-mocking, with a deceptive complexity amid the appearance of massive homogeneity; an occupier of disturbed environments; a fire creature.

But the ideal Australian is also the typical Australian. Its peculiar strengths delineate as well its weaknesses. The hostile environmental conditions that pushed the biota toward sclerophylly, the chronic disturbances that at once simplified and complicated the biotic ensemble, the alliance with fire that allowed a single genus to overrun a continent—all these were enormous strengths so long as those informing circumstances remained more or less in force. While the domain of fire in Australia had expanded, it ruled within an evolved order. If, however, those pressures were removed, if new biotic elements were introduced or significant portions extirpated, if the fire regime were reconstituted by new fuels or new sources of ignition, then those special traits could become liabilities.¹²

The bush was perhaps too dominated by Eucalyptus, and Eucalyptus perhaps too closely reliant on fire and, through fire, on Homo. The eucalypt was less a pyrophyte than a pyrophiliac: fire became a near addiction with its own peculiar perils. The tendency was to create more fire, as though the biotas linked by eucalypt and fire were a kind of chain letter, a leveraged biotic buyout sustained by ever-increasing infusions of fire. Any reform in the fire regime would upset not only the status of Eucalyptus but the entire bush. And in this complex biotic chemistry lies the colossal significance of the genus Homo, advancing on Pleistocene Australia with bold firesticks.