Burning Bush. Stephen J. Pyne
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Название: Burning Bush
Автор: Stephen J. Pyne
Издательство: Ingram
Жанр: Журналы
Серия: Weyerhaueser Cycle of Fire
isbn: 9780295998831
isbn:
Its fire history sums up the rainforest’s various stabilities. In tropical rainforest leaves make up probably 80 percent of the surface fuels and biological agents quickly decompose them. What persists is sparse, perennially wet, and sheltered from dry winds. When fires reach the rainforest border they flash against a green wall, gasp helplessly for fuel, and expire. If rainforest advances or retreats, it does so as a unit in response to broad shifts in climate. Changes in the dry season—greater moisture, fewer fires—allow the rainforest to advance into scleroforest and savanna. The reverse allows fire to eat a little farther into the frontier. Blowdowns along the border open the canopy, dry out surface fuels, and allow fires that normally flame out along the perimeter to enter into the interior according to a scenario that may become irreversible. The burn alters microclimates; fireweeds and pyrophytes invade the site; the new fuels carry additional fires over the burn and incinerate those slow-growing rainforest flora that demand shade and moisture.
In temperate regions, succession into and out of rainforest is less sharply defined. The borders blur; rainforest intercollates with wet scleroforest. Undisturbed, wet scleroforest will pass, over the course of several centuries, into rainforest. Disturbed—burned—it reverts to scleroforest or scleroscrub. What actually exists on any particular site reflects the unique sequencing of its past fires. Small sites are especially susceptible to irreversible change. Once initiated, a rhythm of frequent fire encourages soil erosion and the loss of nutrient capital. This encourages scleromorphs, which accept more fire. In such a scenario wet scleroforest degenerates into dry scleroforest, scleroscrub, or savanna, and rainforest no longer possesses the means to reclaim the site. Without refugia, rainforest vanishes.17
If its heath miniaturizes Australia’s fire geography, its rainforest miniaturizes its fire history. The uniformity of the Gondwana rainforest fractured under the impress of isolation, aridity, and disturbances. Increasingly, the principal disturbance and the great integrator of new conditions—fire—shaped those new regimes. The fragmentation continued, like rocks spalling off a heated cliff. From it came the unique species and unexampled biotas of Old Australia. With the relict rainforest, the story comes full circle. The flames licking at the wet flanks of tropical vine forest or overturning wet scleroforest on a rhythm of centuries are recapitulating a cycle of fire begun with the Great Upheaval.
4
Land of Contrarities
Drought, dry seasons, and, more than all—that deadliest weapon of the tyrant—the bush-fire, reduces and selects the life of the country.
—W.H.L. RANKEN, The Dominion of Australia (1874)
The aspect of the country was fearful. Brown, burnt-up, and sweltering under a broiling sun! … Imagine all the trees and scrub high above your head blazing—all the ranges, as far as the eye can reach, one mass of smoke and fire.
—MARCUS CLARKE, letters
IN ITS ORIGINS, ancestral Australia was all but indistinguishable from the rest of Gondwana. Its biota was similar, if not identical; its climate was mild and wet; its seasons, invariant. But the breakup of the supercontinent had led, inevitably, to changes that demanded, and forged, new identities. Leaching, drying, and burning, each in turn and with cumulative impact, worked over Australia’s Gondwanic legacy. The tempo of disturbance quickened and beat to irregular rhythms. Isolation ensured that recolonization was negligible, that new biotas would have to evolve from the inherited stocks. The Great Upheaval installed to dominance a dramatically different biota. A second revolution within the emergent scleroforest furthered and confirmed that transformation. After Homo infiltrated the continent, the process was irreversible. Out of Gondwana rainforest emerged, through these trials, Australian bush.
By the time Europeans arrived, the bush presented an inverted world, a parallel universe. It was as if a second ark had escaped the Flood, as though a whole continent had passed through an enchanted looking glass. Compared to northern Europe, Australia exuded the alien, the hostile, the sterile, the bizarre. François Peron alluded to “whimsical freaks of Nature” that defied attempts at scientific understanding. James O’Hara disparaged a Nature that apparently “indulged in whim,” such that nothing—neither animal nor vegetable—resembled anything anywhere else. Charles Darwin mused that here at the antipodes “an unbeliever in everything beyond his own reason might exclaim, ‘surely two distinct Creators must have been at work.’” Marcus Clarke invoked a “Weird Melancholy” to conjure the spirit of the bush, later softening that cry with an appeal to “read the hieroglyphs of haggard gum-trees.” Perhaps the most famous denunciation, already couched in sardonic tones, was the declaration of an anonymous colonial poet of the 1850s:
There is a land in distant seas
Full of all contrarities.1
The nature of Australian exceptionalism was difficult to identify precisely. It was there in the bush, certainly, though the bush echoed bits and pieces of other Gondwanic lands. It meant coming to grips with miserable soils, aridity, desert winds. And, everyone agreed, it involved bushfire. Whatever elements led to the bush, fire integrated and accelerated, like a flask of chemicals held over a Bunsen burner. By geologic standards, the bush was a sudden invention, kindled almost instantaneously from drying Gondwanic tinder and the flint of Homo sharply striking the continent. However the bush defined Australia, so fire defined the bush. In ways both obvious and obscure, the land of contrarities was a land of fire.
AN EVER-LIVING FIRE
The geographical border that so sharply segregates rainforest from scleroforest has a temporal analogue in the veritable explosion of fire that raged across Australia during the Holocene. Fire was abrupt, ubiquitous, grasping. It insinuated itself into malleable biotas. It welded the biotic pieces into a dynamic whole. Not fire alone but its versatility—its ability to interact with the other elements of the bush—established its importance. Fire dominated the dynamics of the Australian bush as fully as Eucalyptus dominated the composition of its forests and woodlands.
This was not inevitable. Had Australia rafted into the tropics at a different rate, had its initial floristic composition not included so many scleromorphs, had Acacia replaced the ancestral Eucalyptus as part of the original Gondwanic ark, had Australian soils experienced more general rejuvenation, had other species leaked across its borders, the story might have turned out differently. Instead fire seized the core, not merely recycling habitats and nutrients but diverting the whole biota into new evolutionary pathways from which recovery might be impossible. Fire integrated the elements of the bush, and anything that affected the presence of fire ramified throughout the bush. Above all, fire bonded the bush to humans. The bush could not be understood without its distinctive, singular fires.
But fire did not by itself render Australia a land of contrarities: fire is everywhere on the planet. The evolution of the Earth into a fire planet has paralleled the evolution of life. Marine life gave it an oxygenated atmosphere; terrestrial СКАЧАТЬ