Large, high-severity wildfires, or ‘megafires’, occur periodically in arid Australian spinifex (Triodia spp.) grasslands after high rainfall periods that trigger fuel accumulation. It has been suggested that these fires are unprecedented in the modern era and were formerly constrained by Aboriginal patch-burning that kept landscape fuel levels low. This assumption deserves scrutiny, as evidence from fire-prone systems globally indicates that weather factors often the primary determinant behind megafire incidence, and that fuel management does not mitigate such fires during periods of climatic extreme. We reviewed explorer’s diaries, anthropologist’s reports, and remotely sensed data from the Australian Western Desert for evidence of large rainfall-linked fires during the pre-contact period when traditional Aboriginal patch-burning was still being practiced. We used only observations that contained empiric estimates of fire sizes. Concurrently, we employed remote rainfall data and the Oceanic Niño Index to relate fire size to likely seasonal conditions at the time the observations were made. Numerous records were found of small fires during periods of average and below-average rainfall conditions, but no evidence of large-scale fires during these times. By contrast, there was strong evidence of large-scale wildfires during a high-rainfall period in the early 1870s, some of which are estimated to have burnt areas up to 700 000 ha. Our literature review also identified several Western Desert Aboriginal mythologies that refer to large-scale conflagrations. As oral traditions sometimes corroborate historic events, these myths may add further evidence that large fires are an inherent feature of spinifex grassland fire regimes. Overall, the results suggest that, contrary to predictions of the patch-burn mosaic hypothesis, traditional Aboriginal burning did not modulate spinifex fire size during periods of extreme-high arid zone rainfall. The mechanism behind this appears to be plant assemblages in seral spinifex vegetation that comprise highly flammable non-spinifex tussock grasses that rapidly accumulate high fuel loads under favorable precipitation conditions. Our finding that fuel management does not prevent megafires under extreme conditions in arid Australia has parallels with the primacy of climatic factors as drivers of megafires in the forests of temperate Australia.

中文翻译：

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与降雨有关的大火是澳大利亚干旱的菠菜（Triodia spp。）草原的先天性火政要素

高雨量引发燃料积累后，澳大利亚干旱的菠菜（Triodia spp。）草原会定期发生大型，高强度的野火，即“大火”。有迹象表明，这些大火在现代是史无前例的，以前曾受到原住民斑块燃烧的限制，这些燃烧使景观燃料水平低下。这一假设值得仔细研究，因为全球易火系统的证据表明，天气因素通常是造成大火发生的主要决定因素，并且在气候极端时期，燃料管理并不能减轻此类大火的发生。我们审查了探险家的日记，人类学家的报告，以及来自澳大利亚西部沙漠的遥感数据，以证明在仍在进行传统土著补丁燃烧的预接触期间发生了与降雨有关的大火。我们仅使用了包含火势经验估计值的观测值。同时，我们采用了偏远的降雨数据和大洋Niño指数，将火势与观测时的可能季节状况联系起来。在平均水平和低于平均水平的降雨条件下，有许多火灾的记录，但在这段时间内没有大规模火灾的迹象。相比之下，有强有力的证据表明，在1870年代初期的大雨期间发生了大规模的野火，据估计其中一些烧毁了70万公顷的土地。我们的文献综述还确定了一些涉及大规模大火的西方沙漠土著神话。由于口头传统有时佐证了历史性事件，这些神话可能会提供进一步的证据，证明大火是棘刺草原火灾制度的固有特征。总的来说，结果表明，与斑片烧花叶假说的预测相反，传统的原住民燃烧在干旱区降雨量极高的时期并不能调节棘齿的火势。其背后的机制似乎是在脊柱藻类植被中的植物组合，其中包括高度易燃的非菠菜草，它们在有利的降水条件下迅速积聚了高燃料负荷。