1. The relationships between productivity, fire frequency and fire severity shape the distribution of plant communities globally. Dry forests are expected to burn frequently and wet forests to burn infrequently. However, the effect of productivity on intensity and severity of wildfire is less consistent and poorly understood. One productive ecosystem where this is especially true is the Australian tall wet Eucalyptus-dominated forest (TWEF), which spans wet areas across the continent. This study aims to characterise how climate shapes the likelihood of low- and high-severity wildfire across Australian TWEF.
2. We performed a continental-scale analysis of fuels in 48 permanent plots in early-mature stage TWEF across four climate regions in Australia. We estimated fuel loads and measured understorey microclimate. We then obtained historical fire-weather observations from nearby meteorological stations and used fuel moisture and fire behaviour equations to predict the historical frequency with which TWEF could burn and what fire severities were expected. We investigated how this varies across the different TWEF climate regions. Lastly, we validated our approach by remeasuring eight plots that burned unexpectedly post-measurement.
3. We found that surface fuels in cooler, moister regions were available to burn 1–16 days per year historically, with only low-severity, surface fire possible most of these days: high-severity fire was only possible under rare, extreme fire-weather conditions. However, in warmer, drier regions, fuels were available to burn 23–35 days annually, and high-severity fire was more likely than low-severity fire. Validation showed that we slightly overestimated flame heights, inflating high-severity risk estimates. If we used elevated fuel loads to predict flame heights, however, high-severity fire was more likely than low-severity fire everywhere. Lastly, the likelihood of high-severity fire increased with increasing temperature and worsening fire weather.
4. Synthesis. Fire activity in early-mature TWEF is limited by climatic constraints on fire weather and availability to burn, with high-severity fire more likely in warmer, drier regions than in cooler, wetter ones. This indicates a particularly worrisome vulnerability to climate change, given TWEF's diminished ability to recover from disturbance in a warmer world. The occurrence of both low- and high-severity fire means the fire regimes of TWEF are best described as mixed severity.

中文翻译：

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澳大利亚巨大桉树林地理范围内火灾严重程度的生物气候驱动因素

1. 生产力、火灾频率和火灾严重程度之间的关系塑造了全球植物群落的分布。预计干燥的森林会经常燃烧，而潮湿的森林则很少燃烧。然而，生产力对野火强度和严重程度的影响不太一致，也知之甚少。一个尤其如此的生产生态系统是澳大利亚高大的湿桉树为主的森林 (TWEF)，它横跨整个大陆的潮湿地区。本研究旨在描述气候如何影响澳大利亚 TWEF 发生低度和高度野火的可能性。
2. 我们在澳大利亚四个气候区的早熟阶段 TWEF 的 48 个永久地块中对燃料进行了大陆尺度分析。我们估计了燃料负荷并测量了下层小气候。然后，我们从附近的气象站获得了历史火灾天气观测数据，并使用燃料湿度和火灾行为方程来预测 TWEF 燃烧的历史频率以及预期的火灾严重程度。我们调查了这在不同的 TWEF 气候区域中是如何变化的。最后，我们通过重新测量测量后意外燃烧的八个图来验证我们的方法。
3. 我们发现，历史上较冷、较潮湿地区的地表燃料每年可燃烧 1-16 天，但在这些天的大部分时间里，只有低严重程度的地表火灾可能发生：高严重程度的火灾仅在罕见的极端火灾天气下才有可能发生使适应。然而，在较温暖、较干燥的地区，燃料每年可燃烧 23 至 35 天，高烈度火灾比低烈度火灾更有可能发生。验证表明，我们略微高估了火焰高度，夸大了高危风险估计。然而，如果我们使用升高的燃料负荷来预测火焰高度，那么到处都是高严重性火灾比低严重性火灾的可能性更大。最后，随着温度升高和火灾天气恶化，发生高强度火灾的可能性也增加。
4. 合成。早熟 TWEF 的火灾活动受到火灾天气和可燃性气候限制的限制，在温暖、干燥的地区比在凉爽、潮湿的地区更容易发生高强度火灾。鉴于 TWEF 在变暖的世界中从干扰中恢复的能力减弱，这表明它对气候变化的脆弱性尤其令人担忧。低烈度和高烈度火灾的发生意味着 TWEF 的火灾状况最好被描述为混合严重度。