Fire risk and severity decline with stand development in Tasmanian giant Eucalyptus forest
Fire risk and severity decline with stand development in Tasmanian giant Eucalyptus forest
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塔斯马尼亚巨型桉树林的火灾风险和严重程度随着林分的发展而下降
DOI：
10.1016/j.foreco.2021.119724
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发表时间：
2021
影响因子：
3.7
通讯作者：
D. Bowman
中科院分区：
文献类型：
--
作者：
J. Furlaud;L. Prior;G. Williamson;D. Bowman
森林火灾风险及其随时间的变化对森林动态具有重要影响。描述火灾风险如何随着林分发展而变化的两个常见模型（称为可燃性函数）是（a）“湿度模型”，其中火灾风险最初增加，然后随着火灾后林分的发展而降低，以及（b）“奥尔森模型”，其中火灾风险作为自上次火灾以来的时间函数渐近增加。这两个可燃性函数都被用来描述世界上最高的被子植物森林——澳大利亚高湿桉树森林（TWEF）。然而，尚不清楚哪种功能更适合 TWEF，因为很少有经验数据描述燃料和小气候，而这两个因素在这些森林的漫长生命周期中对火灾风险和潜在严重程度有重要影响。因此，我们使用澳大利亚塔斯马尼亚东南部的 TWEF 林分的时间序列来了解从再生林到老林的四个林分发展阶段中燃料、小气候以及由此产生的火灾风险和潜在火灾严重程度的变化。我们测量了燃料负荷、林下小气候和森林地貌。然后，我们将这些数据与历史火灾天气数据和火灾行为模型结合使用，以估计历史上发生低严重程度和高严重程度火灾的频率。我们还调查了先前骚乱的严重程度是否影响了随后发生严重火灾的可能性。我们发现，虽然燃料负荷在整个时间序列中保持不变，但后期的开发阶段的下层植被明显更加湿润，雨林树木的数量增加，并且垂直不连续的燃料更加丰富。这些因素导致火灾风险显着降低，早期阶段更有可能发生严重火灾。此外，我们发现，由于缺乏剩余的成熟树冠，由林分替换火灾引发的林分比那些经历过非林分替换火灾的林分更容易遭受随后的严重火灾。我们的结论是，与大多数其他依赖火的生态系统（奥尔森曲线是合适的模型）不同，TWEF 中的可燃性函数最好由湿度模型来描述。我们的研究结果表明，TWEF 很容易受到“景观陷阱”效应的影响，即强烈的干扰会造成大面积的再生林，从而增加发生高强度火灾的风险，从而增加了整个景观范围内人口崩溃的可能性。我们建议火灾和森林管理结合模仿低严重干扰的技术，以创造更具弹性的景观。
Forest fire risk, and how it changes over time, has important influences on forest dynamics. Two common models describing how fire risk changes with stand development, known as flammability functions, are (a) the ‘moisture model’, where fire risk initially increases, then decreases, as a stand develops after a fire, and (b) the ‘Olson model’, where fire risk increases asymptotically as a function of time since previous fire. These two flammability functions have both been used to describe the world’s tallest angiosperm forest, the Australian tall wetEucalyptusforest (TWEF). It is unclear, however, which function is more appropriate for TWEF, as there are little empirical data describing fuels and microclimate, two important influences on fire risk and potential severity, across the long lifespan of these forests. Accordingly, we use a chronosequence of TWEF stands in southeast Tasmania, Australia, to see how fuels, microclimate, and resulting fire risk and potential fire severity changed amongst four stand-development stages ranging from regrowth to old forests. We measured fuel loads, understorey microclimate, and forest physiognomy. We then used these data with historical fire weather data and fire behaviour models to estimate how often low- and high-severity fire was possible historically. We also investigated if the severity of the previous disturbance influenced the likelihood of a subsequent high-severity fire. We found that, while fuel loads remained unchanged across the chronosequence, later development stages had a significantly moister understorey, an increased abundance of rainforest trees, and more vertically discontinuous fuels. These factors resulted in a significantly reduced fire risk, with high-severity fire much more likely in the early stages. Further, we found that stands that had been initiated by stand-replacing fire were more susceptible to subsequent high-severity fire than those that experienced non stand-replacing fire, due to a lack of a remaining mature canopy. We concluded that, unlike most other fire-dependent ecosystems where the Olson curve is an appropriate model, the flammability function in TWEF is best described by the moisture model. Our results indicate that TWEF is vulnerable to a ‘landscape trap’ effect, where intensive disturbance creates large areas of regrowth stands with increased risk of high-severity fire, which increases the likelihood of landscape-wide, demographic collapse. We suggest that fire and forest management incorporate techniques mimicking low-severity disturbances to create more resilient landscapes.