Throwing fuel on the fire? Contrasting fine and coarse fuel responses to windthrow in temperate eucalypt forests in south-eastern Australia

IF 3.7 2区 农林科学 Q1 FORESTRY
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Abstract

Windthrow is a disturbance in south-eastern Australian forests which significantly re-arranges forest and fuel structure by removing canopy trees. The implications for fuel dynamics and fire behaviour remains unquantified, making it a concern for fire managers. This study quantifies changes to forest and fuel structure caused by windthrow of varying severity, and uses this data to consider potential implications for fire behaviour. Thirty sites were established across dry eucalypt forests in south-eastern Australia ∼2 years after a severe windstorm resulted in extensive areas of windthrow. Ten sites were selected within each of unimpacted, low and high severity windthrow areas. Fine fuels were assessed using visual estimates of height, cover and percent dead across various fuel strata (surface; near-surface; elevated; bark) to develop fuel hazard scores using established protocols. Coarse fuels (fallen branches, logs) were assessed using a line-intercept survey. Fuel data were used to calculate expected fire behaviour (rate of spread, flame height, total heat output and residence time) across windthrow severity. The trends in both fine and coarse fuels were largely reflective of the forest structural changes induced by windthrow. Surface fuel (i.e. dead litter on the forest floor) decreased in depth and cover, while near-surface fuels increased in cover, height and proportion of dead with increasing windthrow severity. This reflects a reduction in litter inputs from reduced canopy cover, and an increase in the abundance of grasses and fallen canopy debris. Elevated fuels (i.e., shrubs) were unchanged across windthrown and unimpacted sites;bark fuel decreased with increasing windthrow severity, reflecting a reduction in standing basal area at severely impacted sites. Coarse fuel loads substantially increased with windthrow severity: high severity sites had ∼300 Mg/ha of coarse fuel loads compared to ∼20 Mg/ha at unimpacted sites. The changes in fine and coarse fuels resulted in a 1.2-fold increase in predicted flame height and a 17-fold increase in total heat output and residence time in high severity windthrow sites compared with unimpacted sites. Our research shows that windthrow produces complex and contrasting patterns in fine and coarse fuel loads, and the increase in near-surface and coarse fuels confers greater potential fire intensity via increased flame height, total heat output and residence time. Windthrow represents a conundrum for fire managers who are required to balance the reduction in fire risk while also retaining the important habitat resource fallen logs represent.

火上浇油?澳大利亚东南部温带桉树林中细粒和粗粒燃料对风推的反应对比
风倒是澳大利亚东南部森林中的一种干扰因素,它通过移除树冠层树木,极大地改变了森林和燃料结构。它对燃料动力学和火灾行为的影响仍未量化,因此引起了火灾管理者的关注。本研究量化了不同严重程度的风拔对森林和燃料结构造成的变化,并利用这些数据考虑了对火灾行为的潜在影响。在澳大利亚东南部的干燥桉树林中建立了 30 个研究点,这些研究点是在一场严重的暴风雪导致大面积风倒之后 2 年建立的。在未受影响、低严重程度和高严重程度的风卷地区各选择了 10 个地点。通过目测不同燃料层(表层、近表层、高架层、树皮层)的高度、覆盖率和枯死率,对细粒燃料进行评估,并使用既定的规程制定燃料危险评分。粗燃料(倒下的树枝、原木)采用线截面调查法进行评估。燃料数据用于计算不同风拔严重程度的预期火灾行为(蔓延速度、火焰高度、总热量输出和停留时间)。细燃料和粗燃料的变化趋势在很大程度上反映了风卷引起的森林结构变化。表层燃料(即林地上的枯枝落叶)的深度和覆盖度都有所下降,而近表层燃料的覆盖度、高度和枯枝比例则随着风害严重程度的增加而增加。这反映了树冠覆盖率降低导致的枯落物输入量减少,以及草和倒伏的树冠碎屑数量增加。高位燃料(即灌木)在受风灾和未受风灾影响的地点没有变化;树皮燃料随着风灾严重程度的增加而减少,这反映了受严重影响地点的立木基部面积减少。粗燃料负荷随着风拔严重程度的增加而大幅增加:严重程度高的地点的粗燃料负荷为每公顷 3 亿毫克,而未受影响地点的粗燃料负荷为每公顷 2 亿毫克。与未受影响的地点相比,细燃料和粗燃料的变化导致高严重性风切点的预测火焰高度增加了 1.2 倍,总热量输出和停留时间增加了 17 倍。我们的研究表明,风卷起的细粒和粗粒燃料负荷模式复杂且对比强烈,近地表和粗粒燃料的增加通过增加火焰高度、总热量输出和停留时间带来了更大的潜在火灾强度。风倒对火灾管理者来说是一个难题,他们需要在降低火灾风险与保留倒下原木所代表的重要栖息地资源之间取得平衡。
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来源期刊
Forest Ecology and Management
Forest Ecology and Management 农林科学-林学
CiteScore
7.50
自引率
10.80%
发文量
665
审稿时长
39 days
期刊介绍: Forest Ecology and Management publishes scientific articles linking forest ecology with forest management, focusing on the application of biological, ecological and social knowledge to the management and conservation of plantations and natural forests. The scope of the journal includes all forest ecosystems of the world. A peer-review process ensures the quality and international interest of the manuscripts accepted for publication. The journal encourages communication between scientists in disparate fields who share a common interest in ecology and forest management, bridging the gap between research workers and forest managers. We encourage submission of papers that will have the strongest interest and value to the Journal''s international readership. Some key features of papers with strong interest include: 1. Clear connections between the ecology and management of forests; 2. Novel ideas or approaches to important challenges in forest ecology and management; 3. Studies that address a population of interest beyond the scale of single research sites, Three key points in the design of forest experiments, Forest Ecology and Management 255 (2008) 2022-2023); 4. Review Articles on timely, important topics. Authors are welcome to contact one of the editors to discuss the suitability of a potential review manuscript. The Journal encourages proposals for special issues examining important areas of forest ecology and management. Potential guest editors should contact any of the Editors to begin discussions about topics, potential papers, and other details.
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