Characterizing post-fire delayed tree mortality with remote sensing: sizing up the elephant in the room

IF 3.6 3区 环境科学与生态学 Q1 ECOLOGY Fire Ecology Pub Date : 2023-10-26 DOI:10.1186/s42408-023-00223-1
Matthew J. Reilly, Aaron Zuspan, Zhiqiang Yang
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Abstract

Abstract Background Despite recent advances in understanding the drivers of tree-level delayed mortality, we lack a method for mapping delayed mortality at landscape and regional scales. Consequently, the extent, magnitude, and effects of delayed mortality on post-fire landscape patterns of burn severity are unknown. We introduce a remote sensing approach for mapping delayed mortality based on post-fire decline in the normalized burn ratio (NBR). NBR decline is defined as the change in NBR between the first post-fire measurement and the minimum NBR value up to 5 years post-fire for each pixel. We validate the method with high-resolution aerial photography from six wildfires in California, Oregon, and Washington, USA, and then compare the extent, magnitude, and effects of delayed mortality on landscape patterns of burn severity among fires and forest types. Results NBR decline was significantly correlated with post-fire canopy mortality ( r 2 = 0.50) and predicted the presence of delayed mortality with 83% accuracy based on a threshold of 105 NBR decline. Plots with NBR decline greater than 105 were 23 times more likely to experience delayed mortality than those below the threshold ( p < 0.001). Delayed mortality occurred across 6–38% of fire perimeters not affected by stand-replacing fire, generally affecting more areas in cold (22–41%) and wet (30%) forest types than in dry (1.7–19%) types. The total area initially mapped as unburned/very low-severity declined an average of 38.1% and generally persisted in smaller, more fragmented patches when considering delayed mortality. The total area initially mapped as high-severity increased an average of 16.2% and shifted towards larger, more contiguous patches. Conclusions Differences between 1- and 5-year post-fire burn severity maps depict dynamic post-fire mosaics resulting from delayed mortality, with variability among fires reflecting a range of potential drivers. We demonstrate that tree-level delayed mortality scales up to alter higher-level landscape patterns of burn severity with important implications for forest resilience and a range of fire-driven ecological outcomes. Our method can complement existing tree-level studies on drivers of delayed mortality, refine mapping of fire refugia, inform estimates of habitat and carbon losses, and provide a more comprehensive assessment of landscape and regional scale fire effects and trends.
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用遥感表征火灾后延迟树木死亡率:评估房间里的大象
背景尽管最近在了解树木水平延迟死亡的驱动因素方面取得了进展,但我们缺乏在景观和区域尺度上绘制延迟死亡的方法。因此,延迟死亡率对火灾后烧伤严重程度景观模式的程度、程度和影响尚不清楚。我们介绍了一种基于火灾后归一化燃烧比(NBR)下降的遥感方法来绘制延迟死亡率。NBR下降被定义为每个像元在火灾后第一次测量到火灾后5年的最小NBR值之间的NBR变化。我们用来自美国加利福尼亚州、俄勒冈州和华盛顿州的六场野火的高分辨率航空摄影验证了该方法,然后比较了火灾和森林类型中烧伤严重程度的景观模式的延迟死亡率的范围、量级和影响。结果NBR下降与火灾后冠层死亡率显著相关(r 2 = 0.50),基于105 NBR下降阈值预测延迟死亡的准确率为83%。NBR下降大于105的地块延迟死亡的可能性是低于阈值的地块的23倍(p <0.001)。延迟死亡发生在6-38%未受林分替换火影响的火周范围内,通常影响冷林(22-41%)和湿林(30%)类型的地区比干林(1.7-19%)类型的地区更多。当考虑到延迟死亡率时,最初绘制为未燃烧/非常低严重程度的总面积平均下降38.1%,并且通常持续存在更小,更破碎的斑块。最初被标记为高严重性的总面积平均增加了16.2%,并转向更大、更连续的斑块。结论:火灾后1年和5年烧伤严重程度图的差异描述了延迟死亡导致的动态火灾后马赛克,火灾之间的差异反映了一系列潜在的驱动因素。我们证明,树木水平的延迟死亡率扩大到改变烧伤严重程度的更高水平的景观格局,对森林恢复力和一系列火灾驱动的生态结果具有重要意义。我们的方法可以补充现有的树木水平的延迟死亡驱动因素研究,完善火灾避难所的地图,为栖息地和碳损失的估计提供信息,并提供更全面的景观和区域尺度火灾效应和趋势评估。
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来源期刊
Fire Ecology
Fire Ecology ECOLOGY-FORESTRY
CiteScore
6.20
自引率
7.80%
发文量
24
审稿时长
20 weeks
期刊介绍: Fire Ecology is the international scientific journal supported by the Association for Fire Ecology. Fire Ecology publishes peer-reviewed articles on all ecological and management aspects relating to wildland fire. We welcome submissions on topics that include a broad range of research on the ecological relationships of fire to its environment, including, but not limited to: Ecology (physical and biological fire effects, fire regimes, etc.) Social science (geography, sociology, anthropology, etc.) Fuel Fire science and modeling Planning and risk management Law and policy Fire management Inter- or cross-disciplinary fire-related topics Technology transfer products.
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