Rising global fire activity is increasing the prevalence of repeated short‐interval burning (reburning) in forests worldwide. In forests that historically experienced frequent‐fire regimes, high‐severity fire exacerbates the severity of subsequent fires by increasing prevalence of shrubs and/or by creating drier understory conditions. Low‐ to moderate‐severity fire, in contrast, can moderate future fire behavior by reducing fuel loads. The extent to which previous fires moderate future fire severity will powerfully affect fire‐prone forest ecosystem trajectories over the next century. Further, knowing where and when a wildfire may act as a landscape‐scale fuel treatment can help direct pre‐ and post‐fire management efforts. We leverage satellite imagery and fire progression mapping to model reburn dynamics within forests that initially burned at low/moderate severity in 726 unique fire pair events over a 36‐year period across four large fire‐prone Western US ecoregions. We ask (1) how strong are the moderating effects of low‐ to moderate‐severity fire on future fire severity, (2) how long do moderating effects last, and (3) how does the time between fires (a proxy for fuel accumulation) interact with initial fire severity, day‐of‐burning weather conditions, and climate to influence reburn severity. Short‐interval reburns primarily occurred in dry‐ and moist‐mixed conifer forests with historically frequent‐fire regimes. Previous fire moderated reburn severity in all ecoregions with the strongest effects occurring in the California Coast and Western Mountains and the average duration of moderating effects ranging from 13 years in the Western Mountains to >36 years in the California Coast. The strength and duration of moderating effects depended on climate and initial fire severity in some regions, reflecting differences in post‐fire fuel accumulation. In the California Coast, moderating effects lasted longer in cooler and wetter forests. In the Western Mountains, moderating effects were stronger and longer lasting in forests that initially burned at higher severity. Moderating effects were largely robust to fire weather, suggesting that previous fire can mediate future fire severity even under extreme conditions. Our findings demonstrate that low‐ to moderate‐severity fire buffers future fire severity in historically frequent‐fire forests, underlining the importance of wildfire as a restoration tool for adapting to global change.

中文翻译：

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过去野火对再燃严重程度的缓和影响取决于气候和美国西部森林的初始严重程度


全球火灾活动的增加正在增加全球森林中反复短间隔燃烧（再燃烧）的普遍性。在历史上经常发生火灾的森林中，高度严重的火灾会增加灌木的普遍性和/或创造更干燥的林下条件，从而加剧后续火灾的严重性。相比之下，低到中等严重程度的火灾可以通过减少燃料负荷来缓和未来的火灾行为。以前的火灾在多大程度上缓和了未来的火灾严重程度，这将有力地影响下个世纪容易发生火灾的森林生态系统轨迹。此外，了解野火的地点和时间可能作为景观规模的燃料处理有助于指导火灾前后的管理工作。我们利用卫星图像和火灾进展地图来模拟森林内的再燃烧动态，这些森林最初在美国西部四个大型火灾多发生态区的 36 年期间在 726 次独特的火灾对事件中以低/中度严重程度燃烧。我们询问 （1） 低到中度严重程度火灾的调节作用对未来火灾严重程度的强度，（2） 调节作用持续多长时间，以及 （3） 火灾之间的时间（燃料积累的代表）如何与初始火灾严重程度、燃烧当天的天气条件和气候相互作用以影响再燃的严重程度。短间隔再燃烧主要发生在历史上火灾频繁的干燥和潮湿混合针叶林中。以前的火灾缓和了所有生态区的再燃烧严重程度，其中最强的影响发生在加利福尼亚海岸和西部山脉，缓和效应的平均持续时间从西部山脉的 13 年到加利福尼亚海岸的 >36 年不等。 调节效应的强度和持续时间取决于气候和一些地区的火灾初始严重程度，反映了火灾后燃料积累的差异。在加利福尼亚海岸，较凉爽和潮湿的森林中，调节作用持续时间更长。在西部山区，最初燃烧强度较高的森林的调节作用更强、持续时间更长。调节效应在很大程度上对火灾天气具有稳健性，这表明即使在极端条件下，以前的火灾也可以介导未来的火灾严重程度。我们的研究结果表明，在历史上经常发生火灾的森林中，低到中等严重程度的火灾可以缓冲未来的火灾严重程度，这凸显了野火作为适应全球变化的恢复工具的重要性。