Fire frequency in boreal forests has increased via longer burning seasons, drier conditions, and higher temperatures. However, fires have historically self-regulated via fuel limitations, mediating the effects of changes in climate and fire weather. Early post-fire boreal forests (10–15 years postfire) are often dominated by mixed conifer-broadleaf or broadleaf regeneration, considered less flammable due to the higher foliar moisture of broadleaf trees and shrubs compared to their more intact conifer counterparts. However, the strength of self-regulation in the context of changing fire weather and climate combined with the emergence of novel broadleaf forest communities and structures remains unclear. We quantified fuel composition, abundance, and structure in burned and reburned forests in Interior Alaska and used a physics-based fire behavior model (the Wildland-Urban Interface Fire Dynamics Simulator) to simulate how these unique patterns of fuel influence potential rates and sustainability of fire spread. In once-burned forests dominated by mixed conifer-broadleaf regeneration, extreme fire weather conditions allowed for sustained fire spread, suggesting that intense fire conditions can enable reburning, even 10 to 15 years following a previous high-severity fire. However, fire spread was not sustained in thrice-burned regenerating broadleaf forests, where regeneration was often dense but more clumped, and thus less connected, separated by patches of bare soil. Crown fire traveled an average of 50 meters into thrice-burned forests before dying out, even under extreme fire weather conditions. This work suggests that fire spread may be possible in once-burned regenerating forests under extreme fire weather conditions but may be more limited in less connected and less fuel abundant thrice-burned regenerating forests, at least within the 10–15-year window post-fire.

中文翻译：

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燃料限制，而不是火灾天气条件，限制了再燃烧的北方森林的火灾行为


由于燃烧季节延长、条件干燥和温度升高，北方森林的火灾频率增加。然而，火灾历来是通过燃料限制进行自我调节的，介导气候变化和火灾天气的影响。火后早期的北方森林（火后 10-15 年）通常以针阔树或阔叶混合再生为主，由于阔叶树和灌木的叶面水分高于更完整的针叶树，因此被认为不易燃。然而，在不断变化的火灾天气和气候以及新型阔叶林群落和结构的出现下，自我调节的强度仍不清楚。我们量化了阿拉斯加内陆燃烧和再燃烧森林中的燃料成分、丰度和结构，并使用基于物理的火灾行为模型（Wildland-Urban Interface Fire Dynamics Simulator）来模拟这些独特的燃料模式如何影响火灾蔓延的潜在速率和可持续性。在曾经被烧毁的森林中，以针阔草混合再生为主，极端的火灾天气条件允许火势持续蔓延，这表明强烈的火灾条件可以使重新燃烧，甚至在之前的严重火灾后 10 到 15 年也是如此。然而，在三次烧毁的再生阔叶林中，火势蔓延并不持续，那里的再生通常很密集，但更密集，因此连通性较差，被裸露的土壤隔开。即使在极端的火灾天气条件下，Crown Fire 在熄灭之前平均会进入 50 米被烧毁的森林。 这项工作表明，在极端火灾天气条件下，火势可能在曾经被烧毁的再生林中蔓延，但至少在火灾后 10-15 年的窗口内，在连通性较差且燃料丰富的三次燃烧再生林中，火势蔓延可能更加有限。