Linear fuel breaks are being implemented to moderate fire behavior and improve wildfire containment in semiarid landscapes such as the sagebrush steppe of North America, where extensive losses in perennial vegetation and ecosystem functioning are resulting from invasion by exotic annual grasses (EAGs) that foster large and recurrent wildfires. However, fuel-break construction can also pose EAG invasion risks, which must be weighed against the intended fire-moderation benefits of the treatments. We investigated how shrub reductions (mowing, cutting), pre-emergent EAG-herbicides, and/or drill seedings of fire-resistant perennial bunchgrasses (PBGs) recently applied to create a large fuel-break system affected native and exotic plant abundances and their associated fuel loading and predicted fire behavior. In heavily EAG-invaded areas, herbicides reduced EAG and total herbaceous cover without affecting PBGs for 2–3 years and reduced predicted fire behavior for 1 year (from the Fuel Characteristic Classification System). However, surviving post-herbicide EAG cover was still > 30%, which was sufficient fuel to exceed the conventional 1.2-m-flame length (FL) threshold for attempting wildfire suppression with hand tools. In less invaded shrubland, shrub reduction treatments largely reduced shrub cover and height by ~ half without increasing EAGs, but then redistributed the wood to ground level and increased total herbaceous cover. Herbicides and/or drill seeding after shrub reductions did not affect EAG cover, although drill seedings increased PBG cover and exotic forbs (e.g., Russian thistle). Fire behavior was predicted to be moderated in only one of the many yearly observations of the various shrub-reduction treatment combinations. Over all treatments and years, FLs were predicted to exceed 1.2 m in 13% of simulations under average (11 km h−1) or high (47 km h−1) wind speed conditions and exceed the 3.4-m threshold for uncontrollable fire in 11% of simulations under high-wind speeds only. Predicted fire-moderation benefits over the first 4 years of fuel break implementation were modest and variable, but, generally, increases in EAGs and their associated fire risks were not observed. Nonetheless, ancillary evidence from shrublands would suggest that treatment-induced shifts from shrub to herbaceous fuel dominance are expected to improve conditions for active fire suppression in ways not readily represented in available fire models.

中文翻译：

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烧毁的山艾树草原及其周围的植被、燃料和火灾行为对线性燃料中断处理的反应：我们是否正在打破草火循环？

在北美的鼠尾草草原等半干旱地区，正在实施线性燃料中断，以缓和火灾行为并改善野火控制，这些地区的多年生植被和生态系统功能因外来一年生草（EAG）的入侵而造成大量损失，这些草可以培育大型和大型草本植物。反复发生的野火。然而，燃料中断施工也可能带来 EAG 入侵风险，必须权衡处理方法的预期防火效益。我们调查了最近用于创建大型燃料中断系统的灌木减少（割草、切割）、芽前 EAG 除草剂和/或耐火多年生束草 (PBG) 的条播如何影响本地和外来植物丰度及其相关的燃料装载量和预测的火灾行为。在 EAG 严重入侵的地区，除草剂在不影响 PBG 的情况下减少了 EAG 和总草本覆盖 2-3 年，并减少了 1 年的预测火灾行为（来自燃料特性分类系统）。然而，除草剂后 EAG 覆盖率仍> 30%，这足以超过传统的 1.2 米火焰长度 (FL) 阈值，以尝试使用手动工具扑灭野火。在入侵较少的灌木丛中，灌木减少处理在不增加 EAG 的情况下大幅减少了灌木覆盖率和高度约一半，但随后将木材重新分配到地面并增加了总草本覆盖率。灌木减少后除草剂和/或条播不影响 EAG 覆盖，尽管条播增加了 PBG 覆盖和外来草本植物（例如俄罗斯蓟）。在对各种灌木减少处理组合进行的多次年度观察中，只有一项预测火灾行为会得到缓解。在所有处理和年份中，在平均风速 (11 km h−1) 或高风速 (47 km h−1) 条件下，13% 的模拟中 FL 预计将超过 1.2 m，并超过 3.4 m 的不可控制火灾阈值。 11% 的模拟仅在高风速下进行。实施燃料中断的前 4 年预计的火灾缓解效益是适度且可变的，但一般来说，没有观察到 EAG 及其相关火灾风险的增加。尽管如此，来自灌木丛的辅助证据表明，治疗引起的从灌木燃料到草本燃料优势的转变预计会以现有火灾模型中不易体现的方式改善主动灭火的条件。