一项研究报告说，亚北极地区的野火在近几十年发生的频率高于自从3000年前现代植被在该地区生根发展以来的任何其他时候。FengShengHu及其同事使用来自阿拉斯加容易起火的育空平原的木碳和花粉的记录，记录了过去1万年的森林火灾。在6000年前到3000年前，火发生的频率和过火面积增加，这种增加恰逢该地区最易燃的黑云杉的扩张。在1000年前到500年前，有一段温暖干燥的气候环境，与近几十年最类似。在这段时间里，严重的火灾促进了耐火植物物种的丰富程度，这限制了火的频率，尽管环境非常有助于燃烧。近来野火的增加把育空平原的大部分地形转化成了可燃性较低的植被的支离破碎的镶嵌图，而这些发现提示一个活跃但是稳定的火灾状态可能发生演化。这组作者提出，然而，近年来火灾发生频率高也预示着育空平原向空前水平的火灾活动的状态转变。（生物谷 Bioon.com）
生物谷推荐的英文摘要
PNAS doi: 10.1073/pnas.1305069110
Recent burning of boreal forests exceeds fire regime limits of the past 10,000 years
Ryan Kellya, Melissa L. Chipmanb, Philip E. Higuerac, Ivanka Stefanovad, Linda B. Brubakere, and Feng Sheng Hu
Wildfire activity in boreal forests is anticipated to increase dramatically, with far-reaching ecological and socioeconomic consequences. Paleorecords are indispensible for elucidating boreal fire regime dynamics under changing climate, because fire return intervals and successional cycles in these ecosystems occur over decadal to centennial timescales. We present charcoal records from 14 lakes in the Yukon Flats of interior Alaska, one of the most flammable ecoregions of the boreal forest biome, to infer causes and consequences of fire regime change over the past 10,000 y. Strong correspondence between charcoal-inferred and observational fire records shows the fidelity of sedimentary charcoal records as archives of past fire regimes. Fire frequency and area burned increased ∼6,000–3,000 y ago, probably as a result of elevated landscape flammability associated with increased Picea mariana in the regional vegetation. During the Medieval Climate Anomaly (MCA; ∼1,000–500 cal B.P.), the period most similar to recent decades, warm and dry climatic conditions resulted in peak biomass burning, but severe fires favored less-flammable deciduous vegetation, such that fire frequency remained relatively stationary. These results suggest that boreal forests can sustain high-severity fire regimes for centuries under warm and dry conditions, with vegetation feedbacks modulating climate–fire linkages. The apparent limit to MCA burning has been surpassed by the regional fire regime of recent decades, which is characterized by exceptionally high fire frequency and biomass burning. This extreme combination suggests a transition to a unique regime of unprecedented fire activity. However, vegetation dynamics similar to feedbacks that occurred during the MCA may stabilize the fire regime, despite additional warming.
