Centre de Bio-Archéologie et d'Ecologie, Unité Mixte de Recherche, 5059 Centre National de la Recherche Scientifique, Université Montpellier 2, Institut de Botanique, F-34090 Montpellier, France.
Proc Natl Acad Sci U S A. 2012 Dec 18;109(51):20966-70. doi: 10.1073/pnas.1203467109. Epub 2012 Dec 3.
Wildfire activity in North American boreal forests increased during the last decades of the 20th century, partly owing to ongoing human-caused climatic changes. How these changes affect regional fire regimes (annual area burned, seasonality, and number, size, and severity of fires) remains uncertain as data available to explore fire-climate-vegetation interactions have limited temporal depth. Here we present a Holocene reconstruction of fire regime, combining lacustrine charcoal analyses with past drought and fire-season length simulations to elucidate the mechanisms linking long-term fire regime and climatic changes. We decomposed fire regime into fire frequency (FF) and biomass burned (BB) and recombined these into a new index to assess fire size (FS) fluctuations. Results indicated that an earlier termination of the fire season, due to decreasing summer radiative insolation and increasing precipitation over the last 7.0 ky, induced a sharp decrease in FF and BB ca. 3.0 kyBP toward the present. In contrast, a progressive increase of FS was recorded, which is most likely related to a gradual increase in temperatures during the spring fire season. Continuing climatic warming could lead to a change in the fire regime toward larger spring wildfires in eastern boreal North America.
在 20 世纪的最后几十年里，北美的北方森林野火活动增加，部分原因是人类正在造成的气候变化。由于可用的数据来探索火灾-气候-植被相互作用的时间深度有限，这些变化如何影响区域火灾模式（每年燃烧的面积、季节性以及火灾的数量、大小和严重程度）仍然不确定。在这里，我们提出了一个全新世火灾模式的重建，结合湖泊炭分析以及过去干旱和火灾季节长度的模拟，以阐明将长期火灾模式与气候变化联系起来的机制。我们将火灾模式分解为火灾频率（FF）和生物量燃烧（BB），并将这些重新组合成一个新的指数，以评估火灾大小（FS）的波动。结果表明，由于过去 7000 年来夏季辐射光照的减少和降水的增加，火灾季节的结束时间更早，导致大约在 3000 年前，FF 和 BB 急剧减少。相比之下，FS 则呈逐步上升趋势，这很可能与春季火灾季节温度的逐渐升高有关。持续的气候变暖可能导致东部北方森林火灾模式向更大规模的春季野火转变。
