Pierce Jennifer L, Meyer Grant A, Jull A J Timothy
Department of Earth and Planetary Science, University of New Mexico, Albuquerque, New Mexico 87131, USA.
Nature. 2004 Nov 4;432(7013):87-90. doi: 10.1038/nature03058.
Western US ponderosa pine forests have recently suffered extensive stand-replacing fires followed by hillslope erosion and sedimentation. These fires are usually attributed to increased stand density as a result of fire suppression, grazing and other land use, and are often considered uncharacteristic or unprecedented. Tree-ring records from the past 500 years indicate that before Euro-American settlement, frequent, low-severity fires maintained open stands. However, the pre-settlement period between about ad 1500 and ad 1900 was also generally colder than present, raising the possibility that rapid twentieth-century warming promoted recent catastrophic fires. Here we date fire-related sediment deposits in alluvial fans in central Idaho to reconstruct Holocene fire history in xeric ponderosa pine forests and examine links to climate. We find that colder periods experienced frequent low-severity fires, probably fuelled by increased understory growth. Warmer periods experienced severe droughts, stand-replacing fires and large debris-flow events that comprise a large component of long-term erosion and coincide with similar events in sub-alpine forests of Yellowstone National Park. Our results suggest that given the powerful influence of climate, restoration of processes typical of pre-settlement times may be difficult in a warmer future that promotes severe fires.
美国西部的黄松森林最近遭受了大面积的林分更替火灾，随后出现了山坡侵蚀和泥沙淤积。这些火灾通常归因于由于火灾抑制、放牧和其他土地利用导致的林分密度增加，并且常常被认为是非典型的或前所未有的。过去500年的树木年轮记录表明，在欧美移民定居之前，频繁的低强度火灾维持了开阔的林分。然而，公元1500年至1900年左右的定居前时期总体上也比现在更冷，这增加了20世纪快速变暖促使近期发生灾难性火灾的可能性。在这里，我们对爱达荷州中部冲积扇中与火灾相关的沉积物进行年代测定，以重建干旱黄松森林的全新世火灾历史，并研究与气候的联系。我们发现，较冷时期经历了频繁的低强度火灾，可能是由林下生长增加所致。温暖时期经历了严重干旱、林分更替火灾和大规模泥石流事件，这些事件构成了长期侵蚀的很大一部分，并且与黄石国家公园亚高山森林中的类似事件同时发生。我们的结果表明，鉴于气候的强大影响，在促进严重火灾的更温暖的未来，恢复定居前时期典型的过程可能很困难。
