Department of Anthropology, Southern Methodist University, Dallas, TX 75275-0336;
Bureau of Applied Research in Anthropology, School of Anthropology, University of Arizona, Tucson, AZ 85721.
Proc Natl Acad Sci U S A. 2018 Aug 7;115(32):8143-8148. doi: 10.1073/pnas.1805259115. Epub 2018 Jul 23.
Fire use has played an important role in human evolution and subsequent dispersals across the globe, yet the relative importance of human activity and climate on fire regimes is controversial. This is particularly true for historical fire regimes of the Americas, where indigenous groups used fire for myriad reasons but paleofire records indicate strong climate-fire relationships. In North American grasslands, decadal-scale wet periods facilitated widespread fire activity because of the abundance of fuel promoted by pluvial episodes. In these settings, human impacts on fire regimes are assumed to be independent of climate, thereby diminishing the strength of climate-fire relationships. We used an offsite geoarchaeological approach to link terrestrial records of prairie fire activity with spatially related archaeological features (driveline complexes) used for intensive, communal bison hunting in north-central Montana. Radiocarbon-dated charcoal layers from alluvial and colluvial deposits associated with driveline complexes indicate that peak fire activity over the past millennium occurred coincident with the use of these features (ca. 1100-1650 CE). However, comparison of dated fire deposits with Palmer Drought Severity Index reconstructions reveal strong climate-fire linkages. More than half of all charcoal layers coincide with modest pluvial episodes, suggesting that fire use by indigenous hunters enhanced the effects of climate variability on prairie fire regimes. These results indicate that relatively small, mobile human populations can impact natural fire regimes, even in pyrogeographic settings in which climate exerts strong, top-down controls on fuels.
火的使用在人类进化和随后的全球扩散中发挥了重要作用，但人类活动和气候对火灾发生频率的相对重要性仍存在争议。这在美洲的历史火灾模式中尤其如此，当地的原住民出于各种原因而用火，但古火灾记录表明气候与火灾之间存在强烈的关系。在北美的草原地区，由于湿润期的丰沛燃料，十年一遇的湿润期促进了广泛的火灾活动。在这些环境中，人们认为人类对火灾模式的影响独立于气候，从而削弱了气候与火灾之间的关系。我们使用场外地质考古方法将草原火灾活动的陆地记录与空间相关的考古特征（车辙复合体）联系起来，这些考古特征用于在蒙大拿州中北部进行密集的、公共的野牛狩猎。与车辙复合体相关的冲积和坡积沉积物中的放射性碳测年木炭层表明，在过去的一千年中，火灾活动的峰值与这些特征的使用同时发生（约公元 1100-1650 年）。然而，将有日期的火灾沉积物与帕尔默干旱严重程度指数重建进行比较表明，气候与火灾之间存在强烈的联系。超过一半的木炭层与适度的湿润期同时发生，这表明原住民猎人的用火行为增强了气候变异性对草原火灾模式的影响。这些结果表明，相对较小的、流动的人口可以影响自然火灾模式，即使在气候对燃料施加强烈的自上而下控制的火地地理环境中也是如此。
