运城盆地洪积扇全新世时期的野火与环境变化的初步探讨

 通过对运城盆地典型黄土 古土壤剖面磁化率和炭屑含量的分析，研究了洪积扇全新世野火活动的规律及其与环境变化的关系。研究结果表明，在全新世早期（11500～8500 a B.P.）, 气候向温湿过渡，但仍较干旱，炭屑含量较高，野火活动比较频繁，说明气候干旱是野火发生的重要原因。而全新世中期（8500～3100 a B.P.），除夏商文化时期外，炭屑含量在整个全新世时期居于最低，野火活动最为微弱，与此时期气候温暖湿润密切相关。但在夏商文化时期（3800～3500 a B.P.）炭屑浓度出现峰值，野火活动较为频繁，是人类生产和生活活动作用的结果。全新世晚期（3100～0 a B.P.）炭屑含量大幅度增加，野火活动最为频繁，一方面与气候向干旱化发展有关，另一方面与大范围的人类活动密切相关;在干旱的气候背景条件下, 人类活动加速了野火的发生频率和活动强度。

PRELIMINARY STUDIES OF WILD FIRE FREQUENCY AND ENVIRONMENTAL CHANGES DURING THE HOLOCENE ON THE ALLUVIAL PLAIN OF THE YUNCHENG BASIN

Charcoal, the product of the incomplete combustion of plant organisms, remains embedded in the soil and other kinds of sediments and can be used to construct a chronosequence of fire frequency over thousands to tens of thousands of years. The higher the charcoal concentration was, the more intense and frequent the wildfires were. Wildfire activity is related to both climatic changes and human activities, and this study was undertaken to document changes in the frequency of fire during the Holocene and related these to climatic changes and human activities. This research was carried out on the alluvial plain of the Yuncheng Basin in Xiaxian County, northwest of Zhongtiao Mountain. We analyzed charcoal content in soil samples in three different particle fractions obtained from a DXF-S profile. During the early Holocene (11500-8500 a B.P.), the climate was dry although it was becoming warmer and wetter. Large amounts of charcoal found in the soil during this period indicated that wildfires were frequent. The dry climate apparently creating favorable conditions for natural fires to occur, suggested the fire frequency was climatically controlled. The Holocene Megathermal (8500-3100 a B.P.) was the warmest and wettest period during the Holocene, and we found very little charcoal in the soil with the exception of the Xia and Shang dynasties (3800-3500 a B.P.), when a peak in the charcoal content was showed. The high precipitation during this period apparently suppressed natural fires, but human activities increased the fire frequency during the Xia and Shang dynasties.During the late Holocene (3100-0 a B.P.), the climate became drier and conditions were once again favorable for fires to occur naturally. The amount of charcoal in the soil greatly increased during this period that showed the greatest levels of fire activity of the entire Holocene. The high fire frequency was related to both the arid climate and increased human activities. In conclusion, climatic conditions and human activities are two important factors that influence fire frequency. Under drier climatic conditions, natural fires are more prevalent and human activities increase both the frequency and intensity of fires.