大兴安岭全新世的森林火及其对生态系统碳循环的影响

Daxing'an Mountain region is a high incidence area of fire in China because of frequent and intensive fires. However, the causes and consequences of changes in fire in the region remain unclear. Microcharcoal and macrocharcoal analysis of lake and peatland sediments from Daxing’an Mountain will be used to reconstruct Holocene history of fire, vegetation and climate. Numerical models and statistical analysis will be used to calibrate charcoal peaks and IFF (Infferred Fire Frequency) for interpreting fire history..Several factors may affect the accuracy of fire history from sedimentary charcoal records. First, charcoal accumulation rates (CHAR) would include a background component, which may be a low-frequency or slowly varying component; second, charcoal particles are easily broken during preparation, thus creating artificially high abundance of microscopic particles; third, there may exist reworked charcoal in the samples. Multi- proxy including pollen, charcoal, stomata, magnetic susceptibility, molecular marker, TOC and stable isotopes will provide richer information and more accurate constrain on fire regimes through time and aid to establish fire-vegetation-climate history. .Our aims are to appreciate fire’s role in the past, to understand how biomasses burning affect biodiversity and biogeochemical cycling, to examine past fire activity and evaluate the driver and consequence of biomass burning. The study results will provide insights into climate and human influences in fire regimes of the past which would have implications for the future in light of global change.

大兴安岭是我国火险高发区，火产生丰富的炭屑保存于沉积物中成为我们研究火历史的重要材料；同时，该地区广泛分布的泥炭沉积提供了详实的古环境信息，为我们了解火-植被-气候-人类活动关系提供了宝贵的材料。本项目选择大兴安岭两个湖泊和两个泥炭地进行钻孔取样，通过沉积物的炭屑（微炭屑和大炭屑）、孢粉、有机碳含量和稳定同位素等分析，运用多种数理统计和模型模拟的方法来分析炭屑数据，辨识火事件，推测火频率，进而估算全新世不同时期碳排放量；将模型模拟与实验相结合，准确重建该区域全新世火的历史，了解火对生态系统碳循环的影响；从长时间尺度火来阐述火-植被-气候-人类活动的复杂关系，为认识火事件的成因和规律及其对气候变化的影响，有效预测和预防未来火事件的发生和影响提供科学依据。

在全球变暖的背景下，世界各地火灾频发，我们迫切需要了解各地火的演化规律（频率和强度），以有效地预测和预防未来火事件的发生及其对生态系统的影响。从全球古火工作组（GPWG, the Global Paleofire Working Group）所公布的全球炭屑记录研究地点看，中国开展古火研究的地点相对较少，尤其是有着很长火历史的大兴安岭还是一个空白区域。为此，本项目选择大兴安岭湖泊和泥炭地进行钻孔取样，通过沉积物的炭屑（微炭屑和大炭屑）、孢粉、有机碳含量和稳定同位素等分析，运用多种数理统计和模型方法来分析孢粉、炭屑和同位素数据，重建古火、古植被和古气候历史，探究了全新世火活动与植被、气候和碳累积速率的关系。项目主要研究内容已完成，野外调查取样和实验分析工作进展顺利，数据的分析整理和文章撰写仍在进行中。.该项目得到了三个重要结果：1. 大兴安岭的火活动在早全新世（11200 ~ 8000 cal yr BP）相对较弱，中晚全新世（8000 cal yr BP以来）呈现增强的趋势。2. 大兴安岭全新世火活动受到植被和气候因素的共同影响；其中，生物量是最关键的植被因素，火与生物量、植物丰富度、均匀度均显著正相关，而与景观开阔度显著负相关；相对湿度是最关键的气候因素，而温度和降水量对火的影响在不同时期存在一定差异；长时间尺度的火干扰可能是促进有机碳累积的重要因素。3. 现代过程研究表明微炭屑（<125μm）浓度与燃烧面积的大小密切相关；大炭屑（>125μm）浓度不仅与燃烧面积的大小有关，而且还与火烈度、火类型和燃烧植被类型有关。该项目从长时间尺度来探究火-植被-气候-碳累积的复杂关系，有助于认识火事件的成因和规律，为有效预测和预防未来火事件的发生和影响提供科学依据。研究结果对根据火的演化规律，制定合理的管理政策有着重要现实意义。