北大兴安岭寒温带针叶林区全新世火演化及其气候响应

To find the similar geological time and reconstruct the environmental factors and climate responses become an important way of assessing the likely environmental impact of future climate change in the critically-affected areas. As a distinctive and significant ecological factor, natural fire is directly related to vegetation types and climate factors, and it is an important indicator of climate and environment. The northern Greater Khingan Range (GKR), in the northernmost part of northeast China, dominated by cold-temperate coniferous forest, is on the margins of the East Asian Summer Monsoon region and extremely sensitive to changes in temperature and moisture. This area is effected by natural factors, with relatively weak human influence during the Holocene, becoming the ideal region to study vegetation succession and its response to climate change. Therefore, three lake-swamp depositions during the Holocene of different vegetation types in the northern GKR will be selected for this study. Chronological framework will be established through AMS14C dating. Charcoal analysis based on size and shape will be used for fire history quantitative reconstructions. High resolution pollen records will be used to reconstruct the vegetation succession history, and discuss the relationship between vegetation and climate change. Consequently, we try to explore the influence pattern and mechanism of nature fire during the Holocene Megathermal and abrupt cooling events. This study will provide scientific basis for the research of fire activity characteristics and evolution tendency in potential forest fire danger area.

如何从关键区域入手，选择涵盖未来气候变化相类似的地质时段，重建环境因子演化序列及其气候响应，成为评估未来气候变化环境效应的重要途径。天然火作为一种独特且重要的生态环境因子，与植被类型和气候因子关系密切，是反映气候环境变化及其环境效应的重要指标。我国东北地区北大兴安岭发育寒温带针叶林，是我国重特大森林火灾高发区。该区位于东亚夏季风边缘，对气候变化响应敏感，全新世早期人类活动影响较少，是研究天然火演化及其气候环境响应的理想区域。本课题拟选取不同立地条件3个连续且稳定的高分辨率湖相/泥炭剖面，在建立高精度AMS14C年代序列的基础上，通过炭屑粒径和面积浓度分析，定量重建全新世火演化历史；基于高精度花粉记录重建植被演替序列，探讨天然火与植被和气候变化的关系；揭示全新世高温期和气候突变事件对火事件的影响方式和机制，为未来可能增温背景下，高火险林区的火活动特征和变化趋势预测提供科学依据。

寒温带针叶林区地处中高纬度，是对全球增温响应最显著的地区之一。北大兴安岭寒温带针叶林区，是我国重特大森林火灾集中分布区。全球变暖究竟是有利于该区林火活动的增强还是减弱，需借鉴过去长尺度的沉积记录，重建火演化序列及其对气候变化的响应。本项目选取北大兴安岭寒温带针叶林区山地森林（霍拉剖面）、沼泽化草甸（北红剖面）和针阔叶混交林区山地南部森林草原过渡区（五大连池岩芯）3个连续且稳定的泥炭沉积序列，基于精确的AMS14C测年，运用花粉和炭屑沉积记录重建了该区植被和火演化历史，初步探讨了火演化的影响机制。.1. 霍拉剖面和北红剖面的花粉和炭屑记录重建了寒温带针叶林区全新世以来古植被和火演化历史。研究发现，霍拉剖面和北红剖面的炭屑浓度值表现出相似的变化趋势。10000-3000 cal yr BP，气候相对温暖湿润，炭屑浓度较低。3000 cal yr BP以来，东北地区气温降低，季风降水减少，炭屑浓度波动明显，出现峰值。霍拉盆地6000 cal yr BP火事件频率增加，与这一时期的北半球高纬冷事件有较好的对应关系。3000 cal yr BP以来，北半球高纬夏季太阳辐射减弱，东亚夏季风减弱，北大兴安岭地区火事件频率和强度增加。.2. 五大连池地区花粉和炭屑记录重建了末次盛冰期以来的植被和火演化历史。其中，火事件的频发期为19000 cal yr BP，13000 cal yr BP，8000-10000 cal yr BP，6500 cal yr BP，4500 cal yr BP，1000-2000 cal yr BP；分别对应末次盛冰期、新仙女木（Younger Dryars）事件、全新世降温事件。北半球高纬太阳辐射减弱，北半球高纬降温事件，亚洲季风减弱，东北地区降水减少，与五大连池地区火事件频率增加相一致。.北大兴安岭寒温带针叶林区全新世火演化和末次盛冰期以来五大连池地区火演化历史研究表明，火事件频率的增加主要受北半球高纬降温事件的影响，即冷干的气候条件及其影响下的植被类型和盖度成为火演化的重要控制因素。该项工作为认识我国东亚季风北部边缘区火演化规律，预测和评估未来气候变化环境效应提供了重要依据。