【作者】 曹艳峰；

【导师】 黄春长；

【作者基本信息】 陕西师范大学 ， 自然地理学， 2005， 硕士

【摘要】 全新世是人类由蒙昧走向文明的时期,是地球历史最新的一页,与人类的生存和发展密切相关。目前气候变化、植被演替以及人类对环境的影响等问题是国际全新世环境演变研究的热点。自然和人为引起的森林和草原野火,引起生态环境的显著变化。野火活动已被认为是控制地球陆地生态系统演变发展的重要因子。黄土高原的黄土—土壤序列是良好的环境演变信息载体。作为野火活动直接记录的木炭屑,其保存在黄土—土壤中可提供几千年甚至几万年的野火活动的连续记录。因此,通过对野火活动的研究,可以揭示长期的生态演变规律。 本文在了解全新世生态环境演变研究进展的基础上,选定黄土高原全新世时期的野火与环境变化作为课题。通过大量野外细致缜密的考察,在黄土高原选取了东部和西部三个全新世黄土—土壤剖面进行研究。三个剖面地层发育连续完整,保存良好,具有典型性。对其进行了高密度采样,进行了磁化率测定和木炭屑分析,获得了全新世时期野火与环境变化的信息。通过分析各指标在剖面中的变化规律,着重论证了全新世时期以来野火活动的特征及其与气候变化、植被状况和人类活动的关系。本文研究成果为: (1)在末次冰期(～11500 aB.P.),在强大的西北环流的控制下,粉尘堆积显著,生物成壤作用微弱,土壤湿度很低,气候十分干冷,呈现半荒漠草原景观;全新世早期(11500～8500 aB.P.)气候处于从末次冰期的干冷气候向温暖湿润的冰后期过渡的阶段,气温回升,降水量增加,成壤程度由一定加强,植被开始恢复;全新世中期(8500～3100 aB.P.)是全新世最为温暖湿润的时期,由于夏季风增强,温度升高,降水量增加,沙尘天气很少发生,风尘堆积率很低,生物风化成壤作用相当强烈,植被茂盛,但在黄土高原塬区仍无森林生长,只是在黄土高原沟壑地区有森林发育;全新世晚期(3100～0 aB.P.)风尘堆积加速,成壤作用减弱,成为全新世相对干旱的时段。随着气候向干旱化发展,水土资源退化,植被退化。并且随着人类活动的加强,水土资源退化表现更为显著,气候更加干旱。3100 aB.P.以来的气候恶化表明3100 aB.P.左右是一个重要的季风气候转型期。 (2)末次冰期(～11500 aB.P.),气候较为干旱而不稳定,为野火发生提供了气候条件,空气湿度很低,可燃物变的很干燥,尽管植被稀疏,但由于该时期植被主要呈现荒漠草原和半荒漠草原,其燃点较低,因此该时期野火相当频繁,地方性和区域性野火频繁发生;全新世早期(11500～8500 aB.P.),气候开始由冷干向温湿过渡,气温回升,但仍相当干旱,降水量较低,空气相对湿度减小,使可更多还原

【Abstract】 Nowadays, climatic changes, vegetational succession and human effects on the environment etc are hotspots of international research on Holocene environmental changes. The Holocene loess-soil sequence in the loess Plateau constitutes an excellent record of the environmental changes. Charcoal, the product of the incomplete combustion of plant organisms, is embedded in the soil and can be used to reconstruct 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.In this research, three typical high-resolution Holocene soil profiles in the Eastern and western Loess Plateau were studied by proxy environmental data of magnetic susceptibility and charcoal concentration. The result provides insights into the law of Holocene wildfires activities and the relationship with wildfire activities and environmental changes.The results are as follows:1. In the last ice age (~ 11500 aB.P.), the climate was arid and the most deposit of Aeolian dust accumulated in the semi-desert grassland; In the early Holocene(11500~ 8500 aB.P.), the vegetation began to develop with the amelioration of climate. The Holocene Megathermal(8500~3100 aB.P.) was the wettest and warmest during the whole Holocene. In this period, the vegetation was flourishing, but there was still no forest in the tableland region and forest only developed in the gully region; Both the analytical data and literal indicate that increased climatic aridity from 3100 aB.P. caused a considerable environmental deterioration and degradation of natural resource. And degradation of natural resource was accelerated because of the increasing human activities during this period.2. In the last ice age (~ 11500 aB.P.), the climate was arid. At that time, on semi-desert grassland, the local and regional natural wildfire often occurred. In early Holocene(11500~8500 aB.P.), the climate was still drier though it began to become更多还原